An Introduction to Nutrition

An Introduction to Nutrition

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Table of Contents About the Authors………………………………………………………………………………………………….. 1 Acknowledgments ………………………………………………………………………………………………….. 3 Dedications …………………………………………………………………………………………………………….. 4 Preface……………………………………………………………………………………………………………………. 5 Chapter 1: Nutrition and You ………………………………………………………………………………… 9

Defining Nutrition, Health, and Disease ………………………………………………………………………………………. 12 What Are Nutrients? …………………………………………………………………………………………………………………… 18 The Broad Role of Nutritional Science…………………………………………………………………………………………. 26 Health Factors and Their Impact…………………………………………………………………………………………………. 36 Assessing Personal Health…………………………………………………………………………………………………………… 50 A Fresh Perspective: Sustainable Food Systems …………………………………………………………………………… 55 End-of-Chapter Exercises ……………………………………………………………………………………………………………. 63

Chapter 2: Achieving a Healthy Diet ……………………………………………………………………. 65 A Healthy Philosophy toward Food……………………………………………………………………………………………… 69 What Is Nutritional Balance and Moderation? …………………………………………………………………………….. 74 Understanding the Bigger Picture of Dietary Guidelines ……………………………………………………………… 82 National Goals for Nutrition and Health: Healthy People 2020 …………………………………………………….. 88 Recommendations for Optimal Health ………………………………………………………………………………………… 95 Understanding Daily Reference Intakes …………………………………………………………………………………….. 101 Discovering Nutrition Facts ………………………………………………………………………………………………………. 106 When Enough Is Enough……………………………………………………………………………………………………………. 115 Nutrition and the Media……………………………………………………………………………………………………………. 119 End-of-Chapter Exercises ………………………………………………………………………………………………………….. 123

Chapter 3: Nutrition and the Human Body ……………………………………………………….. 125 The Basic Structural and Functional Unit of Life: The Cell …………………………………………………………. 128 Digestion and Absorption………………………………………………………………………………………………………….. 134 Nutrients Are Essential for Organ Function……………………………………………………………………………….. 142 Energy and Calories ………………………………………………………………………………………………………………….. 152 Disorders That Can Compromise Health ……………………………………………………………………………………. 156 End-of-Chapter Exercises ………………………………………………………………………………………………………….. 163

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Chapter 4: Carbohydrates ………………………………………………………………………………….. 165 A Closer Look at Carbohydrates ………………………………………………………………………………………………… 169 Digestion and Absorption of Carbohydrates ………………………………………………………………………………. 176 The Functions of Carbohydrates in the Body……………………………………………………………………………… 188 Looking Closely at Diabetes ………………………………………………………………………………………………………. 194 Health Consequences and Benefits of High-Carbohydrate Diets …………………………………………………. 202 Carbohydrates and Personal Diet Choices………………………………………………………………………………….. 212 The Food Industry: Functional Attributes of Carbohydrates and the Use of Sugar Substitutes …….219 End-of-Chapter Exercises ………………………………………………………………………………………………………….. 231

Chapter 5: Lipids ………………………………………………………………………………………………… 233 What Are Lipids? ………………………………………………………………………………………………………………………. 236 How Lipids Work ………………………………………………………………………………………………………………………. 243 Digestion and Absorption of Lipids ……………………………………………………………………………………………. 252 Understanding Blood Cholesterol ……………………………………………………………………………………………… 257 Balancing Your Diet with Lipids ………………………………………………………………………………………………… 263 Lipids and the Food Industry …………………………………………………………………………………………………….. 268 Lipids and Disease …………………………………………………………………………………………………………………….. 272 A Personal Choice about Lipids …………………………………………………………………………………………………. 276 End-of-Chapter Exercises ………………………………………………………………………………………………………….. 281

Chapter 6: Proteins …………………………………………………………………………………………….. 282 Defining Protein ……………………………………………………………………………………………………………………….. 285 The Role of Proteins in Foods: Cooking and Denaturation………………………………………………………….. 293 Protein Digestion and Absorption……………………………………………………………………………………………… 296 Protein’s Functions in the Body ………………………………………………………………………………………………… 300 Diseases Involving Proteins ………………………………………………………………………………………………………. 308 Proteins, Diet, and Personal Choices………………………………………………………………………………………….. 314 End-of-Chapter Exercises ………………………………………………………………………………………………………….. 333

Chapter 7: Nutrients Important to Fluid and Electrolyte Balance ……………………. 335 Overview of Fluid and Electrolyte Balance…………………………………………………………………………………. 338 Water’s Importance to Vitality………………………………………………………………………………………………….. 342 Regulation of Water Balance……………………………………………………………………………………………………… 346 Electrolytes Important for Fluid Balance …………………………………………………………………………………… 354 Consequences of Deficiency or Excess ……………………………………………………………………………………….. 373 Water Concerns ………………………………………………………………………………………………………………………… 378 Popular Beverage Choices …………………………………………………………………………………………………………. 389 End-of-Chapter Exercises ………………………………………………………………………………………………………….. 402

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Chapter 8: Nutrients Important As Antioxidants ……………………………………………… 403 Generation of Free Radicals in the Body ……………………………………………………………………………………. 406 Antioxidant Micronutrients………………………………………………………………………………………………………. 413 The Whole Nutrient Package versus Disease ……………………………………………………………………………… 438 End-of-Chapter Exercises ………………………………………………………………………………………………………….. 444

Chapter 9: Nutrients Important for Bone Health ……………………………………………… 445 Bone Structure and Function…………………………………………………………………………………………………….. 448 Bone Mineral Density Is an Indicator of Bone Health …………………………………………………………………. 455 Micronutrients Essential for Bone Health: Calcium and Vitamin D …………………………………………….. 457 Other Essential Micronutrients for Bone Health: Phosphorous, Magnesium, Fluoride, and Vitamin K ………………………………………………………………………………………………………………………………………………. 473 Osteoporosis …………………………………………………………………………………………………………………………….. 484 Risk Factors for Osteoporosis ……………………………………………………………………………………………………. 488 Osteoporosis Prevention and Treatment …………………………………………………………………………………… 493 Deficiency, Supplementation, and Choices ………………………………………………………………………………… 498 End-of-Chapter Exercises ………………………………………………………………………………………………………….. 505

Chapter 10: Nutrients Important for Metabolism and Blood Function ……………. 507 Blood’s Function in the Body and in Metabolism Support ………………………………………………………….. 509 Metabolism Overview ……………………………………………………………………………………………………………….. 516 Vitamins Important for Metabolism and for Blood Function and Renewal …………………………………. 523 Minerals Important for Metabolism and for Blood Function and Renewal………………………………….. 537 Iron-Deficiency Anemia…………………………………………………………………………………………………………….. 545 End-of-Chapter Exercises ………………………………………………………………………………………………………….. 552

Chapter 11: Energy Balance and Body Weight…………………………………………………… 553 Indicators of Health: Body Mass Index, Body Fat Content, and Fat Distribution…………………………..557 Balancing Energy Input with Energy Output ……………………………………………………………………………… 562 Too Little or Too Much Weight: What Are the Health Risks?………………………………………………………. 575 Dietary, Behavioral, and Physical Activity Recommendations for Weight Management ………………581 End-of-Chapter Exercises ………………………………………………………………………………………………………….. 589

Chapter 12: Nutrition through the Life Cycle: From Pregnancy to the Toddler Years …………………………………………………………………………………………………………………… 591

The Human Life Cycle ……………………………………………………………………………………………………………….. 594 Pregnancy and Nutrition…………………………………………………………………………………………………………… 598 Infancy and Nutrition……………………………………………………………………………………………………………….. 614 Nutrition in the Toddler Years ………………………………………………………………………………………………….. 632 End-of-Chapter Exercises ………………………………………………………………………………………………………….. 641

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Chapter 13: Nutrition through the Life Cycle: From Childhood to the Elderly Years …………………………………………………………………………………………………………………… 643

The Human Life Cycle Continues……………………………………………………………………………………………….. 646 Childhood and Nutrition …………………………………………………………………………………………………………… 651 Puberty and Nutrition ………………………………………………………………………………………………………………. 659 Older Adolescence and Nutrition ………………………………………………………………………………………………. 665 Young Adulthood and Nutrition………………………………………………………………………………………………… 670 Middle Age and Nutrition …………………………………………………………………………………………………………. 676 Old Age and Nutrition……………………………………………………………………………………………………………….. 681 End-of-Chapter Exercises ………………………………………………………………………………………………………….. 687

Chapter 14: Nutrition and Society: Food Politics and Perspectives ………………….. 689 Historical Perspectives on Food ………………………………………………………………………………………………… 692 The Food Industry…………………………………………………………………………………………………………………….. 699 The Politics of Food…………………………………………………………………………………………………………………… 708 Food Cost and Inflation …………………………………………………………………………………………………………….. 714 The Issue of Food Security ………………………………………………………………………………………………………… 718 Nutrition and Your Health ………………………………………………………………………………………………………… 726 Diets around the World …………………………………………………………………………………………………………….. 732 End-of-Chapter Exercises ………………………………………………………………………………………………………….. 744

Chapter 15: Achieving Optimal Health: Wellness and Nutrition ………………………. 746 Diet Trends and Health……………………………………………………………………………………………………………… 749 Fitness and Health ……………………………………………………………………………………………………………………. 763 Threats to Health ……………………………………………………………………………………………………………………… 770 Foodborne Illness and Food Safety ……………………………………………………………………………………………. 782 Start Your Sustainable Future Today…………………………………………………………………………………………. 797 Careers in Nutrition………………………………………………………………………………………………………………….. 802 End-of-Chapter Exercises ………………………………………………………………………………………………………….. 806

Chapter 16: Appendix A ……………………………………………………………………………………… 807

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About the Authors

Maureen Zimmerman

Dr. Maureen Zimmerman earned her undergraduate degree in Nutrition and Dietetics at Arizona State University, a Master’s Degree in Public Health from the University of Hawaii, and a Doctorate in Educational Leadership, with a specialization in educational research, from Northern Arizona University. She is a Registered Dietitian and has been a residential faculty member at Mesa Community College in Mesa, Arizona since 1991. She has been involved in many aspects of college life, most of them related to improving teaching and learning. She works indefatigably to assure that students enjoy their learning journey, regularly applying learning science to the online and ground classrooms. She is active every day of the week either practicing yoga, biking, hiking, tap dancing, or running. She enjoys reading a variety of genres, and likes to drink good coffee in the company of friends and family. She watches international films regularly, and tries to eat many fruits and vegetables every day. Her food first philosophy is summed up in this statement: “Enjoy real food, enjoy it with others, enjoy it in just the right amounts.”

Beth Snow

Dr. Beth Snow earned a BS (Hons) in Biochemistry (with a minor in Drama) from McMaster University in 1999, an MS in Human Biology & Nutritional Sciences from the University of Guelph in 2000, and a PhD in Human Nutrition from the University of British Columbia in 2006. She also holds a Credentialed Evaluator designation from the Canadian Evaluation Society. Her PhD research focused on the effects of prenatal alcohol exposure on the developing fetal skeleton and she has published in the journals Bone, Alcohol, and Alcoholism: Clinical & Experimental Research. Following her PhD training, she spent two years working at the British Columbia Centre of Excellence for Women’s Health, where she ran an interdisciplinary research training

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program. She currently works as an Evaluation Specialist in Public Health in Vancouver, BC, Canada, where she also teaches at the University of British Columbia and the Justice Institute of British Columbia. Her teaching philosophy involves empowering students to take ownership of their own learning; she uses active learning techniques and encourages students to apply what they learn to real life. Being a lifelong learner herself, Beth is currently working on a Masters of Business Administration at the University of British Columbia, with the goal of combining knowledge about organizations with her health research expertise in order to help get research evidence into Public Health practice. In addition to her busy career, Beth is a true foodie who always makes time to cook and share good food and she enjoys hiking, running, yoga, and, being a Canadian, playing ice hockey.

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Acknowledgments

It takes a village to create a textbook and we are deeply indebted to all those who helped us make this book a reality. First and foremost, our deepest thanks go out to all those who reviewed our chapters and gave us thoughtful feedback on how to make them even better:

• Patricia Abraham, Arkansas State University • Jessica Adams, Colby-Sawyer College • Christine Bieszczad, Colby-Sawyer College • Douglas Bruce, Laney College • Kathleen L. Deegan, California State University, Sacramento • Lindsay Edwards, Hardin-Simmons University • Cathy Headley, Judson University • Laura Hutchinson, Holyoke Community College • Christa Koval, Colorado Christian University • Beth Ann Krueger, Central Arizona College–Aravaipa Campus • Patrick Mathews, Friends University • Jill O’Malley, Erie Community College • Ana Otero, Emmanuel College • Alfred Ordman, Beloit College • Paula Vineyard Most, John A. Logan College • Linda Wright, Dixie State College of Utah

We are especially thankful to Teresa Fung for her expert content editing. Teresa has a keen eye for scientific accuracy. Because she is steeped in the nutrition literature, her input has been invaluable.

The development editors included Melissa Lingohr-Smith, Lisa Benjamin, and Danielle Dresden.

We are also very grateful for the incredible support we received from the teams at Unnamed Publisher and The Research Masters. Melissa Yu of Unnamed Publisher and Amy Bethea of The Research Masters have provided such invaluable support in managing the creation of this book—it could not have happened without them. We would also like to thank Michael Boezi and all the others at Unnamed Publisher who have championed a nonmajors nutrition book.

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Dedications

Maureen Zimmerman

Many people have shaped my professional and personal life. I would be remiss not to acknowledge those who saw potential and hired me in 1991 to develop a nutrition program at Mesa Community College. To those who initiated and maintained the stellar teaching and learning movement in the Maricopa Community College District, I am grateful. To my colleagues and the doctoral faculty who helped form my teaching practice, thank you. Succor comes from my family. My five children, in particular, experienced my nutritional philosophies even before the cradle. They brought hummus to school before it ever hit the grocery store shelves. Studying and teaching nutrition has been a fulfilling part of my life; I am grateful to all who have influenced me, most especially the thousands of students I have learned with through the years.

Beth Snow

I dedicate this book to my mother, Ann Snow, who taught me the fun of cooking, and my father, the late Jack Snow, who showed me the amazing world of biology. Marrying these two interests led to my pursuit of an education in nutritional sciences and, ultimately, to authoring this textbook.

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Preface

Welcome to Essentials of Nutrition: A Functional Approach! This book is written for students who are not majoring in nutrition, but want to learn about the fundamental aspects of nutrition and how it applies to their own lives. We have written this book with the assumption that you have little or no prior knowledge of college level chemistry, biology, or physiology. But that does not mean it’s not scientific! Nutrition is a science-based discipline, so all the material included is backed up by rigorous scientific research, but it is presented in a clear, easy-to- understand fashion without requiring a background in science.

Focus on Sustainability

People are increasingly interested in sustainable food issues. They are looking for favorable ways to impact not only their health, but also the environment and their local economy. However, misinformation about how one can make a positive impact abounds. By highlighting effective sustainable food behaviors, supported by science, this book will provide you with a significant resource for increasing the sustainable practices in your day-to-day life.

Organization

This book is organized using a functional approach, which means that the material is organized around physiological functions, such as fluid and electrolyte balance, antioxidant function, bone health, energy and metabolism, and blood health, instead of organizing it strictly by nutrient. This makes the information easier to understand, retain, and apply to your own life. As this text explores the relationship between nutrition and physiology, you will receive a “behind the scenes” examination of health and disease in the body.

• In Chapter 1 “Nutrition and You”, we provide an overview of nutrition as an evidence-based science and explore the concepts of health, wellness, and disease. We also provide an introduction to the different types of nutrients, health factors, personal health assessment, and the concept of sustainable food systems.

• In Chapter 2 “Achieving a Healthy Diet”, we explore the tools you can use to achieve a healthy diet, as well as important nutrition concepts like balance and moderation.

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• In Chapter 3 “Nutrition and the Human Body”, because we know that you may not have a background in biology, we start with a tour through the human body, from the single cell to the full organism, we set up for a discussion about the processes of digestion and absorption, followed by explorations of the other organ systems. After that, we discuss the concept of energy and calories. We also discuss some disorders and diseases related to nutritional health.

• In Chapter 4 “Carbohydrates”, we explore the many types of carbohydrates, including their functions. We also take a look at diabetes and at sugar substitutes.

• In Chapter 5 “Lipids”, we look at the types, structure, and roles of lipids, and we explain the different types of cholesterol in the blood. We also explore topics of interest such as omega-3 and omega-6 fatty acids and trans fats.

• In Chapter 6 “Proteins”, we cover the structure and roles of protein, and explore the consequences of getting too little or too much protein in your diet. Tips for getting the right amount and quality of protein, as well as a look at special populations, such as the elderly and athletes, are also covered.

• In Chapter 7 “Nutrients Important to Fluid and Electrolyte Balance”, we look at the nutrients important to fluid and electrolyte balance, including water, sodium, chloride, and potassium. We also look at sports drinks, caffeinated beverages, and alcohol.

• In Chapter 8 “Nutrients Important As Antioxidants”, nutrients important as antioxidants are explored, starting with an explanation of what oxidation and antioxidants are, then looking at vitamins E, C, and A, selenium, and phytochemicals.

• In Chapter 9 “Nutrients Important for Bone Health”, we delve into nutrients important for bone health. First, we explore the structure and function of bones, and then calcium, vitamin D, phosphorus, magnesium, fluoride, and vitamin K. A look at osteoporosis and at supplements rounds out this chapter.

• In Chapter 10 “Nutrients Important for Metabolism and Blood Function”, we look at the nutrients important in energy metabolism and blood health, by first looking at blood and at metabolism, and then discussing the B vitamins, vitamin K, magnesium, iron, zinc, and other micronutrients. We also explore iron-deficient anemia and iron toxicity.

• In Chapter 11 “Energy Balance and Body Weight”, we take a look at the obesity epidemic and eating disorders—the extremes of energy imbalance—and we look at evidence-based recommendations for maintaining a healthy weight.

• Chapter 12 “Nutrition through the Life Cycle: From Pregnancy to the Toddler Years” is the first of two chapters exploring nutrition through

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the life cycle and it looks at pregnancy through the toddler years. Topics include pregnancy, breastfeeding, introducing solid foods, and nutrition during the toddler years.

• In Chapter 13 “Nutrition through the Life Cycle: From Childhood to the Elderly Years” we continue to explore nutrition through the life cycle, this time looking at childhood to the elderly years.

• In Chapter 14 “Nutrition and Society: Food Politics and Perspectives”, we explore food politics, sustainability, the food industry, food security, and diets from around the world.

• In Chapter 15 “Achieving Optimal Health: Wellness and Nutrition”, we look at a number of topics of interest to students: diet trends, food supplements and food replacements, fitness, chronic diseases, and food safety. Also included in this chapter are tips for living a sustainable lifestyle, and information about careers in nutrition.

Features

Each chapter starts with a “Big Idea,” which provides a preview of the main theme of the chapter.

You Decide challenges you to apply what you are learning about nutrition topics—sometimes controversial ones—to your own life.

Key Takeaways and Key Terms provide the key take-home messages and definitions from each section, helping you to focus on the main points you should be learning.

Discussion Starters are questions that can prompt discussions with fellow students and your instructor to examine and extend what you’ve learned in the chapter.

There are many Videos available online and it is not always clear which ones have reliable information. We have done the legwork for you by providing interesting videos from reputable sources to accompany and highlight the content. Similarly, we provide links to useful online learning tools through the Interactive feature.

Most of the databases for diet analysis programs primarily feature industrial food. As we promote sustainable food activities in our text, we cannot use these common diet analysis programs because they do not cater to students who eat real food prepared at home. As a result, we provide links to http://www.choosemyplate.gov/ throughout the text. You will be encouraged to create your own meals, shop

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smarter, choose wisely, and, at the same time, foster an active attitude toward food sustainability.

Every chapter ends with Exercises, which are activities that can be used to test what has been learned in the chapter and may be used by your instructor as homework or assignment questions. There are exercises at three different levels (It’s Your Turn, Apply It, and Expand Your Knowledge) to meet the varied needs of different students.

Please do not use this book to substitute for professional medical care or advice. If you have medical concerns or questions, always seek guidance from a health-care professional. The authors and publisher are not responsible for the accuracy of any content added by faculty.

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Chapter 1

Nutrition and You

Big Idea

Nutrition is an evidence-based science. Nutritional scientists continuously advance our knowledge of nutrition by building on prior research.

As we get started on our journey into the world of health and nutrition, our first focus will be to demonstrate that nutritional science is an evolving field of study, continually being updated and supported by research, studies, and trials. Once we establish this, your confidence will be strengthened in nutritional science to help guide your eating habits. Let’s begin with the story of hurry, curry, and worry: the story of H. pylori.

Peptic ulcers are painful sores in the gastrointestinal tract and can cause symptoms of abdominal pain, nausea, loss of appetite, and weight loss. The cure for this ailment took some time for scientists to figure out. If your grandfather complained to his doctor of symptoms of peptic ulcer, he was probably told to avoid spicy foods, alcohol, and coffee, and to manage his stress. In the early twentieth century, the medical community thought peptic ulcers were caused by what you ate and drank,

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and by stress. In 1915, Dr. Bertram W. Sippy devised the “Sippy diet” for treating peptic ulcers. Dr. Sippy advised patients to drink small amounts of cream and milk every hour in order to neutralize stomach acid. And then, increasingly, introduce soft bland foods with frequent meal times. For a while this diet sometimes worked, fooling both doctors and patients. However, the disappearance of peptic ulcer symptoms was likely the result of having a full stomach all the time, as the symptoms more often occur when the stomach is empty. Ultimately, the Sippy diet did not cure peptic ulcers and in the latter 1960s scientists discovered the diet was associated with a significant increase in heart disease due to its high saturated fat content.

In the 1980s, Australian physicians Barry Marshall and Robin WarrenCurrey, R. “Ulcers—The Culprit Is H. Pylori!” National Institutes of Health, Office of Science Education. Accessed November 10, 2011. http://science.education.nih.gov/ home2.nsf/Educational+ResourcesResource+FormatsOnline+Resources+High+ School/928BAB9A176A71B585256CCD00634489 proposed a radical hypothesis—that the cause of ulcers was bacteria that could survive in the acidic environment of the stomach and small intestine. They met with significant opposition to their hypothesis but they persisted with their research. Their research led to an understanding that the spiral shape of the bacterium H. pylori allows it to penetrate the stomach’s mucous lining, where it secretes an enzyme that generates substances to neutralize the stomach’s acidity. This weakens the stomach’s protective mucous, making the tissue more susceptible to the damaging effects of acid, leading to the development of sores and ulcers. H. pylori also prompt the stomach to produce even more acid, further damaging the stomach lining. Marshall actually drank a dish of H. pylori hoping to give himself an ulcer to prove his point. A few days later he was vomiting and had inflamed tissue in his stomach. The presence of H. pylori was confirmed. He then took an antibiotic and the symptoms of H. pylori infection dissipated. Experimental success? It still took years for the medical community to be entirely convinced of the link between peptic ulcers and H. pylori.

In 1994, the National Institutes of Health held a conference on the cause of peptic ulcers. There was scientific consensus that H. pylori cause most peptic ulcers and that patients should be treated with antibiotics. In 1996, the Food and Drug Administration (FDA) approved the first antibiotic that could be used to treat patients with peptic ulcers. Nevertheless, the link between H. pylori and peptic ulcers was not sufficiently communicated to health-care providers. In fact, 75 percent of patients with peptic ulcers in the late 1990s were still being prescribed antacid medications and advised to change their diet and reduce their stress. In 1997, the Centers for Disease Control and Prevention (CDC), alongside other public health organizations, began an intensive educational campaign to convince the public and health-care providers that peptic ulcers are a curable condition

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requiring treatment with antibiotics. Today, if you go to your primary physician you will be given the option of taking an antibiotic to eradicate H. pylori from your gut. Scientists have progressed even further and mapped the entire genome of H. pylori, which will hopefully aid in the discovery of even better drugs to treat peptic ulcers.

The H. pylori discovery was made recently, overturning a theory applied in our own time. The demystification of disease requires the continuous forward march of science, overturning old, traditional theories and discovering new, more effective ways to treat disease and promote health. In 2005, Marshall and Warren were awarded the prestigious Nobel Prize in medicine for their discovery that many stomach ulcers are caused by H. pylori—not by hurry, curry, and worry.

You Decide

Make a commitment to empower yourself with scientific evidence as a strategy for achieving a healthier diet.

A primary goal of this text is to provide you with information backed by nutritional science, and with a variety of resources that use scientific evidence to optimize health and prevent disease. In this chapter you will see that there are many conditions and deadly diseases that can be prevented by good nutrition. You will also discover the many other determinants of health and disease, how the powerful tool of scientific investigation is used to design dietary guidelines, and recommendations that will promote health and prevent disease.

“The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ but ‘That’s funny…’”

– Isaac Asimov (January 2, 1920–April 6, 1992)

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1.1 Defining Nutrition, Health, and Disease

LEARNING OBJECTIVE

1. Explain the terms nutrition, health, health promotion, and disease prevention.

Your View of Food

Americans are bombarded with television programs that show where to find the best dinners, pizzas, and cakes, and the restaurants that serve the biggest and juiciest burgers. Other programs feature chefs battling to prepare meals, and the top places to burst your belly from consuming atomic chicken wings and deli sandwiches longer than a foot. There are also shows that feature bizarre foods from cultures around the world. How do you use the information from popular network food shows to build a nutritious meal? You don’t—these shows are for entertainment. The construction of a nutritious meal requires learning about which foods are healthy and which foods are not, how foods and nutrients function in your body, and how to use scientific resources. This text is designed to provide you with the information necessary to make sound nutritional choices that will optimize health and help prevent disease.

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The word nutrition first appeared in 1551 and comes from the Latin word nutrire, meaning “to nourish.” Today, we define nutrition1 as the sum of all processes involved in how organisms obtain nutrients, metabolize them, and use them to support all of life’s processes. Nutritional science2 is the investigation of how an organism is nourished, and incorporates the study of how nourishment affects personal health, population health, and planetary health. Nutritional science covers a wide spectrum of disciplines. As a result, nutritional scientists can specialize in particular aspects of nutrition such as biology, physiology, immunology, biochemistry, education, psychology, sustainability, and sociology.

Without adequate nutrition the human body does not function optimally, and severe nutritional inadequacy can lead to disease and even death. The typical American diet is lacking in many ways, from not containing the proper amounts of essential nutrients, to being too speedily consumed, to being only meagerly satisfying. Dietitians are nutrition professionals who integrate their knowledge of nutritional science into helping people achieve a healthy diet and develop good dietary habits. The Academy of Nutrition and Dietetics (AND) is the largest organization of nutrition professionals worldwide and dietitians registered with the AND are committed to helping Americans eat well and live healthier lives. To learn more from the AND’s nutritional advice, visit http://www.eatright.org/ default.aspx.

Your ability to wake up, to think clearly, to communicate, to hope, to dream, to go to school, to gain knowledge, to go to work, to earn a living, and to do all of the things that you like to do are dependent upon one factor—your health. Good health means you are able to function normally and work hard to achieve your goals in life. For the next few minutes, take some time to view snapshots of the insides of the refrigerators of American mechanics, doctors, school teachers, hunters, short- order cooks, college students, vegans, and more. Visit Mark Menjivar’s portrait exhibition, “You Are What You Eat” (Note 1.7 “Interactive 1.1”). Menjivar hopes these images will invoke new thoughts about, “How we care for our bodies. How we care for others. And how we care for the land.” As you look at these images think about your personal health, the health of your family and friends, and the health of this planet. These hopes encompass the inspirations for this book.

1. The sum of all processes involved in how organisms obtain nutrients, metabolize them, and use them to support all of life’s processes.

2. The investigation of how an organism is nourished, and how nourishment affects personal health, population health, and planetary health.

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Interactive 1.1

Mark Menjivar has traveled around the United States taking photographs of the contents of refrigerators of numerous types of people. The portraits are available for viewing on his website under “You Are What You Eat.”

http://markmenjivar.com/you-are-what-you-eat/statement/

Nutrition and Health and Disease

In 1946, the World Health Organization (WHO) defined health3 as “a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity.”World Health Organization. Preamble to the Constitution of the World Health Organization as adopted by the International Health Conference, New York, June 19–July 22, 1946. http://www.who.int/suggestions/faq/en/ This definition was adopted into the WHO consititution in 1948 and has not been ammended since. A triangle is often used to depict the equal influences of physical, mental, and social well-being on health. Disease4 is defined as any abnormal condition affecting the health of an organism, and is characterized by specific signs and symptoms. Signs refer to identifying characteristics of a disease such as swelling, weight loss, or fever. Symptoms are the features of a disease recognized by a patient and/or their doctor. Symptoms can include nausea, fatigue, irritability, and pain. Diseases are broadly categorized as resulting from pathogens (i.e., bacteria, viruses, fungi, and parasites), deficiencies, genetics, and physiological dysfunction. Diseases that primarily affect physical health are those that impair body structure (as is the case with osteoporosis), or functioning (as is the case with cardiovascular disease). Mental illnesses primarily affect mental and social well- being.

3. A state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity.

4. Any abnormal condition that affects the health of an organism and is characterized by specific signs and symptoms.

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The foods we eat affect all three aspects of our health. For example, a teen with Type 2 diabetes (a disease brought on by poor diet) is first diagnosed by physical signs and symptoms such as increased urination, thirstiness, and unexplained weight loss. But research has also found that teens with Type 2 diabetes have impaired thinking and do not interact well with others in school, thereby affecting mental and social well- being. Type 2 diabetes is just one example of a physiological disease that affects all aspects of health—physical, mental, and social.

Public Health and Disease Prevention

In 1894, the first congressional funds were appropriated to the US Department of Agriculture (USDA) for the study of the relationship between nutrition and human health. Dr. Wilbur Olin Atwater was appointed as the Chief of Nutrition Investigations and is accoladed as the “Father of Nutrition Science” in America.Combs, G.F. “Celebration of the Past: Nutrition at USDA.” J Nutr 124, no. 9 supplement (1994): 1728S–32S. http://jn.nutrition.org/content/124/9_Suppl/ 1728S.long Under his guidance the USDA released the first bulletin to the American public that contained information on the amounts of fat, carbohydrates, proteins, and food energy in various foods. Nutritional science advanced considerably in these early years, but it took until 1980 for the USDA and the US Department of Health and Human Services (HHS) to jointly release the first edition of Nutrition and Your Health: Dietary Guidelines for Americans.

Although wide distribution of dietary guidelines did not come about until the 1980s, many historical events that demonstrated the importance of diet to health preceded their release. Assessments of the American diet in the 1930s led President Franklin D. Roosevelt to declare in his inaugural address on January 20, 1937, “I see one-third of our nation is ill-housed, ill-clad, and ill-nourished.” From the time of Atwater until the onset of the Great Depression nutritional scientists had discovered many of the vitamins and minerals essential for the functioning of the human body. Their work and the acknowledgement by President FDR of the nutritional inadequacy of the American diet evoked a united response between scientists and government leading to the enrichment of flour, the development of school lunch programs, and advancements of nutritional education in this country.

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Figure 1.2 The Federal Government’s New and Improved Tool of Nutritional Communication

In the latter part of the twentieth century nutritional scientists, public health organizations, and the American public increasingly recognized that eating too much of certain foods is linked to chronic diseases. We now know that diet-related conditions and diseases include hypertension (high blood pressure), obesity, Type 2 diabetes, cardiovascular disease, some cancers, and osteoporosis. These diet-related conditions and diseases are some of the biggest killers of Americans. The HHS reports that unhealthy diets and inactivity cause between 310,000 and 580,000 deaths every single year.Center for Science in the Public Interest. “Nutrition Policy.” Accessed March 1, 2012. http://www.cspinet.org/nutritionpolicy/ nutrition_policy.html#disease According to the USDA, eating healthier could save Americans over $70 billion per year and this does not include the cost of obesity, which is estimated to cost a further $117 billion per year.Combs, G.F. “Celebration of the Past: Nutrition at USDA.” J Nutr 124, no. 9 supplement (1994): 1728S–32S. http://jn.nutrition.org/content/124/9_Suppl/1728S.long Unfortunately, despite the fact that the prevalence of these diseases can be decreased by healthier diets and increased physical activity, the CDC reports that the federal government spends one thousand times more to treat disease than to prevent it ($1,390 versus $1.21 per person each year).Combs, G.F. “Celebration of the Past: Nutrition at USDA.” J Nutr 124, no. 9 supplement (1994): 1728S–32S. http://jn.nutrition.org/content/124/ 9_Suppl/1728S.long In 2010, the new edition of the dietary guidelines identified

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obesity as the number one nutritional-related health problem in the United States and established strategies to combat its incidence and health consequences in the American population. A 2008 study in the journal Obesity reported that if current trends are not changed, 100 percent of Americans will be overweight or obese in 2048!Wang Y, et al. “Will All Americans Become Overweight or Obese? Estimating the Progression and Cost of the US Obesity Epidemic.” Obesity 10, no. 16 (October 2008): 2323–30. http://www.nature.com/oby/journal/v16/n10/full/ oby2008351a.html In 2011, the US federal government released a new multimedia tool that aims to help Americans choose healthier foods from the five food groups (grains, vegetables, fruits, dairy, and proteins). The tool, called “Choose MyPlate,” is available at choosemyplate.gov.

KEY TAKEAWAYS

• Health is defined as “a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity.”World Health Organization. “WHO definition of health.” http://www.who.int/ about/definition/en/print.html.

• Disease is defined as any abnormal condition that affects the health of an organism, and is characterized by specific signs and symptoms.

• Disease affects all three aspects of the health triangle. • Good nutrition provides a mechanism to promote health and prevent

disease. • Diet-related conditions and diseases include obesity, Type 2 diabetes,

cardiovascular disease, some cancers, and osteoporosis. • It took until the 1980s for the US federal government to develop a diet-

related public policy designed to equip Americans with the tools to change to a healthier diet.

DISCUSSION STARTERS

1. How might the way we nourish our bodies affect planetary health? 2. Debate your classmates: Should the federal government be concerned

with what Americans eat?

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1.2 What Are Nutrients?

LEARNING OBJECTIVES

1. Define the word “nutrient” and identify the six classes of nutrients essential for health.

2. List the three energy-yielding nutrients and their energy contribution.

What’s in Food?

The foods we eat contain nutrients5. Nutrients are substances required by the body to perform its basic functions. Nutrients must be obtained from diet, since the human body does not synthesize them. Nutrients are used to produce energy, detect and respond to environmental surroundings, move, excrete wastes, respire

5. Substances required by the body that must be obtained from the diet.

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(breathe), grow, and reproduce. There are six classes of nutrients required for the body to function and maintain overall health. These are carbohydrates, lipids, proteins, water, vitamins, and minerals. Foods also contain nonnutrients that may be harmful (such as cholesterol, dyes, and preservatives) or beneficial (such as antioxidants). Nonnutrient substances in food will be further explored in Chapter 8 “Nutrients Important As Antioxidants”.

Macronutrients

Nutrients that are needed in large amounts are called macronutrients6. There are three classes of macronutrients: carbohydrates, lipids, and proteins. These can be metabolically processed into cellular energy. The energy from macronutrients comes from their chemical bonds. This chemical energy is converted into cellular energy that is then utilized to perform work, allowing our bodies to conduct their basic functions. A unit of measurement of food energy is the calorie. On nutrition food labels the amount given for “calories” is actually equivalent to each calorie multiplied by one thousand. A kilocalorie (one thousand calories, denoted with a small “c”) is synonymous with the “Calorie” (with a capital “C”) on nutrition food labels. Water is also a macronutrient in the sense that you require a large amount of it, but unlike the other macronutrients it does not yield calories.

Carbohydrates

Carbohydrates7 are molecules composed of carbon, hydrogen, and oxygen. The major food sources of carbohydrates are grains, milk, fruits, and starchy vegetables like potatoes. Nonstarchy vegetables also contain carbohydrates, but in lesser quantities. Carbohydrates are broadly classified into two forms based on their chemical structure: fast-releasing carbohydrates, often called simple sugars, and slow-releasing carbohydrates.

Fast-releasing carbohydrates consist of one or two basic units. Examples of simple sugars include sucrose, the type of sugar you would have in a bowl on the breakfast table, and glucose, the type of sugar that circulates in your blood.

6. Nutrients that are needed in large amounts. Includes carbohydrates, lipids, proteins, and water.

7. Organic molecules composed of carbon, hydrogen, and oxygen. There are two basic forms: simple sugars and complex sugars.

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Slow-releasing carbohydrates are long chains of simple sugars that can be branched or unbranched. During digestion, the body breaks down all slow-releasing carbohydrates to simple sugars, mostly glucose. Glucose is then transported to all our cells where it is stored, used to make energy, or used to build macromolecules. Fiber is also a slow-releasing carbohydrate, but it cannot be broken down in the human body and passes through the digestive tract undigested unless the bacteria that inhabit the gut break it down.

One gram of carbohydrates yields four kilocalories of energy for the cells in the body to perform work. In addition to providing energy and serving as building blocks for bigger macromolecules, carbohydrates are essential for proper functioning of the nervous system, heart, and kidneys. As mentioned, glucose can be stored in the body for future use. In humans, the storage molecule of carbohydrates is called glycogen and in plants it is known as starches. Glycogen and starches are slow-releasing carbohydrates.

Lipids

Lipids8 are also a family of molecules composed of carbon, hydrogen, and oxygen, but unlike carbohydrates, they are insoluble in water. Lipids are found predominately in butter, oils, meats, dairy products, nuts, and seeds, and in many processed foods. The three main types of lipids are triglycerides (triacylglycerols),

8. A family of organic compounds composed of carbon, hydrogen, and oxygen. They are insoluble in water. The three main types of lipids are triglycerides, phospholipids, and sterols.

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phospholipids, and sterols. The main job of lipids is to store energy. Lipids provide more energy per gram than carbohydrates (nine kilocalories per gram of lipids versus four kilocalories per gram of carbohydrates). In addition to energy storage, lipids serve as cell membranes, surround and protect organs, aid in temperature regulation, and regulate many other functions in the body.

Proteins

Proteins9 are macromolecules composed of chains of subunits called amino acids. Amino acids are simple subunits composed of carbon, oxygen, hydrogen, and nitrogen. The food sources of proteins are meats, dairy products, seafood, and a variety of different plant-based foods, most notably soy. The word protein comes from a Greek word meaning “of primary importance,” which is an apt description of these macronutrients; they are also known colloquially as the “workhorses” of life. Proteins provide four kilocalories of energy per gram; however providing energy is not protein’s most important function. Proteins provide structure to bones, muscles and skin, and play a role in conducting most of the chemical reactions that take place in the body. Scientists estimate that greater than one-hundred thousand different proteins exist within the human body.

Water

There is one other nutrient that we must have in large quantities: water. Water does not contain carbon, but is composed of two hydrogens and one oxygen per molecule of water. More than 60 percent of your total body weight is water. Without it, nothing could be transported in or out of the body, chemical reactions would not occur, organs would not be cushioned, and body temperature would fluctuate widely. On average, an adult consumes just over two liters of water per day from food and drink. According to the “rule of threes,” a generalization supported by survival experts, a person can survive three minutes without oxygen, three days without water, and three weeks without food. Since water is so critical for life’s basic processes, the amount of water input and output is supremely important, a topic we will explore in detail in Chapter 7 “Nutrients Important to Fluid and Electrolyte Balance”.

Micronutrients

Micronutrients10 are nutrients required by the body in lesser amounts, but are still essential for carrying out bodily functions. Micronutrients include all the essential minerals and vitamins. There are sixteen essential minerals and thirteen vitamins (See Table 1.1 “Minerals and Their Major Functions” and Table 1.2 “Vitamins and Their Major Functions” for a complete list and their major functions). In contrast to carbohydrates, lipids, and proteins, micronutrients are not directly used for making

9. Macromolecules composed of chains of organic monomeric subunits, called amino acids. Amino acids are simple monomers composed of carbon, oxygen, hydrogen, and nitrogen.

10. Nutrients needed in smaller amounts. Includes vitamins and minerals.

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energy, but they assist in the process as being part of enzymes (i.e., coenzymes). Enzymes are proteins that catalyze chemical reactions in the body and are involved in all aspects of body functions from producing energy, to digesting nutrients, to building macromolecules. Micronutrients play many roles in the body.

Minerals

Minerals are solid inorganic substances that form crystals and are classified depending on how much of them we need. Trace minerals, such as molybdenum, selenium, zinc, iron, and iodine, are only required in a few milligrams or less and macrominerals, such as calcium, magnesium, potassium, sodium, and phosphorus, are required in hundreds of milligrams. Many minerals are critical for enzyme function, others are used to maintain fluid balance, build bone tissue, synthesize hormones, transmit nerve impulses, contract and relax muscles, and protect against harmful free radicals.

Table 1.1 Minerals and Their Major Functions

Minerals Major Functions

Macro

Sodium Fluid balance, nerve transmission, muscle contraction

Chloride Fluid balance, stomach acid production

Potassium Fluid balance, nerve transmission, muscle contraction

Calcium Bone and teeth health maintenance, nerve transmission, musclecontraction, blood clotting

Phosphorus Bone and teeth health maintenance, acid-base balance

Magnesium Protein production, nerve transmission, muscle contraction

Sulfur Protein production

Trace

Iron Carries oxygen, assists in energy production

Zinc Protein and DNA production, wound healing, growth, immune systemfunction

Iodine Thyroid hormone production, growth, metabolism

Selenium Antioxidant

Copper Coenzyme, iron metabolism

Manganese Coenzyme

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Minerals Major Functions

Fluoride Bone and teeth health maintenance, tooth decay prevention

Chromium Assists insulin in glucose metabolism

Molybdenum Coenzyme

Vitamins

The thirteen vitamins are categorized as either water-soluble or fat-soluble. The water-soluble vitamins are vitamin C and all the B vitamins, which include thiamine, riboflavin, niacin, pantothenic acid, pyroxidine, biotin, folate and cobalamin. The fat-soluble vitamins are A, D, E, and K. Vitamins are required to perform many functions in the body such as making red blood cells, synthesizing bone tissue, and playing a role in normal vision, nervous system function, and immune system function.

Vitamin deficiencies can cause severe health problems. For example, a deficiency in niacin causes a disease called pellagra, which was common in the early twentieth century in some parts of America. The common signs and symptoms of pellagra are known as the “4D’s—diarrhea, dermatitis, dementia, and death.” Until scientists found out that better diets relieved the signs and symptoms of pellagra, many people with the disease ended up in insane asylums awaiting death. Other vitamins were also found to prevent certain disorders and diseases such as scurvy (vitamin C), night blindness (vitamin A), and rickets (vitamin D).

Table 1.2 Vitamins and Their Major Functions

Vitamins Major Functions

Water-soluble

B1 (thiamine) Coenzyme, energy metabolism assistance

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Vitamins Major Functions

B2 (riboflavin) Coenzyme, energy metabolism assistance

B3 (niacin) Coenzyme, energy metabolism assistance

B5 (pantothenic acid) Coenzyme, energy metabolism assistance

B6 (pyroxidine) Coenzyme, amino acid synthesis assistance

Biotin Coenzyme

Folate Coenzyme, essential for growth

B12 (cobalamin) Coenzyme, red blood cell synthesis

C Collagen synthesis, antioxidant

Fat-soluble

A Vision, reproduction, immune system function

D Bone and teeth health maintenance, immune system function

E Antioxidant, cell membrane protection

K Bone and teeth health maintenance, blood clotting

Food Quality

One measurement of food quality is the amount of nutrients it contains relative to the amount of energy it provides. High-quality foods are nutrient dense, meaning they contain lots of the nutrients relative to the amount of calories they provide. Nutrient-dense foods are the opposite of “empty-calorie” foods such as carbonated sugary soft drinks, which provide many calories and very little, if any, other nutrients. Food quality is additionally associated with its taste, texture, appearance, microbial content, and how much consumers like it.

Food: A Better Source of Nutrients

It is better to get all your micronutrients from the foods you eat as opposed to from supplements. Supplements contain only what is listed on the label, but foods contain many more macronutrients, micronutrients, and other chemicals, like antioxidants that benefit health. While vitamins, multivitamins, and supplements are a $20 billion industry in this country and more than 50 percent of Americans purchase and use them daily, there is no consistent evidence that they are better than food in promoting health and preventing disease. Dr. Marian Neuhouser, associate of the Fred Hutchinson Cancer Research Center in Seattle, says that “…scientific data are lacking on the long-term health benefits of supplements. To our surprise, we found that multivitamins did not lower the risk of the most

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common cancers and also had no impact on heart disease.”Woodward, K. “Multivitamins Each Day Will Not Keep Common Cancers Away; Largest Study of Its Kind Provides Definitive Evidence that Multivitamins Will Not Reduce Risk of Cancer or Heart Disease in Postmenopausal Women.” Fred Hutchinson Cancer Research Center. Center News 16 (February 2009). http://www.fhcrc.org/about/ pubs/center_news/online/2009/02/multivitamin_study.html

KEY TAKEAWAYS

• Foods contain nutrients that are essential for our bodies to function. • Four of the classes of nutrients required for bodily function are needed

in large amounts. They are carbohydrates, lipids, proteins, and water, and are referred to as macronutrients.

• Two of the classes of nutrients are needed in lesser amounts, but are still essential for bodily function. They are vitamins and minerals.

• One measurement of food quality is the amount of essential nutrients a food contains relative to the amount of energy it has (nutrient density).

DISCUSSION STARTERS

1. Make a list of some of your favorite foods and visit the “What’s In the Foods You Eat?” search tool provided by the USDA. What are some of the nutrients found in your favorite foods?

http://www.ars.usda.gov/Services/docs.htm?docid=17032

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1.3 The Broad Role of Nutritional Science

LEARNING OBJECTIVE

1. Provide an example of how the scientific method works to promote health and prevent disease.

How to Determine the Health Effects of Food and Nutrients

Similar to the method by which a police detective finally charges a criminal with a crime, nutritional scientists discover the health effects of food and its nutrients by first making an observation. Once observations are made, they come up with a hypothesis, test their hypothesis, and then interpret the results. After this, they gather additional evidence from multiple sources and finally come up with a conclusion on whether the food suspect fits the claim. This organized process of inquiry used in forensic science, nutritional science, and every other science is called the scientific method11.

Below is an illustration of the scientific method at work—in this case to prove that iodine is a nutrient.Zimmerman, M.B. “Research on Iodine Deficiency and Goiter in the 19th and Early 20th Centuries.” J Nutr 138, no. 11 (November 2008): 2060–63. http://jn.nutrition.org/content/138/11/2060.full, Carpenter, K.J. “David Marine and the Problem of Goiter.” J Nutr 135, no.4 (April 2005): 675–80. http://jn.nutrition.org/content/135/4/675.full?sid=d06fdd35-566f -42a2-a3fd- efbe0736b7ba In 1811, French chemist Bernard Courtois was isolating saltpeter for producing gunpowder to be used by Napoleon’s army. To carry out this isolation he burned some seaweed and in the process observed an intense violet vapor that crystallized when he exposed it to a cold surface. He sent the violet crystals to an expert on gases, Joseph Gay-Lussac, who identified the crystal as a new element. It was named iodine, the Greek word for violet. The following scientific record is some of what took place in order to conclude that iodine is a nutrient.

Observation. Eating seaweed is a cure for goiter, a gross enlargement of the thyroid gland in the neck.

Hypothesis. In 1813, Swiss physician Jean-Francois Coindet hypothesized that the seaweed contained iodine and he could use just iodine instead of seaweed to treat his patients.

11. The process of inquiry that involves making an observation, coming up with a hypothesis, conducting a test of that hypothesis, evaluating results, gathering more supporting evidence, and coming up with a conclusion.

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Experimental test. Coindet administered iodine tincture orally to his patients with goiter.

Interpret results. Coindet’s iodine treatment was successful.

Gathering more evidence. Many other physicians contributed to the research on iodine deficiency and goiter.

Hypothesis. French chemist Chatin proposed that the low iodine content in food and water of certain areas far away from the ocean were the primary cause of goiter and renounced the theory that goiter was the result of poor hygiene.

Experimental test. In the late 1860s the program, “The stamping-out of goiter,” started with people in several villages in France being given iodine tablets.

Results. The program was effective and 80 percent of goitrous children were cured.

Hypothesis. In 1918, Swiss doctor Bayard proposed iodizing salt as a good way to treat areas endemic with goiter.

Experimental test. Iodized salt was transported by mules to a small village at the base of the Matterhorn where more than 75 percent of school children were goitrous. It was given to families to use for six months.

Results. The iodized salt was beneficial in treating goiter in this remote population.

Experimental test. Physician David Marine conducted the first experiment of treating goiter with iodized salt in America in Akron, Ohio.

Results. This study conducted on over four-thousand school children found that iodized salt prevented goiter.

Conclusions. Seven other studies similar to Marine’s were conducted in Italy and Switzerland that also demonstrated the effectiveness of iodized salt in treating goiter. In 1924, US public health officials initiated the program of iodizing salt and started eliminating the scourge of goiterism. Today more than 70 percent of American households use iodized salt and many other countries have followed the same public health strategy to reduce the health consequences of iodine deficiency.

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Evidence-Based Approach to Nutrition

It took more than one hundred years from iodine’s discovery as an effective treatment for goiter until public health programs recognized it as such. Although a lengthy process, the scientific method is a productive way to define essential nutrients and determine their ability to promote health and prevent disease. The scientific method is part of the overall evidence-based approach to designing nutritional guidelines. An evidence-based approach to nutrition includes:Briss, P.A., et al. “Developing an Evidence-Based Guide to Community Preventive Services—Methods.” Am J Prev Med 18, no. 1S (2000): 35–43., Myers, E. “Systems for Evaluating Nutrition Research for Nutrition Care Guidelines: Do They Apply to Population Dietary Guidelines?” J Am Diet Assoc 103, no. 12, supplement 2 (December 2003): 34–41.

• Defining the problem or uncertainty (e.g., the rate of colon cancer is higher in people who eat red meat)

• Formulating it as a question (e.g., Does eating red meat contribute to colon cancer?)

• Setting criteria for quality evidence • Evaluating the body of evidence • Summarizing the body of evidence and making decisions • Specifying the strength of the supporting evidence required to make

decisions • Disseminating the findings

The Food and Nutrition Board of the Institute of Medicine, a nonprofit, nongovernmental organization, constructs its nutrient recommendations (i.e., Dietary Reference Intakes, or DRI) using an evidence-based approach to nutrition. The entire procedure for setting the DRI is documented and made available to the public. The same approach is used by the USDA and HHS, which are departments of the US federal government. The USDA and HHS websites are great tools for discovering ways to optimize health; however, it is important to gather nutrition information from multiple resources as there are often differences in opinion among various scientists and public health organizations. While the new Dietary Guidelines, published in 2010, have been well-received by some, there are nongovernmental public health organizations that are convinced that some pieces of the guidelines may be influenced by lobbying groups and/or the food industry. For example, the Harvard School of Public Health (HSPH) feels the government falls short by being “too lax on refined grains.”The Harvard School of Public Health. “New US Dietary Guidelines: Progress, Not Perfection.” © 2012 The President and Fellows of Harvard College. http://www.hsph.harvard.edu/nutritionsource/what- should-you-eat/dietary-guidelines -2010/index.html The guidelines recommend

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getting at least half of grains from whole grains—according to the HSPH this still leaves too much consumption of refined grains.

For a list of reliable sources that advocate good nutrition to promote health and prevent disease using evidence-based science see Table 1.3 “Web Resources for Nutrition and Health”. In Chapter 2 “Achieving a Healthy Diet”, we will further discuss distinguishing criteria that will enable you to wade through misleading nutrition information and instead gather your information from reputable, credible websites and organizations.

Table 1.3 Web Resources for Nutrition and Health

Organization Website

Governmental

US Department of Agriculture http://www.usda.gov/wps/portal/usda/usdahome

USDA Center for Nutrition Policy and Promotion http://www.cnpp.usda.gov/

US Department of Health and Human Services http://www.hhs.gov/

Centers for Disease Control and Prevention http://www.cdc.gov/

Food and Drug Administration http://www.fda.gov/

Healthy People http://www.healthypeople.gov/2020/default.aspx

Office of Disease Prevention and Health Promotion http://odphp.osophs.dhhs.gov/

Health Canada http://www.hc-sc.gc.ca/

International

World Health Organization http://www.who.int/en/

Food and Agricultural Organization of the United Nations http://www.fao.org/

Nongovernmental

Harvard School of Public Health http://www.hsph.harvard.edu/nutritionsource/index.html

Mayo Clinic http://www.mayoclinic.com/

Linus Pauling Institute http://lpi.oregonstate.edu/

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Organization Website

American Society for Nutrition http://www.nutrition.org/

American Medical Association http://www.ama-assn.org/

American Diabetes Association http://www.diabetes.org/

The Academy of Nutrition and Dietetics http://www.eatright.org/

Institute of Medicine: Food and Nutrition http://www.iom.edu/Global/Topics/Food-Nutrition.aspx

Dietitians of Canada http://www.dietitians.ca/

Types of Scientific Studies

There are many types of scientific studies that can be used to provide supporting evidence for a particular hypothesis. The various types of studies include epidemiological studies, interventional clinical trials, and randomized clinical interventional trials.

Epidemiological studies12 are observational studies and are often the front-line studies for public health. The CDC defines epidemiological studies as scientific investigations that define frequency, distribution, and patterns of health events in a population. Thus, these studies describe the occurrence and patterns of health events over time. The goal of an epidemiological study is to find factors associated with an increased risk for a health event, though these sometimes remain elusive. An example of an epidemiological study is the Framingham Heart Study, a project of the National Heart, Lung and Blood Institute and Boston University that has been ongoing since 1948. This study first examined the physical health and lifestyles of 5,209 men and women from the city of Framingham, Massachusetts and has now incorporated data from the children and grandchildren of the original participants. One of the seminal findings of this ambitious study was that higher cholesterol levels in the blood are a risk factor for heart disease.The Framingham Heart Study, a project of the National Heart, Lung, and Blood Institute and Boston University. “History of the Framingham Heart Study.” © 2012 Framingham Heart Study. http://www.framinghamheartstudy.org/about/history.html Epidemiological studies are a cornerstone for examining and evaluating public health and some of their advantages are that they can lead to the discovery of disease patterns and risk factors for diseases, and they can be used to predict future healthcare needs and provide information for the design of disease prevention strategies for entire populations. Some shortcomings of epidemiological studies are that investigators cannot control environments and lifestyles, a specific group of people studied may not be an accurate depiction of an entire population, and these types of scientific studies cannot directly determine if one variable causes another.

12. Scientific investigations that define frequency, distribution, and patterns of health events in a population.

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Interventional clinical trial studies13 are scientific investigations in which a variable is changed between groups of people. When well done, this type of study allows one to determine causal relationships. An example of an interventional clinical trial study is the Dietary Approaches to Stop Hypertension (DASH) trial published in the April 1997 issue of The New England Journal of Medicine.Appel, L. J., et al. “A Clinical Trial of the Effects of Dietary Patterns on Blood Pressure.,” N Engl J Med 336 (April 1997): 1117–24. http://www.nejm.org/doi/full/10.1056/ NEJM199704173361601 In this study, 459 people were randomly assigned to three different groups; one was put on an average American control diet, a second was put on a diet rich in fruits and vegetables, and the third was put on a combination diet rich in fruits, vegetables, and low-fat dairy products with reduced saturated and total fat intake. The groups remained on the diets for eight weeks. Blood pressures were measured before starting the diets and after eight weeks. Results of the study showed that the group on the combination diet had significantly lower blood pressure at the end of eight weeks than those who consumed the control diet. The authors concluded that the combination diet is an effective nutritional approach to treat high blood pressure. The attributes of high-quality clinical interventional trial studies are:

• those that include a control group, which does not receive the intervention, to which you can compare the people who receive the intervention being tested;

• those in which the subjects are randomized into the group or intervention group, meaning a given subject has an equal chance of ending up in either the control group or the intervention group. This is done to ensure that any possible confounding variables are likely to be evenly distributed between the control and the intervention groups;

• those studies that include a sufficient number of participants.

What are confounding variables? These are factors other than the one being tested that could influence the results of the study. For instance, in the study we just considered, if one group of adults did less physical activity than the other, then it could be the amount of physical activity rather than the diet being tested that caused the differences in blood pressures among the groups.

The limitations of these types of scientific studies are that they are difficult to carry on for long periods of time, are costly, and require that participants remain compliant with the intervention. Furthermore, it is unethical to study certain interventions. (An example of an unethical intervention would be to advise one group of pregnant mothers to drink alcohol to determine the effects of alcohol intake on pregnancy outcome, because we know that alcohol consumption during pregnancy damages the developing fetus.)

13. Scientific investigations in which a variable is changed between groups of people.

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Randomized clinical interventional trial studies14 are powerful tools to provide supporting evidence for a particular relationship and are considered the “gold standard” of scientific studies. A randomized clinical interventional trial is a study in which participants are assigned by chance to separate groups that compare different treatments. Neither the researchers nor the participants can choose which group a participant is assigned. However, from their limitations it is clear that epidemiological studies complement interventional clinical trial studies and both are necessary to construct strong foundations of scientific evidence for health promotion and disease prevention.

Other scientific studies used to provide supporting evidence for a hypothesis include laboratory studies conducted on animals or cells. An advantage of this type of study is that they typically do not cost as much as human studies and they require less time to conduct. Other advantages are that researchers have more control over the environment and the amount of confounding variables can be significantly reduced. Moreover, animal and cell studies provide a way to study relationships at the molecular level and are also helpful in determining the exact mechanism by which a specific nutrient causes a change in health. The disadvantage of these types of studies are that researchers are not working with whole humans and thus the results may not be relevant. Nevertheless, well- conducted animal and cell studies that can be repeated by multiple researchers and obtain the same conclusion are definitely helpful in building the evidence to support a scientific hypothesis.

Evolving Science

Science is always moving forward, albeit sometimes slowly. One study is not enough to make a guideline or a recommendation or cure a disease. Science is a stepwise process that builds on past evidence and finally culminates into a well-accepted conclusion. Unfortunately, not all scientific conclusions are developed in the interest of human health and it is important to know where a scientific study was conducted and who provided the money. Indeed, just as an air quality study paid for by a tobacco company diminishes its value in the minds of readers, so does one on red meat performed at a laboratory funded by a national beef association.

Science can also be contentious even amongst experts that don’t have any conflicting financial interests. Contentious science is actually a good thing as it forces researchers to be of high integrity, well-educated, well-trained, and dedicated. It also instigates public health policy makers to seek out multiple sources of evidence in order to support a new policy. Agreement involving many experts across multiple scientific disciplines is necessary for recommending dietary changes to improve health and prevent disease. Although a somewhat slow process,

14. Scientific investigations which incorporate a change in the variable being tested between groups of people and are therefore capable of determining a causal relationship.

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it is better for our health to allow the evidence to accumulate before incorporating some change in our diet.

Nutritional Science Evolution

One of the newest areas in the realm of nutritional science is the scientific discipline of nutritional genetics, also called nutrigenomics. Genes are part of DNA and contain the genetic information that make up all our traits. Genes are codes for proteins and when they are turned “on” or “off,” they change how the body works. While we know that health is defined as more than just the absence of disease, there are currently very few accurate genetic markers of good health. Rather, there are many more genetic markers for disease. However, science is evolving and nutritional genetics aims to identify what nutrients to eat to “turn on” healthy genes and “turn off” genes that cause disease. Eventually this field will progress so that a person’s diet can be tailored to their genetics. Thus, your DNA will determine your optimal diet.

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Using Science and Technology to Change the Future

As science evolves, so does technology. Both can be used to create a healthy diet, optimize health, and prevent disease. Picture yourself not too far into the future: you are wearing a small “dietary watch” that painlessly samples your blood, and downloads the information to your cell phone, which has an app that evaluates the nutrient profile of your blood and then recommends a snack or dinner menu to assure you maintain adequate nutrient levels. What else is not far off? How about another app that provides a shopping list that adheres to all dietary guidelines and is emailed to the central server at your local grocer who then delivers the food to your home? The food is then stored in your smart fridge which documents your daily diet at home and delivers your weekly dietary assessment to your home computer. At your computer, you can compare your diet with other diets aimed at weight loss, optimal strength training, reduction in risk for specific diseases or any other health goals you may have. You may also delve into the field of nutritional genetics and download your gene expression profiles to a database that analyzes yours against millions of others.

KEY TAKEAWAYS

• The scientific method is an organized process of inquiry used in nutritional science to determine if the food suspect fits the claim.

• The scientific method is part of the overall evidence-based approach to designing nutritional guidelines that are based on facts.

• There are different types of scientific studies—epidemiological studies, randomized clinical interventional trial studies, and laboratory animal and cell studies—which all provide different, complementary lines of evidence.

• It takes time to build scientific evidence that culminates as a commonly accepted conclusion.

• Agreement of experts across multiple scientific disciplines is a necessity for recommending dietary changes to improve health and help to prevent disease.

• Science is always evolving as more and more information is collected.

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DISCUSSION STARTERS

1. What are some of the ways in which you think like a scientist and use the scientific method in your everyday life? Any decision-making process uses at least pieces of the scientific method. Think about some of the major decisions you have made in your life and the research you conducted that supported your decision. For example, what computer brand do you own? Where is your money invested? What college do you attend?

2. Do you use technology, appliances, and/or apps that help you to optimize your health?

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1.4 Health Factors and Their Impact

LEARNING OBJECTIVES

1. Explain the role that genetics, environment, life cycle, and lifestyle play in health status.

2. Describe economic, social, cultural, and emotional determinants that affect personal choices of foods.

In addition to nutrition, health is affected by genetics, the environment, life cycle, and lifestyle. These factors are referred to as “determinants” of health and they all interact with each other. For example, family income influences the food choices available and the quantity and quality of food that can be purchased, which of course affects nutrition. Except for nutrition and lifestyle, these factors can be difficult or impossible to change.

Genetics

Everyone starts out in life with the genes handed down to them from the families of their mother and father. Genes15 are responsible for your many traits as an individual and are defined as the sequences of DNA that code for all the proteins in your body. The expression of different genes can determine the color of your hair, skin, and eyes, and even if you are more likely to be fat or thin and if you have an increased risk for a certain disease. The sequence of DNA that makes up your genes determines your genetic makeup, also called your genome16, which is inherited from your mother and father. In 2003, the Human Genome Project was completed and now the entire sequence of DNA in humans is known. It consists of about three billion individual units and contains between twenty-five and thirty thousand genes. The human genome that was sequenced was taken from a small population of donors and is used as a reference DNA sequence for the entire population. Each of us has a similar but unique DNA sequence. Only identical twins and cloned animals have the exact same DNA sequence.

15. The sequences of DNA that code for all the proteins in your body.

16. Entire genetic information contained in an individual which is inherited from their parents.

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Now that we understand the map of the human genome, let’s enter the fields of nutrigenomics and epigenetics. Recall that nutrigenomics17 is an emerging scientific discipline aimed at defining healthy genes and not-so- healthy genes and how nutrients affect them. Currently, scientists cannot change a person’s DNA sequence. But they have discovered that chemical reactions in the body can turn genes “on” and “off,” causing changes in the amounts and types of proteins expressed. Epigenetics18 is another rapidly advancing scientific field in which researchers study how chemical reactions turn genes “on” and “off” and the factors that influence the chemical reactions. Some of these factors are now known to be nutrients. Researchers at the Genetic

Science Learning Center at the University of Utah conducted an experiment in which some pregnant mice were fed a diet containing folate, choline, vitamin B12, and betaine, and other pregnant mice were fed a diet that did not contain these nutrients and chemicals. Both groups of pregnant mice were also fed bisphenol A, a chemical in plastic, which alters DNA by inhibiting a specific chemical reaction. The mice born from the mother fed the supplemented diet were brown, thin, and healthy. The mice born from the mother fed the unsupplemented diet were yellow, fat, and unhealthy. This is a dramatic example of how nutrients change not the sequence of DNA, but which genes are expressed. These two mice look different, but have identical DNA sequences. Thus, not only do the things you eat determine your health, but so do the things your mother ate during pregnancy. Moreover, other studies have demonstrated what your dad ate—and what your grandmother ate while she was pregnant with your mother!—also can affect your gene expression and, consequently, your health. Does this make it OK for you to blame your mother and father for all of your shortcomings? No. Genetics are important in determining your health, but they are certainly not the only determinant.

17. An emerging scientific discipline that studies how nutrients affect gene expression.

18. A rapidly advancing scientific field, in which researchers study how non-gene factors affect gene expression.

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Interactive 1.2

This is a good animation of the central foundation of modern biology. Turn “on” a gene, make messenger RNA, and make protein. Spin the dial all the way to the left to turn off the expression, and then slowly move it to the right.

http://learn.genetics.utah.edu/content/epigenetics/control/

Source: Genetic Science Learning Center at the University of Utah.

The Life Cycle

The life cycle19 of human beings originates from a fertilized egg, which develops into a fetus that is eventually born as a baby. A baby develops into a child, transitions through the wonderful phase of adolescence, becomes an adult, and then advances into old age and eventually death. The current average life expectancy in America is approaching eighty. To see how this compares with other countries, see Note 1.39 “Interactive 1.3”.

19. The stages of life one passes through until death.

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Interactive 1.3

Visit this public database from the World Bank to learn how the life expectancy in America differs from those in other countries.

http://www.google.com/publicdata?ds=wb- wdi&met_y=sp_dyn_le00_in&idim=country:USA&dl=en&hl= en&q=america+average+life+expectancy

A person’s stage of life influences their health and nutritional requirements. For example, when you are an adolescent, your bones grow quickly. More calcium, a bone-building nutrient, is required in the diet during this life stage than at other ages. As you get older, the aging process affects how your body functions. One effect of aging, apparently earlier in women than in men, is the deterioration of bone tissue. As a result, women over age fifty-one need more calcium in their diet than younger adult women. Another life-cycle stage, pregnancy, requires several adjustments to nutrition compared to nonpregnant women. It is recommended that

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a pregnant woman consume more protein than a nonpregnant woman to support growth and development, and to consume more of some vitamins, such as folate, to prevent certain birth defects. The USDA provides information on healthy diets for many different stages of the life cycle on their website. Healthy aging requires eating a diet that matches one’s life stages to support the body’s specific physiological requirements. What else is known to help a person age slowly and gracefully? Diets high in vegetables and fruits are associated with increased longevity and a decreased risk of many diseases.

Environment

Your environment has a large influence on your health, genetics, life cycle, and lifestyle. Scientists say that the majority of your expressed traits are a product of your genes and environment, of which nutrition is a component. An example of this interaction can be observed in people who have the rare genetic disorder, phenylketonuria (PKU). The clinical signs of PKU are mental retardation, brain

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damage, and seizures and are caused by the build-up of the amino acid phenylalanine and its metabolites (breakdown products produced during metabolism) in the body. The high level of phenylalanine in a person who has PKU is the result of a change in the gene that encodes for an enzyme that converts phenylalanine into the amino acid tyrosine. This genetic change, called a mutation, causes the enzyme to not function properly. In this country and many others all newborn babies are screened for PKU in order to diagnose and treat the disease before the development of mental retardation and brain damage. Once diagnosed, PKU is treated by strict adherence to a diet low in phenylalanine, consisting mostly of fruits, vegetables, and grains. Adhering to this diet for life allows an individual with PKU to lead a normal life without suffering the consequences of brain damage, mental retardation, or seizures. In the example of PKU, the consequences of a genetic mutation are modified by diet. Thus, a person’s genes can make them more susceptible to a particular disease, or cause a disease, and their environment can decrease or increase the progression and severity of the condition.

Socioeconomic Status

Multiple aspects of a person’s environment can affect nutrition, which in turn affects health. One of the best environmental predictors of a population’s health is socioeconomic status. Socioeconomic status20 is a measurement made up of three variables: income, occupation, and education. Socioeconomic status affects nutrition by influencing what foods you can afford and consequently, food choice and food quality. Nutrition and health are generally better in populations that have higher incomes, better jobs, and more education. On the other hand, the burden of disease is highest in the most disadvantaged populations. A commentary in the Journal of the American Medical Association reports that the lower life expectancy of populations of lower socioeconomic status is largely attributable to increased death from heart disease.Fiscella, K. and D. Tancredi. “Socioeconomic Status and Coronary Heart Disease Risk Prediction.” JAMA 300, no. 22 (2008): 2666–68. The American Heart Association states that having a healthy diet is one of the best weapons to fight heart disease and it is therefore essential that all socioeconomic status groups have access to high-quality, nutrient-dense foods. The disparities in nutrition and health in America are directly related to the disparity in socioeconomic status. Other dimensions that affect health disparity are race, ethnic group, sex, sexual identity, age, disability, and geographic location. The issue of inequitable health among Americans is recognized by the federal government and one of the overarching goals of Healthy People 2020, a large program managed by the HHS, is to “Achieve health equity, eliminate disparities, and improve the health of all groups.” To work toward this monumentous goal, the HHS is actively tracking disease patterns, chronic conditions, and death rates among the many different types of people that live in the United States. This will be further discussed in Chapter 2 “Achieving a Healthy Diet”.

20. A measurement dependent on three variables; income, occupation, and education.

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Interactive 1.4

To see the differences in causes of death for different sexes, races, and age groups, visit the website of Healthy People and compare the top ten causes of death for different populations.

http://www.healthypeople.gov/2020/default.aspx

Lifestyle

One facet of lifestyle is your dietary habits. Recall that we discussed briefly how nutrition affects health. A greater discussion of this will follow in subsequent chapters in this book as there is an enormous amount of information regarding this aspect of lifestyle. Dietary habits include what a person eats, how much a person eats during a meal, how frequently meals are consumed, and how often a person eats out at restaurants. Other aspects of lifestyle21 include physical activity level, recreational drug use, and sleeping patterns, all of which play a role in health and impact nutrition. Following a healthy lifestyle improves your overall health.

In 2008, the HHS released the Physical Activity Guidelines for Americans. The HHS states that “Being physically active is one of the most important steps that Americans of all ages can take to improve their health. The 2008 Physical Activity Guidelines for Americans provides science-based guidance to help Americans aged six and older improve their health through appropriate physical activity.” The guidelines recommend exercise programs for people in many different stages of their lifecycle and for pregnant women and adults and children who have disabilities. The HHS reports that there is strong evidence that increased physical activity decreases the risk of early death, heart disease, stroke, Type 2 diabetes, high blood pressure, and certain cancers; prevents weight gain and falls; and improves cognitive function in the elderly. Also unveiled recently are the Canadian Physical Activity Guidelines, which are available at the website of The Canadian Society for Exercise Physiology (http://www.csep.ca/english/view.asp?x=804).

21. Components of lifestyle are dietary habits, physical activity level, recreational drug use, and sleeping patterns, all of which play a role in health and impact nutrition.

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Interactive 1.5

Go to the HHS website to access the entire 2008 Physical Activity Guidelines for Americans.

http://www.health.gov/PAGuidelines/default.aspx

Recreational Drug Use

Recreational drug use, which includes tobacco-smoking and alcohol consumption along with narcotic and other illegal drug use, has a large impact on health. Smoking cigarettes causes lung cancer, eleven other types of cancer, heart disease, and several other disorders or diseases that markedly decrease quality of life and increase mortality. In the United States, smoking causes more than four hundred thousand deaths every single year, which is far more than deaths associated with any other lifestyle component.Centers for Disease Control and Prevention. “Smoking and Tobacco Use.” Last updated March 21, 2011. http://www.cdc.gov/ tobacco/data_statistics/fact_sheets/health_effects/tobacco_related_mortality/ index.htm Also, according to the CDC, excessive alcohol intake causes an estimated seventy-five thousand deaths per year.Centers for Disease Control and Prevention. “Alcohol and Drug Use.” Last updated June 7, 2012. http://www.cdc.gov/ healthyyouth/alcoholdrug/ Staying away from excessive alcohol intake lowers blood pressure, the risk from injury, heart disease, stroke, liver problems, and some types of cancer. Abstaining from alcohol also aids in weight loss and increases the money in your wallet. While heavy drinking of alcoholic beverages is associated with several bad health effects, consuming alcohol in moderation has been found to promote health such as reducing the risk for heart disease and Type 2 diabetes in some people. The HHS defines drinking in moderation as no more than one drink a day for women and two drinks a day for men.

Illicit and prescription drug abuse are associated with decreased health and is a prominent problem in the United States. The health effects of drug abuse can be far-reaching including increased risk for stroke, heart disease, cancer, lung disease, and liver disease.

Sleeping Patterns

Inadequate amounts of sleep, or not sleeping well, can also have remarkable effects on a person’s health. In fact, sleeping can affect your health just as much as diet or

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exercise. At least 10 percent of Americans have chronic insomnia.National Sleep Foundation. “Can’t Sleep? What to Know about Insomnia.” Accessed February 12, 2012. http://www.sleepfoundation.org/article/sleep-related-problems/insomnia- and-sleep. Scientific studies have shown that insufficient sleep increases the risk for heart disease, Type 2 diabetes, obesity, and depression. Abnormal breathing during sleep, a condition called sleep apnea, is also linked to an increased risk for chronic disease.

Interactive 1.6

Go to the HHS website and discover the many tools at your fingertips to live a healthier lifestyle.

http://www.healthfinder.gov/prevention/

Nutrition, Genetics, Environment, and Lifestyle Interact to Affect Health

The Pima Indians who inhabit parts of southern Arizona and the Pima Indians that live across the border in Mexico are genetically and culturally similar, but there are vast differences in the health of these two populations. In America, the Pima Indians have the highest rate of obesity and Type 2 diabetes compared to any other ethnic group. However, the Pima Indians who live in Mexico do not share these same health problems because of a complex interplay between nutrition, genetics, environment, and lifestyle. Over one hundred years ago, the Pima Indians were farmers, hunters, and gatherers and their diets consisted of about 70 percent carbohydrate, 15 percent protein, and 10 to 15 percent fat. Typical of the lives of farmers, hunters, and gatherers a century ago, they lived through times of feast and times of famine. The geneticist James Neel proposed in 1962 that the Pima Indians carried a “thrifty gene” that makes them very efficient at storing fat during times of plenty so they do not starve when food is scarce.

After World War II, the Pima Indians in America either went back to reservations in southern Arizona or moved to the cities for work. They rapidly adopted the American diet and lifestyle and consumed high-fat, processed foods and refined grains and were more sedentary than their counterparts in Mexico, who retained their more traditional diet and lifestyle. Today, the typical American Pima Indian diet obtains more than 40 percent of calories from fat. The “thrifty gene” in the American Pima Indian population increased their susceptibility to the consequences

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of the high-fat American diet and sedentary lifestyle because they were genetically better at storing fat than others. The story of the Pima Indians and the difference between the health of their populations in America and Mexico demonstrates the interactions between nutrition, genetics, environment, and lifestyle. Indeed, preliminary studies suggest that when American Pima Indians switch back to the diets of their ancestors and consume beans, corn, grains, and greens and other low- fat, high-fiber plant foods, the benefits are weight loss and reduced risk of chronic disease. The health status of American Pima Indians is considered “a canary in the coal mine, ” meaning they provide a warning to the American people.

Although the health consequences of the American diet and lifestyle in Pima Indians appeared rapidly in their population, all Americans that partake in the current trends of American diet and lifestyle are at risk. On the lighter side (literally!), the new studies that show changing back to more traditional diets markedly improved the health of the American Pima Indians suggest that all Americans can reduce their risk for diet-related diseases even when their genetic susceptibility for these diseases is high.

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Tools for Change

Heed the warning of the Pima Indians and seek out ways to establish a more traditional dietary pattern. The American diet in the nineteenth century consisted of less meat, less processed food, and more home-grown fruits, vegetables, and whole grains. Think of ways to include these types of foods in your diet or partake in some of the traditional foods of a particular ethnic group in your community. Visit the following websites to find out the unique foods of some traditional diets.

Traditional Mediterranean diet: http://www.oldwayspt.org/mediterraneandiet

Native Tech: http://www.nativetech.org/recipes/index.php

Traditional foods, with recipes, by country: http://www.foodbycountry.com/ index.html

Personal Choice: The Challenge of Choosing Foods

From visiting websites about traditional foods of different cultures and ethnic groups, you may have noticed that a few more things besides environment and lifestyle that influence the foods you choose to eat. Different foods affect energy level, mood, how much is eaten, how long before you eat again, and if cravings are satisfied. We have talked about some of the physical effects of food on your body, but there are other effects too. Food regulates your appetite and how you feel. Multiple studies have demonstrated that some high- fiber foods and high-protein foods decrease appetite by slowing the digestive process and prolonging the feeling of being full. The effects of individual foods and

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nutrients on mood are not backed by consistent scientific evidence, but in general most studies support that healthier diets are associated with a decrease in depression and improved well-being. To date, science has not been able to track the exact path in the brain that occurs in response to eating a particular food, but it is quite clear that foods, in general, stimulate emotional responses in people.

Food also has psychological, cultural, and religious significance, so your personal choices of food affect your body, mind, and soul. The social implications of food have a great deal to do with what people eat, as well as how and when. Special events in individual lives—from birthdays to funerals—are commemorated with equally special foods. Being aware of these forces can help people make healthier food choices—and still honor the traditions and ties they hold dear. Typically, eating kosher food means a person is Jewish; eating fish on Fridays during Lent means a person is Catholic; fasting during the ninth month of the Islamic calendar means a person is Muslim. On New Year’s Day, people from New England like to combine pork and sauerkraut as a way to eat their way to luck. Several hundred miles away in the southern United States, people eat Hoppin’ John, a favorite local dish made with black-eyed peas and pork, while fish is the “lucky” food of choice for Japanese Americans. National food traditions are carried to other countries when people immigrate. American cuisine would not be what it is today without the contributions of Italian, Chinese, Mexican, and other immigrants.

Factors that Drive Food Choices

Along with these influences, a number of other factors affect the dietary choices individuals make, including:

• Taste, texture, and appearance. Individuals have a wide range of tastes which influence their food choices, leading some to dislike milk and others to hate raw vegetables. Some foods that are very healthy, such as tofu, may be unappealing at first to many people. However, creative cooks can adapt healthy foods to meet most peoples’ taste.

• Economics. Access to fresh fruits and vegetables may be scant, particularly for those who live in economically disadvantaged or remote areas, where cheaper food options are limited to convenience stores and fast food.

• Early food experiences. People who were not exposed to different foods as children, or who were forced to swallow every last bite of overcooked vegetables, may make limited food choices as adults.

• Habits. It’s common to establish eating routines, which can work both for and against optimal health. Habitually grabbing a fast food sandwich for breakfast can seem convenient, but might not offer

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substantial nutrition. Yet getting in the habit of drinking an ample amount of water each day can yield multiple benefits.

• Culture. The culture in which one grows up affects how one sees food in daily life and on special occasions.

• Geography. Where a person lives influences food choices. For instance, people who live in Midwestern US states have less access to seafood than those living along the coasts.

• Advertising. The media greatly influences food choice by persuading consumers to eat certain foods.

• Social factors. Any school lunchroom observer can testify to the impact of peer pressure on eating habits, and this influence lasts through adulthood. People make food choices based on how they see others and want others to see them. For example, individuals can purchase cheap and fast pizzas or opt for high-end versions at fancy restaurants.

• Health concerns. Some people have significant food allergies, to lactose or peanuts for example, and need to avoid those foods. Others may have developed health issues, which require them to follow a low- salt diet. In addition, people who have never worried about their weight have a very different approach to eating than those who have long struggled with excess pounds.

• Emotions. There is a wide range in how emotional issues affect eating habits. When faced with a great deal of stress, some people tend to overeat, while others find it hard to eat at all.

• Green food/Sustainability choices. Based on a growing understanding of diet as a public and personal issue, more and more people are starting to make food choices based on their environmental impact. Realizing that their food choices help shape the world, many individuals are opting for a vegetarian diet, or, if they do eat animal products, striving to find the most “cruelty-free” options possible. Purchasing local and organic food products and items grown through sustainable products also helps shrink the size of one’s dietary footprint.

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KEY TAKEAWAYS

In this section, you discovered that there are many determinants that affect your health status. You can change some of them and others you cannot. All the determinants of health interact together in influencing your health.

• The expression of genes determines all of your traits including your risk for certain diseases. Nutrients can change the way genes are turned “on” and “off,” consequently affecting health.

• Certain stages of life require changes in nutrition to maintain bodily functions, such as growing.

• The traits that a person has are largely a product of their genes and environment. One aspect of a person’s environment is socioeconomic status, which is dependent on income, occupation, and education. Socioeconomic status is one of the best environmental predictors of a population’s health.

• Besides dietary habits, other components of lifestyle which affect health are physical activity level, recreational drug use, and sleeping patterns.

• Nutrition, genetics, environment, and lifestyle interplay on health. • Cultural and religious tradition, along with social values can affect food

choices. The foods you choose to eat affect your appetite and feelings. Numerous factors other than nutrition drive food choices.

DISCUSSION STARTERS

1. What types of diseases and/or conditions are present in your family? 2. Discuss the different cultures and religions that are represented by the

people in your classroom and learn the different foods that they choose to eat.

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1.5 Assessing Personal Health

LEARNING OBJECTIVES

1. Discuss ways of assessing your personal health status and your diet. 2. Set a goal to adopt, maintain, or improve a nutrition-related practice. 3. Formulate an effective, long-term, personal health and nutrition plan.

You may remember that when you were younger your mother or grandmother made you swallow that teaspoonful of cod liver oil because she said it was good for you. You don’t have to have a PhD to know some of the basic ways you can adapt your life to be healthier. However, the mainstream media inundates the American population with health cures and tips, making it confusing to develop the best plan for your health. This section will equip you with tools to assess and improve your health. To find some other reliable sources on health see Note 1.49 “Interactive 1.7”.

Interactive 1.7

The American Association for the Advancement of Science has listed the top ten resources on the internet for consumer health. Forget the blogs and discover sources that use science to back up their information on promoting health and preventing disease.

http://www.healthlit.org/health_resources/top_10_sites.htm

Personal Health Assessment

One of the easiest places to begin a personal health assessment is by examining the results from your last physical. Often a person will leave the doctor’s office without these results. Remember that the results belong to you and having this information on hand provides you with much of what you need to keep track of your health. During a physical, after obtaining weight and height measurements, a nurse will typically examine blood pressure. Blood pressure is a measurement of the forces in the arteries that occur during each heart beat. It is a principle vital sign and an indicator of cardiovascular health. A desirable blood pressure is 120 over 80 mmHg.

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In most circumstances a physical includes blood tests, which measure many health indicators, and you have to request the results. Once you have the results in hand, it is good practice to file them in a binder so you can compare them from year to year. This way you can track your blood-cholesterol levels and other blood-lipid levels and blood-glucose levels. These are some of the more general measurements taken, but in many instances blood tests also examine liver and kidney function, vitamin and mineral levels, hormone levels, and disease markers. Your doctor uses all of these numbers to assess your health and you can use them to play a more active role in keeping track of your health.

Hearing and vision are additionally part of a general health assessment. If you wear glasses, contacts, or a hearing aid you already are aware of how important it is to know the results of these exams. If you have not experienced vision or hearing problems yet your likelihood of experiencing them markedly increases over the age of forty. Another component of overall health is oral health. The health of your teeth, gums, and everything else in your mouth are an integral component of your overall health. This becomes apparent when a person experiences a tooth infection, which if left untreated significantly impairs physical, mental, and social well-being.

Other indicators of health that you can measure yourself are body mass index (BMI) and fitness. BMI refers to an individual’s body weight (in kilograms, or kg) divided by the square of their height (in meters) and the unit of measurement is kg/m2. You can calculate this yourself or use one of the many BMI calculators on the web (see Note 1.50 “Interactive 1.8”). BMI is a standardized measurement that indicates if a person is underweight, of normal weight, overweight, or obese and is based on data from the average population. It has some limitations. One limitation is that it does not take into account how much of your weight is made up of muscle mass, which weighs more than fat tissue. BMI and other measurements of body composition and fitness are more fully discussed in Chapter 11 “Energy Balance and Body Weight”.

This personal health assessment has focused primarily on physical health, but remember that mental and social well-being also affect health. During a physical, a doctor will ask how you are feeling, if you are depressed, and if you are experiencing behavioral problems. Be prepared to answer these questions truthfully, so that your doctor can develop a proper treatment plan to manage these aspects of health. Note 1.50 “Interactive 1.8” provides some tools to assess your mental and social well-being.

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Taking charge of your health will pay off and equip you with the knowledge to better take advantage of your doctor’s advice during your next physical. Health calculators, such as those that calculate BMI, ideal weight, target heart rate among many others, and personal health assessments will help you to take charge of your health, but they should not take the place of visiting your doctor.

Interactive 1.8

One of the better websites for assessing your health is available at the Institute for Good Medicine from the Pennsylvania Medical Society.

http://www.myfamilywellness.org/MainMenuCategories/YouYourPhysician/ YourHealthToolkit

Dietary Assessment

The first step in assessing your diet is to find out if the foods you eat are good for your health and provide you with all the nutrients you need. Begin by recording in a journal what you eat every day, including snacks and beverages. Then visit the USDA website, http://www.choosemyplate.gov/myplate/index.aspx, which has various tools to help you assess your diet. You can track calories over time, diet quality, and find many other tools to evaluate your daily food consumption. The questions these tools can help answer include: How much food do you have to eat to match your level of activity? How many calories should you eat? What are the best types of food to get the most nutrients? What nutrients are contained in different foods? How do you plan a menu that contains all the nutrients you need? Make the first step and assess your diet. This book will provide you with interactive resources, videos, and audio files to empower you to create a diet that improves your health.

Family Medical History

Because genetics play a large role in defining your health it is a good idea to take the time to learn some of the diseases and conditions that may affect you. To do this, you need to record your family’s medical history. Start by simply drawing a chart that details your immediate family and relatives. Many families have this and you may have a good start already. The next time you attend a family event start filling in the blanks. What did people die from? What country did Grandpa come from? While this may be a more interesting project historically, it can also provide

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you with a practical tool to determine what diseases you might be more susceptible to. This will allow you to make better dietary and lifestyle changes early on to help prevent a disease from being handed down from your family to you. It is good to compile your information from multiple relatives.

Lifestyle Assessment

A lifestyle assessment includes evaluating your personal habits, level of fitness, emotional health, sleep patterns, and work-life balance. Many diseases are preventable by simply staying away from certain lifestyles. Don’t smoke, don’t drink excessively, and don’t do recreational drugs. Instead, make sure you exercise. Find out how much to exercise by reading the 2008 Physical Activity Guidelines for Americans. There is a wealth of scientific evidence that increased physical activity promotes health, prevents disease, and is a mood enhancer. Emotional health is often hard to talk about; however a person’s quality of life is highly affected by emotional stability. Harvard’s Women’s Health Watch notes six reasons to get enough sleep: Sleep promotes healthy brain function, while lack of sleep can cause weight gain and increase appetite, decrease safety (falling asleep while driving), make a person moody and irritable, decrease health of the cardiovascular system and prevent the immune system from functioning well.Harvard Health Publications. “Importance of Sleep: Six Reasons Not to Scrimp on Sleep.” Harvard’s Women’s Health Watch (January 2006). © 2000–2012 Harvard University. http://www.health.harvard.edu/press_releases/importance_of_sleep_and _health Finding balance between work and life is a difficult and continuous process involving keeping track of your time, taking advantage of job flexibility options, saying no, and finding support when you need it. Work-life balance can influence what you eat too.

KEY TAKEAWAYS

This section equips you with some tools to assess your lifestyle and make changes towards a healthier one.

• Step 1. Take charge of tracking your personal health. • Step 2. Assess your diet and identify where it can be changed to

promote health and prevent disease. • Step 3. Start finding out the medical history of your family and identify

the diseases you may be more susceptible to getting. • Step 4. Assess your lifestyle by evaluating your personal habits,

emotional health, sleep patterns, and work-life balance. • Step 5. Start living a healthier life.

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DISCUSSION STARTERS

1. What websites in Note 1.50 “Interactive 1.8” did you find to be the most helpful in the assessment of your health?

2. Share your comments on these tools with your classmates and get their opinions, too.

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1.6 A Fresh Perspective: Sustainable Food Systems

LEARNING OBJECTIVE

1. Discuss some approaches to building a sustainable food system in your community.

The science of nutrition includes the study of how organisms obtain food from their environment. An ecosystem22 is defined as the biological and physical environments and their interactions with the community of organisms that inhabit those environments as well as the interactions among the organisms. Human nutrition and the health of the world’s ecosystem are interdependent, meaning that what we eat and where we get it from affects the world. In turn the health of the earth influences our health. The term sustainability23 is used to indicate the variety of approaches aimed at improving our way of life. Sustainability promotes the development of conditions under which people and nature can interact harmoniously. It is based upon the principle that everything needed for human survival depends upon the natural environment. A major theme of sustainability is to ensure that the resources needed for human and environmental health will

22. The biological and physical environments and their interactions with the community of organisms that inhabit it, and also the interactions among the organisms.

23. Describes the variety of approaches aimed at improving our way of life. Sustainability promotes the development of conditions under which people and nature can interact harmoniously. It is based upon the principle that everything needed for human survival depends upon the natural environment.

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continue to exist. A healthy ecosystem, one that is maintained over time, is harmonious and allows for social and economic fulfillment for present and future generations. Nutritious foods come from our ecosystem and to ensure its availability for generations to come, it must be produced and distributed in a sustainable way. The American Public Health Association (APHA) defines a sustainable food system24 as “one that provides healthy food to meet current food needs while maintaining healthy ecosystems that can also provide food for generations to come with minimal negative impact to the environment.”American Public Health Association. “Towards a Healthy, Sustainable Food System.” Policy Statement Database. Policy no. 200712 (November 6, 2007). http://www.apha.org/ advocacy/policy/policysearch/default.htm?id=1361 It also states that the attributes of a sustainable food system are:

• availability • accessibility • affordability to all • humane • just

A sustainable food system does not just include the food and those who consume the food, but also those that produce the food, like farmers and fishermen, and those who process, package, distribute, and regulate food. Unfortunately, we have a long way to go to build a sustainable food system.

The Challenges

The most prominent challenge to building a sustainable food system is to make food available and accessible to all. The Food and Agricultural Organization of the United Nations (FAO) states the right to food is a fundamental human right and its mission is to assist in building a food-secure world. Food security25 in America is defined as the “access by all people at all times to enough food for an active, healthy life.”US Department of Agriculture, Economic Research Service. “Food Security in the United States: Key Statistics and Graphics.” Last updated June 4, 2012. http://www.ers.usda.gov/Briefing/FoodSecurity/stats_graphs.htm#food_secure As of 2009, 14.9 percent of households, or 17.4 million people in the United States, had very low or low food security and these numbers have risen in recent years (Figure 1.9 “Food Insecurity: A Global Perspective”).Food and Agricultural Organization of the United Nations. “Food Security: Concepts and Measurement.” In Corporate Document Repository, ID: 144369. 2003. http://www.fao.org/docrep/005/y4671e/ y4671e06.htm

24. A system that can meet the needs of the current generation while providing food for generations to come without negatively impacting the environment.

25. A state in which all persons in a community’s population obtain a nutritionally adequate diet that is culturally acceptable throughout the year that is not dependent on emergency aid sources, but more so from local production.

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Food security is defined by the FAO as existing “when all people, at all times, have physical, social, and economic access to sufficient, safe, and nutritious food which meets their dietary needs and food preferences for an active and healthy life.”Food and Agriculture Organization of the United Nations. “How Does International Price Volatility Affect Domestic Economies and Food Security? In The State of Food Insecurity in the World. 2011. http://www.fao.org/publications/sofi/en/ The FAO estimates that 925 million worldwide were undernourished in 2010. Although there was a recent decline in overall food insecurity (attributable mostly to a decline in undernourished people in Asia), the number of undernourished people world-wide is still higher than it was in 1970, despite many national and international goals to reduce it.

Another challenge to building a sustainable food system is to supply high-quality nutritious food. The typical American diet does not adhere to dietary guidelines and recommendations, is unhealthy, and thus costs this country billions of dollars in healthcare. The average American diet contains too many processed foods with added sugars and saturated fats and not enough fruits, vegetables, and whole grains. Moreover, the average American takes in more kilocalories each day than ever before. This shift of the population toward unhealthy, high-calorie diets has fueled the obesity and diet-related disease crisis in this nation. Overall the cost of food for the average American household has declined since the 1970s; however, there has been a growth of “food deserts.” A food desert26 is a location that does not provide access to affordable, high-quality, nutritious food. One of the best examples of a “food desert” is in Detroit, Michigan. The lower socioeconomic status of the people who live in this city does not foster the building of grocery stores in the community. Therefore, the most accessible foods are the cheap, high-caloric ones sold in convenience stores. As a result, people who live in Detroit have some of the highest incidences of obesity, Type 2 diabetes, and cardiovascular disease in the country.

26. A location that does not provide access to affordable nutritious food.

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A fourth challenge to building a sustainable food system is to change how we produce, process, and distribute food. Large agribusiness, complex industrial processing, and massive retail conglomerations distort the connection we have between the food on our plate and where it came from. More food is being produced in this nation than ever before, which might sound good at first. However, some factors that have contributed to higher food production include using genetically engineered plants, excessive use of herbicides and pesticides, and the selective promotion of only a few crops by the policy of crop-specific subsidies (money given to farmers by the federal government). The subsidies are given toward the support of only about eight crops, most notably corn and soybeans. This policy diminishes the variety of crops, decreases biodiversity among crops, and supports large agribusiness while disadvantaging small- and medium-sized farms. Additionally, the whole system of food production, processing, and distribution is lengthy, requiring a great deal of energy and fossil fuels, and promotes excessive use of chemicals to preserve foods during transportation and distribution. In fact, the current US food system uses approximately 22 percent of the energy in this country and is responsible for at least 20 percent of greenhouse gas emissions.Canning, P. et al.“Energy Use in the US Food System.” US Department of Agriculture, Economic Research Report, no. ERR-94 (March 2010). http://www.ers.usda.gov/Publications/ ERR94/ERR94_ReportSummary.pdf

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Solutions to the Challenges

While these challenges are daunting there are many potential solutions that are gaining momentum in the United States. The APHA advocates expanding the infrastructure for locally grown food, improving access to healthy and local food for low-income Americans, providing education on food origin and production, building up the livelihoods of local farmers, and using sustainable farming methods. Detroit is currently a “food desert,” but there is a fantastic example of how to positively impact the growth of a sustainable food system within the city. It is called the Eastern Market and it is a six-block inner city market with over 250 vendors marketing local produce, meat, seafood, plants, fresh-cut flowers and much, much more. Unlike many urban farmers’ markets it sells foods that are of better quality and lower prices than grocery stores. Its forty-thousand visitors every Saturday demonstrate its success as a community-based way to foster good nutrition, good health, and social interaction.

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Tools for Change

Ten Steps You Can Take to Help Build a Sustainable Food System in Your Community

1. Eat a “low-carbon diet.” This is one where the foods that you eat require less energy and fuel to produce, process, and distribute than other foods.

2. Join a community-based farmers’ market. 3. Have a garden at home and join a network of home gardeners. Find

out how by visiting the USDA website on gardening: http://www.usda.gov/wps/portal/usda/ usdahome?navid=GARDENING &parentnav=CONSUMER_CITIZEN&navtype=RT and the National Garden Association, http://www.garden.org/.

4. Compost your food and garden waste. Learn some of the essentials of composting by visiting “Composting at home,” a fact sheet

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provided by Ohio State University (http://ohioline.osu.edu/hyg- fact/1000/1189.html).

5. Buy local food—make at least 10 percent of your food purchases local and share what you know about local food with friends and family.

6. Pool your resources with family and friends to purchase locally. 7. Drink tap water instead of bottled water. 8. When purchasing foods, choose the ones with less packaging. 9. Support state initiatives that support local farmers and build

infrastructure to sell more healthy food. 10. When dining out, ask what nutrients are in the food and where the

food labels are on the menu (to encourage the restaurants to label). Also, visit the restaurant’s website as the information may be posted there with a space for comments.

These are some great steps to build a more sustainable food system for you and your family, friends, neighborhood, community, city, state, nation, and world. Throughout this book we will highlight multiple steps you can take toward building a sustainable food system in the Tools for Change sections, so stay tuned.

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KEY TAKEAWAYS

• Sustainability promotes the development of conditions under which people and nature can interact harmoniously. It is based upon the principle that everything needed for human survival depends upon the natural environment. A sustainable food system includes not only the food and those who consume the food, but also those who produce food (such as farmers and fishermen), and process, package, distribute, and regulate food.

• The challenges to building a sustainable food system are many, from providing affordable and accessible food, to supplying nutritious, high- quality, low-cost food regardless of socioeconomic status, to changing the ways foods are produced, processed, and distributed.

• There are many solutions to the challenges of building a sustainable flood system. Some of the solutions are to: expand the infrastructure for locally grown food, improve access to healthy and local food for low- income Americans, provide education on food origin and production, build up the livelihoods of local farmers, and use sustainable farming methods.

• You can take action individually and locally to help build a sustainable food system.

DISCUSSION STARTERS

1. Share with each other in the classroom some of the things you might have already done to help build a sustainable food system in your community.

2. Form debate teams in the classroom and have a formal debate on the topic of the regulation of food. One side must present the reasons it is beneficial for the government to regulate food. The other side will argue the reasons it is better for people to grow their food locally.

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1.7 End-of-Chapter Exercises

IT ’S YOUR TURN

1. You are writing a short article for the Daily News. Explain how health means much more than a mere absence of disease.

2. Create a table that summarizes the six classes of nutrients and their major functions.

3. List five ideas on how to change the nutrition of Americans to protect their health and the health of the planet.

APPLY IT

1. Explore the nutritional and health information provided by the USDA, the HSS, and the IOM. Make a pros and cons list on how helpful the information from each of these sources was to you.

2. Revisit the photographs of the inner contents of refrigerators by Mark Menjivar. Describe how factors associated with a person’s environment, lifestyle, and culture may affect the personal food choices in at least six different refrigerators.

3. Write a paragraph on your opinion of the role of the federal government in promoting health and preventing disease in Americans.

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EXPAND YOUR KNOWLEDGE

1. Conduct an assessment of your diet. Begin by recording what you eat every day, including snacks and beverages, in a journal. Then visit the website, http://www.choosemyplate.gov/myplate/index.aspx, which has tools to help you assess your diet. Calculate your average daily calorie consumption.

2. Conduct an informal survey of five of your friends and family members. Create a questionnaire with ten to fifteen questions pertaining to their perception of food, their favorite food shows, what restaurants they frequent, what they purchase from the grocery store each week, etc. Ask questions about their general eating habits and record the answers. Next, get a camera and take pictures of the insides of their refrigerators. What have you learned about their eating habits? What advice would you give them? Review all the material and put it together in a report. Be prepared to share your findings.

3. Define eight steps your community can take to build a more sustainable food system. Visit the websites of Toronto’s and California’s plans to help provide you with some good ideas to accomplish the challenge.

Toronto’s plan for a sustainable food system: http://wx.toronto.ca/inter/health/food.nsf/Resources/ 340ACEEDBF1B2D6085257738000B22F2/$file/ Cultivating%20Food%20Connections%20report.pdf

California’s plan for a sustainable food system: http://www.vividpicture.net/

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Chapter 2

Achieving a Healthy Diet

Big Idea

The dietary toolkit contains numerous ideas to help you achieve a healthy diet.

Let’s talk about a toolkit for a healthy diet. The first thing in it would be the Recommended Daily Allowances (RDAs). Then we could add the Dietary Reference Intakes (DRIs), the Estimated Average Requirements (EARs), and the Tolerable Upper Limits (ULs). All of these tools are values for important nutrients, calculated to meet the health needs of different age groups. But long before the dietary toolkit full of acronyms such as DRI, RDA, EAR, and UL, daily standards were created with the single goal of keeping workers alive and toiling in the factories and workhouses of the early Industrial Revolution. In the late nineteenth century powerhouse tycoons operated without fear of legal consequences and paid their workers as little as possible in order to maximize their own profits. Workers could barely afford housing, and depended on what their bosses fed them at the workhouses to fend off starvation.

Living conditions in those days show that the term “starvation wages” was not just a figure of speech. Here’s a typical day’s menu:

• Breakfast. 1 pint porridge, one 6-ounce piece of bread.

• Lunch. Beef broth one day, boiled pork and potatoes the next.

• Dinner. 1 pint porridge, one 6-ounce piece of bread.

As public awareness about these working conditions grew, so did public indignation. Experts were eventually called in to create the first dietary guidelines, which

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were designed only to provide a typical individual with what they needed to survive each day, and no more. It wasn’t until World War I that the British Royal Society first made recommendations about the nutrients people needed to be healthy, as opposed to merely surviving. They included ideas we now take for granted, such as making fruit and vegetables part of the diet and giving milk to children. Since then, most governments have established their own dietary standards. Food is a precious commodity, like energy, and controlling the way it is distributed confers power. Sometimes this power is used to influence other countries, as when the United States withholds food aid from countries with regimes of which it disapproves. Governments can also use their power over food to support their most fragile citizens with food relief programs, such as the Supplemental Nutrition Assistance Program (SNAP) and the Women, Infants, and Children Supplemental Food Program (WIC).

The US government has also established dietary standards to help citizens follow a healthy diet. The first of these were the Recommended Daily Allowances (RDAs), published in 1943 because of the widespread food shortages caused by World War II. During the war, the government rationed sugar, butter, milk, cheese, eggs, coffee, and canned goods. Limited transportation made it hard to distribute fruits and vegetables. To solve this problem, the government encouraged citizens to plant “victory gardens” to produce their own fruits and vegetables. More than twenty million people began planting gardens in backyards, empty lots, and on rooftops. Neighbors pooled their resources and formed cooperatives, planting in the name of patriotism.

Today in the United States, there are various measures used to maintain access to nutritious, safe, and sufficient food to the citizenry. Many of these dietary guidelines are provided by the government, and are found at the Food and Drug Administration’s (FDA) new website, ChooseMyPlate.gov. We call this collection of guidelines the “dietary toolkit.”

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You Decide

How will you use the dietary toolkit?

The government works to provide citizens with information, guidance, and access to healthy foods. How will you decide which information to follow? What are the elements of a healthy diet, and how do you figure out ways to incorporate them into your personal diet plan? The dietary toolkit can be likened to a mechanics toolkit, with every tool designed for a specific task(s). Likewise, there are many tools in the dietary toolkit that can help you build, fix, or maintain your diet for good health. In this chapter you will learn about many of the tools available to you.

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Today, the US government sets dietary guidelines that provide evidence-based nutrition information designed to improve the health of the population.

ChooseMyPlate comprises public domain material from the U.S. Department of Agriculture.

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2.1 A Healthy Philosophy toward Food

LEARNING OBJECTIVE

1. Explain why nutrition is important to health.

“Tell me what you eat, and I will tell you what you are” wrote the French lawyer and politician, Antheime Brillat-Savarin in his book, Physiologie du Gout, ou Meditations de Gastronomie Transcendante, in 1826. Almost one hundred years later, nutritionist Victor Lindlahr wrote in an ad in 1923, “Ninety percent of the diseases known to man are caused by cheap foodstuffs. You are what you eat.” Today, we know this phrase simply as, “You are what you eat.”Phrase Finder. Accessed July 6, 2011. http://www.phrases.org.uk/meanings/ you%20are%20what%20you%20eat.html

Good nutrition equates to receiving enough (but not too much) of the macronutrients (proteins, carbohydrates, fats, and water) and micronutrients (vitamins and minerals) so that the body can stay healthy, grow properly, and work effectively. The phrase “you are what you eat” refers to the fact that your body will respond to the food it receives, either good or bad. Processed, sugary, high-fat, and excessively salted foods leave the body tired and unable to perform effectively. By contrast, eating fresh, natural whole foods fuels the body by providing what it needs to produce energy, promote metabolic activity, prevent micronutrient deficiencies, ward off chronic disease, and to promote a sense of overall health and well-being.

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Table 2.1 Why Nutrition Is Important to Health

Protein Necessary for tissue formation, cell reparation, and hormone and enzyme production. It is essential for building strong muscles and a healthy immune system.

Carbohydrates Provide a ready source of energy for the body and provide structuralconstituents for the formation of cells.

Fat

Provides stored energy for the body, functions as structural components of cells and also as signaling molecules for proper cellular communication. It provides insulation to vital organs and works to maintain body temperature.

Vitamins Regulate body processes and promote normal body-system functions.

Minerals Regulate body processes, are necessary for proper cellular function, andcomprise body tissue.

Water Transports essential nutrients to all body parts, transports waste productsfor disposal, and aids with body temperature maintenance.

Undernutrition, Overnutrition, and Malnutrition

For many, the word “malnutrition” produces an image of a child in a third-world country with a bloated belly, and skinny arms and legs. However, this image alone

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is not an accurate representation of the state of malnutrition. For example, someone who is 150 pounds overweight can also be malnourished. Malnutrition1 refers to one not receiving proper nutrition and does not distinguish between the consequences of too many nutrients or the lack of nutrients, both of which impair overall health. Undernutrition2 is characterized by a lack of nutrients and insufficient energy supply, whereas overnutrition3 is characterized by excessive nutrient and energy intake. Overnutrition can result in obesity4, a growing global health threat. Obesity is defined as a metabolic disorder that leads to an overaccumulation of fat tissue.

Although not as prevalent in America as it is in developing countries, undernutrition is not uncommon and affects many subpopulations, including the elderly, those with certain diseases, and those in poverty. Many people who live with diseases either have no appetite or may not be able to digest food properly. Some medical causes of malnutrition include cancer, inflammatory bowel syndrome, AIDS, Alzheimer’s disease, illnesses or conditions that cause chronic pain, psychiatric illnesses, such as anorexia nervosa, or as a result of side effects from medications. Overnutrition is an epidemic in the United States and is known to be a risk factor for many diseases, including Type 2 diabetes, cardiovascular disease, inflammatory disorders (such as rheumatoid arthritis), and cancer.

Growth and Development

Proper growth throughout the life stages depends upon proper nutrition. 2016, UMUC

1. A condition where one does not receive proper amounts of nutrients. This condition may have resulted from an inadequate or unbalanced diet, digestive and absorption problems, or other medical issues.

2. A condition where a person is not consuming enough nutrients, which leads to malnutrition.

3. A condition where a person is consuming too much food and too many nutrients, which may lead to malnutrition.

4. A metabolic disorder that leads to the overaccumulation of fat tissue, compromising overall health.

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From birth to adulthood, nutrients fuel proper growth and function of all body cells, tissue, and systems. Without proper amounts of nutrients, growth and development are stunted. Some nutrient deficiencies manifest right away, but sometimes the effects of undernutrition aren’t seen until later in life. For example, if children do not consume proper amounts of calcium and vitamin D, peak bone mass will be reduced compared to what it would be had adequate amounts of these nutrients been consumed. When adults enter old age without adequate bone mass, they are more susceptible to osteoporosis, putting them at risk for bone fractures. Therefore, it is vital to build bone strength through proper nutrition during youth because it cannot be done in later life.MedicineNet.com. “Nutrients for the Growing Years.” Last reviewed August 13, 2003. http://www.medicinenet.com/script/main/ art.asp?articlekey=10054.

The Healing Process

With all wounds, from a paper cut to major surgery, the body must heal itself. Healing is facilitated through proper nutrition,MacKay, D., ND, and A. L. Miller, ND. “Nutritional Support for Wound Healing.” Alternative Medicine Review 8, no. 4 (2003): 359–77. while malnutrition inhibits and complicates this vital process. The following nutrients are important for proper healing:

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• Vitamin A. Helps to enable the epithelial tissue (the thin outer layer of the body and the lining that protects your organs) and bone cells form.

• Vitamin C. Helps form collagen, an important protein in many body tissues.

• Protein. Facilitates tissue formation. • Fats. Play a key role in the formation and function of cell membranes. • Carbohydrates. Fuel cellular activity, supplying needed energy to

support the inflammatory response that promotes healing.

Now that we have discussed the importance of proper nutrition for your body to perform normal tissue growth, repair, and maintenance, we will discuss ways of achieving a healthy diet.

KEY TAKEAWAYS

• Nutrition promotes vitality and an overall sense of health and well- being by providing the body with energy and nutrients that fuel growth, healing, and all body systems and functions. Good nutrition will also help to ward off the development of chronic disease.

• A person is malnourished by being either undernourished or overnourished. Malnutrition results when the body does not receive the required amounts of calories, fats, proteins, carbohydrates, vitamins, and minerals necessary to keep the body and its systems in good functioning order.

DISCUSSION STARTER

1. Describe what the phrase, “You are what you eat” means. Do you notice how you feel after eating certain types of foods? How might this relate to your overall health?

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2.2 What Is Nutritional Balance and Moderation?

LEARNING OBJECTIVE

1. Define the components of a healthful diet.

Achieving a Healthy Diet

Achieving a healthy diet is a matter of balancing the quality and quantity of food that is eaten. There are five key factors that make up a healthful diet:

• A diet must be adequate5, by providing sufficient amounts of each essential nutrient, as well as fiber and calories.

• A balanced diet6 results when you do not consume one nutrient at the expense of another, but rather get appropriate amounts of all nutrients.

• Calorie control7 is necessary so that the amount of energy you get from the nutrients you consume equals the amount of energy you expend during your day’s activities.

• Moderation8 means not eating to the extremes, neither too much nor too little.

• Variety9 refers to consuming different foods from within each of the food groups on a regular basis.

A healthy diet is one that favors whole foods. As an alternative to modern processed foods, a healthy diet focuses on “real” fresh whole foods that have been sustaining people throughout the millenniums. Whole foods supply the needed vitamins, minerals, protein, carbohydrates, fats, and fiber that are essential to good health. Commercially prepared and fast foods are often lacking nutrients and often contain inordinate amounts of sugar, salt, saturated and trans fats, all of which are associated with the development of diseases such as atherosclerosis, heart disease, stroke, cancer, obesity, high cholesterol, diabetes, and other illnesses. A balanced diet is a mix of food from the different food groups (vegetables, legumes, fruits, grains, protein foods, and dairy).

Adequacy

An adequate diet is one that favors nutrient-dense foods. Nutrient-dense foods10 are defined as foods that contain many essential nutrients per calorie. Nutrient-

5. A dietary term signifying a diet that provides all nutrients, fiber, and energy in amounts sufficient to maintaining good health and body weight.

6. A balanced diet supplies various types of foods in proportion to one another. With balance, foods rich in one nutrient leave room for foods that are rich in other nutrients.

7. Controlling energy intake so that energy requirements are being met but not exceeded.

8. Not eating to the extremes, neither too much nor too little.

9. Consuming an abundance of foods from different food groups on a regular basis.

10. Foods that contain many nutrients per calorie.

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dense foods are the opposite of “empty-calorie” foods, such as sugary carbonated beverages, which are also called “nutrient-poor.” Nutrient-dense foods include fruits and vegetables, lean meats, poultry, fish, low-fat dairy products, and whole grains. Choosing more nutrient-dense foods will facilitate weight loss, while simultaneously providing all necessary nutrients.

Tools for Change

Does your diet contain nutrient-dense foods? Record your eating habits for one week. Note the sugary, fatty, and calorie-heavy foods you most often consume.

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Balance

Balance the foods in your diet. Achieving balance in your diet entails not consuming one nutrient at the expense of another. For example, calcium is essential for healthy teeth and bones, but too much calcium will interfere with iron absorption. Most foods that are good sources of iron are poor sources of calcium, so in order to get the necessary amounts of calcium and iron from your diet, a proper balance between food choices is critical. Another example is that while sodium is a vital nutrient, an overabundance of it can contribute to congestive heart failure and chronic kidney disease. Remember, everything must be consumed in the proper amounts.

Moderation

Eat in moderation. Moderation is crucial for optimal health and survival. Burgers, French fries, cake, and ice cream each night for dinner will lead to health complications. But as part of an otherwise healthful diet and consumed only on a weekly basis, this should not have too much of an impact on overall health. If this is done once per month, it will have even less of an impact upon overall health. It’s important to remember that eating is, in part, about enjoyment and indulging with a spirit of moderation. This fits within a healthy diet.

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Monitor food portions. For optimum weight maintenance, it is important to ensure that energy consumed from foods meets the energy expenditures required for body functions and activity. If not, the excess energy contributes to gradual, steady weight gain. In order to lose weight, you need to ensure that more calories are burned than consumed. Likewise, in order to gain weight, calories must be eaten in excess of what is expended daily.

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Carrot, Kale, Walnuts, Tomatoes, by Deborah Breen Whiting, comprises public domain material worldwide.

Variety

Variety involves eating different foods from all the food groups. Eating a varied diet helps to ensure that you receive all the nutrients necessary for a healthy diet. One of the major drawbacks of a monotonous diet is the risk of consuming too much of some nutrients and not enough of others. Trying new foods can also be a source of pleasure—you never know what foods you might like until you try them.

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Developing a healthful diet can be rewarding, but be mindful that all of the principles presented must be followed to derive maximal health benefits. For instance, introducing variety in your diet can still result in the consumption of too many high-calorie, nutrient- poor foods and inadequate nutrient intake if you do not also employ moderation and calorie control. Using all of these principles together will afford you lasting health benefits.

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KEY TAKEAWAYS

• A healthful diet is adequate in providing proper amounts of nutrient- dense foods, is balanced in relation to food types so that one nutrient is not consumed at the expense of another, practices calorie control by supplying food energy to match energy output, is moderate in unwanted constituents, and draws from a variety of nutritious foods.

• Nutrient-dense foods contribute to daily nutritional requirements while limiting caloric intake, thus allowing people to either lose weight safely or to maintain a healthy weight.

DISCUSSION STARTERS

1. Discuss the principles of a healthy diet. How can you employ these principles in your diet, if you are not already?

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2.3 Understanding the Bigger Picture of Dietary Guidelines

LEARNING OBJECTIVE

1. Describe the major themes of the 2010 Dietary Guidelines for Americans.

The first US dietary recommendations were set by the National Academy of Sciences in 1941. The recommended dietary allowances (RDA) were first established out of concern that America’s overseas World War II troops were not consuming enough daily nutrients to maintain good health. The first Food and Nutrition Board was created in 1941, and in the same year set recommendations for the adequate intakes of caloric energy and eight essential nutrients. These were disseminated to

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officials responsible for food relief for armed forces and civilians supporting the war effort. Since 1980, the dietary guidelines have been reevaluated and updated every five years by the advisory committees of the US Department of Agriculture (USDA) and the US Department of Health and Human Services (HHS). The guidelines are continually revised to keep up with new scientific evidence-based conclusions on the importance of nutritional adequacy and physical activity to overall health. While dietary recommendations set prior to 1980 focused only on preventing nutrient inadequacy, the current dietary guidelines have the additional goals of promoting health, reducing chronic disease, and decreasing the prevalence of overweight and obesity.

Why Are Guidelines Needed?

Instituting nation-wide standard policies provides consistency across organizations and allows health-care workers, nutrition educators, school boards, and elder- care facilities to improve nutrition and subsequently the health of their respective populations. At the same time, the goal of the 2010 Dietary Guidelines is to provide packaged informative guidelines that will help any interested person in obtaining optimal nutritional balance and health. The seventh edition of the Dietary Guidelines was released in 2010 and focuses mainly on combating the obesity epidemic. USDA secretary Tom Vilsack says, “The bottom line is that most Americans need to trim their waistlines to reduce the risk of developing diet-related chronic disease. Improving our eating habits is not only good for every individual and family, but also for our country.” The Dietary Guidelines are formulated by the Food and Nutrition Board of the Institute of Medicine (IOM) from the review of thousands of scientific journal articles by a consensus panel consisting of more than two thousand nutrition experts with the overall mission of improving the health of the nation.Johnson, T.D. “Online Only: New Dietary Guidelines Call for Less Salt, Fewer Calories, More Exercise.” Nation’s Health 41, no. 2 (March 2011): E6. http://thenationshealth.aphapublications.org/content/41/2/E6.full.

Major Themes of the 2010 Dietary Guidelines

The 2010 Dietary Guidelines consists of four major action steps for the American public to improve the overall health of the country. These steps are as follows:

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1. Reduce the incidence and prevalence of overweight and obesity of the US population by reducing overall calorie intake and increasing physical activity.

2. Shift food intake patterns to a diet that emphasizes vegetables, cooked dry beans, and peas, fruits, whole grains, nuts, and seeds. In addition, increase the intake of seafood and fat-free and low-fat milk and milk products and consume only moderate amounts of lean meats, poultry, and eggs.

3. Significantly reduce intake of foods containing solid fats and added sugars (SoFAS) because these dietary components contribute excess calories and few, if any, nutrients. In addition, reduce sodium intake and lower intake of refined grains that are coupled with added sugar, solid fat, and sodium.

4. Meet the 2008 Physical Activity Guidelines for Americans. (http://www.cnpp.usda.gov/Publications/DietaryGuidelines/2010/ PolicyDoc/Chapter1.pdf)

We will discuss the highlights of each chapter of the 2010 Dietary Guidelines; however if you are interested in reading more, visit the USDA website, http://www.cnpp.usda.gov/DGAs2010 -PolicyDocument.htm.

How should you develop a healthy eating plan to best achieve your goals of losing weight, gaining weight, or maintaining weight? We will start with some basics and move on to healthy eating patterns.

To achieve the goal of reducing caloric intake, the 2010 Dietary Guidelines promote the following:

1. Increase intake of whole grains, fruits, and vegetables. 2. Reduce intake of sugar-sweetened beverages. 3. Monitor intake of 100 percent fruit juice for children and adolescents,

especially those who are overweight or obese. 4. Monitor calorie intake from alcoholic beverages for adults.

Foods and Food Components to Reduce

Table 2.4 A Little Less of These, Please

Dietary Constituent Health Implications Recommendations

Excess sodium High blood pressure Limit intake to 2,300 mg daily

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Dietary Constituent Health Implications Recommendations

Too much saturated fat Cardiovascular disease Limit intake to < 10 percent of total calories

Trans fats Cardiovascular disease Minimal, if any consumption

Excess cholesterol Atherosclerosis Limit intake to below 300 mg daily

SoFAS (solid fats and added sugars)

Obesity, Type 2 diabetes Avoid if possible

Too much alcohol

Impaired liver function, impaired motor function

No more than one drink per day for women; No more than two drinks per day for men

High consumptions of certain foods, such as those high in saturated or trans fat, sodium, added sugars, and refined grains may contribute to the increased incidence of chronic disease. Additionally, excessive consumption of these foods replaces the intake of more nutrient-dense foods.

The average person consumes 3,400 milligrams of sodium per day, mostly in the form of table salt. The 2010 Dietary Guidelines recommend that Americans reduce their daily sodium intake to less than 2,300 milligrams. If you are over the age of fifty-one, are African American, or have cardiovascular risk factors, such as high blood pressure or diabetes, sodium intake should be reduced even further to 1,500 milligrams. The Dietary Guidelines also recommend that less than 10 percent of calories come from saturated fat, and that fat calories should be obtained by eating foods high in unsaturated fatty acids. Cholesterol intake should be decreased to below 300 milligrams per day and trans fatty acid consumption kept to a bare minimum. The Dietary Guidelines stresses the importance of limiting the consumption of foods with refined grains and added sugars, and introduce the new term, SoFAS11, which is an acronym for solid fats and added sugars, both of which are to be avoided in a healthy diet plan.Nelson, J. and K. Zeratsky. “Dietary Guidelines Connect SoFAS and Weight Gain.” Mayo Clinic, Nutrition-Wise (blog). August 25, 2010. http://www.mayoclinic.com/health/dietary-guidelines/MY01417. Moreover, if alcohol is consumed, it should be consumed only in moderation, which for women it is not more than one drink per day and for men is not more than two drinks per day. The macronutrients protein, carbohydrates, and fats contribute considerably to total caloric intake. The IOM has made recommendations for different age groups on the percentage of total calories that should be obtained from each macronutrient class.

11. An acronym for solid fats and added sugars.

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Foods and Nutrients to Increase

The typical American diet lacks sufficient amounts of vegetables, fruits, whole grains, and high-calcium foods, causing concern for deficiencies in certain nutrients important for maintaining health. The 2010 Dietary Guidelines provide the following suggestions on food choices to achieve a healthier diet:

1. Eat a variety of vegetables, especially dark green, red, and orange vegetables.

2. Choose at least half of your grains consumed from whole-grain foods. 3. For dairy products, eat the low-fat versions. 4. Don’t get your protein only from red meats; choose instead seafood,

poultry, eggs, beans, peas, nuts, seeds, and soy products. 5. Replace butter with oils. 6. Choose foods dense in the nutrients potassium, calcium, and vitamin D. 7. Increase intake of dietary fiber.

Building Healthy Eating Patterns

The 2010 Dietary Guidelines recommend that people make an effort to reduce their caloric consumption, reduce the intake of nutrient-poor foods, and increase the intake of nutrient-dense foods. To accomplish these tasks it is necessary to incorporate moderation and variety. The goal is not only choosing specific foods for your diet, but also the development of a healthy eating pattern. Several studies provide good evidence that certain dietary patterns increase overall health and decrease the risk of chronic disease. The Dietary Approaches to Stop Hypertension trial, or DASH, reports

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that men and women who consumed more than eight servings per day of fruits and vegetables had lower blood pressures than a control group that consumed under four servings per day of fruits and vegetables. Sacks, F.M, et al., “Effects on Blood Pressure of Reduced Dietary Sodium and the Dietary Approaches to Stop Hypertension (DASH) Diet.” N Engl J Med. 344, no. 1 (January 2001): 3–10. http://www.nejm.org/doi/full/ 10.1056/NEJM200101043440101. Other studies investigating the benefits of the DASH diet have also found it to be protective against cardiovascular disease and decrease overall mortality. Another well-known diet is the Mediterranean diet. In general, the Mediterranean diet is described as one that emphasizes fruits, vegetables, whole grains, and nuts, and olive oil as a replacement for butter. Few meats and high-fat dairy products are eaten. Observational studies have linked the Mediterranean diet to reduced cardiovascular disease and decreased mortality. Vegetarian diets, which emphasize many of the same foods as the DASH and Mediterranean diets have also been linked to a decrease in incidences of some chronic diseases.

KEY TAKEAWAYS

• US dietary guidelines are based on evolving scientific evidence and are updated every five years. The goals of the 2010 Dietary Guidelines are to prevent nutrient inadequacy, promote health, reduce chronic disease, and decrease the prevalence of overweight and obesity.

• To have a healthy eating pattern, reduce the intake of sodium, saturated and trans fats, cholesterol, added sugars, and refined grains. Increase the consumption of fruits, vegetables, low-fat dairy products, dietary fiber, and oils.

• Healthy eating patterns prevent chronic disease and provide nutrient adequacy.

DISCUSSION STARTER

1. Discuss with your classmates suggestions from the 2010 Dietary Guidelines that you should incorporate into your diet. How can you align your personal dietary goals with these recommendations?

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2.4 National Goals for Nutrition and Health: Healthy People 2020

LEARNING OBJECTIVES

1. State the Healthy People 2020 nutrition- and weight-status goals. 2. List three related objectives for the Healthy People 2020 program.

The Healthy People 2020 program, launched in 2010, is a ten-year national program instituted by the US government with objectives aimed toward improving the health of all Americans. Similar to the 2010 Dietary Guidelines, it has been established to promote longer lives free of preventable disease, disability, injury, and premature death. With a revived intent on identifying, measuring, tracking, and reducing health disparities through a “determinants of health approach,” Healthy People 2020 will strive to create the social and physical environments that promote good health for all and to promote quality of life, healthy development, and healthy behaviors across all life stages. This means that the understanding of what makes and keeps people healthy is consistently refined. The determinants of health approach12 reflects the evidence from outside factors that greatly affect the health of individuals. US Department of Health and Human Services. “About Healthy People.” Last updated March 29, 2012. http://www.healthypeople.gov/2020/about/ default.aspx It takes into consideration the circumstances in which people are born, live, work, and age. It also reflects the conditions that shape their circumstances such as money, power, and resources at the local, national, and global levels. Social determinants of health are primarily accountable for the lack of fair health opportunities and the unjust differences in health status that exist within and between countries. World Health Organization. “Social Determinants of Health.” © 2012. http://www.who.int/social_determinants/en/.

Helping People Make Healthy Choices

It is not just ourselves, the food industry, and federal government that shape our choices of food and physical activity, but also our sex, genetics, disabilities, income, religion, culture, education, lifestyle, age, and environment. All of these factors

12. These are the conditions reflective of the circumstances in which people are born, live, work, and age. It assesses the conditions that shape circumstances such as money, power, and resources at the local, national and global levels.

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must be addressed by organizations and individuals that seek to make changes in dietary habits. The socioeconomic model incorporates all of these factors and is used by health-promoting organizations, such as the USDA and the HHS to determine multiple avenues through which to promote healthy eating patterns, to increase levels of physical activity, and to reduce the risk of chronic disease for all Americans. Lower economic prosperity influences diet specifically by lowering food quality, decreasing food choices, and decreasing access to enough food. As a result of the recent financial crisis in America the number of people who struggle to have enough to eat is rising and approaching fifty million. In response to these recent numbers, USDA Secretary Tom Vilsack said, “These numbers are a wake-up call…for us to get very serious about food security and hunger, about nutrition and food safety in this country.”Amy Goldstein, “Hunger a Growing Problem in America, USDA Reports,” Washington Post, 17 November 2009. http://www.washingtonpost.com/wp-dyn/content/article/2009/11/16/ AR2009111601598.html.

The socioeconomic model helps organizations and the government to plan and promote effective healthy- eating programs tailored to specific populations. © 2016, UMUC.

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Goals for Nutrition and Weight Status

While Healthy People 2020 has many goals and objectives, we are going to focus on the two goals for nutrition and weight status. They are to promote health and reduce the risk of developing chronic diseases by encouraging Americans to consume healthful diets and to achieve and maintain healthy body weights. Nutrition criteria are reflective of a solid scientific foundation for health and weight management. Emphasis is on modifying individual behavior patterns and habits, and having policies and environments that will support these behaviors in various settings, such as schools and local community-based organizations.

Healthy People 2020 has defined their mission as:

• Identify nationwide health improvement priorities

• Increase public awareness and understanding of the determinants of health, disease, and disability, and the opportunities for progress

• Provide measurable objectives and goals that are applicable at the national, state, and local levels

• Engage multiple sectors to take actions to strengthen policies and improve practices that are driven by the best knowledge

• Identify critical research, evaluation, and data-collection needs

Healthy People 2020 has set key recommendations as follows:

• Consume a variety of nutrient-dense foods within and across the food groups, especially whole grains, fruits, vegetables, low-fat or fat-free milk or milk products, and lean meats and other protein sources

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Consuming nutrient-dense foods and limiting portion sizes of food will contribute to weight management. Avoiding excessive amounts of anything allows room for many food types in the diet.

Apple and Scale comprises public domain material worldwide.

• Limit the intake of saturated fat and trans fats, cholesterol, added sugars, sodium (salt), and alcohol

• Limit caloric intake to meet caloric needsUS Department of Health and Human Services. “Nutrition and Weight Status.” HealthyPeople.gov. Last updated May 1, 2012. http://healthypeople.gov/2020/ topicsobjectives2020/ overview.aspx?topicid=29

Tools for Change

If you wait many hours between meals, there is a good chance you will overeat. To refrain from overeating try consuming small meals at frequent intervals throughout the day as opposed to two or three large meals. Eat until you are satisfied, not until you feel “stuffed.” Eating slowly and savoring your food allows you to both enjoy what you eat and have time to realize that you are full before you get overfull. Your stomach is about the size of your fist but it expands if you eat excessive amounts of food at one sitting. Eating smaller meals will diminish the size of your appetite over time so you will feel satisfied with smaller amounts of food.

Benefits of Following the Healthy People 2020 Goals

Nutrition and weight status are important to children’s growth and development. In addition, healthy eating habits will decrease risks for developing chronic health conditions such as obesity, malnutrition, anemia, cardiovascular disease, high blood pressure, dyslipidemia (poor lipid profiles), Type 2 diabetes, osteoporosis, dental disease, constipation, diverticular disease, and certain types of cancer.National Digestive Disease Information Clearinghouse, a service of National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health. “Am I at Risk for Type 2 Diabetes?” NIH Publication No. 09-4805 (November 2008). Last updated December 6, 2011. http://diabetes.niddk.nih.gov/dm/pubs/riskfortype2/.

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Meeting the recommended intake for energy needs by adopting a balanced eating regimen as promoted by the USDA’s My Food Plate tool will assist people in losing and maintaining weight and in improving overall health.

Objectives Related to the Healthy People 2020 Goals

Seven out of every ten deaths in the United States are caused by chronic diseases, such as heart disease, cancer, and diabetes, and three-quarters of the country’s health spending goes toward the cost of treating these diseases. Helping people lose weight, maintain a healthy weight, and prevent chronic disease by improving dietary habits requires providing education about food and nutrition, assuring access to healthier food options, and promoting the desire and ability to become physically active. Some of the Healthy People 2020 program’s related objectives are discussed below.

1. Improve health, fitness, and quality of life through daily physical activity. The Healthy People 2020 objectives for physical activity are based on the 2008 Physical Activity Guidelines for Americans, and reflect the strong scientific evidence supporting the benefits of physical activity. More than 80 percent of the current US population, from youth to adults, is not meeting these guidelines. Healthy People 2020 highlights the way that one’s level of physical activity is affected by environmental factors such as the availability of safe sidewalks, bike lanes, trails, and parks. It also highlights the legislative policies that improve access to facilities that promote physical activity. Understanding that personal, social, economic, and environmental barriers to physical activity all have a part in determining a population’s physical activity level, is an important part of being able to provide interventions that foster physical activity. Consistent physical activity is necessary for preventing chronic disease, improving bone health, decreasing body fat, and preventing an early death.

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1. Increase the quality, availability, and effectiveness of educational and community-based programs designed to prevent disease and injury, improve health, and enhance quality of life. Healthy eating is a learned behavior. By increasing the number of community-based programs (schools, workplace, health-care facilities, local community groups) that offer guidance for healthy eating and lifestyle choices, people of all ages will learn good eating habits and will gain access to good food choices to help improve their diet and overall health.

2. Improve the development, health, safety, and well-being of adolescents and young adults. Adolescents (ten to nineteen years of age) and young adults (twenty to twenty-four years of age) constitute 21 percent of the population of the United States. The financial burdens of preventable health problems and associated long-term costs of chronic diseases in this demographic group have the potential to be vast, and will be the result of attitudes and behaviors initiated during adolescence. For example, the annual adult health-related financial burden of cigarette smoking, which usually starts by age eighteen, is $193 billion.Adhikari, B. et al. “Smoking-Attributable Mortality, Years of Potential Life Lost, and Productivity Losses—United States, 2000–2004.” MMWR CDC Surveill Summ 57, no. 45 (November 14, 2008): 1226–8. http://www.cdc.gov/mmwr/preview/mmwrhtml/ mm5745a3.htm.

1. Reduce the consumption of calories from SoFAS in the population aged two years and older. A diet high in SoFAS contributes to excessive weight gain and poor health. Added sugars provide no nutritional value to foods. Excessive fat and sugar intake promotes tooth decay, obesity, Type 2 diabetes, unhealthy cholesterol levels, and heart disease. Being overweight increases susceptibility for developing high blood pressure, diabetes, cardiovascular diseases, and certain types of cancer. The evidence is clear that many chronic diseases are linked to unhealthy dietary patterns. Excessive consumption of SoFAS, in combination with the lack of plant-based foods, may contribute to higher rates of developing chronic diseases.

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For more information on Healthy People 2020 and its related objectives for nutrition and weight status, please visit the website http://www.healthypeople.gov/2020.

KEY TAKEAWAYS

• Healthy People 2020 is a health initiative with a ten-year objective of helping Americans improve health and well-being, and to live long, healthy lives. Among its many objectives are to promote health and reduce the risk of developing chronic diseases by encouraging Americans to consume healthful diets and to achieve and maintain healthy body weights.

• The goals of Healthy People 2020 are founded upon a determinants of health approach, which means they are reflective of the circumstances in which people are born, live, and work, as well as the conditions that shape their circumstances such as money, power, and resources at the local, national, and global levels. Diet patterns are influenced by genetics, environment, and cultural values. All of these things must be considered to provide the optimal approach to improving the health of the American population.

• Decreasing caloric intake and increasing physical activity are important strategies in achieving the goals of the Healthy People 2020 program.

DISCUSSION STARTERS

1. Think of fun ways to increase physical activity in your life.

2. Review some of the Healthy People 2020 nutrition and physical activity program objectives. What objectives would you like to see enacted in your community? Why is this important to you?

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2.5 Recommendations for Optimal Health

LEARNING OBJECTIVES

1. Design a quality diet plan using MyPlate Daily Food Plan. 2. State recommendation(s) for fruit and vegetable consumption and list

the potential benefits of this eating program.

For many years, the US government has been encouraging Americans to develop healthful dietary habits. In 1992 the food pyramid was introduced, and in 2005 it was updated. This was the symbol of healthy eating patterns for all Americans. However, some felt it was difficult to understand, so in 2011, the pyramid was replaced with Choose MyPlate.

The Choose MyPlate program uses a tailored approach to give people the needed information to help design a healthy diet. The plate is divided according to the amount of food and nutrients you should consume for each meal. Each food group is identified with a different color, showing the food variety that all plates must have. Aside from educating people about the type of food that is best to support optimal health, the new food plan offers the advice that it is okay to enjoy food, just eat less of it.US Department of Agriculture. Accessed July 22, 2012. http://www.choosemyplate.gov/.

Building a Healthy Plate: Choose Nutrient-Rich Foods

Planning a healthy diet using the MyPlate approach is not difficult. According to the icon, half of your plate should have fruits and vegetables, one-quarter should have whole grains, and one-quarter should have protein. Dairy products should be low- fat or non-fat. The ideal diet gives you the most nutrients within the fewest calories. This means choosing nutrient-rich foods.

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Fill half of your plate with red, orange, and dark green vegetables and fruits, such as kale, collard greens, tomatoes, sweet potatoes, broccoli, apples, oranges, grapes, bananas, blueberries, and strawberries in main and side dishes. Vary your choices to get the benefit of as many different vegetables and fruits as you can. You may choose to drink fruit juice as a replacement for eating fruit. (As long as the juice is 100 percent fruit juice and only half your fruit intake is replaced with juice, this is an acceptable exchange.) For snacks, eat fruits, vegetables, or unsalted nuts.

Fill a quarter of your plate with whole grains such as 100 percent whole-grain cereals, breads, crackers, rice, and pasta. Half of your daily grain intake should be whole grains. Read the ingredients list on food labels carefully to determine if a food is comprised of whole grains.

Select a variety of protein foods to improve nutrient intake and promote health benefits. Each week, be sure to include a nice array of protein sources in your diet, such as nuts, seeds, beans, legumes, poultry, soy, and seafood. The recommended consumption amount for seafood for adults is two 4-ounce servings per week. When choosing meat, select lean cuts. Be conscious to prepare meats using little or no added saturated fat, such as butter.

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If you enjoy drinking milk or eating milk products, such as cheese and yogurt, choose low-fat or nonfat products. Low-fat and nonfat products contain the same amount of calcium and other essential nutrients as whole-milk products, but with much less fat and calories. Calcium, an important mineral for your body, is also available in lactose-free and fortified soy beverage and rice beverage products. You can also get calcium in vegetables and other fortified foods and beverages.

Oils are essential for your diet as they contain valuable essential fatty acids, but the type you choose and the amount you consume is important. Be sure the oil is plant-based rather than based on animal fat. You can also get oils from many types of fish, as well as avocados, and unsalted nuts and seeds. Although oils are essential for health they do contain about 120 calories per tablespoon. It is vital to balance oil consumption with total caloric intake. The Nutrition Facts label provides the information to help you make healthful decisions.

In short, substituting vegetables and fruit in place of unhealthy foods is a good way to make a nutrient-poor diet healthy again. Vegetables are full of nutrients and antioxidants that help promote good health and reduce the risk for developing chronic diseases such as stroke, heart disease, high blood pressure, Type 2 diabetes, and certain types of cancer. Regularly eating fresh fruits and vegetables will boost your overall health profile.

Discretionary Calories

When following a balanced, healthful diet with many nutrient-dense foods, you may consume enough of your daily nutrients before you reach your daily calorie limit. The remaining calories are discretionary (to be used according to your best judgment). To find out your discretionary calorie allowance, add up all the calories you consumed to achieve the recommended nutrient intakes and then subtract this number from your recommended daily caloric allowance. For example, someone who has a recommended 2,000-calorie per day diet may eat enough nutrient-dense foods to meet requirements after consuming only 1,814 calories. The remaining 186 calories are discretionary. These calories may be obtained from eating an additional piece of fruit, adding another teaspoon of olive oil on a salad or butter on a piece of bread, adding sugar or honey to cereal, or consuming an alcoholic beverage.US

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Department of Agriculture. “MyPyramid Education Framework.” Accessed July 22, 2012. http://www.choosemyplate.gov

The amount of discretionary calories increases with physical activity level and decreases with age. For most physically active adults, the discretionary calorie allowance is, at most, 15 percent of the recommended caloric intake. By consuming nutrient-dense foods, you afford yourself a discretionary calorie allowance.

Table 2.6 Sample Menu Plan Containing 2,000 Calories

Meal Calories Total Meal/Snack Calories

Breakfast

1 scrambled egg 92

with sliced mushrooms and spinach 7

½ whole-wheat muffin 67

1 tsp. margarine-like spread 15

1 orange 65

8 oz. low-sodium tomato juice 53 299

Snack

6 oz. fat-free flavored yogurt 100

with ½ c. raspberries 32 132

Lunch

1 sandwich on pumpernickel bread 160

with smoked turkey deli meat, 30

4 slices tomato 14

2 lettuce leaves 3

1 tsp. mustard 3

1 oz. baked potato chips 110

½ c. blueberries, with 1 tsp. sugar 57

8 oz. fat-free milk 90 467

Snack

1 banana 105

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Meal Calories Total Meal/Snack Calories

7 reduced-fat high-fiber crackers 120 225

Dinner

1 c. Greek salad (tomatoes, cucumbers, feta) 150

with 5 Greek olives, 45

with 1.5 tsp. olive oil 60

3 oz. grilled chicken breast 150

½ c. steamed asparagus 20

with 1 tsp. olive oil, 40

with 1 tsp. sesame seeds 18

½ c. cooked wild rice 83

with ½ c. chopped kale 18

1 whole-wheat dinner roll 4

with 1 tsp. almond butter 33 691

(Total calories from all meals and snacks = 1,814)

Discretionary calorie allowance: 186

Healthy Eating Index

To assess whether the American diet is conforming to the 2010 Dietary Guidelines, the Center for Nutrition Policy and Promotion (CNPP), a division of the USDA, uses a standardized tool called the Healthy Eating Index (HEI)13.US Department of Agriculture. “Healthy Eating Index.” Last modified March 14, 2012. http://www.cnpp.usda.gov/healthyeatingindex.htm. The first HEI was developed in 1995 and revised in 2006. This tool is a simple scoring system of dietary components. The data for scoring diets is taken from national surveys of particular population subgroups, such as children from low-income families or Americans over the age of sixty-five. Diets are broken down into several food categories including milk, whole fruits, dark green and orange vegetables, whole grains, and saturated fat, and then a score is given based on the amount consumed. For example, a score of ten is given if a 2,000-kilocalorie diet includes greater than 2.6 cups of milk per day. If less than 10 percent of total calories in a diet are from saturated fat, a score of eight is given. All of the scores are added up from the different food categories and the diets are given a HEI score. Using this standardized diet-assessment tool at different times, every ten years for instance, the CNPP can determine if the eating habits of certain groups of the American

13. A standardized tool based on a simple scoring system of dietary components used to assess whether the diets of Americans are improving and adhering to the dietary guidelines.

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population are getting better or worse. The HEI tool provides the federal government with information to make policy changes to better the diets of American people. For more information on the HEI, visit this website: http://www.cnpp.usda.gov/healthyeatingindex.htm.

KEY TAKEAWAYS

• The Food Pyramid has been replaced by MyPlate, a system that was designed to be easier to implement. The new MyPlate encourages all plates to be filled with fruits and vegetables (50 percent), protein (25 percent), and grains (25 percent). Half of daily grain intake should be from whole-grain sources. Dairy choices should be switched to low-fat or non-fat sources.

• A diet rich in fresh fruits and vegetables will help you lose and/or maintain weight, will lower your risk for stroke, heart disease, high blood pressure, Type 2 diabetes, and certain types of cancer, and will boost your overall health profile.

• By choosing nutrient-dense foods, you may have discretionary calories to “spend” at the end of the day.

DISCUSSION STARTER

1. As you analyze the new MyPlate, how do your regular dietary habits compare to this new format? What changes, if any, will you have to make to your breakfast? Lunch? Dinner?

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2.6 Understanding Daily Reference Intakes

LEARNING OBJECTIVE

1. Use the Dietary Reference Intakes to determine daily nutrient recommendations.

Dietary Reference Intakes (DRI)14 are the recommendation levels for specific nutrients and consist of a number of different types of recommendations. This DRI system is used in both the United States and Canada.

Daily Reference Intakes: A Brief Overview

“Dietary Reference Intakes” (DRI) is an umbrella term for four reference values:

• Estimated Average Requirements (EAR)15 • Recommended Dietary Allowances (RDA)16 • Adequate Intakes (AI)17 • Tolerable Upper Intake Levels (UL)18

The DRIs are not minimum or maximum nutritional requirements and are not intended to fit everybody. They are to be used as guides only for the majority of the healthy population.Deng, S., B. J. West, and C. J. Jensen. “A Quantitative Comparison of Phytochemical Components in Global Noni Fruits and Their Commercial Products.” Food Chemistry 122, no. 1 (September 1, 2010): 267–70. http://www.sciencedirect.com/science/article/pii/S0308814610001111.

DRIs are important not only to help the average person determine whether their intake of a particular nutrient is adequate, they are also used by health-care professionals and policy makers to determine nutritional recommendations for special groups of people who may need help reaching nutritional goals. This includes people who are participating in programs such as the Special Supplemental Food Program for Women, Infants, and Children. The DRI is not appropriate for people who are ill or malnourished, even if they were healthy previously.

14. A set of nutrient recommendations that includes the Estimated Average Requirements (EAR), Recommended Dietary Allowances (RDA), Adequate Intakes (AI), Tolerable Upper Intake Levels (UL) and Acceptable Macronutrient Distribution Range (AMDR).

15. Average daily intake levels for nutrients estimated to meet the needs of 50 percent of the target group. Used in nutrition research and policy-making. EARs form the basis for which RDA values are set.

16. Based upon the EAR, these are nutrient-intake goals designed to meet the requirements of 97 to 98 percent of the target group for a given nutrient.

17. If scientific data is insufficient to establish an EAR value, an AI is established based on the scientific data that is available. As with the RDA, the AI serves a nutrient-intake goal.

18. The highest average daily nutrient-intake level at which a nutrient can be consumed before it poses a risk of toxicity.

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Determining Dietary Reference Intakes

Each DRI value is derived in a different way. See below for an explanation of how each is determined:

1. Estimated Average Requirements. The EAR for a nutrient is determined by a committee of nutrition experts who review the scientific literature to determine a value that meets the requirements of 50 percent of people in their target group within a given life stage and for a particular sex. The requirements of half of the group will fall below the EAR and the other half will be above it. It is important to note that, for each nutrient, a specific bodily function is chosen as the criterion on which to base the EAR. For example, the EAR for calcium is set using a criterion of maximizing bone health. Thus, the EAR for calcium is set at a point that will meet the needs, with respect to bone health, of half of the population. EAR values become the scientific foundation upon which RDA values are set.

2. Recommended Daily Allowances. Once the EAR of a nutrient has been established, the RDA can be mathematically determined. While the EAR is set at a point that meets the needs of half the population, RDA values are set to meet the needs of the vast majority (97 to 98 percent) of the target healthy population. It is important to note that RDAs are not the same thing as individual nutritional requirements. The actual nutrient needs of a given individual will be different than the RDA. However, since we know that 97 to 98 percent of the population’s needs are met by the RDA, we can assume that if a person is consuming the RDA of a given nutrient, they are most likely meeting their nutritional need for that nutrient. The important thing to remember is that the RDA is

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meant as a recommendation and meeting the RDA means it is very likely that you are meeting your actual requirement for that nutrient.

Understanding the Difference

There is a distinct difference between a requirement and a recommendation. For instance, the DRI for vitamin D is a recommended 600 international units each day. However, in order to find out your true personal requirements for vitamin D, a blood test is necessary. The blood test will provide an accurate reading from which a medical professional can gauge your required daily vitamin D amounts. This may be considerably more or less than the DRI, depending on what your level actually is.

1. Adequate Intake. AIs are created for nutrients when there is insufficient consistent scientific evidence to set an EAR for the entire population. As with RDAs, AIs can be used as nutrient-intake goals for a given nutrient. For example, there has not been sufficient scientific research into the particular nutritional requirements for infants. Consequently, all of the DRI values for infants are AIs derived from nutrient values in human breast milk. For older babies and children, AI values are derived from human milk coupled with data on adults. The AI is meant for a healthy target group and is not meant to be sufficient for certain at-risk groups, such as premature infants.

2. Tolerable Upper Intake Levels. The UL was established to help distinguish healthful and harmful nutrient intakes. Developed in part as a response to the growing usage of dietary supplements, ULs indicate the highest level of continuous intake of a particular nutrient that may be taken without causing health problems. When a nutrient does not have any known issue if taken in excessive doses, it is not assigned a UL. However, even when a nutrient does not have a UL it is not necessarily safe to consume in large amounts.

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Figure 2.1 DRI Graph

This graph illustrates the risks of nutrient inadequacy and nutrient excess as we move from a low intake of a nutrient to a high intake. Starting on the left side of the graph, you can see that when you have a very low intake of a nutrient, your risk of nutrient deficiency is high. As your nutrient intake increases, the chances that you will be deficient in that nutrient decrease. The point at which 50 percent of the population meets their nutrient need is the EAR, and the point at which 97 to 98 percent of the population meets their needs is the RDA. The UL is the highest level at which you can consume a nutrient without it being too much—as nutrient intake increases beyond the UL, the risk of health problems resulting from that nutrient increases. © 2016, UMUC.

1. Acceptable Macronutrient Distribution Ranges. The Acceptable Macronutrient Distribution Range (AMDR)19 is the calculated range of how much energy from carbohydrates, fats, and protein is recommended for a healthy diet. People who do not reach the AMDRs for their target group increase their risk of developing health complications. See Chapter 10 “Nutrients Important for Metabolism and Blood Function” for more information on calculating requirements.

19. The value of the energy- yielding nutrients carbohydrates, protein, and fat, expressed as percentages of total daily calorie intake, sufficient to provide total adequate energy needs; staying within the AMDR is associated with reducing the risks for developing chronic disease.

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Tips for Using the Dietary Reference Intakes to Plan Your Diet

You can use the DRIs to help assess and plan your diet. Keep in mind when evaluating your nutritional intake that the values established have been devised with an ample safety margin and should be used as guidance for optimal intakes. Also, the values are meant to assess and plan average intake over time; that is, you don’t need to meet these recommendations every single day—meeting them on average over several days is sufficient.

KEY TAKEAWAYS

• Nutrient-intake recommendations set for healthy people living in the United States and Canada are known as Dietary Reference Intakes.

• The DRIs includes the AI, EAR, RDA, and UL for micronutrients and the AMDR ranges for energy-yielding macronutrients. The DRI provide a set of standards for researchers and government policy-makers, and specifies nutrient consumption guidelines for individuals.

DISCUSSION STARTER

1. Why do you think it is important for the government to set the DRI standards? How will you use this information for your personal dietary choices?

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2.7 Discovering Nutrition Facts

LEARNING OBJECTIVE

1. Use the Nutrition Facts panel to discover the nutritional information of food.

The Labels on Your Food

Understanding the significance of dietary guidelines and how to use DRIs in planning your nutrient intakes can make you better equipped to select the right foods the next time you go to the supermarket.

In the United States, the Nutrition Labeling and Education Act passed in 1990 and came into effect in 1994. In Canada, mandatory labeling came into effect in 2005. As a result, all packaged foods sold in the United States and Canada must have nutrition labels that accurately reflect the contents of the food products. There are several mandated nutrients and some optional ones that manufacturers or packagers include.

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There are other types of information that are required by law to appear somewhere on the consumer packaging. They include:

• Name and address of the manufacturer, packager, or distributor • Statement of identity, what the product actually is • Net contents of the package: weight, volume, measure, or numerical

count • Ingredients, listed in descending order by weight • Nutrient information of serving size and daily valuesUS Food and Drug

Administration. “Food Labeling.” http://www.fda.gov/Food/ GuidanceComplianceRegulatoryInformation/GuidanceDocuments/ FoodLabelingNutrition/FoodLabelingGuide/default.htm

The Nutrition Facts panel20 provides a wealth of information about the nutritional content of the product. The information also allows shoppers to compare products. Because the serving sizes are included on the label, you can see how much of each nutrient is in each serving to make the comparisons. Knowing how to read the label is important because of the way some foods are presented. For example, a bag of peanuts at the grocery store may seem like a healthy snack to eat on the way to class. But have a look at that label. Does it contain one serving, or multiple servings? Unless you are buying the individual serving packages, chances are the bag you picked up is at least eight servings, if not more.

According to the 2010 health and diet survey released by the FDA, 54 percent of first-time buyers of a product will check the food label and will use this information to evaluate fat, calorie, vitamin, and sodium content.US Food and Drug Administration. “Survey Shows Gain in Food-Label Use, Health/Diet Awareness.” March 2, 2010. http://www.fda.gov/ForConsumers/ConsumerUpdates/ ucm202611.htm#FoodLabelHighlights. The survey also notes that more Americans are using food labels and are showing an increased awareness of the connection between diet and health. Having reliable food labels is a top priority of the FDA, which has a new initiative to prepare guidelines for the food industry to construct “front of package” labeling that will make it even easier for Americans to choose healthy foods. Stay tuned for the newest on food labeling by visiting the FDA website: http://www.fda.gov/Food/LabelingNutrition/default.htm.

20. Found on most packaged foods, it contains specific amounts of nutrients and also compares the amounts of nutrients in the food and the recommended intake values. These comparisons are reported as percent DV.

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Reading the Label

The first part of the Nutrition Facts panel gives you information on the serving size and how many servings are in the container. For example, a label on a box of crackers might tell you that twenty crackers equals one serving and that the whole box contains 10 servings. All other values listed thereafter, from the calories to the dietary fiber, are based on this one serving. On the panel, the serving size is followed by the number of calories and then a list of selected nutrients. You will also see “Percent Daily Value” on the far right-hand side. This helps you determine if the food is a good source of a particular nutrient or not. The Daily Value (DV)21 represents the recommended amount of a given nutrient based on the RDI of that nutrient in a 2,000-kilocalorie diet. The percentage of Daily Value (percent DV)22 represents the proportion of the total daily recommended amount that you will get from one serving of the food. For example, in the food label in Figure 2.2 “Determining Your Nutrient Allowances per Day”, the percent DV of calcium for one serving of macaroni-and-cheese is 20 percent, which means that one serving of macaroni and cheese provides 20 percent of the daily recommended calcium intake. Since the DV for calcium is 1,000 milligrams, the food producer determined the percent DV for calcium by taking the calcium content in milligrams in each serving, and dividing it by 1,000 milligrams, and then multiplying it by 100 to get it into percentage format. Whether you consume 2,000 calories per day or not you can still use the percent DV as a target reference.

Generally, a percent DV of 5 is considered low and a percent DV of 20 is considered high. This means, as a general rule, for fat, saturated fat, trans fat, cholesterol, or sodium, look for foods with a low percent DV. Alternatively, when concentrating on essential mineral or vitamin intake, look for a high percent DV. To figure out your fat allowance remaining for the day after consuming one serving of macaroni-and-

21. Based upon the RDI of a specific nutrient in a 2,000 kilocalorie diet.

22. The percentage of the amount of the nutrient in relationship to the DV. They are applicable only for a 2,000-calorie daily diet (not 2,500 calories).

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cheese, look at the percent DV for fat, which is 18 percent, and subtract it from 100 percent. To know this amount in grams of fat, read the footnote of the food label to find that the recommended maximum amount of fat grams to consume per day for a 2,000 kilocalories per day diet is 65 grams. Eighteen percent of sixty-five equals about 12 grams. This means that 53 grams of fat are remaining in your fat allowance. Remember, to have a healthy diet the recommendation is to eat less than this amount of fat grams per day, especially if you want to lose weight.

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Of course, this is a lot of information to put on a label and some products are too small to accommodate it all. In the case of small packages, such as small containers of yogurt, candy, or fruit bars, permission has been granted to use an abbreviated version of the Nutrition Facts panel. To learn additional details about all of the information contained within the Nutrition Facts panel, see the following website: http://www.fda.gov/Food/ResourcesForYou/Consumers/NFLPM/ucm274593.htm

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Claims on Labels

In addition to mandating nutrients and ingredients that must appear on food labels, any nutrient-content claims must meet certain requirements. For example, a manufacturer cannot claim that a food is fat-free or low-fat if it is not, in reality, fat-free or low-fat. Low-fat indicates that the product has three or fewer grams of fat; low salt indicates there are fewer than 140 milligrams of sodium, and low- cholesterol indicates there are fewer than 20 milligrams of cholesterol and two grams of saturated fat. “Additional Requirements for Nutrient Content Claims.” Appendix B in Food Labeling Guide (October 2009). http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/ GuidanceDocuments/FoodLabelingNutrition/FoodLabelingGuide/ucm064916.htm.

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Health Claims

Often we hear news of a particular nutrient or food product that contributes to our health or may prevent disease. A health claim is a statement that links a particular food with a reduced risk of developing disease. As such, health claims such as “reduces heart disease,” must be evaluated by the FDA before it may appear on packaging. Prior to the passage of the NLEA products that made such claims were categorized as drugs and not food. All health claims must be substantiated by scientific evidence in order for it to be approved and put on a food label. To avoid having companies making false claims, laws also regulate how health claims are presented on food packaging. In addition to the claim being backed up by scientific evidence, it may never claim to cure or treat the disease. For a detailed list of approved health claims, visit: http://www.fda.gov/Food/LabelingNutrition/ LabelClaims/HealthClaimsMeeting SignificantScientificAgreementSSA/ default.htm#Approved_Health_Claims.

Qualified Health Claims

While health claims must be backed up by hard scientific evidence, qualified health claims have supportive evidence, which is not as definitive as with health claims. The evidence may suggest that the food or nutrient is beneficial. Wording for this type of claim may look like this: “Supportive but not conclusive research shows that consumption of EPA and DHA omega-3 fatty acids may reduce the risk of coronary artery disease. One serving of [name of food] provides [X] grams of EPA and DHA omega-3 fatty acids. [See nutrition information for total fat, saturated fat, and cholesterol content.]US Food and Drug Administration. “FDA Announces Qualified Health Claims for Omega-3 Fatty Acids.” September 8, 2004. http://www.fda.gov/ SiteIndex/ucm108351.htm.

Structure/Function Claims

Some companies claim that certain foods and nutrients have benefits for health even though no scientific evidence exists. In these cases, food labels are permitted to claim that you may benefit from the food because it may boost your immune system, for example. There may not be claims of diagnosis, cures, treatment, or disease prevention, and there must be a disclaimer that the FDA has not evaluated the claim.US Food and Drug Administration. “Claims That Can Be Made for Conventional Foods and Dietary Supplements.” September 2003. http://www.fda.gov/Food/LabelingNutrition/LabelClaims/ucm111447.htm.

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Allergy Warnings

Food manufacturers are required by the FDA to list on their packages if the product contains any of the eight most common ingredients that cause food allergies. These eight common allergens are as follows: milk, eggs, peanuts, tree nuts, fish, shellfish, soy, and wheat. (More information on these allergens will be discussed in Chapter 11 “Energy Balance and Body Weight”.) The FDA does not require warnings that cross contamination may occur during packaging, however most manufacturers include this advisory as a courtesy. For instance, you may notice a label that states, “This product is manufactured in a factory that also processes peanuts.” If you have food allergies, it is best to avoid products that may have been contaminated with the allergen.

KEY TAKEAWAYS

• The Nutrition Labeling and Education Act made it a law that foods sold in the United States have a food label that provides the accurate contents of nutrients within them. Canada has a similar law.

• A Nutrition Facts panel gives information on the amount of servings per container, the amount of calories per serving, and the amounts of certain nutrients.

• The percent DV is the percentage of the amount of the nutrient in the food in relationship to its recommended intake. It is a guide to help you determine if a food is a good or poor source of nutrients.

• To keep companies from making false claims, the FDA provides regulation for food manufacturers in putting labels on packages that promote health. Allergens must also be listed on food labels. Sometimes cross contamination does occur during packaging. Most food manufacturers voluntarily list this information. If you have a food allergy, it is best to avoid any product that has even had the possibility of coming in contact with a known allergen.

DISCUSSION STARTER

1. Recall the food you buy from the supermarket on a regular basis. How many of the food products you purchase regularly are nutrient-dense? How many are nutrient-poor? What foods can you substitute in place of the nutrient-poor food choices?

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2.8 When Enough Is Enough

LEARNING OBJECTIVE

1. Judge food portion sizes for adequacy.

Estimating Portion Size

Have you ever heard the expression, “Your eyes were bigger than your stomach?” This means that you thought you wanted a lot more food than you could actually eat. Amounts of food can be deceiving to the eye, especially if you have nothing to compare them to. It is very easy to heap a pile of mashed potatoes on your plate, particularly if it is a big plate, and not realize that you have just helped yourself to three portions instead of one.

The food industry makes following the 2010 Dietary Guidelines a challenge. In many restaurants and eating establishments, portion sizes have increased, use of SoFAS has increased, and consequently the typical meal contains more calories than it used to. In addition, our sedentary lives make it difficult to expend enough calories during normal daily activities. In fact, more than one-third of adults are not physically active at all.

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Dietitians have come up with some good hints to help people tell how large a portion of food they really have. Some suggest using common items such as a deck of cards while others advocate using your hand as a measuring rule. See Table 2.11 “Determining Food Portions” for some examples.American Cancer Society. “Controlling Portion Sizes.” Last revised January 12, 2012. http://www.cancer.org/ Healthy/EatHealthyGetActive/TakeControlofYourWeight/controlling-portion-sizes.

Table 2.11 Determining Food Portions

Food Product Amount Object Comparison Hand Comparison

Pasta, rice ½ c. Tennis ball Cupped hand

Fresh vegetables 1 c. Baseball

Cooked vegetables ½ c. Cupped hand

Meat, poultry, fish 3 oz. Deck of cards Palm of your hand

Milk or other beverages 1 c. Fist

Salad dressing 1 Tbsp. Thumb

Oil 1 tsp. Thumb tip

MyPlate Planner

Estimating portions can be done using the MyPlate Planner. Recall that the MyPlate symbol is divided according to how much of each food group should be included with each meal. Note the MyPlate Planner Methods of Use:

• Fill half of your plate with vegetables such as carrots, broccoli, salad, and fruit.

• Fill one-quarter of your plate with lean meat, chicken, or fish (about 3 ounces)

• Fill one-quarter of your plate with a whole grain such as ⅓ cup rice • Choose one serving of dairy

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• Add margarine or oil for preparation or addition at the table

Table 2.12 Meal Planning Guidelines

Carbohydrates Meats/Proteins Fats Free Foods

Choose three servings with each meal.

Choose one to three servings with each meal.

Choose one to two servings with each meal. Use as desired.

Examples of one serving: Examples of oneserving: Examples of one serving: Examples

Breads and Starches

• 1 slice bread or small roll

• ⅓ c. rice or pasta

• ½ c. of cooked cereal or potatoes

• ¾ c. dry cereal

• ½ c. corn

• 1 oz. lean meat, poultry, or fish

• 1 egg

• 1 oz. cheese

• ¾ c. low-fat cottage cheese

• 1 tsp. margarine, oil, or mayonnaise

• 1 Tbsp. salad dressing or cream cheese

Foods with less than 20 calories per serving.*

• Most vegetables

• Sugar- free soda

• Black coffee or plain tea

Fruits

• 1 piece, such as a small pear

• 1 c. fresh fruit

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Carbohydrates Meats/Proteins Fats Free Foods

• ½ c. canned fruit

• ½ c. fruit juice

Milk

• 1 c. skim or low fat

• 1 c. unsweetened low-fat yogurt

KEY TAKEAWAY

• Judging portion sizes can be done using your hand or household objects in comparison. It can also be done using the MyPlate guide to determine how much food is a portion for that meal.

DISCUSSION STARTER

1. Why is it important to judge portion sizes properly? Explain why it can be tricky to read food labels and figure out the caloric content for one serving.

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2.9 Nutrition and the Media

LEARNING OBJECTIVE

1. List at least four sources of reliable and accurate nutrition information.

A motivational speaker once said, “A smart person believes half of what they read. An intelligent person knows which half to believe.” In this age of information where instant Internet access is just a click away, it is easy to be misled if you do not know where to go for reliable nutrition information. There are a few websites that can be consistently relied upon for accurate material that is updated regularly.

Using Eyes of Discernment

“New study shows that margarine contributes to arterial plaque.” “Asian study reveals that two cups of coffee per day can have detrimental effects on the nervous system.” How do you react when you read news of this nature? Do you boycott margarine and coffee? When reading nutrition-related claims, articles, websites, or advertisements always remember that one study does not substantiate a fact. One study neither proves nor disproves anything. Readers who may be looking for complex answers to nutritional dilemmas can quickly misconstrue such statements and be led down a path of misinformation. Listed below are ways that you can develop discerning eyes when reading nutritional news.

1. The scientific study under discussion should be published in a peer- reviewed journal, such as the Journal of the International Society of Sports Nutrition. Question studies that come from less trustworthy sources (such as non peer-reviewed journals or websites) or that are not published.

2. The report should disclose the methods used by the researcher(s). Did the study last for three or thirty weeks? Were there ten or one hundred participants? What did the participants actually do? Did the researcher(s) observe the results themselves or did they rely on self reports from program participants?

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3. Who were the subjects of this study? Humans or animals? If human, are any traits/characteristics noted? You may realize you have more in common with certain program participants and can use that as a basis to gauge if the study applies to you.

4. Credible reports often disseminate new findings in the context of previous research. A single study on its own gives you very limited information, but if a body of literature supports a finding, it gives you more confidence in it.

5. Peer-reviewed articles deliver a broad perspective and are inclusive of findings of many studies on the exact same subject.

6. When reading such news, ask yourself, “Is this making sense?” Even if coffee does adversely affect the nervous system, do you drink enough of it to see any negative effects? Remember, if a headline professes a new remedy for a nutrition-related topic, it may well be a research- supported piece of news, but more often than not it is a sensational story designed to catch the attention of an unsuspecting consumer. Track down the original journal article to see if it really supports the conclusions being drawn in the news report.

When reading information on websites, remember the following criteria for discerning if the site is valid:

1. Who sponsors the website? 2. Are names and credentials disclosed? 3. Is an editorial board identified? 4. Does the site contain links to other credible informational websites?

Even better, does it reference peer-reviewed journal articles? If so, do those journal articles actually back up the claims being made on the website?

5. How often is the website updated? 6. Are you being sold something at this website? 7. Does the website charge a fee?

Trustworthy Sources

Now let’s consider some reputable organizations and websites from which you can obtain valid nutrition information.

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Organizations Active in Nutrition Policy and Research

• Centers for Disease Control and Prevention (CDC) • The Academy of Nutrition and Dietetics (AND) • US Department of Agriculture (USDA) • US Department of Health and Human Services (HHS) • Dietitians of Canada • Health Canada

1. US Department of Agriculture Food and Nutrition Information Center. The USDA site http://fnic.nal.usda.gov has more than twenty- five hundred links to dietary, nutrition, diet and disease, weight and obesity, food-safety and food-labeling, packaging, dietary supplement and consumer questions sites. Using this interactive site, you can find tips and resources on how to eat a healthy diet, my Foodapedia, and a food planner, among other sections.

2. The Academy of Nutrition and Dietetics (AND). The AND promotes scientific evidenced-based, research-supported food and nutrition related information on its website, http://www.eatright.org. It is focused on informing the public about recent scientific discoveries and studies, weight-loss concerns, food safety topics, nutrition issues, and disease prevention.

3. Department of Health and Human Services. The HHS website, HealthFinder.gov, provides credible information about healthful lifestyles and the latest in health news. A variety of online tools are available to assist with food-planning, weight maintenance, physical activity, and dietary goals. You can also find healthful tips for all age groups, tips for preventing disease, and on daily health issues in general.

4. Centers for Disease Control and Prevention. The Centers for Disease Control and Prevention (http://www.cdc.gov) distributes an online newsletter called CDC Vital Signs. This newsletter is a valid and credible source for up-to-date public health information and data regarding food, nutrition, cholesterol, high blood pressure, obesity, teenage drinking, and tobacco usage.

5. Dietitians of Canada. Dietitians of Canada, http://www.dietitians.ca/, is the national professional association for dietitians. It provides trusted nutrition information to Canadians and health professionals.

6. Health Canada. Health Canada, http://www.hc-sc.gc.ca/index- eng.php, is the Federal department that helps Canadians improve their

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health. Its website also provides information about health-related legislation.

KEY TAKEAWAY

• Reliable nutritional news will be based upon solid scientific evidence, supported by multiple studies, and published in peer-reviewed journals. Be sure the website you use for information comes from a credible and trustworthy source, such as the USDA Food and Nutrition Center, the HHS, and the CDC.

DISCUSSION STARTER

1. Discuss why it is important to get information from proper and credible sources and not to rely upon single study findings.

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2.10 End-of-Chapter Exercises

IT ’S YOUR TURN

1. Draw a diagram that shows the role that nutrition plays in human health.

2. Write three ways in which cultural, religious, and social values affect dietary eating patterns.

3. Compare and contrast the Nutrition Facts label on two of your favorite foods. Make a smart choice for eating the most nutrient-dense food option. Which food did you select and why?

APPLY IT

1. You have been hired to write a two-page article for a weekly magazine about why nutrition is important to health. Using simple terms and a good supply of photographs, create your article. Be prepared to share your project with the class.

2. Record a food diary this week. At the end of the week, circle the foods that contain SoFAS. Next to each food, write a substitute food to replace it. Record a food diary next week. Be sure to eat the substitute foods you have selected to replace the foods that contained the SoFAS.

3. Search the Internet for sites that claim to give you nutritional advice. Check to see who sponsors the sites and if the site is trying to sell you a product or service. Compare the information found on the sites to those recommended in this text. What similarities do you notice? What differences do you notice?

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EXPAND YOUR KNOWLEDGE

1. You have just been hired at the local Boys and Girls club in an inner city neighborhood that happens to have a large high school drop-out rate. You have been put in charge of creating physical and nutritional opportunities for the community. Your goal for the first quarter is to enroll one hundred students in an exercise/ nutrition program. You must develop two programs.

◦ Define each program and state its objectives ◦ Describe the ways in which the program will benefit

participants ◦ List ways in which you will encourage enrollment ◦ Create a marketing flyer for each program

2. You are planning a big meal for a surprise graduation party for your friend. You expect fifty guests to attend. Using the information you have learned regarding healthy eating and food portions, plan a healthful meal. Determine how much protein, vegetables, fruits, and starch you will need to purchase to feed everyone comfortably. Write down a detailed list so that you can shop and prepare your budget accordingly. Share your results with the class.

3. You are a Registered Dietitian who has been asked to help a vegan patient adjust their eating habits to get more nutrients from their diet and halt unwanted weight loss. Develop a week’s worth of meals to help this person have balance in their diet.

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Chapter 3

Nutrition and the Human Body

Big Idea

Eat your way to health.

“Let food be thy medicine and medicine be thy food.” These words, espoused by Greek physician Hippocrates over two thousand years ago, bear much relevance on our food choices and their connection to our health. Today, the scientific community echoes Hippocrates’ statement as it recognizes some foods as functional foods. The Academy of Nutrition and Dietetics defines functional foods as “whole foods and fortified, enriched, or enhanced foods that have a potentially beneficial effect on health when consumed as part of a varied diet on a regular basis, at effective levels.”

In the latter nineteenth century, a Russian doctor of immunology, Elie Metchnikoff, was intrigued by the healthy life spans of people who lived in the tribes of the northern Caucasus Mountains. What contributed to their long life span and their resistance to life- threatening diseases? A possible factor lay wrapped up in a leather satchel used to hold fermented milk. One legend recounts that Mohammed, the great prophet of Islam, revealed this recipe to members of the Orthodox faith on the condition that they would not tell anyone outside of the faith how to create such a good-feeling beverage. The tribes, under Mohammed’s direction, combined a tiny amount of small grains that resembled white broccoli with milk in a leather satchel. This bag was hung from a doorway in a house, so that all who passed would hit the bag, mixing up the contents. The result was a refreshing, slightly carbonated, creamy beverage with tangy overtones.

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Observing the connection between the beverage and longevity, Dr. Elie Metchnikoff began his research on beneficial bacteria and the longevity of life that led to his book, The Prolongation of Life. He studied the biological effects and chemical properties of the kefir elixir whose name came from the Turkish word “kef” or “pleasure.” Intrigued, the Russian Society of Physicians went on a quest to locate the recipe in order to prescribe this drink to their patients. However, just as instructed, no one would share the recipe. As a result, the mission of obtaining this highly guarded recipe was placed on the Blandov brothers, who owned the Moscow Dairy and some holdings in the Caucasus Mountains.

The Blandov brothers had a beautiful employee, Irina Sakharova, whom they sent to the courts of the Caucasus tribe of Prince Bek-Mirza Barchorov in order to charm the recipe out of him. The prince immediately fell in love with Irina. As time went on, Irina asked the prince for some kefir grains. He refused, explaining that he was forbidden from sharing this secret and feared the consequences of violating religious law. Irina returned home when she realized that she would never pry the recipe from the prince. However, on orders from the heartbroken prince, Irina was kidnapped and brought back to marry him. She was taken aback and refused this proposal. Her refusal was rejected and the marriage was arranged. The Blandov brothers courageously stole into the tribe the night before the marriage and managed to free Irina. Insulted and still seeing a way to retrieve the kefir grains, Irina brought her case before the Russian Czar, charging the prince with kidnapping. Upon review of the evidence, it was ruled in her favor and Irina won her case. As part of her grievance repayment Irina requested some kefir grains. Bound by law, the prince had to comply. Irina gave the grains to the Blandov brothers who mass-produced kefir from these kernels. To this day, kefir is one of the most widely enjoyed beverages in Russia.

Kefir has since found its way into America, where it is marketed in several flavors and can be found at your local grocery store. It is one product of the billion-dollar functional food industry marketed with all sorts of health claims from improving digestion to preventing cancer. What is the scientific evidence that kefir is a functional food? Expert nutritionists agree that probiotics, such as kefir, reduce the symptoms of lactose intolerance and can ward off virally caused diarrhea. While some health claims remain unsubstantiated, scientific studies are ongoing to determine the validity of other health benefits of probiotics.

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You Decide

Will you eat your way to health with probiotic foods?

Knowing how to maintain the balance of friendly bacteria in your intestines through proper diet can promote overall health. Recent scientific studies have shown that probiotic supplements positively affect intestinal microbial flora, which in turn positively affect immune system function. As good nutrition is known to influence immunity, there is great interest in using probiotic foods and other immune-system-friendly foods as a way to prevent illness. In this chapter we will explore not only immune system function, but also all other organ systems in the human body. We will learn the process of nutrient digestion and absorption, which further reiterates the importance of developing a healthy diet to maintain a healthier you. The evidence abounds that food can indeed be “thy medicine.”

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3.1 The Basic Structural and Functional Unit of Life: The Cell

LEARNING OBJECTIVES

1. Diagram the components of a cell. 2. Describe the organization of the human body.

What distinguishes a living organism from an inanimate object? A living organism conducts self-sustaining biological processes. A cell is the smallest and most basic form of life. Robert Hooke, one of the first scientists to use a light microscope, discovered the cell in 1665. In all life forms, including bacteria, plants, animals, and humans, the cell1 was defined as the most basic structural and functional unit. Based on scientific observations over the next 150 years, scientists formulated the cell theory2, which is used for all living organisms no matter how simple or complex. The cell theory incorporates three principles:

• Cells are the most basic building units of life.

• All living things are composed of cells. • New cells are made from preexisting cells, which divide into two.

Who you are has been determined because of two cells that came together inside your mother’s womb. The two cells containing all of your genetic information (DNA) united to begin making new life. Cells divided and differentiated into other cells with specific roles that led to the formation of the body’s numerous body organs, systems, blood, blood vessels, bone, tissue, and skin. As an adult, you are comprised of trillions of cells. Each of your individual cells is a compact and efficient form of life—self-sufficient, yet interdependent upon the other cells within your body to supply its needs.

Independent single-celled organisms must conduct all the basic processes of life: it must take in nutrients (energy capture), excrete wastes, detect and respond to its environment, move, breathe, grow, and reproduce. Even a one-celled organism must be organized to perform these essential processes. All cells are organized from the atomic level to all its larger forms. Oxygen and hydrogen atoms combine to

1. Basic structural and functional unit of all life.

2. Cells are the most basic building units of life, all living things are composed of cells, and new cells are made from preexisting cells, which divide into two.

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make the molecule water (H2O). Molecules bond together to make bigger macromolecules. The carbon atom is often referred to as the backbone of life because it can readily bond with four other elements to form long chains and more complex macromolecules. Four macromolecules—carbohydrates, lipids, proteins, and nucleic acids—make up all of the structural and functional units of cells.

Although we defined the cell as the “most basic” unit of life, it is structurally and functionally complex. A cell can be thought of as a mini-organism consisting of tiny organs called organelles. The organelles3 are structural and functional units constructed from several macromolecules bonded together. A typical animal cell contains the following organelles: the nucleus (which houses the genetic material DNA), mitochondria (which generate energy), ribosomes (which produce protein), the endoplasmic reticulum (which is a packaging and transport facility), and the golgi apparatus (which distributes macromolecules). In addition, animal cells contain little digestive pouches, called lysosomes and peroxisomes, which break down macromolecules and destroy foreign invaders. All of the organelles are anchored in the cell’s cytoplasm via a cytoskeleton. The cell’s organelles are isolated from the surrounding environment by a plasma membrane.

3. A structural or functional unit in a cell that is constructed from several macromolecules bonded together.

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Tissues, Organs, Organ Systems, and Organisms

Unicellular (single-celled) organisms can function independently, but the cells of multicellular organisms are dependent upon each other and are organized into five different levels in order to coordinate their specific functions and carry out all of life’s biological processes.

• Cells. Cells are the basic structural and functional unit of all life. Examples include red blood cells and nerve cells.

• Tissues. Tissues4 are groups of cells that share a common structure and function and work together. There are four types of human tissues: connective, which connects tissues; epithelial, which lines and protects organs; muscle, which contracts for movement and support; and nerve, which responds and reacts to signals in the environment.

• Organs. Organs5 are a group of tissues arranged in a specific manner to support a common physiological function. Examples include the brain, liver, and heart.

• Organ systems. Organ systems6 are two or more organs that support a specific physiological function. Examples include the digestive system and central nervous system. There are eleven organ systems in the human body (see Table 3.1 “The Eleven Organ Systems in the Human Body and Their Major Functions”).

• Organism. An organism7 is the complete living system capable of conducting all of life’s biological processes.

Table 3.1 The Eleven Organ Systems in the Human Body and Their Major Functions

Organ System Organ Components Major Function

Circulatory heart, blood/lymph vessels, blood,lymph Transport nutrients and waste products

4. A group of cells that share a common structure and function and that work together.

5. A group of tissues arranged in a specific manner to support a common function.

6. Two or more organs that support a specific physiological function.

7. The complete living system capable of conducting all basic life processes.

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Organ System Organ Components Major Function

Digestive mouth, esophagus, stomach,intestines Digestion and absorption

Endocrine all glands (thyroid, ovaries,pancreas) Produce and release hormones

Immune white blood cells, lymphatic tissue,marrow Defend against foreign invaders

Integumentary skin, nails, hair, sweat glands Protective, body temperatureregulation

Muscular skeletal, smooth, and cardiac muscle Body movement

Nervous brain, spinal cord, nerves Interprets and responds to stimuli

Reproductive gonads, genitals Reproduction and sexualcharacteristics

Respiratory lungs, nose, mouth, throat, trachea Gas exchange

Skeletal bones, tendons, ligaments, joints Structure and support

Urinary kidneys, bladder, ureters Waste excretion, water balance

Figure 3.2 Organ Systems in the Human Body

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An Organism Requires Energy and Nutrient Input

Energy is required in order to build molecules into larger macromolecules, and to turn macromolecules into organelles and cells, and then turn those into tissues, organs, and organ systems, and finally into an organism. Proper nutrition provides the necessary nutrients to make the energy that supports life’s processes. Your body builds new macromolecules from the nutrients in food.

Nutrient and Energy Flow

Energy is stored in a nutrient’s chemical bonds. Energy comes from sunlight, which plants then capture and, via photosynthesis, use it to transform carbon dioxide in the air into the molecule, glucose. When the glucose bonds are broken, energy is released. Bacteria, plants, and animals (including humans) harvest the energy in glucose via a biological process called cellular respiration8. In this process the chemical energy of glucose is transformed into cellular energy in the form of the molecule, adenosine triphosphate (ATP). Cellular respiration requires oxygen (aerobic) and it is provided as a waste product of photosynthesis. The waste products of cellular respiration are carbon dioxide (CO2) and water, which plants use to conduct photosynthesis again. Thus, energy is constantly cycling between plants and animals. As energy is consumed nutrients are recycled within it.

8. The process by which the stored chemical energy in nutrients is transformed into cellular energy.

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In this section, we have learned that all life is composed of cells capable of transforming small organic molecules into energy. How do complex organisms such as humans convert the large macromolecules in the foods that we eat into molecules that can be used by cells to make cellular energy? In the next section, we will discuss the physiological process of digestion to answer this question.

KEY TAKEAWAYS

• The cell is the basic structural and functional unit of life. Cells are independent, single-celled organisms that take in nutrients, excrete wastes, detect and respond to their environment, move, breathe, grow, and reproduce. The macromolecules carbohydrates, proteins, lipids, and nucleic acids make up all of the structural and functional units of cells.

• In complex organisms, cells are organized into five levels so that an organism can conduct all basic processes associated with life.

• There are eleven organ systems in the human body that work together to support life, all of which require nutrient input.

• Energy is constantly cycling between plants and animals. As energy is consumed nutrients are recycled within it.

DISCUSSION STARTER

1. Discuss the importance of organization in the human body. If the body becomes disorganized by a disease or disorder what happens to its function? Can you think of a good example (what about leg fracture and movement)?

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3.2 Digestion and Absorption

LEARNING OBJECTIVE

1. Sketch and label the major organs of the digestive system and state their functions.

Digestion begins even before you put food into your mouth. When you feel hungry, your body sends a message to your brain that it is time to eat. Sights and smells influence your body’s preparedness for food. Smelling food sends a message to your brain. Your brain then tells the mouth to get ready, and you start to salivate in preparation for a delicious meal.

Once you have eaten, your digestive system9 (Figure 3.4 “The Human Digestive System”) breaks down the food into smaller components. To do this, it functions on two levels, mechanical and chemical. Once the smaller particles have been broken down, they will be absorbed and processed by cells throughout the body for energy or used as building blocks for new cells. The digestive system is one of the eleven organ systems of the human body and it is composed of several hollow tube-shaped organs including the mouth, pharynx, esophagus, stomach, small intestine, large

9. The body system responsible for breaking down complex food particles into smaller absorbable components. The entire system is composed of several hollow, tube-shaped organs including the mouth, pharynx, esophagus, stomach, small intestine, large intestine (or colon), rectum, and anus.

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intestine (or colon), rectum, and anus. It is lined with mucosal tissue that secretes digestive juices (which aid in the breakdown of food) and mucus (which facilitates the propulsion of food through the tract). Smooth muscle tissue surrounds the digestive tract and its contraction produces waves, known as peristalsis10, that propel food down the tract. Nutrients as well as some nonnutrients are absorbed. Substances such as fiber get left behind and are appropriately excreted.

From the Mouth to the Stomach

Figure 3.4 The Human Digestive System

Digestive System by Blausen.com staff, from the Wikiversity Journal of Medicine, is available under a Creative Commons Attribution 3.0 Unported license.

There are four steps in the digestion process (Figure 3.4 “The Human Digestive System”). The first step is ingestion11, which is the collection of food into the digestive tract. It may seem a simple process, but ingestion involves smelling food, thinking about food, and the involuntary release of saliva in the mouth to prepare for food entry. In the mouth, where the second step of digestion occurs, the mechanical and chemical breakdown of food begins. The chemical breakdown12 of food involves enzymes, which break apart the components in food. Theses enzymes

10. Waves of smooth muscle contraction that propel food down the digestive tract.

11. Collection of nutrients into the alimentary canal.

12. The breaking apart of food macromolecules by enzymes secreted by the salivary glands, stomach, pancreas, and small intestine. Additionally, bile emulsifies fats.

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are secreted by the salivary glands, stomach, pancreas, and small intestine. Mechanical breakdown13 starts with mastication (chewing) in the mouth. Teeth crush and grind large food particles, while saliva initiates the chemical breakdown of food and enables its movement downward. The slippery mass of partially broken- down food is called bolus, which moves down the digestive tract as you swallow. Swallowing may seem voluntary at first because it requires conscious effort to push the food with the tongue back toward the throat, but after this, swallowing proceeds involuntarily, meaning it cannot be stopped once it begins. As you swallow, the bolus is pushed from the mouth through the pharynx and into a muscular tube called the esophagus. As it travels through the pharynx, a small flap called the epiglottis closes, to prevent choking by keeping food from going into the trachea. Peristaltic contractions in the esophagus propel the food down to the stomach. At the junction between the esophagus and stomach there is a sphincter muscle that remains closed until the food bolus approaches. The pressure of the food bolus stimulates the lower esophageal sphincter to relax and open and food then moves from the esophagus into the stomach. The mechanical breakdown of food is accentuated by the muscular contractions of the stomach and small intestine that mash, mix, slosh, and propel food down the alimentary canal. Solid food takes between four and eight seconds to travel down the esophagus, and liquids take about one second.

From the Stomach to the Small Intestine

When food enters the stomach, a highly muscular organ, powerful peristaltic contractions help mash, pulverize, and churn food into chyme. Chyme14 is a semiliquid mass of partially digested food that also contains gastric juices secreted by cells in the stomach. Cells in the stomach also secrete hydrochloric acid and the enzyme pepsin, that chemically breaks down food into smaller molecules. The stomach has three basic tasks:

1. To store food 2. To mechanically and chemically break down food 3. To empty partially broken-down food into the small intestine

The length of time food spends in the stomach varies by the macronutrient composition of the meal. A high-fat or high-protein meal takes longer to break down than one rich in carbohydrates. It usually takes a few hours after a meal to empty the stomach contents completely.

13. Includes mastication (chewing) and the muscular contractions of the stomach and small intestine that mash, mix, slosh, and propel food down the alimentary canal.

14. A semiliquid mass of partially digested food that also contains gastric juices.

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The small intestine is divided into three structural parts: the duodenum, the jejunum, and the ileum. Once the chyme enters the duodenum (the first segment of the small intestine), the pancreas and gallbladder are stimulated and release juices that aid in digestion. The pancreas secretes up to 1.5 liters of pancreatic juice through a duct into the duodenum per day. This fluid consists mostly of water, but it also contains bicarbonate ions that neutralize the acidity of the stomach-derived chyme and enzymes that further breakdown proteins, carbohydrates, and lipids. The gallbladder secretes a much smaller amount of bile to help digest fats, also through a duct that leads to the duodenum. Bile is made in the liver and stored in the gall bladder. Bile’s components act like detergents by surrounding fats similar to the way dish soap removes grease from a frying pan. This allows for the movement of fats in the watery environment of the small intestine. Two different types of muscular contractions, called peristalsis and segmentation, move and mix the food in various stages of digestion through the small intestine. Similar to what occurs in the esophagus and stomach, peristalsis is circular waves of smooth muscle contraction that propel food forward. Segmentation sloshes food back and forth in both directions promoting further mixing of the chyme. Almost all the components of food are completely broken down to their simplest unit within the first 25 centimeters of the small intestine. Instead of proteins, carbohydrates, and lipids, the chyme now consists of amino acids, monosaccharides, and emulsified fatty acids.

The next step of digestion (nutrient absorption) takes place in the remaining length of the small intestine, or ileum (> 5 meters).

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Figure 3.5

The way the small intestine is structured gives it a huge surface area to maximize nutrient absorption. The surface area is increased by folds, villi, and microvilli. Digested nutrients are absorbed into either capillaries or lymphatic vessels contained within each microvilli.

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The small intestine is perfectly structured for maximizing nutrient absorption. Its surface area is greater than 200 square meters, which is about the size of a tennis court. The surface area of the small intestine increases by multiple levels of folding. The internal tissue of the small intestine is covered in villi, which are tiny finger- like projections that are covered with even smaller projections, called microvilli (Figure 3.5). The digested nutrients pass through the absorptive cells of the intestine via diffusion or special transport proteins. Amino acids and monosaccharides (sugars) are transported from the intestinal cells into capillaries, but the much larger emulsified fatty acids, fat-soluble vitamins, and other lipids are transported first through lymphatic vessels, which soon meet up with blood vessels.

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From the Small Intestine to the Large Intestine

The process of digestion is fairly efficient. Any food that is still incompletely broken down (usually less than ten percent of food consumed) and the food’s indigestible fiber content moves from the small intestine to the large intestine (colon) through a connecting valve. The main task of the large intestine is to reabsorb water. Remember, water is present not only in solid foods, but also the stomach releases a few hundred millilters of gastric juice and the pancreas adds approximately another 500 milliliters during the digestion of the meal. For the body to conserve water, it is important that the water be reabsorbed. In the large intestine, no further chemical or mechanical breakdown of food takes place, unless it is accomplished by the bacteria that inhabit this portion of the digestive tract. The number of bacteria residing in the large intestine is estimated to be greater than 10(14), which is more than the total number of cells in the human body (10(13)). This may seem rather unpleasant, but the great majority of bacteria in the large intestine are harmless and some are even beneficial.

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Tools for Change

There has been significant talk about pre- and probiotic foods in the mainstream media. The World Health Organization defines probiotics as live bacteria that confer beneficial health effects on their host. They are sometimes called “friendly bacteria.” The most common bacteria labeled as probiotic is lactic acid bacteria (lactobacilli). They are added as live cultures to certain fermented foods such as yogurt. Prebiotics are indigestible foods, primarily soluble fibers, that stimulate the growth of certain strains of bacteria in the large intestine and provide health benefits to the host. A review article in the June 2008 issue of the Journal of Nutrition concludes that there is scientific consensus that probiotics ward off viral-induced diarrhea and reduce the symptoms of lactose intolerance.Farnworth, E. R. “The Evidence to Support Health Claims for Probiotics.” J Nutr 138, no. 6 (2008): 1250S–4S. http://jn.nutrition.org/content/138/6/1250S.long. Expert nutritionists agree that more health benefits of pre- and probiotics will likely reach scientific consensus. As the fields of pre- and probiotic manufacturing and their clinical study progress, more information on proper dosing and what exact strains of bacteria are potentially “friendly” will become available.

You may be interested in trying some of these foods in your diet. A simple food to try is kefir. Several websites provide good recipes, including http://www.kefir.net/recipes.htm.

From the Large Intestine to the Anus

After a few hours in the stomach, plus three to six hours in the small intestine, and about sixteen hours in the large intestine, the digestion process enters step four, which is the elimination of indigestible food as feces. Feces contain indigestible food and gut bacteria (almost 50 percent of content). It is stored in the rectum until it is expelled through the anus via defecation.

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KEY TAKEAWAYS

• The breakdown of complex macromolecules in foods to simple absorbable components is accomplished by the digestive system. These components are processed by cells throughout the body into energy or are used as building blocks.

• The digestive system is composed of the mouth, pharynx, esophagus, stomach, small intestine, large intestine (or colon), rectum, and anus. There are four steps in the digestion process: ingestion, the mechanical and chemical breakdown of food, nutrient absorption, and elimination of indigestible food.

• The mechanical breakdown of food occurs via muscular contractions called peristalsis and segmentation. Enzymes secreted by the salivary glands, stomach, pancreas, and small intestine accomplish the chemical breakdown of food. Additionally, bile emulsifies fats.

DISCUSSION STARTER

1. Decide whether you want to consume pre- and probiotic foods to benefit your health. Visit the websites below to help in your decision-making process. Defend your decision scientifically.

http://www.health.harvard.edu/fhg/updates/update0905c.shtml

http://nccam.nih.gov/research/results/spotlight/110508.htm

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3.3 Nutrients Are Essential for Organ Function

LEARNING OBJECTIVES

1. Generalize how the body distributes nutrients to the rest of the body. 2. Summarize the importance of adequate nutrition on other organ

systems.

When the digestive system has broken down food to its nutrient components the body eagerly awaits delivery. The first stop of most absorbed nutrients is the liver. One of the liver’s primary functions is to regulate metabolic homeostasis. Metabolic homeostasis15 may be defined as when the nutrients consumed and absorbed matches the energy required to carry out life’s biological processes. Simply put, nutrient energy intake equals energy output. Through the body’s network of blood vessels and veins, glucose and amino acids are directly transported from the small intestine to the liver. Lipids are transported to the liver by a more circuitous route involving the lymphatic system, which contains vessels similar to the circulatory system that transport white blood cells called lymph.

15. The nutrients consumed and absorbed matches the energy required to carry out life’s biological processes.

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The liver is the checkpoint for metabolic activity.

Anatomy Man by Gerd Altmann comprises public domain material worldwide.

Maintaining the body’s energy status quo is crucial because when metabolic homeostasis is disturbed by an eating disorder or disease, bodily function suffers. This will be discussed in more depth in the last section of this chapter. The liver is the only organ in the human body that is capable of exporting nutrients for energy production to other tissues. Therefore, when a person is in between meals (fasted state) the liver exports nutrients and when a person has just eaten (fed state) the liver stores nutrients within itself. Nutrient levels and the hormones that respond to their levels in the blood provide the input so that the liver can distinguish between the fasted and fed states and distribute nutrients appropriately.

All eleven organ systems in the human body require nutrient input to perform their specific biological functions. No energy in means no work output. Overall health and the ability to carry out all of life’s basic processes is fueled by nutrients. Without them organ systems would fail, humans would not reproduce, and the race would disappear. In this section, we will discuss some of the critical nutrients that support specific organ system functions.

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The Circulatory System

The circulatory system16 is one of the eleven organ systems of the human body. Its main function is to transport nutrients to cells and wastes from cells. This system consists of the heart, blood, and blood vessels. The heart pumps the blood, and the blood is the transportation fluid. The transportation route to all tissues is a highly intricate blood-vessel network, comprised of arteries, veins, and capillaries. Nutrients absorbed in the small intestine travel mainly to the liver through the hepatic portal vein. From the liver, nutrients travel upward through the inferior vena cava blood vessel to the heart. The heart forcefully pumps the nutrient-rich blood first to the lungs to pick up some oxygen and then to all other cells in the body. Arteries become smaller and smaller on their way to cells, so that by the time blood reaches a cell, the artery’s diameter is extremely small and the vessel is now called a capillary. The reduced diameter of the blood vessel substantially slows the speed of blood flow. This dramatic reduction in blood flow gives cells time to

16. Comprised of the heart, blood, and blood vessels. Its main functions are to transport nutrients to all cells and transport wastes from all cells.

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harvest the nutrients in blood and exchange metabolic wastes.

The Central Nervous System

The human brain (which weighs only about 3 pounds, or 1,300 kilograms) is estimated to contain over one hundred billion neurons. Neurons form the core of the central nervous system17, which consists of the brain, spinal cord, and other nerve bundles in the body. The main function of the central nervous system is to sense changes in the external environment and create a reaction to them. For instance, if your finger comes into contact with a thorn on a rose bush, a sensory neuron transmits a signal from your finger up through the spinal cord and into the brain. Another neuron in the brain sends a signal that travels back to the muscles in your hand and stimulates muscles to contract and you jerk your finger away. All of this happens within a tenth of a second. All nerve impulses travel by the movement of charged sodium, potassium, calcium, and chloride atoms. These are some of the essential minerals in our diets—essential because they are absolutely required for central nervous system function. Nerves communicate with each other via chemicals built from amino acids called neurotransmitters. Eating adequate protein from a variety of sources will ensure the body gets all of the different amino acids that are so important for central nervous system function.

Every day the brain uses over 20 percent of the energy obtained from nutrients. Its main fuel is glucose and only in extreme starvation will it use anything else. For acute mental alertness and clear thinking, glucose must be systematically delivered to your brain. This does not mean that sucking down a can of sugary soda before your next exam is a good thing. Just as too much glucose is bad for other organs, such as the kidneys and pancreas, it also produces negative effects upon the brain. Excessive glucose levels in the blood can cause a loss of cognitive function and chronically high blood- glucose levels can damage brain cells. The brain’s cognitive functions include language processing, learning, perceiving, and thinking. Recent scientific studies demonstrate that having continuously high blood-glucose levels substantially elevates the risk for developing Alzheimer’s disease, which is the greatest cause of age-related cognitive decline.

The good news is that much research is directed toward determining the best diets and foods that slow cognitive decline and maximize brain health. A study in the

17. Neurons form the core of the central nervous system, which consists of the brain, spinal cord, and other nerve bundles. The main function of the central nervous system is to sense changes in the external environment and create a reaction to them.

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June 2010 issue of the Archives of Neurology reports that people over age sixty-five who adhered to diets that consisted of higher intakes of nuts, fish, poultry, tomatoes, cruciferous vegetables, fruits, salad dressing, and dark green, and leafy vegetables, as well as a lower intake of high-fat dairy products, red meat, organ meat, and butter, had a much reduced risk for Alzheimer’s disease.Gu, Y., PhD et al. “Food Combination and Alzheimer Disease Risk: A Protective Diet.” Arch Neurol 67, no. 6 (2010): 699–706. doi: 10./1001/archneurol.2010.84. Other scientific studies provide supporting evidence that foods rich in omega-3 fatty acids and/or antioxidants provide the brain with protection against Alzheimer’s disease. One potential “brain food” is the blueberry. The protective effects of blueberries upon the brain are linked to their high content of anthocyanins, which are potent antioxidants and reduce inflammation. A small study published in the April 2010 issue of the Journal of Agricultural and Food Chemistry found that elderly people who consumed blueberry juice every day for twelve weeks had improved learning and memorization skills in comparison to other subjects given a placebo drink.Krikorian, R. et al. “Blueberry Supplementation Improves Memory in Older Adults.” J Agric Food Chem 58, no. 7 (2010): 3996–4000. doi: 10.1021/jf9029332. More clinical trials are evaluating the effects of blueberries and other foods that benefit the brain and preserve its function as we age.

The Muscular System

The muscular system18 allows the body to move voluntarily, but it also controls involuntary movements of other organ systems such as heartbeat in the circulatory system and peristaltic waves in the digestive system. It consists of over six hundred skeletal muscles, as well as the heart muscle, the smooth muscles that surround your entire alimentary canal, and all your arterial blood vessels. Muscle contraction relies on energy delivery to the muscle. Each movement uses up cellular energy and without an adequate energy supply muscle function suffers. Muscle, like the liver, can store the energy from glucose in the large polymeric molecule glycogen. But unlike the liver, muscles use up all of their own stored energy and do not export it to other organs in the body. When muscle energy stores are diminished, muscle contraction weakens. However, muscle is not as susceptible to low levels of blood glucose as the brain because it will readily use alternate fuels, such as fatty acids and protein to produce cellular energy.

18. The muscular system allows voluntary movement as well as involuntary movements of other organ systems. It consists of skeletal muscle, the heart muscle, and smooth muscles.

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“Hitting the Wall” or “Bonking”

If you are familiar with endurance sports, you may have heard of “hitting the wall” or “bonking.” These colloquial terms refer to the extreme fatigue that sets in after about 120 minutes of performing an endurance sport, such as marathon running or long-distance cycling. The physiology underlying “hitting the wall” means that muscles have used up all their stored glycogen and are therefore dependent on other nutrients to support their energy needs. Fatty acids are transported from fat-storing cells to the muscle to rectify the nutrient deficit. However, fatty acids take more time to convert to energy than glucose, thus decreasing performance levels. To avoid “hitting the wall” or “bonking,” endurance athletes load up on carbohydrates a few days before the event. This will maximize an athlete’s amount of glycogen stored in their liver and muscle tissues. It is important not to assume that carbohydrate loading works for everyone. Without accompanied endurance training you will not increase the amount of stored glucose. If you plan on running a five-mile race for fun with your friend and decide to eat a large amount of carbohydrates in the form of a big spaghetti dinner the night before, the excess carbohydrates will be stored fat. Another way for athletes to avoid “hitting the wall” is to consume carbohydrate-containing drinks and foods during an endurance event. In fact, throughout the Tour de France—a twenty-two-day, twenty-four-hundred-mile race—the average cyclist consumes greater than 60 grams of carbohydrates per hour.

The Endocrine System

The functions of the endocrine system19 are intricately connected to the body’s nutrition. This organ system is responsible for regulating appetite, nutrient absorption, nutrient storage, and nutrient usage, in addition to other functions, such as reproduction. The glands in the endocrine system are the pituitary, thyroid, parathyroid, adrenals, thymus, pineal, pancreas, ovaries, and testes. The glands secrete hormones20, which are biological molecules that regulate cellular processes in other target tissues, so they require transportation by the circulatory system. Adequate nutrition is critical for the functioning of all the glands in the endocrine system. A protein deficiency impairs gonadal-hormone release, preventing reproduction. Athletic teenage girls with very little body fat often do not menstruate. Children who are malnourished usually do not produce enough growth hormone and fail to reach normal height for their age group. Probably the most popularized connection between nutrition and the functions of the endocrine

19. Organ system that is responsible for regulating nutrient intake, absorption, storage, and usage, in addition to many other things, most notably reproduction. The glands in the endocrine system are the pituitary, thyroid, parathyroid, adrenal, thymus, and pineal gland, as well as the pancreas, ovaries, and testes.

20. Biological molecules transported in the blood that regulate cellular processes in other target tissues.

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system is that unhealthy dietary patterns are linked to obesity and the development of Type 2 diabetes. The Centers for Disease Control and Prevention (CDC) estimates that twenty-six million Americans have Type 2 diabetes as of 2011. This is 8.3 percent of the US population. The maps in Note 3.35 “Interactive 3.1” show the percentage of adults who are obese, and those with diagnosed Type 2 diabetes within all American counties. You can see that those counties with the highest incidence of obesity also have the highest incidence of Type 2 diabetes. To see how the rise in obesity in this country is paralleled by the rise in Type 2 diabetes, watch the PowerPoint presentation prepared by the CDC (Note 3.35 “Interactive 3.1”).

Interactive 3.1

Take a look at the PowerPoint presentation prepared by the CDC that captures the concurrent rises of obesity and Type 2 diabetes in this country. Click on “Maps of Trends in Diabetes and Obesity.”

http://www.cdc.gov/diabetes/statistics/diabetes_slides.htm

What is the causal relationship between overnutrition and Type 2 diabetes? The prevailing theory is that the overconsumption of high-fat and high-sugar foods causes changes in muscle, fat, and liver cells that leads to a diminished response from the pancreatic hormone insulin. These cells are called “insulin-resistant.” Insulin is released after a meal and instructs the liver and other tissues to take up glucose and fatty acids that are circulating in the blood. When cells are resistant to insulin they do not take up enough glucose and fatty acids and so glucose and fatty acids remain at high concentrations in the blood. The continuously high amounts of glucose and fatty acids in the blood impair the release of insulin from the pancreas, further exacerbating the situation. The chronic elevation of glucose and fatty acids in the blood also causes damage to other tissues over time, so that people who have

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Type 2 diabetes are at increased risk for cardiovascular disease, kidney disease, nerve damage, and eye disease.

Tools for Change

Do your part to slow the rising tide of obesity and Type 2 diabetes in this country. On the individual level, improve your own family’s diet; at the local community level, support the development of more nutritious school lunch programs; and at the national level, support your nation’s nutrition goals. Visit the CDC Diabetes Public Health Resource website at http://www.cdc.gov/ diabetes/. It provides information on education resources, projects, and programs, and spotlights news on diabetes and obesity. The CDC also has a new workplace program called CDC’s LEAN Works! (LEAN: Leading Employees to Activity and Nutrition). The program provides free web-based resources with the mission of designing worksites that prevent obesity. See http://www.cdc.gov/leanworks/ for more details.

The Immune System

The immune system21 is comprised of several types of white blood cells that circulate in the blood and lymph. Their jobs are to seek, recruit, attack, and destroy foreign invaders, such as bacteria and viruses. Other less realized components of the immune system are the skin (which acts as a barricade), mucus (which traps and entangles microorganisms), and even the bacteria in the large intestine (which prevent the colonization of bad bacteria in the gut). Immune system functions are completely dependent on dietary nutrients. In fact, malnutrition is the leading cause of immune-system deficiency worldwide. When immune system functions are inadequate there is a marked increase in the chance of getting an infection. Children in many poor, developing countries have protein- and/or energy-deficient diets that are causative of two different syndromes, kwashiokors and marasmus. These children often die from infections that their bodies could normally have fought off, but because their protein and/or energy intake is so low, the immune system cannot perform its functions.

Other nutrients, such as zinc, selenium, copper, folate, and vitamins A, B6, C, D, and E, all provide benefits to immune system function. Deficiencies in these nutrients can cause an increased risk for infection and death. Zinc deficiency results in suppression of the immune system’s barrier functions by damaging skin cells; it is also associated with a decrease in the number of circulating white blood cells. A

21. The immune system is made up of several different types of white blood cells and other components that act as barricades to foreign invaders. The functions of the immune system are to barricade, seek, recruit, attack, and destroy foreign invaders, such as bacteria and viruses.

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review of several studies in the journal Pediatrics concluded that zinc supplements administered to children under age five for longer than three months significantly reduces the incidence and severity of diarrhea and respiratory illnesses.Aggarwal R., MD, DM, J. Sentz, MPH and M. A. Miller, MD. “Role of Zinc Administration in Prevention of Childhood Diarrhea and Respiratory Illnesses: A Meta-Analysis.” Pediatrics 119, no. 6 (2007): 1120–30. doi: 10.1542/peds.2006–3481. Zinc supplementation has also been found to be therapeutically beneficial for the treatment of leprosy, tuberculosis, pneumonia, and the common cold. Equally important to remember is that multiple studies show that it is best to obtain your minerals and vitamins from eating a variety of healthy foods.

Tools for Change

To ensure that your diet includes zinc-friendly foods, try these foods high in zinc and other immune-system friendly nutrients: oysters, poultry, baked beans, chick peas, cashews, sesame seeds, peanuts, whole grains, and zinc- fortified cereals.

Just as undernutrition compromises immune system health, so does overnutrition. People who are obese are at increased risk for developing immune system disorders such as asthma, rheumatoid arthritis, and some cancers. Both the quality and quantity of fat affect immune system function. High intakes of saturated and trans fats negatively affect the immune system, whereas increasing your intake of omega-3 fatty acids, found in salmon and other oily fish, decreases inflammatory responses. High intakes of omega-3 fatty acids are linked to a reduction in the risk of developing certain autoimmune disorders, such as rheumatoid arthritis, and are used as part of a comprehensive treatment for rheumatoid arthritis.

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KEY TAKEAWAYS

• Metabolic homeostasis occurs when the amount of nutrients consumed matches the energy required to carry out life’s biological processes.

• The circulatory system transports nutrients to cells and transports wastes from them.

• The essential minerals sodium, potassium, calcium, and chloride, and the macronutrients protein and carbohydrates, are required for central nervous system function. Fat is also critical for central nervous system function (see the Discussion Starter below).

• Without energy from nutrients, muscles cannot contract. • Undernutrition and overnutrition compromise endocrine and immune

system functions. Type 2 diabetes, increased rates of infection, and inflammatory disorders are symptoms of an imbalance in the diet.

DISCUSSION STARTER

1. Find out how fat supports brain function and protects nerves by visiting the Franklin Institute Resources for Science Learning website.

http://www.fi.edu/learn/brain/fats.html

Now look at the websites below to see how too much of the wrong kind of fats may be bad for the brain, while other types of fat are good for the brain.

http://archneur.ama-assn.org/cgi/content/full/60/2/194

http://www.sciencedaily.com/releases/2007/12/ 071210163251.htm

http://www.webmd.com/alzheimers/news/20070418/ omeg-3-fatty-acid-slows-alzheimers

After viewing all of the videos, discuss the importance of “good fats” in the diet for optimizing brain function and preventing diseases such as Alzheimer’s.

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3.4 Energy and Calories

LEARNING OBJECTIVE

1. Estimate your total daily caloric /energy needs based upon your physical activity level.

Energy22 is essential to life. You must eat to have energy. You must go to bed at a decent time, so that when you wake up in the morning, you will not be too tired and you will have sufficient energy for the next day’s activities. Energy is also everywhere in our environment: sunlight, wind, water, plants, and animals. All living things use energy every day. Energy can be defined as the quantity of work a particular system can perform, whether it be a growing child’s body or a train transporting passengers from one place to another. Energy also helps us perform daily functions and tasks such as breathing, walking up a flight of steps, and studying for a test.

Energy is classified as either potential or kinetic. Potential energy23 is stored energy, or energy waiting to happen. Kinetic energy24 is energy in motion. To illustrate this, think of an Olympic swimmer standing at the pool’s edge awaiting the sound of the whistle to begin the race. While he waits for the signal, he has potential energy. When the whistle sounds and he dives into the pool and begins to swim, his energy is kinetic (in motion).

Some basic forms of energy are:

1. Thermal (heat) energy. We can say that a cup of hot tea has thermal energy. Thermal energy is defined as the collective, microscopic, kinetic, and potential energy of the molecules within matter. In a cup of tea, the molecules have kinetic energy because they are moving and oscillating, but they also possess potential energy due to their shared attraction to each other.

2. Chemical energy. In your body, blood sugar (glucose) possesses chemical energy25. When glucose reacts chemically with oxgen, energy is released from the glucose. Once the energy is released, your muscles will utilize it to produce mechanical force and heat.

3. Electrochemical energy. In the body, electrical impulses travel to and from the brain encoded as nerve impulses. Once the brain receives an electrical impulse it causes the release of a messenger chemical

22. The quantity of work a particular system can perform.

23. Stored energy.

24. Moving energy.

25. Potential energy in chemical bonds.

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(glutamate, for example). This in turn facilitates electrical impulses as they move from one neuron to another.

The Calorie Is a Unit of Energy

The amount of energy in nutrients can be quantified into specific units that can be measured. The unit of measurement that defines the energy contained in a energy- yielding nutrient is called a calorie. A calorie26 is the amount of energy in the form of heat that is required to heat one gram of water one degree Celsius. To measure the number of calories in a particular food substance, a certain amount of food is burned in a device called a calorimeter. As the food burns, heat is created. The heat dissipates to the surrounding water while a thermometer detects the change in temperature of the water. You can even perform calorimetry at home with a more basic device. However, it is not likely that you will use this device to measure calorie content in the foods that you eat since mathematical formulas have been developed to estimate caloric content.

Estimating Caloric Content

The energy contained in energy-yielding nutrients differs because the energy- yielding nutrients are composed of different types of chemical bonds. A carbohydrate or a protein yields 4 kilocalories per gram, whereas a lipid yields 9 kilocalories per gram. A kilocalorie (Calorie)27 is the amount of heat generated by a particular macronutrient that raises the temperature of 1 kilogram of water 1 degree Celsius. A kilocalorie of energy performs one thousand times more work than a calorie. On the Nutrition Facts panel, the calories within a particular food are expressed as kilocalories, which is commonly denoted as “Calories” with a capital “C” (1 kcal = 1 Calorie = 1,000 calories).

Calculating the number of Calories in commercially prepared food is made fairly easy since the total number of Calories in a serving of a particular food is listed on the Nutrition Facts panel. If you wanted to know the number of Calories in the breakfast you consumed this morning just add up the number of Calories in each food. For example, if you ate one serving of yogurt that contained 150 Calories, on which you sprinkled one half of a cup of low-fat granola cereal that contained 209 Calories, and drank a glass of orange juice that contained 100 Calories, the total number of Calories you consumed at breakfast is 150 + 209 + 100 = 459 Calories. If you do not have a Nutrition Facts panel for a certain food, such as a half cup of blueberries, and want to find out the amount of Calories it contains, go to MyFood- a-pedia, a website maintained by the USDA (see Note 3.48 “Interactive 3.2”).

26. A unit of energy; equivalent to the amount of energy required to heat 1 gram of water 1 degree Celsius.

27. A kilocalorie is the amount of heat generated by a particular macronutrient that raises the temperature of 1 kilogram of water 1 degree Celsius (this is what is denoted on the Nutrition Facts panel).

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Interactive 3.2

My Food-a-pedia is a tool that calculates the Calories in foods. It also compares the caloric content between foods.

http://apps.usa.gov/myfood-a-pedia.shtml

Estimating the Amount of Energy from Each Macronutrient

Also listed on the Nutrition Facts panel are the amounts of total fat, total carbohydrate, and protein in grams. To calculate the contribution of each macronutrient to the total kilocalories in a serving, multiply the number of grams by the number of kilocalories yielded per gram of nutrient. From the Nutrition Facts panel for yogurt, the protein content in one serving is 7 grams. Protein yields 4 kilocalories per gram. The number of kilocalories from protein is calculated by using the following equation:

# of grams of protein × 4 kilocalories/gram of protein

7 grams × 4 kilocalories/gram = 28 kilocalories

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Because the total number of kilocalories in each serving of yogurt is 150, the percent of energy obtained from protein is calculated by using the following equation:

(# kilocalories from protein ÷ total kilocalories per serving) × 100

(28 ÷ 150) × 100 = 18.7 percent

KEY TAKEAWAYS

• Energy is vital to life and is categorized into two types—kinetic and potential. There are also different forms of energy such as thermal, chemical, and electrochemical.

• Calories are a measurement of a specific quantity of energy contained in foods. The number of calories contained in a commercially prepared food is listed on the Nutrition Facts panel.

DISCUSSION STARTER

1. Estimate the total number of kilocalories that you have eaten so far today. What percentage of the kilocalories you consumed was obtained from carbohydrates? Protein? Fat?

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3.5 Disorders That Can Compromise Health

LEARNING OBJECTIVE

1. Interpret why certain disorders and diseases, such as gastroesophageal reflux disease (GERD), celiac disease, and irritable bowel syndrome compromise overall health.

When nutrients and energy are in short supply, cells, tissues, organs, and organ systems do not function properly. Unbalanced diets can cause diseases and, conversely, certain illnesses and diseases can cause an inadequate intake and absorption of nutrients, simulating the health consequences of an unbalanced diet. Overeating high-fat foods and nutrient-poor foods can lead to obesity and exacerbate the symptoms of gastroesophageal reflux disease (GERD) and irritable bowel syndrome (IBS). Many diseases and illnesses, such as celiac disease, interfere with the body getting its nutritional requirements. A host of other conditions and illnesses, such as food allergies, cancer, stomach ulcers, Crohn’s disease, and kidney and liver disease, also can impair the process of digestion and/or negatively affect nutrient balance and decrease overall health.

Gastroesophageal Reflux Disease

Gastroesophageal reflux disease (GERD)28 is a persistent form of acid reflux that occurs more than two times per week. Acid reflux occurs when the acidic contents of the stomach leak backward into the esophagus and cause irritation. It is estimated that GERD affects 25 to 35 percent of the US population. An analysis of several studies published in the August 2005 issue of Annals of Internal Medicine concludes that GERD is much more prevalent in people who are obese.Hampel, H. MD, PhD, N. S. Abraham, MD, MSc(Epi) and H. B. El-Serag, MD, MPH. “Meta-Analysis: Obesity and the Risk for Gastroesophageal Reflux Disease and Its Complications.” Ann Intern Med 143, no. 3 (2005): 199–211. http://www.ncbi.nlm.nih.gov/pubmed/ 16061918 While the links between obesity and GERD are not completely known, they likely include that excess body fat puts pressure on the stomach, overeating increases pressure in the stomach, and fatty foods are triggers for GERD symptoms. The most common GERD symptom is heartburn, but people with GERD may also experience regurgitation (flow of the stomach’s acidic contents into the mouth), frequent coughing, and trouble swallowing. Approximately 35 percent of children born in the United States have GERD. In babies the symptoms are more difficult to distinguish from what babies do normally. The symptoms are spitting up more than

28. A persistant form of acid reflux, in which acidic contents of the stomach leak backward into the esophagus and cause irritation.

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normal, incessant crying, refusal to eat, burping, and coughing. Most babies outgrow GERD before their first birthday but a small percentage do not.

Additional Facts about GERD

There are other causative factors of GERD that may be separate from or intertwined with obesity. The sphincter that separates the stomach’s internal contents from the esophagus often does not function properly and acidic gastric contents seep upward. Sometimes the peristaltic contractions of the esophagus are also sluggish and compromise the clearance of acidic contents. In addition to having an unbalanced, high-fat diet, some people with GERD are sensitive to particular foods—chocolate, garlic, spicy foods, fried foods, and tomato-based foods—which worsen symptoms. Drinks containing alcohol or caffeine may also worsen GERD symptoms. GERD is diagnosed most often by a history of the frequency of recurring symptoms. A more proper diagnosis can be made when a doctor inserts a small device into the lower esophagus that measures the acidity of the contents during one’s daily activities. Sometimes a doctor may use an endoscope, which is a long tube with a camera at the end, to view the tissue in the esophagus. About 50 percent of people with GERD have inflamed tissues in the esophagus. A condition known as Barrett’s esophagus may develop over time in some people who have GERD. Barrett’s esophagus refers to a structural difference in the tissue of the esophagus, which is caused by recurrent tissue damage. It occurs in 5 to 15 percent of patients diagnosed with GERD and less than 1 percent of these patients may develop cancer of the esophagus, a highly lethal cancer.

The first approach to GERD treatment is dietary and lifestyle modifications. Suggestions are to reduce weight if you are overweight or obese, avoid foods that worsen GERD symptoms, eat smaller meals, stop smoking, and remain upright for at least three hours after a meal. There is some evidence that sleeping on a bed with the head raised at least six inches helps lessen the symptoms of GERD. People with GERD may not take in the nutrients they need because of the pain and discomfort associated with eating. As a result, GERD can be caused by an unbalanced diet and its symptoms can lead to a worsening of nutrient inadequacy, a viscious cycle that further compromises health. Many medications are available to treat GERD, including antacids, histamine2 (H2) blockers, and proton-pump inhibitors. Some evidence from scientific studies indicates that medications used to treat GERD may accentuate certain nutrient deficiencies, namely zinc and magnesium. When these

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treatment approaches do not work surgery is an option. The most common surgery involves reinforcing the sphincter that serves as a barrier between the stomach and esophagus.

Irritable Bowel Syndome

Irritable bowel syndrome (IBS)29 is characterized by muscle spasms in the colon that result in abdominal pain, bloating, constipation, and/or diarrhea. Interestingly, IBS produces no permanent structural damage to the large intestine as often happens to patients who have Crohn’s disease or inflammatory bowel disease. It is estimated that one in five Americans displays symptoms of IBS. The disorder is more prevalent in women than men. Two primary factors that contribute to IBS are an unbalanced diet and stress. There is no specific test to diagnose IBS, but other conditions that have similar symptoms (such as celiac disease) must be ruled out. This involves stool tests, blood tests, and having a colonoscopy (which involves the insertion of a flexible tube with a tiny camera on the end through the anus so the doctor can see the colon tissues).

Symptoms of IBS significantly decrease a person’s quality of life as they are present for at least twelve consecutive or nonconsecutive weeks in a year. Large meals and foods high in fat and added sugars, or those that contain wheat, rye, barley, peppermint, and chocolate intensify or bring about symptoms of IBS. Additionally, beverages containing caffeine or alcohol may worsen IBS. Stress and depression compound the severity and frequency of IBS symptoms. As with GERD, the first treatment approaches for IBS are diet and lifestyle modifications. People with IBS are often told to keep a daily food journal to help identify and eliminate foods that cause the most problems. Other recommendations are to eat slower, add more fiber to the diet, drink more water, and to exercise. There are some medications (many of which can be purchased over-the-counter) to treat IBS and the resulting diarrhea or constipation. Sometimes antidepressants and drugs to relax the colon are prescribed.

Celiac Disease

Celiac disease30 is an autoimmune disorder affecting between 0.5 and 1.0 percent of Americans—that is, one in every one- to two-hundred people. It is caused by an abnormal immune reaction of small intestine cells to a type of protein, called gluten. Gluten forms in the presence of water and is composed of two protein parts, glutenin and gliadin. Glutenin and gliadin are found in grains that are commonly used to make bread, such as wheat, rye, and barley. When bread is made, yeast eats the flour and makes a waste product, carbon dioxide, which forms bubbles in the dough. As the dough is kneaded, gluten forms and stretches. The carbon dioxide gas bubbles infiltrate the stretchy gluten, giving bread its porosity and tenderness. For

29. A disorder characterized by muscle spasms in the colon that result in abdominal pain, bloating, constipation, and/or diarrhea. There is no permanent structural damage to the large intestine.

30. An autoimmune disorder caused by an abnormal reaction of cells in the small intestine to a type of protein, called gluten.

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those who are sensitive to gluten, it is good to know that corn, millet, buckwheat, and oats do not contain the proteins that make gluten. However, some people who have celiac disease also may have a response to products containing oats. This is most likely the result of cross-contamination of grains during harvest, storage, packaging, and processing.

Celiac disease is most common in people of European descent and is rare in people of African American, Japanese, and Chinese descent. It is much more prevalent in women and in people with Type 1 diabetes, autoimmune thyroid disease, and Down and Turner syndromes. Symptoms can range from mild to severe and can include pale, fatty, loose stools, gastrointestinal upset, abdominal pain, weight loss and, in children, a failure to grow and thrive. The symptoms can appear in infancy or much later in life, even by age seventy. Celiac disease is not always diagnosed because the

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symptoms may be mild. A large number of people have what is referred to as “silent” or “latent” celiac disease.

Celiac disease diagnosis requires a blood test and a biopsy of the small intestine. Because celiac disease is an autoimmune disease, antibodies produced by white blood cells circulate in the body and can be detected in the blood. When gluten- containing foods are consumed the antibodies attack cells lining the small intestine leading to a destruction of the small villi projections. This tissue damage can be detected with a biopsy, a procedure that removes a portion of tissue from the damaged organ. Villi destruction is what causes many of the symptoms of celiac disease. The destruction of the absorptive surface of the small intestine also results in the malabsorption of nutrients, so that while people with this disease may eat enough, nutrients do not make it to the bloodstream because absorption is reduced. The effects of nutrient malabsorption are most apparent in children and the elderly as they are especially susceptible to nutrient deficiencies. Over time these nutrient deficiencies can cause health problems. Poor absorption of iron and folic acid can cause anemia, which is a decrease in red blood cells. Anemia impairs oxygen transport to all cells in the body. Calcium and vitamin D deficiences can lead to osteoporosis, a disease in which bones become brittle (we will explore this in detail in Chapter 9 “Nutrients Important for Bone Health”).

If you think you or someone close to you may have celiac disease, do not despair; it is a very treatable disease. Once diagnosed, a person follows a gluten-free diet for life. This requires dedication and careful detective work to seek out foods with hidden gluten, but some stores carry gluten-free foods. After eliminating gluten from the diet, the tissues of the small intestine rapidly repair themselves and heal in less than six months.

Food Allergies

Paying attention to the way individuals react to various foods is essential in determining what foods may specifically affect a person adversely. Food allergies are one of the many ways in which different body make-ups affect nutritional concerns. Although an estimated twelve million Americans have food allergies, there are likely many more people who say they have food allergies than actually do. This is because food sensitization is different from a medically-determined food allergy. When someone has a food allergy31, the immune system mistakenly attacks a certain kind of food (usually the protein component of a food), such as peanuts, as if it were a threat and IgE antibodies are produced. Doctors sometimes test for food allergies by using skin-prick tests or blood tests to look for the presence of IgE antibodies. However, these types of tests are not always reliable as they can sometimes yield a false positive result. By far, the most valuable tests for determining a food allergy is the Double Blind Placebo Controlled Food Challenge

31. After eating certain kinds of food, the immune system reacts shortly thereafter producing symptoms such as digestive troubles, swollen airways, hives, or possible death.

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(DBPCFC), which involves administering the food orally and then denoting the signs and symptoms of the allergic response.

Food allergy symptoms usually develop within a few minutes to two hours after a person has eaten a food to which they are allergic. These symptoms can range from the annoying to the potentially fatal, and include:

• A tingling mouth • Swelling tongue and/or throat • Difficulty breathing • Hives • Stomach cramps • Diarrhea • Vomiting • Drop in blood pressure • Loss of consciousness • Death

There are no clear treatments for food allergies. Epinephrine is sometimes used to control severe reactions, and individuals with known and dangerous allergies may get prescriptions for self-injectable devices. The only certain way to avoid allergic reactions to food is to avoid the foods that cause them. Beyond avoidance, this can mean reading food labels carefully, or even calling manufacturers for product information.

Ninety percent of food allergies are caused by these eight foods:

1. Milk 2. Eggs 3. Peanuts 4. Tree nuts 5. Fish 6. Shellfish 7. Wheat 8. Soy

The prevalence of food allergies is a complex and growing problem. In response to this situation, the National Institute of Allergy and Infectious Diseases (NIAID) collaborated with thirty-four professional organizations, federal agencies, and patient-advocacy groups to develop a comprehensive guide to diagnosing and

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managing food allergies and treating acute food allergy reactions. The guide defines various food allergies, allergens, and reactions, provides comprehensive information on the prevalence of different food allergies, tracks the history of food allergies, and reviews medical management techniques for people with food allergies.

KEY TAKEAWAYS

• Unbalanced diets can cause diseases and, conversely, certain disorders and diseases can cause an inadequate intake and absorption of nutrients simulating the health consequences of an unbalanced diet.

• Unbalanced, high-fat diets can exacerbate the symptoms of GERD and IBS.

• Celiac disease and anorexia can lead to nutritional deficiencies, which compromise functioning of the organ systems and decrease health.

• Food allergies affect roughly twelve million Americans, with symptoms that range from mild to deadly. Proper diagnosis leads to better management of food allergies and sensitivities.

DISCUSSION STARTER

1. The next time you visit the grocery store, be a “gluten detective” and use the ingredients list to identify all the foods you might normally purchase that contain gluten. Discuss how you can use food labels to avoid products containing gluten.

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3.6 End-of-Chapter Exercises

IT ’S YOUR TURN

1. Summarize the organization of the human body in a flow chart. 2. Determine how many calories you ate of a particular food yesterday and

calculate the percent of calories that came from carbohydrates, protein, and fat.

3. Watch the video on celiac disease at http://visibleproductions.com/ index.php?page=asset_detail&asset_id=vpl_0458_001 and summarize how this ailment leads to decreased nutrient absorption.

APPLY IT

1. Draw a flow chart that summarizes the steps of digestion that take place in each organ of the digestive system.

2. Calculate the calories derived from protein, fats, and carbohydrates from five different foods you often eat.

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EXPAND YOUR KNOWLEDGE

1. Find out how fat supports brain function and protects nerves by visiting the following website: http://www.fi.edu/learn/brain/ fats.html. Now look at these other websites to see how too much of the wrong kind of fats may be bad for the brain, while other types of fat are good for the brain.

http://archneur.ama-assn.org/cgi/content/full/60/2/194

http://www.sciencedaily.com/releases/2007/12/ 071210163251.htm

http://www.webmd.com/alzheimers/news/20070418/ omeg-3-fatty-acid-slows-alzheimers.

Discuss how a balanced fat intake that contains “good fats” helps optimize brain function and prevent diseases such as Alzheimer’s.

2. Estimate the total number of kilocalories that you have eaten so far today. What percentage of the kilocalories you consumed was obtained from carbohydrates, protein, and fat? Compare the percentage of calories from carbohydrates, protein, and fat that you consumed to their Acceptable Macronutrient Distribution Ranges.

3. On your next trip to the grocery store, pretend you have a child with a peanut allergy and determine which foods you need to avoid purchasing to prevent your child from having an allergic response.

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Chapter 4

Carbohydrates

Big Idea

Whole grains are an energy source with nutritional punch.

You likely eat grains every day—cereal, a sandwich, pasta, or your favorite rice dish. Whole grains are vital to a healthful diet. In addition to fiber, whole grains offer other slow-releasing carbohydrates, antioxidants, vitamins, and minerals, all of which are needed for good health. Maybe you are on a diet and have been told to limit or restrict your carbohydrate intake. How much is too much and which carbohydrates are better for you? Can you promote a healthy weight with a balanced intake of whole grains? Before we answer these questions, let’s examine in brief the history of grain.

In ancient times whole grains were cracked open using quern stones that required hours of hand labor. As technology slowly advanced, the quern stone was modified into the millstone. It wasn’t until the advent of water wheels that human labor to produce grains was reduced. About 2,500 years ago the Romans started milling flour by turning one millstone wheel against another that did not move. The turning was done by animals, slaves, and later by waterwheels. The process of milling breaks the hard outer bran coat of the wheat seeds. The bran and germ, which contain the majority of fiber, vitamins, and minerals, are removed by sifting. In the earliest days, the whitest flour was chosen to make bread for the wealthy, and the coarsest was given to the poor. One’s economic status was depicted by the color of bread

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they ate. Wheat was the grain of choice for many cultures, as it not only produced white flour but also contained gluten which gives wheat bread its elasticity and lightness in texture. The word “flour” comes from a French word meaning “blossom” and is metaphoric for the finest part of the meal. Bakers highly prized their art and it was kept from the masses. In fact the baker’s mark was one of the first trademarks.

In America, Oliver Evans built the first flour mill, which was powered by a watermill. It used a series of elevators that moved grain through the mill, cleaning it first, then grinding and sifting it. Today, modern milling produces three types of flour; whole meal containing 100 percent of the grain, with nothing added or removed; brown flour, containing 85 percent of the original grain with some bran and germ and white flour, containing 75 percent of the wheat grain with the most bran and germ removed. The vast majority of flour milled and used in foods and cooking in America is white flour. The modern milling process of preparing white flour removes between 50 and 85 percent of B vitamins, vitamin E, calcium, iron, potassium, chromium, phosphorus, zinc, magnesium manganese, and cobalt.

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In the early nineteenth century several diseases stemming from vitamin and mineral deficiencies, such as pellagra (niacin, B3), beriberi (thiamine, B1), and anemia (iron), plagued many inhabitants of the nation. One of the first public health campaigns was to improve the health of Americans by enriching flour, a dietary staple. The B vitamins, niacin, thiamine, riboflavin, and folate were added along with iron to combat dietary deficiencies and proved a successful strategy to improve public health. However, enriched flour contains only 6 percent or less of the recommended daily intake of the vitamins and minerals it “replaces.” Overwhelming scientific evidence now shows that diets containing high amounts of whole grains rather than refined white flour decrease weight gain and the risk for many chronic diseases, including certain types of cancer and diabetes. Whole grains contain a whole nutrient package that is not replaced by enriched flour. Consumers are becoming more aware of the many health benefits of whole grains. However, the food industry has created a puzzle for consumers in determining if a product is made from 100 percent whole grains. “Whole wheat” does not always mean the product is made with 100 percent whole grains, and brown breads are not always healthier than white as the color may come from added caramel. The Food and Drug Administration (FDA) has provided the food industry with specifics on how to label whole-grain foods—to label it as made from 100 percent whole grains. The best

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method to ensure the product is made from 100 percent whole grains is to check the ingredient list. One-hundred percent whole-grain products list whole grains or whole-wheat flour most often as the first ingredient and do not contain wheat flour, white flour, yellow corn flour, semolina flour, degerminated flour, or durum flour. In America, whole-grain choices are improving, but progress still needs to be made on reducing the added sugar content of many industrially prepared breads, assuring added fiber comes from good sources, eliminating ambiguous labels and claims on packaging, and reducing the costs of whole-grain breads, which still exceed that of white bread.

You Decide

What 100 percent whole-grain products can you include in your diet to improve health, prevent disease, and be tastefully satisfied?

As you read on, you will learn the different types of carbohydrates, their essential roles in the body, the potential health consequences and benefits of diets rich in particular carbohydrates, and the many foods available that are rich in carbohydrates as well as nutritious and satisfying. After reading this chapter, you will be better equipped to decide the best way to get your nutritional punch from various carbohydrates in your diet.

“If thou tastest a crust of bread, thou tastest all the stars and all the heavens.”

– Robert Browning, English poet and playwright (May 1812–December 1889)

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4.1 A Closer Look at Carbohydrates

LEARNING OBJECTIVES

1. Describe some of the distinguishing features of carbohydrates. 2. Describe the differences between fast-releasing and slow-releasing

carbohydrates.

What Exactly Are Carbohydrates and How Many Types Are There?

Carbohydrates are the perfect nutrient to meet your body’s nutritional needs. They nourish your brain and nervous system, provide energy to all of your cells (and within proper caloric limits), and help keep your body fit and lean. Specifically, digestible carbohydrates provide bulk in foods, vitamins, and minerals, while indigestible carbohydrates provide a good amount of fiber with a host of other health benefits.

Plants synthesize the fast-releasing carbohydrate, glucose, from carbon dioxide in the air and water, and by harnessing the sun’s energy. Recall from Chapter 3 “Nutrition and the Human Body” that plants convert the energy in sunlight to chemical energy in the molecule, glucose. Plants use glucose to make other larger, more slow-releasing carbohydrates. When we eat plants we harvest the energy of glucose to support life’s processes.

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Carbohydrates are a group of organic compounds containing a ratio of one carbon atom to two hydrogen atoms to one oxygen atom. Basically, they are hydrated carbons. The word “carbo” means carbon and “hydrate” means water. Glucose1, the most abundant carbohydrate in the human body, has six carbon atoms, twelve hydrogen atoms, and six oxygen atoms. The chemical formula for glucose is written as C6H12O6. Synonymous with the term carbohydrate is the Greek word “saccharide,” which means sugar. The simplest unit of a carbohydrate is a monosaccharide2. Carbohydrates are broadly classified into two subgroups, “fast- releasing” and “slow-releasing.” Fast-releasing carbohydrates are further grouped into the monosaccharides and dissacharides. Slow-releasing carbohydrates are long chains of monosaccharides.

Fast-Releasing Carbohydrates

Fast-releasing carbohydrates are also known more simply as “sugars.” Fast- releasing carbohydrates are grouped as either monosaccharides or dissacharides.

1. The most abundant carbohydrate in the human body. It has six carbon atoms, twelve hydrogen atoms, and six oxygen atoms.

2. The simplest unit of a carbohydrate.

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Monosaccharides include glucose, fructose, and galactose, and the dissacharides include, lactose, maltose, and sucrose.

Monosaccharides

For all organisms from bacteria to plants to animals, glucose is the preferred fuel source. The brain is completely dependent on glucose as its energy source (except during extreme starvation conditions). The monosaccharide galactose differs from glucose only in that a hydroxyl (−OH) group faces in a different direction on the number four carbon. This small structural alteration causes galactose to be less stable than glucose. As a result, the liver rapidly converts it to glucose. Most absorbed galactose is utilized for energy production in cells after its conversion to glucose. (Galactose is one of two simple sugars that are bound together to make up the sugar found in milk. It is later freed during the digestion process.)

Fructose also has the same chemical formula as glucose but differs in its chemical structure, as the ring structure contains only five carbons and not six. Fructose, in contrast to glucose, is not an energy source for other cells in the body. Mostly found in fruits, honey, and sugarcane, fructose is one of the most common monosaccharides in nature. It is also found in soft drinks, cereals, and other products sweetened with high fructose corn syrup.

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Less common monosaccharides are the pentoses, which have only five carbons and not six. The pentoses are abundant in the nucleic acids RNA and DNA, and also as components of fiber.

Lastly, there are the sugar alcohols, which are industrially synthesized derivatives of monosaccharides. Some examples of sugar alcohols are sorbitol, xylitol, and glycerol. (Xylitol is similar in sweetness as table sugar.) Sugar alcohols are often used in place of table sugar to sweeten foods as they are incompletely digested and absorbed, and therefore less caloric. The bacteria in your mouth opposes them, hence sugar alcohols do not cause tooth decay. Interestingly, the sensation of “coolness” that occurs when chewing gum that contains sugar alcohols comes from them dissolving in the mouth, a chemical reaction that requires heat from the inside of the mouth.

Disaccharides

Disaccharides3 are composed of pairs of two monosaccharides linked together. Disaccharides include sucrose, lactose, and maltose. All of the disaccharides contain at least one glucose molecule.

Sucrose, which contains both glucose and fructose molecules, is otherwise known as table sugar. Sucrose is also found in many fruits and vegetables, and at high concentrations in sugar beets and sugar cane, which are used to make table sugar. Lactose, which is commonly known as milk sugar, is composed of one glucose unit and one galactose unit. Lactose is prevalent in dairy products such as milk, yogurt, and cheese. Maltose consists of two glucose molecules bonded together. It is a common breakdown product of plant starches and is rarely found in foods as a disaccharide.

Slow-Releasing Carbohydrates

Slow-releasing carbohydrates are polysaccharides4, long chains of monosaccharides that may be branched or not branched. There are two main groups of polysaccharides: starches and fibers.

Starches

Starch molecules are found in abundance in grains, legumes, and root vegetables, such as potatoes. Amylose, a plant starch, is a linear chain containing hundreds of glucose units. Amylopectin, another plant starch, is a branched chain containing thousands of glucose units. These large starch molecules form crystals and are the energy-storing molecules of plants. These two starch molecules (amylose and

3. Two monosaccharides joined together.

4. A long chain of monosaccharides that may be branched or not branched.

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amylopectine) are contained together in foods, but the smaller one, amylose, is more abundant. Eating raw foods containing starches provides very little energy as the digestive system has a hard time breaking them down. Cooking breaks down the crystal structure of starches, making them much easier to break down in the human body. The starches that remain intact throughout digestion are called resistant starches. Bacteria in the gut can break some of these down and may benefit gastrointestinal health. Isolated and modified starches are used widely in the food industry and during cooking as food thickeners.

Humans and animals store glucose energy from starches in the form of the very large molecule, glycogen5. It has many branches that allow it to break down quickly when energy is needed by cells in the body. It is predominantly found in liver and muscle tissue in animals.

Dietary Fibers

Dietary fibers6 are polysaccharides that are highly branched and cross-linked. Some dietary fibers are pectin, gums, cellulose, and lignin. Humans do not produce the enzymes that can break down dietary fiber; however, bacteria in the large intestine (colon) do. Dietary fibers are very beneficial to our health. The Dietary Guidelines Advisory Committee states that there is enough scientific evidence to support that diets high in fiber reduce the risk for obesity and diabetes, which are primary risk factors for cardiovascular disease.US Department of Agriculture. “Part D. Section 5: Carbohydrates.” In Report of the DGAC on the Dietary Guidelines for Americans, 2010. Accessed September 30, 2011. http://www.cnpp.usda.gov/ Publications/DietaryGuidelines/2010/DGAC/Report/D-5-Carbohydrates.pdf. Dietary

5. A highly branched macromolecule consisting of thousands of glucose monomers held together by chemical bonds.

6. Polysaccharides that are highly branched and cross-linked and only found in plant-based foods, with the exception of chitin (which forms the exoskeletons of some animals).

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fiber is categorized as either water-soluble or insoluble. Some examples of soluble fibers are inulin, pectin, and guar gum and they are found in peas, beans, oats, barley, and rye. Cellulose and lignin are insoluble fibers and a few dietary sources of them are whole-grain foods, flax, cauliflower, and avocados. Cellulose is the most abundant fiber in plants, making up the cell walls and providing structure. Soluble fibers are more easily accessible to bacterial enzymes in the large intestine so they can be broken down to a greater extent than insoluble fibers, but even some breakdown of cellulose and other insoluble fibers occurs.

The last class of fiber is functional fiber. Functional fibers have been added to foods and have been shown to provide health benefits to humans. Functional fibers may be extracted from plants and purified or synthetically made. An example of a functional fiber is psyllium-seed husk. Scientific studies show that consuming psyllium-seed husk reduces blood-cholesterol levels and this health claim has been approved by the FDA. Total dietary fiber intake is the sum of dietary fiber and functional fiber consumed.

KEY TAKEAWAYS

• Carbohydrates are a group of organic compounds containing a ratio of one carbon atom to two hydrogen atoms to one oxygen atom. Carbohydrates are broadly classified into two subgroups, fast-releasing and slow-releasing carbohydrates.

• Fast-releasing carbohydrates are sugars and they include the monosaccharides and disaccharides. Slow-releasing carbohydrates include the polysaccharides, amylose, amylopectin, glycogen, dietary fiber, and functional fiber.

• Glucose is the most important monosaccharide in human nutrition. Many other monosaccharides and disaccharides become glucose in the body.

• Fiber-rich foods are scientifically proven to reduce the risk of obesity and diabetes. Functional fibers are added to foods because they are proven to have added health benefits.

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DISCUSSION STARTERS

1. What do you eat most of: fast-releasing carbohydrates, starches, or fiber?

2. Bring in the packages for the breads you eat and compare the different ingredients lists with your classmates. Are they labeled well? Do they contain any health claims? Are they made from 100 percent whole grain? Do they contain added sugars? For more help on defining products made with whole grains, visit the website of the Whole Grains Council.

http://www.wholegrainscouncil.org/whole-grains-101/ definition-of-whole-grains

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4.2 Digestion and Absorption of Carbohydrates

LEARNING OBJECTIVE

1. Discuss how carbohydrates are digested and absorbed in the human body.

Sweetness is one of the five basic taste sensations of foods and beverages and is sensed by protein receptors in cells of the taste buds. Fast-releasing carbohydrates stimulate the sweetness taste sensation, which is the most sensitive of all taste sensations. Even extremely low concentrations of sugars in foods will stimulate the sweetness taste sensation. Sweetness varies between the different carbohydrate types—some are much sweeter than others. Fructose is the top naturally occurring sugar in sweetness value. See Table 4.1 “Sweetness Comparison of Carbohydrates” for sweetness comparisons among different naturally-occurring carbohydrates. Sweetness is a pleasurable sensation and some people enjoy the taste more than others. In a colloquial sense we identify such people as having a “sweet tooth.” This does not mean that the less-sweet whole grains containing more starches and fiber are less satisfying. Whole grains take longer to chew and get sweeter the more you chew them. Additionally, once in the stomach, whole-grain foods take longer to digest, and keep you full longer. Remember too that they contain fiber which makes elimination much smoother. Whole-grain foods satisfy the body the entire way through the digestive tract and provide the nutrients that also better satisfy the body’s functional needs.

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Relative Sweetness of Sugars and Sweeteners by Ewen comprises public domain material in the United States.

From the Mouth to the Stomach

The mechanical and chemical digestion of carbohydrates begins in the mouth. Chewing, also known as mastication, crumbles the carbohydrate foods into smaller and smaller pieces. The salivary glands in the oral cavity secrete saliva that coats the food particles. Saliva contains the enzyme, salivary amylase7. This enzyme breaks the bonds between the monomeric sugar units of disaccharides, oligosaccharides8, and starches. The salivary amylase breaks down amylose and amylopectin into smaller chains of glucose, called dextrins and maltose. The increased concentration of maltose in the mouth that results from the mechanical and chemical breakdown of starches in whole grains is what enhances their sweetness. Only about five percent of starches are broken down in the mouth. (This is a good thing as more glucose in the mouth would lead to more tooth decay.) When carbohydrates reach the stomach no further chemical breakdown occurs because the amylase enzyme does not function in the acidic conditions of the stomach. But mechanical breakdown is ongoing—the strong peristaltic contractions of the stomach mix the carbohydrates into the more uniform mixture of chyme.

7. Enzyme secreted by the salivary glands in the mouth that breaks down carbohydrates by breaking the glycosidic bonds between monomers.

8. A carbohydrate that is a chain of a few (between three and ten) monosaccharides.

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From the Stomach to the Small Intestine

The chyme is gradually expelled into the upper part of the small intestine. Upon entry of the chyme into the small intestine, the pancreas releases pancreatic juice through a duct. This pancreatic juice contains the enzyme, pancreatic amylase9, which starts again the breakdown of dextrins into shorter and shorter carbohydrate chains. Additionally, enzymes are secreted by the intestinal cells that line the villi. These enzymes, known collectively as disaccharides, are sucrase, maltase, and lactase. Sucrase breaks sucrose into glucose and fructose molecules. Maltase breaks the bond between the two glucose units of maltose, and lactase breaks the bond between galactose and glucose. Once carbohydrates are chemically broken down into single sugar units they are then transported into the inside of intestinal cells.

When people do not have enough of the enzyme lactase, lactose is not sufficiently broken down resulting in a condition called lactose intolerance10. The undigested lactose moves to the large intestine where bacteria are able to digest it. The

9. Enzyme secreted by the pancreas that breaks down carbohydrates in the small intestine by breaking the glycosidic bonds between monomers.

10. A condition in which there is incomplete digestion of lactose. It is caused by a deficiency in the enzyme, lactase. Symptoms include diarrhea, bloating, and abdominal cramps.

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bacterial digestion of lactose produces gases leading to symptoms of diarrhea, bloating, and abdominal cramps. Lactose intolerance usually occurs in adults and is associated with race. The National Digestive Diseases Information Clearing House states that African Americans, Hispanic Americans, American Indians, and Asian Americans have much higher incidences of lactose intolerance while those of northern European descent have the least.National Digestive Diseases Information Clearing House. “Lactose Intolerance.” Last updated April 23, 2012. http://digestive.niddk.nih.gov/ddiseases/pubs/lactoseintolerance/. Most people with lactose intolerance can tolerate some amount of dairy products in their diet. The severity of the symptoms depends on how much lactose is consumed and the degree of lactase deficiency.

Absorption: Going to the Blood Stream

The cells in the small intestine have membranes that contain many transport proteins in order to get the monosaccharides and other nutrients into the blood where they can be distributed to the rest of the body. The first organ to receive glucose, fructose, and galactose is the liver. The liver takes them up and converts galactose to glucose, breaks fructose into even smaller carbon-containing units, and either stores glucose as glycogen or exports it back to the blood. How much glucose the liver exports to the blood is under hormonal control and you will soon discover that even the glucose itself regulates its concentrations in the blood.

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Maintaining Blood Glucose Levels: The Pancreas and Liver

Glucose levels in the blood are tightly controlled, as having either too much or too little glucose in the blood can have health consequences. Glucose regulates its levels in the blood via a process called negative feedback. An everyday example of negative feedback is in your oven because it contains a thermostat. When you set the temperature to cook a delicious homemade noodle casserole at 375°F the thermostat senses the temperature and sends an electrical signal to turn the elements on and heat up the oven. When the temperature reaches 375°F the thermostat senses the temperature and sends a signal to turn the element off. Similarly, your body senses blood glucose levels and maintains the glucose “temperature” in the target range. The glucose thermostat is located within the cells of the pancreas. After eating a meal containing carbohydrates glucose levels rise in the blood.

Insulin-secreting cells in the pancreas sense the increase in blood glucose and release the hormonal message, insulin, into the blood. Insulin sends a signal to the body’s cells to remove glucose from the blood by transporting to the insides of cells and to use it to make energy or for building macromolecules. In the case of muscle tissue and the liver, insulin sends the biological message to store glucose away as glycogen. The presence of insulin in the blood signifies to the body that it has just been fed and to use the fuel. Insulin has an opposing hormone called glucagon. As the time after a meal increases, glucose levels decrease in the blood. Glucagon- secreting cells in the pancreas sense the drop in glucose and, in response, release glucagon into the blood. Glucagon communicates to the cells in the body to stop using all the glucose. More specifically, it signals the liver to break down glycogen and release the stored glucose into the blood, so that glucose levels stay within the target range and all cells get the needed fuel to function properly.

Leftover Carbohydrates: The Large Intestine

Almost all of the carbohydrates, except for dietary fiber and resistant starches, are efficiently digested and absorbed into the body. Some of the remaining indigestible carbohydrates are broken down by enzymes released by bacteria in the large intestine. The products of bacterial digestion of these slow-releasing carbohydrates are short-chain fatty acids and some gases. The short-chain fatty acids are either used by the bacteria to make energy and grow, are eliminated in the feces, or are

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absorbed into cells of the colon, with a small amount being transported to the liver. Colonic cells use the short-chain fatty acids to support some of their functions. The liver can also metabolize the short-chain fatty acids into cellular energy. The yield of energy from dietary fiber is about 2 kilocalories per gram for humans, but is highly dependent upon the fiber type, with soluble fibers and resistant starches yielding more energy than insoluble fibers. Since dietary fiber is digested much less in the gastrointestinal tract than other carbohydrate types (simple sugars, many starches) the rise in blood glucose after eating them is less, and slower. These physiological attributes of high-fiber foods (i.e. whole grains) are linked to a decrease in weight gain and reduced risk of chronic diseases, such as Type 2 diabetes and cardiovascular disease.

A Carbohydrate Feast

It’s Thanksgiving and you have just consumed turkey with mashed potatoes, stuffing smothered in gravy, green beans topped with crispy fried onions, a hot roll dripping with butter, and cranberry sauce. Less than an hour later you top it all off with a slice of pumpkin pie and then lie down on the couch to watch the football game. What happens in your body after digesting and absorbing the whopping amount of nutrients in this Thanksgiving feast? The “hormone of plenty,” insulin, answers the nutrient call. Insulin sends out the physiological message that glucose and everything else is in abundant supply in the blood, so cells absorb and then use or store it. The result of this hormone message is maximization of glycogen stores and all the excess glucose, protein, and lipids are stored as fat.

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A typical American Thanksgiving meal contains many foods that are dense in carbohydrates, with the majority of those being simple sugars and starches. These types of carbohydrate foods are rapidly digested and absorbed. Blood glucose levels rise quickly causing a spike in insulin levels. Contrastingly, foods containing high amounts of fiber are like time-release capsules of sugar. A measurement of the effects of a carbohydrate-containing food on blood-glucose levels is called the glycemic response.

Glycemic Index

The glycemic responses of various foods have been measured and then ranked in comparison to a reference food, usually a slice of white bread or just straight glucose, to create a numeric value called the glycemic index (GI)11. Foods that have a low GI do not raise blood-glucose levels neither as much nor as fast as foods that have a higher GI. A diet of low-GI foods has been shown in epidemiological and clinical trial studies to increase weight loss and reduce the risk of obesity, Type 2 diabetes, and cardiovascular disease.Brand-Miller, J., PhD, et al. “Dietary Glycemic Index: Health Implications.” J Am Coll Nutr 28, no. 4, supplement (2009): 446S–49S. http://www.jacn.org/content/28/4_Supplement_1/446S.long.

11. A measurement of the effects of carbohydrate-containing foods on blood-glucose levels.

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Table 4.2 The Glycemic Index

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How To Eat Foods Low On The Glycemic Index from WikiVisual is available under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported license.

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The carbohydrate type within a food affects the GI, but so does its fat and fiber content (which reduce the GI). Increased fat and fiber in foods increases the time required for digestion and delays the rate of gastric emptying into the small intestine. Processing and cooking additionally affect a food’s GI by increasing their digestibility. Advancements in the technologies of food processing and the high consumer demand for convenient, precooked foods in the United States have created foods that are digested and absorbed more rapidly, independent of the fiber content. Modern breakfast cereals, breads, pastas, and many prepared foods have a high GI. In contrast, most raw foods have a lower GI. (However, the more ripened a fruit or vegetable is, the higher its GI.) The GI can be used as a guide for choosing healthier carbohydrate choices but has some limitations. One is that the GI does not take into account the amount of carbohydrates in a portion of food, only the type of carbohydrate. Another is that combining low- and high-GI foods changes the GI for the meal. Also, some nutrient-dense foods have higher GIs than less nutritious food. (For instance, oatmeal has a higher GI than chocolate because the fat content of chocolate is higher.) Lastly, meats and fats do not have a GI since they do not contain carbohydrates.

Interactive 4.1

Visit this online database of glycemic indices of foods.

http://www.gilisting.com/

Balancing the Thanksgiving Feast

To balance the high-GI foods on the Thanksgiving table with low-GI foods, follow some of these suggestions:

• Serve a winter fruit salad. • Leave the skins on the potatoes. The skin contains fiber and adds

texture to mashed potatoes. Do not use instant potatoes. • Instead of canned green beans with cream of mushroom soup and fried

onions for a side dish, combine butter beans and green peas for a colorful, low-GI food.

• Make your stuffing with whole-grain bread and add mushrooms and extra celery and onions.

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• Try a new low-sugar pumpkin pie recipe and make the crust from whole-grain flour.

• Offer homemade banana bread for dessert.

KEY TAKEAWAYS

• Carbohydrate digestion begins in the mouth with the mechanical action of chewing and the chemical action of salivary amylase. Carbohydrates are not chemically broken down in the stomach, but rather in the small intestine. Pancreatic amylase and the disaccharidases finish the chemical breakdown of digestible carbohydrates.

• The monosaccharides are absorbed into the bloodstream and delivered to the liver.

• Some of the indigestible carbohydrates are digested by bacteria in the large intestine.

• Glucose itself participates in regulating its levels in the blood. Not all carbohydrates have the same effect on blood-glucose levels. The glycemic response is a measurement of the effects of a carbohydrate- containing food on blood-glucose levels.

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DISCUSSION STARTERS

1. Experience the taste sensations of different carbohydrates. What are some foods that satisfy your sweetness sensation?

2. Even though fiber contains calories, albeit less than half of other carbohydrates, why do we generally discount its caloric contribution from our diets?

3. How long a person feels full after eating a carbohydrate-rich meal depends on the type of carbohydrate consumed and what other nutrients are in the meal. Conduct an experiment and determine how long you feel full after eating a candy bar; after eating a slice of whole- grain bread; after eating an apple; and after eating a potato. Compare your results with your classmates and discuss why some of these carbohydrate foods make you feel full longer than others.

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4.3 The Functions of Carbohydrates in the Body

LEARNING OBJECTIVE

1. List four primary functions of carbohydrates in the human body.

There are five primary functions of carbohydrates in the human body. They are energy production, energy storage, building macromolecules, sparing protein, and assisting in lipid metabolism.

Energy Production

The primary role of carbohydrates is to supply energy to all cells in the body. Many cells prefer glucose as a source of energy versus other compounds like fatty acids. Some cells, such as red blood cells, are only able to produce cellular energy from glucose. The brain is also highly sensitive to low blood-glucose levels because it uses only glucose to produce energy and function (unless under extreme starvation conditions). About 70 percent of the glucose entering the body from digestion is redistributed (by the liver) back into the blood for use by other tissues. Cells that require energy remove the glucose from the blood with a transport protein in their membranes. The energy from glucose comes from the chemical bonds between the carbon atoms. Sunlight energy was required to produce these high-energy bonds in the process of photosynthesis. Cells in our bodies break these bonds and capture the energy to perform cellular respiration. Cellular respiration is basically a controlled burning of glucose versus an uncontrolled burning. A cell uses many chemical reactions in multiple enzymatic steps to slow the release of energy (no explosion) and more efficiently capture the energy held within the chemical bonds in glucose.

The first stage in the breakdown of glucose is called glycolysis. Glycolysis12, or the splitting of glucose, occurs in an intricate series of ten enzymatic-reaction steps. The second stage of glucose breakdown occurs in the energy factory organelles, called mitochondria. One carbon atom and two oxygen atoms are removed, yielding more energy. The energy from these carbon bonds is carried to another area of the mitochondria, making the cellular energy available in a form cells can use.

12. The first stage of glucose breakdown; a ten-step enzymatic process that splits glucose into two three-carbon molecules and yields two molecules of ATP.

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Energy Storage

If the body already has enough energy to support its functions, the excess glucose is stored as glycogen (the majority of which is stored in the muscle and liver). A molecule of glycogen may contain in excess of fifty thousand single glucose units and is highly branched, allowing for the rapid dissemination of glucose when it is needed to make cellular energy.

The amount of glycogen in the body at any one time is equivalent to about 4,000 kilocalories—3,000 in muscle tissue and 1,000 in the liver. Prolonged muscle use (such as exercise for longer than a few hours) can deplete the glycogen energy reserve. Remember also from Chapter 3 “Nutrition and the Human Body” that this is referred to as “hitting the wall” or “bonking” and is characterized by fatigue and a decrease in exercise performance. The weakening of muscles sets in because it takes longer to transform the chemical energy in fatty acids and proteins to usable energy than glucose. After prolonged exercise, glycogen is gone and muscles must

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rely more on lipids and proteins as an energy source. Athletes can increase their glycogen reserve modestly by reducing training intensity and increasing their carbohydrate intake to between 60 and 70 percent of total calories three to five days prior to an event. People who are not hardcore training and choose to run a 5-kilometer race for fun do not need to consume a big plate of pasta prior to a race since without long-term intense training the adaptation of increased muscle glycogen will not happen.

The liver, like muscle, can store glucose energy as a glycogen, but in contrast to muscle tissue it will sacrifice its stored glucose energy to other tissues in the body when blood glucose is low. Approximately one-quarter of total body glycogen content is in the liver (which is equivalent to about a four-hour supply of glucose) but this is highly dependent on activity level. The liver uses this glycogen reserve as a way to keep blood-glucose levels within a narrow range between meal times. When the liver’s glycogen supply is exhausted, glucose is made from amino acids obtained from the destruction of proteins in order to maintain metabolic homeostasis.

Building Macromolecules

Although most absorbed glucose is used to make energy, some glucose is converted to ribose and deoxyribose, which are essential building blocks of important macromolecules, such as RNA, DNA, and ATP (Figure 4.6). Glucose is additionally utilized to make the molecule NADPH, which is important for protection against oxidative stress and is used in many other chemical reactions in the body. If all of the energy, glycogen-storing capacity, and building needs of the body are met, excess glucose can be used to make fat. This is why a diet too high in carbohydrates and calories can add on the fat pounds—a topic that will be discussed shortly.

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Figure 4.6

The sugar molecule deoxyribose is used to build the backbone of DNA.

Deoxyribose Structure by Yikrazuul comprises public domain material in the United States.

Chemical Structure of Ribose and Deoxyribose by Genomics Education Programme is available under a Creative Commons Attribution 2.0 Generic license.

Sparing Protein

In a situation where there is not enough glucose to meet the body’s needs, glucose is synthesized from amino acids. Because there is no storage molecule of amino acids, this process requires the destruction of proteins, primarily from muscle tissue. The presence of adequate glucose basically spares the breakdown of proteins from being used to make glucose needed by the body.

Lipid Metabolism

As blood-glucose levels rise, the use of lipids as an energy source is inhibited. Thus, glucose additionally has a “fat-sparing” effect. This is because an increase in blood glucose stimulates release of the hormone insulin, which tells cells to use glucose (instead of lipids) to make energy. Adequate glucose levels in the blood also prevent the development of ketosis. Ketosis is a metabolic condition resulting from an elevation of ketone bodies in the blood. Ketone bodies are an alternative energy source that cells can use when glucose supply is insufficient, such as during fasting. Ketone bodies are acidic and high elevations in the blood can cause it to become too acidic. This is rare in healthy adults, but can occur in alcoholics, people who are malnourished, and in individuals who have Type 1 diabetes. The minimum amount of carbohydrate in the diet required to inhibit ketosis in adults is 50 grams per day.

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Carbohydrates are critical to support life’s most basic function—the production of energy. Without energy none of the other life processes are performed. Although our bodies can synthesize glucose it comes at the cost of protein destruction. As with all nutrients though, carbohydrates are to be consumed in moderation as having too much or too little in the diet may lead to health problems.

KEY TAKEAWAYS

• The four primary functions of carbohydrates in the body are to provide energy, store energy, build macromolecules, and spare protein and fat for other uses.

• Glucose energy is stored as glycogen, with the majority of it in the muscle and liver. The liver uses its glycogen reserve as a way to keep blood-glucose levels within a narrow range between meal times. Some glucose is also used as building blocks of important macromolecules, such as RNA, DNA, and ATP.

• The presence of adequate glucose in the body spares the breakdown of proteins from being used to make glucose needed by the body.

DISCUSSION STARTERS

1. Discuss two reasons it is essential to include carbohydrates in your diet. 2. Why is it necessary for the body to spare protein?

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4.4 Looking Closely at Diabetes

LEARNING OBJECTIVE

1. Summarize the long-term health implications and the dietary approaches to living with Type 1 and Type 2 diabetes.

What Is Diabetes?

Diabetes is one of the top three diseases in America. It affects millions of people and causes tens of thousands of deaths each year. Diabetes is a metabolic disease of insulin deficiency and glucose over-sufficiency. Like other diseases, genetics, nutrition, environment, and lifestyle are all involved in determining a person’s risk for developing diabetes. One sure way to decrease your chances of getting diabetes is to maintain an optimal body weight by adhering to a diet that is balanced in carbohydrate, fat, and protein intake. There are three different types of diabetes: Type 1 diabetes, Type 2 diabetes, and gestational diabetes.

Type 1 Diabetes

Type 1 diabetes13 is a metabolic disease in which insulin-secreting cells in the pancreas are killed by an abnormal response of the immune system, causing a lack of insulin in the body. Its onset typically occurs before the age of thirty. The only way to prevent the deadly symptoms of this disease is to inject insulin under the skin. Before this treatment was discovered, people with Type 1 diabetes died rapidly after disease onset. Death was the result of extremely high blood-glucose levels affecting brain function and leading to coma and death. Up until 1921, patients with Type 1 diabetes, the majority of them children, spent their last days in a ward where they lapsed into a coma awaiting death. One of the most inspiring acts in medical history is that of the scientists who discovered, isolated, and purified insulin and then went on to find out that it relieved the symptoms of Type 1 diabetes, first in dogs and then in humans. Frederick Banting, Charles Best, and James Collip went into a hospital ward in Toronto, Canada and injected comatose children with insulin. Before they completed their rounds children were already awakening to the cheers of their families.

A person with Type 1 diabetes usually has a rapid onset of symptoms that include hunger, excessive thirst and urination, and rapid weight loss. Because the main function of glucose is to provide energy for the body, when insulin is no longer

13. A metabolic disease in which cells in the pancreas are killed by an abnormal response of the immune system, causing a lack of insulin in the body.

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present there is no message sent to cells to take up glucose from the blood. Instead, cells use fat and proteins to make energy, resulting in weight loss. If Type 1 diabetes goes untreated individuals with the disease will develop a life-threatening condition called ketoacidosis. This condition occurs when the body uses fats and not glucose to make energy, resulting in a build-up of ketone bodies in the blood. It is a severe form of ketosis with symptoms of vomiting, dehydration, rapid breathing, and confusion and eventually coma and death. Upon insulin injection these severe symptoms are treated and death is avoided. Unfortunately, while insulin injection prevents death, it is not considered a cure. People who have this disease must adhere to a strict diet to prevent the development of serious complications. Type 1 diabetics are advised to consume a diet low in the types of carbohydrates that rapidly spike glucose levels (high-GI foods), to count the carbohydrates they eat, to consume healthy-carbohydrate foods, and to eat small meals frequently. These guidelines are aimed at preventing large fluctuations in blood glucose. Frequent exercise also helps manage blood-glucose levels. Type 1 diabetes accounts for between 5 and 10 percent of diabetes cases.

Type 2 Diabetes

The other 90 to 95 percent of diabetes cases are Type 2 diabetes. Type 2 diabetes14 is defined as a metabolic disease of insulin insufficiency, but it is also caused by muscle, liver, and fat cells no longer responding to the insulin in the body (Figure 4.7). In brief, cells in the body have become resistant to insulin and no longer receive the full physiological message of insulin to take up glucose from the blood. Thus, similar to patients with Type 1 diabetes, those with Type 2 diabetes also have high blood-glucose levels.

For Type 2 diabetics, the onset of symptoms is more gradual and less noticeable than for Type 1 diabetics. The symptoms are increased thirst and urination, unexplained weight loss, and hunger. The first stage of Type 2 diabetes is characterized by high glucose and insulin levels. This is because the insulin- secreting cells in the pancreas attempt to compensate for insulin resistance by making more insulin. In the second stage of Type 2 diabetes, the insulin-secreting cells in the pancreas become exhausted and die. At this point, Type 2 diabetics also have to be treated with insulin injections. Healthcare providers is to prevent the second stage from happening. As with Type 1 diabetes, chronically high-glucose levels cause big detriments to health over time, so another goal for patients with Type 2 diabetes is to properly manage their blood-glucose levels. The front-line approach for treating Type 2 diabetes includes eating a healthy diet and increasing physical activity.

The Centers for Disease Control Prevention (CDC) estimates that as of 2010, 25.8 million Americans have diabetes, which is 8.3 percent of the population.Centers for

14. A metabolic disease of insulin insufficiency; also caused by muscle, liver, and fat cells no longer responding to the insulin in the body.

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Disease Control and Prevention. “Diabetes Research and Statistics.” Accessed September 30, 2011. http://www.cdc.gov/diabetes/consumer/research.htm. In 2007 the cost of diabetes to the United States was estimated at $174 billion.Centers for Disease Control and Prevention. “CDC Statements on Diabetes Issues.” Accessed September 30, 2011. http://www.cdc.gov/diabetes/news/docs/dpp.htm. The incidence of Type 2 diabetes has more than doubled in America in the past thirty years and the rise is partly attributed to the increase in obesity in this country. Genetics, environment, nutrition, and lifestyle all play a role in determining a person’s risk for Type 2 diabetes. We learned in Chapter 1 “Nutrition and You” that we have the power to change some of the determinants of disease but not others. The Diabetes Prevention Trial that studied lifestyle and drug interventions in more than three thousand participants who were at high risk for Type 2 diabetes found that intensive lifestyle intervention reduced the chances of getting Type 2 diabetes by 58 percent.Knowler, W. C. et al. “Reduction in the Incidence of Type 2 Diabetes with Lifestyle Intervention or Metformin.” N Engl J Med 346, no. 6 (2002): 393–403. http://www.nejm.org/doi/full/10.1056/NEJMoa012512.

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Figure 4.8 Metabolic Syndrome: A Combination of Risk Factors Increasing the Chances for Chronic Disease

Having more than one risk factor for Type 2 diabetes substantially increases a person’s chances for developing the disease. Metabolic syndrome15 refers to a medical condition in which people have three or more risk factors for Type 2 diabetes and cardiovascular disease (Figure 4.8 “Metabolic Syndrome: A Combination of Risk Factors Increasing the Chances for Chronic Disease”). According to the International Diabetes Federation (IDF) people are diagnosed with

15. A medical condition in which people have three or more risk factors for Type 2 diabetes and cardiovascular disease.

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Metabolic Syndrome Mind Map by Madhero88 is available under a Creative Commons Attribution 3.0 Unported license.

this syndrome if they have central (abdominal) obesity and any two of the following health parameters: triglycerides greater than 150 mg/dL; high density lipoproteins (HDL) lower than 40 mg/dL; systolic blood pressure above 100 mmHg, or diastolic above 85 mmHg; fasting blood-glucose levels greater than 100 mg/dL.International Diabetes Federation. “The IDF Consensus Worldwide Definition of the Metabolic Syndrome.” Accessed September 30, 2011. http://www.idf.org/webdata/docs/ IDF_Meta_def_final.pdf. The IDF estimates that between 20 and 25 percent of adults worldwide have metabolic syndrome. Studies vary, but people with metabolic syndrome have between a 9 and 30 times greater chance for developing Type 2 diabetes than those who do not have the syndrome.International Diabetes Federation. “The IDF Consensus Worldwide Definition of the Metabolic Syndrome.” Accessed September 30, 2011. http://www.idf.org/webdata/docs/ IDF_Meta_def_final.pdf.

Gestational Diabetes

During pregnancy some women develop gestational diabetes16. Gestational diabetes is characterized by high blood-glucose levels and insulin resistance. The exact cause is not known but does involve the effects of pregnancy hormones on how cells respond to insulin. Gestational diabetes can cause pregnancy complications and it is common practice for healthcare practitioners to screen pregnant women for this metabolic disorder. The disorder normally ceases when the pregnancy is over, but the National Diabetes Information Clearing House notes that women who had gestational diabetes have between a 40 and 60 percent likelihood of developing Type 2 diabetes within the next ten years.National Diabetes Information Clearing House. “Diabetes Overview.” Accessed September 30, 2011. http://diabetes.niddk.nih.gov/dm/pubs/overview/. Gestational diabetes not only affects the health of a pregnant woman but also is associated with an increased risk of obesity and Type 2 diabetes in her child.

Prediabetes

As the term infers, prediabetes17 is a metabolic condition in which people have moderately high glucose levels, but do not meet the criteria for diagnosis as a diabetic. Over seventy-nine million Americans are prediabetic and at increased risk for Type 2 diabetes and cardiovascular disease.National Diabetes Information Clearing House. “Diabetes Overview.” Accessed September 30, 2011. http://diabetes.niddk.nih.gov/dm/pubs/overview/. The National Diabetes Information Clearing House reports that 35 percent of adults aged twenty and older, and 50 percent of those over the age of sixty-five have prediabetes.National Diabetes Information Clearing House. “Diabetes Overview.” Accessed September 30, 2011. http://diabetes.niddk.nih.gov/dm/pubs/overview/.

16. A metabolic condition similar to Type 2 diabetes that occurs in some pregnant women.

17. A metabolic condition in which people have moderately high glucose levels, but do not meet the criteria for diagnosis as a diabetic.

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Long-Term Health Consequences of Diabetes

The long-term health consequences of diabetes are severe. They are the result of chronically high glucose concentrations in the blood accompanied by other metabolic abnormalities such as high blood-lipid levels. People with diabetes are between two and four times more likely to die from cardiovascular disease. Diabetes is the number one cause of new cases of blindness, lower-limb amputations, and kidney failure. Many people with diabetes develop peripheral neuropathy, characterized by muscle weakness, loss of feeling and pain in the lower extremities. More recently, there is scientific evidence to suggest people with diabetes are also at increased risk for Alzheimer’s disease.

Diabetes Treatment

Keeping blood-glucose levels in the target range (70–130 mg/dL before a meal) requires careful monitoring of blood-glucose levels with a blood-glucose meter, strict adherence to a healthy diet, and increased physical activity. Type 1 diabetics begin insulin injections as soon as they are diagnosed. Type 2 diabetics may require oral medications and insulin injections to maintain blood-glucose levels in the target range. The symptoms of high blood glucose, also called hyperglycemia, are difficult to recognize, diminish in the course of diabetes, and are mostly not apparent until levels become very high. The symptoms are increased thirst and frequent urination. Having too low blood glucose levels, known as hypoglycemia, is also detrimental to health. Hypoglycemia is more common in Type 1 diabetics and is most often caused by injecting too much insulin or injecting it at the wrong time. The symptoms of hypoglycemia are more acute including shakiness, sweating, nausea, hunger, clamminess, fatigue, confusion, irritability, stupor, seizures, and coma. Hypoglycemia can be rapidly and simply treated by eating foods containing about ten to twenty grams of fast-releasing carbohydrates. If symptoms are severe a person is either treated by emergency care providers with an intravenous solution of glucose or given an injection of glucagon, which mobilizes glucose from glycogen in the liver. Some people who are not diabetic may experience reactive hypoglycemia. This is a condition in which people are sensitive to the intake of sugars, refined starches, and high GI foods. Inviduals with reactive hypoglycemia have some symptoms of hypoglycemia. Symptoms are caused by a higher than

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normal increase in blood-insulin levels. This rapidly decreases blood-glucose levels to a level below what is required for proper brain function.

The major determinants of Type 2 diabetes that can be changed are overnutrition and a sedentary lifestyle. Therefore, reversing or improving these factors by lifestyle interventions markedly improve the overall health of Type 2 diabetics and lower blood-glucose levels. In fact it has been shown that when people are overweight, losing as little as nine pounds (four kilograms) decreases blood-glucose levels in Type 2 diabetics. The Diabetes Prevention Trial demonstrated that by adhering to a diet containing between 1,200 and 1,800 kilocalories per day with a dietary fat intake goal of less than 25 percent and increasing physical activity to at least 150 minutes per week, people at high risk for Type 2 diabetes achieved a weight loss of 7 percent and significantly decreased their chances of developing Type 2 diabetes.Knowler, W. C. et al. “Reduction in the Incidence of Type 2 Diabetes with Lifestyle Intervention or Metformin.” N Engl J Med 346, no. 6 (2002): 393–403. http://www.nejm.org/doi/full/10.1056/NEJMoa012512.

The American Diabetes Association (ADA) has a website that provides information and tips for helping diabetics answer the question, “What Can I Eat” (see Note 4.34 “Interactive 4.2”). In regard to carbohydrates the ADA recommends diabetics keep track of the carbohydrates they eat and set a limit. These dietary practices will help keep blood-glucose levels in the target range.

Interactive 4.2

The ADA has a website containing great information and tips on how to eat a healthy diet that helps keep blood-glucose levels in the target range. Visit it to learn more on how to prevent serious complications of this disease.

http://www.diabetes.org/food-and-fitness/food/what-can-i- eat/?utm_source=WWW&utm_medium= DropDownFF&utm_content=WhatCanIEat&utm_campaign=CON

An unfortunate problem is that most diabetics do not adhere to the lifestyle interventions long-term. This is partly because of individual disinclination, but is also because health insurance companies do not provide continued financial support for dietary guidance and because primary care physicians do not prescribe dietary guidance from a dietitian. This shifts the way diabetes is treated away from

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lifestyle intervention toward medications, as the goal still remains to manage blood-glucose levels. Numerous oral medications are available on the market and are often prescribed to Type 2 diabetics in combination.

KEY TAKEAWAYS

• Diabetes is a disease of insulin deficiency and glucose oversufficiency. Like other diseases, genetics, nutrition, environment, and lifestyle are all involved in determining a person’s risk for developing diabetes.

• Type 1 diabetes was once a death sentence, but now can be treated with insulin injections. However, insulin injections do not cure the disease, and diabetics can suffer many disease complications. Diabetes complications can be relieved by strictly managing blood-glucose levels, adhering to a healthy diet, and increasing physical activity.

• The incidence of Type 2 diabetes has more than doubled in America in the past thirty years and the rise is partly attributed to the increase in obesity. The front-line approach for treating Type 2 diabetes includes eating a healthy diet and increasing physical activity.

• The long-term health consequences of diabetes are severe. They are the result of chronically high glucose concentrations in the blood and other metabolic abnormalities such as high blood-lipid levels.

DISCUSSION STARTERS

1. If you owned a grocery store what are some practices you could introduce to combat the epidemic of Type 2 diabetes in this country?

2. What are some options for you to intervene in your lifestyle and decrease your risk for Type 2 diabetes?

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4.5 Health Consequences and Benefits of High-Carbohydrate Diets

LEARNING OBJECTIVE

1. Identify the health benefits of eating a diet rich in whole grains.

Can America blame its obesity epidemic on the higher consumption of added sugars and refined grains? This is a hotly debated topic by both the scientific community and the general public. In this section, we will give a brief overview of the scientific evidence.

Added Sugars

The Food and Nutrition Board of the Institute of Medicine (IOM) defines added sugars18 as “sugars and syrups that are added to foods during processing or preparation.” The IOM goes on to state, “Major sources of added sugars include soft drinks, sports drinks, cakes, cookies, pies, fruitades, fruit punch, dairy desserts, and

18. Sugars and syrups that are added to foods during processing or preparation.

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candy.” Processed foods, even microwaveable dinners, also contain added sugars. Added sugars do not include sugars that occur naturally in whole foods (such as an apple), but do include natural sugars such as brown sugar, corn syrup, dextrose, fructose, fruit juice concentrates, maple syrup, sucrose, and raw sugar that are then added to create other foods (such as cookies). Currently, nutrition labels do not distinguish between added and naturally occurring sugars and give only the total sugar content, making it difficult for consumers to determine their consumption of added sugars. Results from a survey of forty-two thousand Americans reports that in 2008 the average intake of added sugars is 15 percent of total calories, a drop from 18 percent of total calories in 2000.Welsh J. A. et al. “Consumption of Added Sugars Is Decreasing in the United States.” Am J Clin Nutr 94, no. 3 (2011): 726–34. http://www.ncbi.nlm.nih.gov/pubmed/21753067. This is still above the recommended intake of less than 10 percent of total calories. The US Department of Agriculture (USDA) reports that sugar consumption in the American diet in 2008 was, on average, 28 teaspoons per day.

Obesity, Diabetes, and Heart Disease and Their Hypothesized Link to Excessive Sugar and Refined Carbohydrate Consumption

To understand the magnitude of the health problem in the United States consider this—in the United States approximately 130 million adults are overweight, and 30 percent of them are considered obese. The obesity epidemic has reached young adults and children and will markedly affect the prevalence of serious health consequences in adulthood. Health consequences linked to being overweight or obese include Type 2 diabetes, cardiovascular disease, arthritis, depression, and some cancers. An infatuation with sugary foods and refined grains likely contributes to the epidemic proportion of people who are overweight or obese in this country, but so do the consumption of high-calorie foods that contain too much saturated fat and the sedentary lifestyle of most Americans. There is much disagreement over whether high-carbohydrate diets increase weight-gain and disease risk, especially when calories are not significantly higher between compared diets. Many scientific studies demonstrate positive correlations between diets high in added sugars with weight gain and disease risk, but some others do not show a significant relationship. In regard to refined grains, there are no studies that show consumption of refined grains increases weight gain or disease risk. What is clear, however, is that getting more of your carbohydrates from dietary sources containing whole grains instead of refined grains stimulates weight loss and reduces disease risk.

A major source of added sugars in the American diet is soft drinks. There is consistent scientific evidence that consuming sugary soft drinks increases weight gain and disease risk. An analysis of over thirty studies in the American Journal of

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Clinical Nutrition concluded that there is much evidence to indicate higher consumption of sugar-sweetened beverages is linked with weight gain and obesity.Malik, V. S., M. B. Schulze, and F. B. Hu. “Intake of Sugar-Sweetened Beverages and Weight Gain: A Systematic Review.” Am J Clin Nutr 84, no. 2 (2006): 274–88. http://www.ajcn.org/content/84/2/274.long. A study at the Harvard School of Public Health linked the consumption of sugary soft drinks to an increased risk for heart disease.Harvard School of Public Health. “Public HealthTakes Aim at Sugar and Salt.” Accessed September 30, 2011. http://www.hsph.harvard.edu/news/ hphr/fall-2009/sugar-and-salt.html. While the sugar and refined grains and weight debate rages on, the results of all of these studies has led some public health organizations like the American Heart Association (AHA) to recommend even a lower intake of sugar per day (fewer than 9 teaspoons per day for men and fewer than 6 teaspoons for women) than what used to be deemed acceptable. After its 2010 scientific conference on added sugars, the AHA made the following related dietary recommendations:

• First, know the number of total calories you should eat each day. • Consume an overall healthy diet and get the most nutrients for the

calories, using foods high in added sugars as discretionary calories (those left over after getting all recommended nutrients subtracted from the calories used).

• Lower sugar intake, especially when the sugars in foods are not tied to positive nutrients such as in sugary drinks, candies, cakes, and cookies.

• Focus on calories in certain food categories such as beverages and confections, and encourage consumption of positive nutrients and foods such as cereals and low-fat or fat-free dairy products.Van Horn, L. et al. “Added Sugars and Health.” Research reviewed at the AHA Added Sugars Conference, 2010. Circulation 122 (2010): 2470–90. doi: 10.1161/CIR.0b013e3181ffdcb0.

The Most Notorious Sugar

Before high-fructose corn syrup (HCFS) was marketed as the best food and beverage sweetener, sucrose (table sugar) was the number-one sweetener in America. (Recall that sucrose, or table sugar, is a disaccharide consisting of one glucose unit and one fructose unit.) HFCS also contains the simple sugars fructose and glucose, but with fructose at a slightly higher concentration. In the production of HFCS, corn starch is broken down to glucose and fructose, and some of the glucose is then converted to fructose. Fructose is sweeter than glucose; hence many food manufacturers choose to sweeten foods with HFCS. HFCS is used as a sweetener for carbonated beverages, condiments, cereals, and a great variety of other processed foods.

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Some scientists, public health personnel, and healthcare providers believe that fructose is the cause of the obesity epidemic and its associated health consequences. The majority of their evidence stems from the observation that since the early 1970s the number of overweight or obese Americans has dramatically increased and so has the consumption of foods containing HFCS. However, as discussed, so has the consumption of added sugars in general. Animal studies that fuel the fructose opponents show fructose is not used to produce energy in the body; instead it is mostly converted to fat in the liver—potentially contributing to insulin resistance and the development of Type 2 diabetes. Additionally, fructose does not stimulate the release of certain appetite-suppressing hormones, like insulin, as glucose does. Thus, a diet high in fructose could potentially stimulate fat deposition and weight gain.

In human studies, excessive fructose intake has sometimes been associated with weight gain, but results are inconsistent. Moderate fructose intake is not associated with weight gain at all. Moreover, other studies show that some fructose in the diet actually improves glucose metabolism especially in people with Type 2 diabetes.Elliott, S. S. et al. “Fructose, Weight Gain, and the Insulin Resistance Syndrome.” Am J Clin Nutr 76, no. 5 (2002): 911–22. http://www.ajcn.org/content/ 76/5/911.full. In fact, people with diabetes were once advised to use fructose as an alternative sweetener to table sugar. Overall, there is no good evidence that moderate fructose consumption contributes to weight gain and chronic disease. At this time conclusive evidence is not available on whether fructose is any worse than any other added sugar in increasing the risk for obesity, Type 2 diabetes, and cardiovascular disease.

Interactive 4.3

The USDA is in the process of developing a database on the added sugars in many different foods and has made the information accessible. You might be frightened by what you discover when perusing it. For instance, one 6-ounce container (170 grams) of flavored yogurt contains 20 grams (5 teaspoons) of added sugars.

http://www.ars.usda.gov/SP2UserFiles/Place/12354500/Data/Add_Sug/ addsug01.pdf

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Figure 4.10 Gingivitis

One way to prevent gingivitis and subsequent tooth decay is to lower consumption of sugary drinks. Gingivitis by Lesion is available under a Creative Commons Attribution-ShareAlike 3.0 Unported license.

Oral Disease

Oral health refers not only to healthy teeth and gums, but also to the health of all the supporting tissues in the mouth such as ligaments, nerves, jawbone, chewing muscles, and salivary glands. Over ten years ago the Surgeon General produced its first report dedicated to oral health, stating that oral health and health in general are not separate entities.Surgeon General. “National Call to Action to Promote Oral Health.” Accessed September 30, 2011. http://www.surgeongeneral.gov/library/ calls/oralhealth/nationalcalltoaction.html. Instead, oral health is an integral part of overall health and well-being. Soft drinks, sports drinks, candies, desserts, and fruit juices are the main sources of “fermentable sugars19” in the American diet. (Fermentable sugars are those that are easily metabolized by bacteria in a process known as fermentation. Glucose, fructose, and maltose are three examples.) Bacteria that inhabit the mouth metabolize fermentable sugars and starches in refined grains to acids that erode tooth enamel and deeper bone tissues. The acid creates holes (cavities) in the teeth that can be extremely painful (Figure 4.10 “Gingivitis”). Gums are also damaged by bacteria produced by acids, leading to gingivitis (characterized by inflamed and bleeding gums). Saliva is actually a natural mouthwash that neutralizes the acids and aids in building up teeth that have been damaged.

According to Healthy People 2010, 23 percent of US children have cavities by the age of four, and by second grade, one-half of all children in this country have at least one cavity.Continuing MCH Education in Oral Health. “Oral Health and Health Care.” Accessed September 30, 2011. http://ccnmtl.columbia.edu/ projects/otm/index.html. Cavities are an epidemic health problem in the United States and are associated with poor diet, but other contributors include poor dental hygiene and the inaccessibility to regular oral health care. A review in Academic Pediatrics reports that “frequent consumption of fast-releasing carbohydrates, primarily in the form of dietary sugars, is significantly associated with increased dental caries risk.”Mobley C., PhD, et al. “The Contribution of Dietary Factors to Dental Caries and Disparities in Caries.” Acad Pediatr 9, no. 6 (2009): 410–14. doi: 10.1016/j.acap.2009.09.008. In regards to sugary soft drinks, the American Dental Association says that drinking sugary soft drinks increases the risk of decay formation.American Dental Association. “Diet and Oral Health.” Accessed September 30, 2011. http://www.ada.org/2984.aspx#eatoothdecay.

19. Sugars such as glucose, fructose, and maltose that are easily metabolized by bacteria in a process known as fermentation.

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Interactive 4.4

The Harvard School of Public Health Nutrition Source has developed a guide called “How Sweet Is It?” that notes the calories and sugar contents of many popular beverages. Visit the site to determine drinks that are better for your oral and overall health.

http://www.hsph.harvard.edu/nutritionsource/files/how-sweet-is-it-color.pdf

Tools for Change

Save your teeth and gums and choose to drink a beverage that does not contain excess added sugars. An idea: brew some raspberry tea, add some sparkling mineral water, a raspberry or two, some ice, and a mint leaf. Then sit back and refresh.

Do Low-Carbohydrate Diets Affect Health?

Since the early 1990s, marketers of low-carbohydrate diets have bombarded us with the idea that eating fewer carbohydrates promotes weight loss and that these diets are superior to others in their effects on weight loss and overall health. The most famous of these low-carbohydrate diets is the Atkin’s diet. Others include the “South Beach” diet, the “Zone” diet, and the “Earth” diet. Despite the claims these diets make, there is little scientific evidence to support that low-carbohydrate diets are significantly better than other diets in promoting long-term weight loss. A study in The Nutritional Journal concluded that all diets, (independent of carbohydrate, fat, and protein content) that incorporated an exercise regimen significantly decreased weight and waist circumference in obese women.Kerksick, C. M. et al. “Changes in Weight Loss, Body Composition, and Cardiovascular Disease Risk after Altering Macronutrient Distributions During a Regular Exercise Program in Obese Women.” J Nutr 9, no. 59 (2010). doi: 10.1186/1475-2891-9-59. Some studies do provide evidence that in comparison to other diets, low-carbohydrate diets improve insulin levels and other risk factors for Type 2 diabetes and cardiovascular disease. The overall scientific consensus is that consuming fewer calories in a balanced diet will promote health and stimulate weight loss, with significantly better results achieved when combined with regular exercise.

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Health Benefits of Whole Grains in the Diet

While excessive consumption of fast-releasing carbohydrates is potentially bad for your health, consuming more slow-releasing carbohydrates is extremely beneficial to health. There is a wealth of scientific evidence supporting that replacing refined grains with whole grains decreases the risk for obesity, Type 2 diabetes, and cardiovascular disease. Whole grains are great dietary sources of fiber, vitamins, minerals, healthy fats, and a vast amount of beneficial plant chemicals, all of which contribute to the effects of whole grains on health. Americans typically do not consume the recommended amount of whole grains, which is 50 percent or more of grains from whole grains.

Diets high in whole grains have repeatedly been shown to decrease weight. A large group of studies all support that consuming more than two servings of whole grains per day reduces one’s chances of getting Type 2 diabetes by 21 percent.de Munter, J. S. L. et al. “Whole Grain, Bran, and Germ Intake and Risk of Type 2 Diabetes: A Prospective Cohort Study and Systematic Review.” PLoS Medicine, no. 8 (2007): e261. doi: 10.1371/journal.med.0040261. The Nurses’ Health Study found that women who consumed two to three servings of whole grain products daily were 30 percent less likely to have a heart attack.Liu, S. et al. “Whole-Grain Consumption and Risk of Coronary Heart Disease: Results from the Nurses’ Health Study.” Am J Clin Nutr 70, no. 3 (1999): 412–19. http://www.ajcn.org/content/70/3/412.long. The AHA makes the following statements on whole grains:

• “Dietary fiber from whole grains, as part of an overall healthy diet, helps reduce blood cholesterol levels and may lower risk of heart disease.”

• “Fiber-containing foods, such as whole grains, help provide a feeling of fullness with fewer calories and may help with weight management.”American Heart Association. “Whole Grains and Fiber.” Accessed September 30, 2011. http://www.heart.org/HEARTORG/ GettingHealthy/NutritionCenter/HealthyDietGoals/Whole-Grains-and- Fiber_UCM_303249_Article.jsp.

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Colon Health

A substantial health benefit of whole grain foods is that fiber actively supports digestion and optimizes colon health. (This can be more specifically attributed to the insoluble fiber content of whole grains.) There is good evidence supporting that insoluble fiber prevents the irritating problem of constipation and the development of diverticulosis and diverticulitis. Diverticulosis20 is a benign condition characterized by out-pocketings of the colon. Diverticulitis21 occurs when the out- pocketings in the lining of the colon become inflamed. Interestingly, diverticulitis did not make its medical debut until the early 1900s, and in 1971 was defined as a deficiency of whole-grain fiber. According to the National Digestive Diseases Information Clearinghouse, 10 percent of Americans over the age of forty have diverticulosis, and 50 percent of people over the age of sixty have the disorder.National Digestive Diseases Information Clearinghouse, a service of National Institute of Diabetes and Digestive and Kidney Diseases, National Institute of Health. “Diverticulosis and Diverticulitis.” NIH Publication No. 08-1163 (July 2008). http://digestive.niddk.nih.gov/ddiseases/pubs/diverticulosis/. Ten to 25 percent of people who have diverticulosis go on to develop diverticulitis.National Digestive

20. A benign condition characterized by out- pocketings of the colon.

21. A condition that occurs when the out-pocketings in the lining of the colon become inflamed. Symptoms include lower abdominal pain, nausea, and alternating between constipation and diarrhea.

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Diseases Information Clearinghouse, a service of National Institute of Diabetes and Digestive and Kidney Diseases, National Institute of Health. “Diverticulosis and Diverticulitis.” NIH Publication No. 08-1163 (July 2008). Symptoms include lower abdominal pain, nausea, and alternating between constipation and diarrhea.

The chances of developing diverticulosis can be reduced with fiber intake because of what the breakdown products of the fiber do for the colon. The bacterial breakdown of fiber in the large intestine releases short-chain fatty acids. These molecules have been found to nourish colonic cells, inhibit colonic inflammation, and stimulate the immune system (thereby providing protection of the colon from harmful substances). Additionally, the bacterial indigestible fiber, mostly insoluble, increases stool bulk and softness increasing transit time in the large intestine and facilitating feces elimination. One phenomenon of consuming foods high in fiber is increased gas, since the byproducts of bacterial digestion of fiber are gases.

Some studies have found a link between high dietary-fiber intake and a decreased risk for colon cancer. However an analysis of several studies, published in the

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Journal of the American Medical Association in 2005, did not find that dietary-fiber intake was associated with a reduction in colon cancer risk.Park, Y. et al. “Dietary Fiber Intake and Risk of Colorectal Cancer.” JAMA 294, no. 22 (2005): 2849–57. doi: 10.1001/jama.294.22.2849. There is some evidence that specific fiber types (such as inulin) may protect against colon cancer, but more studies are needed to conclusively determine how certain fiber types (and at what dose) inhibit colon cancer development.

KEY TAKEAWAYS

• Whole grain dietary sources stimulate weight loss and reduce disease risk. Excessive high fructose consumption has been shown to cause weight gain. A primary source of added sugars in the American diet is sugary soft drinks.

• While excessive consumption of some fast-releasing carbohydrates and refined grains is potentially bad for your health, consuming whole grains made up of nutrient-dense slow-releasing carbohydrates is extremely beneficial to health.

DISCUSSION STARTERS

1. Have a debate in your classroom on the USDA restriction on the sale of carbonated beverages in schools. Find out more information on this topic by reading “Soft Drinks and School-Age Children: Trends, Effects, Solutions,” developed by the North Carolina School Nutrition Action Committee.

http://nepc.colorado.edu/files/CERU-0203-41-OWI.pdf

2. Learn about the “Australian Paradox:” How decreased sugar consumption paralleled increased rates of overweight and obese people. Read the study and have a classroom debate over the weight of evidence that supports that diets high in added sugars actually increase weight gain.

http://www.mdpi.com/2072-6643/3/4/491/pdf

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4.6 Carbohydrates and Personal Diet Choices

LEARNING OBJECTIVES

1. Define the Acceptable Macronutrient Distribution Range for carbohydrates, the Adequate Intake for fiber, and recommended intake of added sugars.

2. List five foods that are good sources of slow-releasing carbohydrates. 3. Identify three to five foods high in fiber and carbohydrates from whole,

unrefined sources.

In this chapter, you learned what carbohydrates are, the different types of carbohydrates in your diet, and that excess consumption of some types of carbohydrates cause disease while others decrease disease risk. Now that we know the benefits of eating the right carbohydrate, we will examine exactly how much should be eaten to promote health and prevent disease.

How Many Carbohydrates Does a Person Need?

The Food and Nutrition Board of IOM has set the Recommended Dietary Allowance (RDA) of carbohydrates for children and adults at 130 grams per day. This is the average minimum amount the brain requires to function properly. The Acceptable Macronutrient Distribution Range (AMDR) for carbohydrates is between 45 and 65 percent. This means that on a 2,000 kilocalorie diet, a person should consume between 225 and 325 grams of carbohydrate each day. According to the IOM not more than 25 percent of total calories consumed should come from added sugars. The World Health Organization and the AHA recommend much lower intakes of added sugars—10 percent or less of total calories consumed. The IOM has also set Adequate Intakes for dietary fiber, which are 38 and 25 grams for men and women, respectively. The recommendations for dietary fiber are based upon the intake levels known to prevent against heart disease.

Table 4.3 Dietary Reference Intakes for Carbohydrates and Fiber

Carbohydrate Type RDA (g/day) AMDR (% calories)

Total Carbohydrates 130 45–65

* denotes Adequate Intake

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Carbohydrate Type RDA (g/day) AMDR (% calories)

Added Sugars < 25

Fiber 38 (men),* 25 (women)*

* denotes Adequate Intake

Dietary Sources of Carbohydrates

Carbohydrates are contained in all five food groups: grains, fruits, vegetables, meats, and beans (only in some processed meats and beans), and dairy products. Fast-releasing carbohydrates are more prevalent in fruits, fruit juices, and dairy products, while slow-releasing carbohydrates are more plentiful in starchy vegetables, beans, and whole grains. Fast-releasing carbohydrates are also found in large amounts in processed foods, soft drinks, and sweets. On average, a serving of fruits, whole grains, or starches contains 15 grams of carbohydrates. A serving of dairy contains about 12 grams of carbohydrates, and a serving of vegetables contains about 5 grams of carbohydrates.

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It’s the Whole Nutrient Package

In choosing dietary sources of carbohydrates the best ones are those that are nutrient dense, meaning they contain more essential nutrients per calorie of energy. In general, nutrient-dense carbohydrates are minimally processed and include whole-grain breads and cereals, low-fat dairy products, fruits, vegetables, and beans. In contrast, empty-calorie carbohydrate foods are highly processed and often contain added sugars and fats. Soft drinks, cakes, cookies, and candy are examples of empty-calorie carbohydrates. They are sometimes referred to as ‘bad carbohydrates,’ as they are known to cause health problems when consumed in excess.

Interactive 4.5

This interactive USDA tool allows you to enter the foods and serving size of what you’re eating and find out the whole nutrient package.

http://www.ars.usda.gov/Services/docs.htm?docid=17032

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Understanding Carbohydrates from Product Information

While nutrition facts labels aid in determining the amount of carbohydrates you eat, they do not help in determining whether a food is refined or not. The ingredients list provides some help in this regard. It identifies all of the food’s ingredients in order of concentration, with the most concentrated ingredient first. When choosing between two breads, pick the one that lists whole wheat (not wheat flour) as the first ingredient, and avoid those with other flour ingredients, such as white flour or corn flour. (Enriched wheat flour refers to white flour with added vitamins.) Eat less of products that list HFCS and other sugars such as sucrose, honey, dextrose, and cane sugar in the first five ingredients. If you want to eat less processed foods then, in general, stay away from products with long ingredient lists. On the front of food and beverages the manufacturers may include claims such as “sugar-free,” “reduced sugar,” “high fiber,” etc.. The Nutrition and Labeling Act of 1990 has defined for the food industry and consumers what these labels mean.

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In addition, the FDA permits foods that contain whole oats (which contain soluble fiber) to make the health claim on the package that the food reduces the risk of coronary heart disease. The FDA no longer permits Cheerios to make the claim that by eating their cereal “you can lower your cholesterol four percent in six weeks.”

The Bottom Line

Read the labels and ingredient lists of foods to determine your carbohydrate intake and know the types of carbohydrate you consume.

Personal Choices

Carbohydrates are in most foods so you have a great variety of choices with which to meet the carbohydrates recommendations for a healthy diet. The 2010 Dietary Guidelines recommends eating more unrefined carbohydrates and more fiber, and reducing consumption of foods that are high in added sugars. To accomplish these recommendations use some or all of the following suggestions:

• Get more daily carbohydrate servings from whole grains by eating a whole-grain cereal for breakfast, using whole-grain bread to make a sandwich for lunch, and eating a serving of beans and/or nuts with dinner.

• Make sure to get at least three servings (or more) of all the grains you eat as whole grains every day. A serving of whole grains is equal to one

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slice of whole-wheat bread, one ounce of whole-grain cereal, and one- half cup of cooked cereal, brown rice, or whole-wheat pasta.

• Food products made with cornmeal use the whole grain so choose tortillas, corn cereals, and corn breads with cornmeal listed as the first ingredient.

• When baking, substitute whole-wheat flour or other whole-grain flour for some of the refined white flour.

• If you like bread at dinner, choose a whole-grain muffin over a Kaiser roll or baguette.

• Add beans, nuts, or seeds to salad—they add texture and taste. • Choose whole-grain pastas and brown rice, cook al dente, and add

some beans and vegetables in equal portions. • Change it up a bit and experience the taste and satisfaction of other

whole grains such as barley, quinoa, and bulgur. • Eat snacks high in fiber, such as almonds, pistachios, raisins, and air-

popped popcorn. • Add an artichoke and green peas to your dinner plate more often. • Calm your “sweet tooth” by eating fruits, such as berries or an apple. • Replace sugary soft drinks with seltzer water, tea, or a small amount of

100 percent fruit juice added to water or soda water.

KEY TAKEAWAYS

• The IOM has set the Recommended Dietary Allowance of carbohydrates for children and adults at 130 grams per day. This is the average minimum amount the brain requires to function properly. The Acceptable Macronutrient Distribution Range for total carbohydrates is 45 to 65 percent.

• Carbohydrates are contained in all five food groups: grains, fruits, vegetables, meats and beans (only in some processed meats and beans), and dairy products.

• The 2010 Dietary Guidelines recommends eating more slow-releasing carbohydrates and more fiber, and reducing consumption of foods that are high in added sugars. This involves choosing carbohydrate sources that are nutrient-dense, with more essential nutrients per calorie of energy.

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DISCUSSION STARTERS

1. Are you getting the recommended amount of dietary fiber in your diet?

2. Visit the USDA “Database for the Added Sugars Content of Selected Foods” and find the added sugar contents of foods common in your diet. Discuss some of the “surprises” that you discover with your classmates.

http://www.nal.usda.gov/fnic/foodcomp/Data/add_sug/ addsug01.pdf

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4.7 The Food Industry: Functional Attributes of Carbohydrates and the Use of Sugar Substitutes

LEARNING OBJECTIVE

1. Discuss the usefulness (or lack thereof) of consuming foods containing sugar substitutes.

In the food industry, both fast-releasing and slow-releasing carbohydrates are utilized to give foods a wide spectrum of functional attributes, including increased sweetness, viscosity, bulk, coating ability, solubility, consistency, texture, body, and browning capacity. The differences in chemical structure between the different carbohydrates confer their varied functional uses in foods. Starches, gums, and pectins are used as thickening agents in making jam, cakes, cookies, noodles, canned products, imitation cheeses, and a variety of other foods. Molecular gastronomists use slow-releasing carbohydrates, such as alginate, to give shape and texture to their fascinating food creations. Adding fiber to foods increases bulk. Simple sugars are used not only for adding sweetness, but also to add texture, consistency, and browning. In ice cream, the combination of sucrose and corn syrup imparts sweetness as well as a glossy appearance and smooth texture. Added sugars include white, brown, and raw sugar, corn syrup, HFCS, malt and maple syrups, liquid fructose, honey, molasses, agave nectar, and crystal dextrose.

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Due to the potential health consequences of consuming too many added sugars, sugar substitutes have replaced them in many foods and beverages. Sugar substitutes22 may be from natural sources or artificially made. Those that are artificially made are called artificial sweeteners23 and must be approved by the FDA for use in foods and beverages. The artificial sweeteners approved by the FDA are saccharin, aspartame, acesulfame potassium, neotame, and sucralose. Stevia is an example of a naturally derived sugar substitute. It comes from a plant commonly known as sugarleaf and does not require FDA approval. Sugar alcohols24, such as xylitol, sorbitol, erythritol, and mannitol, are carbohydrates that occur naturally in some fruits and vegetables. However, they are industrially synthesized with yeast and other microbes for use as food additives. The FDA requires that foods disclose the fact that they contain sugar alcohols, but does not require scientific testing of it. (Though many of them have undergone studies anyway.) In comparison to sucrose, artificial sweeteners are significantly sweeter (in fact, by several hundred times), but sugar alcohols are more often less sweet than sucrose. Artificial sweeteners and Stevia are not digested or absorbed in significant amounts and therefore are not a significant source of calories in the diet. Sugar alcohols are somewhat digested and absorbed and, on average, contribute about half of the calories as sucrose (4 kilocalories/gram). These attributes make sugar substitutes attractive for many people—especially those who want to lose weight and/or better manage their blood-glucose levels.

22. Sugar replacements, including artificial sweeteners, sugar alcohols, and natural sources such as sugarleaf.

23. Sugar substitutes that are chemically synthesized and must be approved by the FDA prior to their use in the food and beverage industry.

24. Carbohydrates that occur naturally in some fruits and vegetables; however they are industrially synthesized by yeast and other microbes for use as food additives.

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Benefits of Sugar Substitutes

Consuming foods and beverages containing sugar substitutes may benefit health by reducing the consumption of simple sugars, which are higher in calories, cause tooth decay, and are potentially linked to chronic disease. Artificial sweeteners are basically nonnutrients though not all are completely calorie-free. However, because they are so intense in sweetness they are added in very small amounts to foods and beverages. Artificial sweeteners and sugar alcohols are not “fermentable sugars” and therefore they do not cause tooth decay. Chewing gum with artificial sweeteners is the only proven way that artificial sweeteners promote oral health. The American Dental Association (ADA) allows manufacturers of chewing gum to label packages with an ADA seal if they have convincing scientific evidence demonstrating their product either reduces plaque acids, cavities, or gum disease, or promotes tooth remineralization.

There is limited scientific evidence that consuming products with artificial sweeteners decreases weight. In fact, some studies suggest the intense sweetness of these products increases appetite for sweet foods and may lead to increased weight gain. Also, there is very limited evidence that suggests artificial sweeteners lower blood-glucose levels. Additionally, many foods and beverages containing artificial sweeteners and sugar alcohols are still empty-calorie foods (i.e. chewing sugarless gum or drinking diet soda pop) are not going to better your blood-glucose levels or your health.

Health Concerns

The most common side effect of consuming products containing sugar substitutes is gastrointestinal upset, a result of their incomplete digestion. Since the introduction of sugar substitutes to the food and beverage markets, the public has expressed concern about their safety. The health concerns of sugar substitutes originally

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stemmed from scientific studies, which were misinterpreted by both scientists and the public.

In the early 1970s scientific studies were published that demonstrated that high doses of saccharine caused bladder tumors in rats. This information fueled the still- ongoing debate of the health consequences of all artificial sweeteners. In actuality, the results from the early studies were completely irrelevant to humans. The large doses (2.5 percent of diet) of saccharine caused a pellet to form in the rat’s bladder. That pellet chronically irritated the bladder wall, eventually resulting in tumor development. Since this study, scientific investigation in rats, monkeys, and humans have not found any relationship between saccharine consumption and bladder cancer. In 2000, saccharin was removed from the US National Toxicology Program’s list of potential carcinogens.National Cancer Institute. “Artificial Sweeteners and Cancer.” Accessed September 30, 2011. http://www.cancer.gov/ cancertopics/factsheet/Risk/artificial-sweeteners.

There have been health concerns over other artificial sweeteners, most notably aspartame (sold under the trade names of NutraSweet and Equal). The first misconception regarding aspartame was that it was linked with an increase in the incidence of brain tumors in the United States. It was subsequently discovered that the increase in brain tumors started eight years prior to the introduction of aspartame to the market. Today, aspartame is accused of causing brain damage, autism, emotional disorders, and a myriad of other disorders and diseases. Some even believe aspartame is part of a governmental conspiracy to make people dumber. The reality is there is no good scientific evidence backing any of these accusations, and that aspartame has been the most scientifically tested food additive. It is approved for use as an artificial sweetener in over ninety countries.

Aspartame is made by joining aspartic acid and phenylalanine to amino acids. When digested, it is broken down to aspartic acid, phenylalanine, and methanol. People who have the rare genetic disorder phenylketonuria (PKU) have to avoid products containing aspartame. Individuals who have PKU do not have a functional enzyme that converts phenylalanine to the amino acid tyrosine. This causes a build-up of phenylalanine and its metabolic products in the body. If PKU is not treated, the build-up of phenylalanine causes progressive brain damage and seizures. The FDA requires products that contain aspartame to state on the product label, “Phenylketonurics: Contains Phenylalanine.”

For more details on sugar substitutes please refer to Table 4.7 “Sweeteners”.

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Table 4.7 Sweeteners

Sweeteners with Trade Name Calories Source/Origin

Consumer Recommendations Controversial Issues Product Uses

Aspartame

• NutraSweet • Equal

4 kcal/g

Composed of two amino acids (phenylalanine + aspartic acid) + methanol.

Two hundred times sweeter than sucrose.

FDA set maximum Acceptable Daily Intakes (ADI):

50 mg/kg body weight = 16 12 oz. diet soft drinks for adults.

*Cannot be used in products requiring cooking.

People with PKU should not consume aspartame.

Children have potential to reach ADI if consuming many beverages, desserts, frozen desserts, and gums containing aspartame routinely.

Beverages, gelatin desserts, gums, fruit spreads.

Saccharin

• Sweet ‘n’ Low

0 kcal/g

Discovered in 1878. The basic substance is benzoic sulfinide.

Three hundred times sweeter than sucrose.

ADI: 5 mg/kg body weight.

*Can be used in cooking.

1970s, high doses of saccharin associated with bladder cancer in laboratory animals. In 1977, FDA proposed banning saccharin from use in food

• protest launched by consumer

General purpose sweetener in all foods and beverages.

Sold as Sweet ‘n’ Low in United States; also found in cosmetics and pharmaceutical products.

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Sweeteners with Trade Name Calories Source/Origin

Consumer Recommendations Controversial Issues Product Uses

& interest groups

• warning label listed on products about saccharin and cancer risk in animals until 2001 when studies concluded that it did not cause cancer in humans

Acesulfame K

• Sunnette • Sweet One

0 kcal/g

Discovered in 1967. Composed of an organic salt, potassium (K). Structure is very similar to saccharin’s.

It passes through the body unchanged which means it does not

ADI: 15 mg/kg body weight.

Body cannot digest it.

*Can be used in cooking.

Chewing gum, powdered beverage mixes, nondairy creamers, gelatins, puddings, instant teas and coffees.

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Sweeteners with Trade Name Calories Source/Origin

Consumer Recommendations Controversial Issues Product Uses

provide energy.

Two hundred times sweeter than sucrose.

Cyclamates

• Sugar Twin (Canada only)

0 kcal/g

Thirty times sweeter than sucrose.

Discovered in 1937.

No ADI available.

1949, cyclamate approved by FDA for use. Cyclamate was classified as GRAS (Generally Recognized As Safe) until 1970 when it was removed from GRAS status and banned from use in all food and beverage products within the United States on the basis of one study that indicated it caused bladder cancer in rats. Approval still pending for use in the United States since the ban.

Canada and other countries use this type of sweetener.

Recommended as a substitute for table sugar for diabetics in 1950s, baked goods.

Sucralose

• Splenda

1 Splenda packet contains 3.31

First discovered in 1976. Approved for use in 1998 in

ADI: 5 mg/kg body weight.

General purpose sweetener, baked goods, beverages,

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Sweeteners with Trade Name Calories Source/Origin

Consumer Recommendations Controversial Issues Product Uses

calories = 1g

the United States and in 1991 in Canada.

Derived from sucrose in which three of its hydroxyl (OH) groups are replaced by chlorine (Cl−).

Six hundred times sweeter than sugar.

*Can be used in cooking.

gelatin desserts, frozen dairy desserts, canned fruits, salad dressings, dietary supplements; currently recommended as a replacement for table sugar and additive for diabetics.

Stevioside

• Stevia • Sweet Leaf

N/A

Derived from stevia plant found in South America. Stevia rebaudianan leaves.

Classified as GRAS.

Considered to be a dietary supplement and approved not as an additive, but as a dietary supplement.

Used sparingly, stevia may do little harm, but FDA could not approve extensive use of this sweetener due to concerns regarding its effect on reproduction, cancer development, and energy metabolism.

Sold in health food stores as a dietary supplement.

Sucrose

• Sugar

~4 kcal/ g

Extracted from either sugar beets or sugar cane, which is then

It is illegal to sell true raw sugar in the United States because when raw it contains

Over-consumption has been linked to several health effects such as tooth decay or dental caries and contributes

Biscuits, cookies, cakes, pies, candy canes, ice cream, sorbets,

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Sweeteners with Trade Name Calories Source/Origin

Consumer Recommendations Controversial Issues Product Uses

purified and crystallized.

dirt and insect parts, as well as other byproducts. Raw sugar products sold in the United States have actually gone through more than half of the same steps in the refining process as table sugar.

to increased risk for chronic diseases.

and as a food preservative.

Honey 3 kcal/g

Made from sucrose. Contains nectar of flowering plants. Made by bees.

Sucrose is fructose + glucose; however, honey contains more calories than sucrose because honey is denser.

*Considered safe for baking and cooking.

Infants under twelve months old should not be given honey because their digestive tracts cannot handle the bacteria found in honey. Older children and adults are immune to these effects. Honey contains some harmful bacteria that can cause fatal food

Sweeteners in various foods and beverages such as sodas, teas, alcoholic beverages, and baked goods.

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Sweeteners with Trade Name Calories Source/Origin

Consumer Recommendations Controversial Issues Product Uses

poisoning in infants.

HFCS

• high fructose corn syrup

Dry form: 4 kcal/g; Liquid form: 3 kcal/g

Corn is milled to produce corn starch, then the corn starch is further processed to yield corn syrup.

Controversial because it is found ubiquitously in processed food products, which could lead to over- consumption. Study results are varied regarding its role in chronic disease.

Soft drinks, desserts, candies, jellies.

Sugar Alcohols

• Sorbital • Xylitol • Mannitol

2–4 kcal/g.

Not calorie free

Sugar alcohols.

Sorbitol is derived from glucose.

Less likely to cause tooth decay than sucrose.

Sugar alcohols have a laxative effect.

May cause diarrhea and gastrointestinal distress if consumed in large amounts.

Provide bulk and sweetness in the following sugar-free items: cookies, jams, jellies, chewing gum, candies, mints, pharmaceutical and oral health products.

Regulation

Prior to introducing any new artificial sweetener into foods it is rigorously tested and must be legally approved by the FDA. The FDA regulates artificial sweeteners along with other food additives, which number in the thousands. The FDA is responsible for determining whether a food additive presents “a reasonable certainty of no harm” to consumers when used as proposed. The FDA uses the best scientific evidence available to make the statement of no harm, but it does declare

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that science has its limits and that the “FDA can never be absolutely certain of the absence of any risk from the use of any substance.”US Food and Drug Administration. “Food Ingredients and Colors.” Accessed September 30, 2011. http://www.fda.gov/food/foodingredientspackaging/ucm094211.htm. The FDA additionally has established ADIs for artificial sweeteners. The ADIs are the maximum amount in milligrams per kilogram of body weight considered safe to consume daily (mg/kg bw/day) and incorporates a large safety factor. The following list contains the artificial sweeteners approved for use in foods and beverages in the United States, and their ADIs:

• Acesulfame potassium (Sunett, Sweet One). ADI = 15 mg/kg bw/day • Aspartame (Equal, NutraSweet). ADI = 50 mg/kg bw/day • Neotame. ADI = 18 mg/kg bw/day • Saccharin (SugarTwin, Sweet’N Low). ADI = 5 mg/kg bw/day • Sucralose (Splenda). ADI = 5 mg/kg bw/day

Carbohydrates in a Kernel

Referring back to the wheat kernel mentioned at the opening of this chapter, recall that all components of the wheat kernel are required in order to build an optimal healthy diet. The endosperm provides the carbohydrates, and the bran and germ contain the majority of protein, vitamins, minerals, and fiber. Eating foods made with whole grains provides a better nutritional punch for your health. Once whole grains are processed and refined, enrichment in only a few of these removed nutrients does not offset the gain from consuming whole-grain products. Other dietary sources of carbohydrates that maximize nutrient uptake are vegetables, fruits, beans, and low-fat dairy products. To avoid compromising your health, do not consume excessive amounts of carbohydrate foods that contain added sugars, or that are high in sodium and saturated fat. Processed foods contain all of these ingredients in an unwelcome nutrient package that negatively impacts health. Sugar substitutes provide one avenue of decreasing the intake of fast-releasing carbohydrates, but there are others. Know that consumer demand for healthy carbohydrate choices is on the rise, so in the future you can expect decreased prices, more variety of whole-grain products, and less added sugars.

The Bottom Line

Choose more slow-releasing carbohydrates, eat more fiber, and reduce consumption of foods high in added sugars.

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KEY TAKEAWAYS

• In the food industry both fast-releasing and slow-releasing carbohydrates are utilized to give foods a wide spectrum of functional attributes. The differences in chemical structure between the different carbohydrates confer their many different functional uses in foods.

• Due to the health consequences of consuming too many added sugars, sugar substitutes are widely used in many foods and beverages.

• Consuming foods and beverages containing sugar substitutes may benefit health by reducing the consumption of simple sugars, which are higher in calories, cause tooth decay, and are potentially linked to chronic disease. However, the most common side effect of consuming products containing sugar substitutes is gastrointestinal upset, a result of their incomplete digestion.

• Prior to introducing any new artificial sweetener into foods it is rigorously tested and must be legally approved by the FDA.

DISCUSSION STARTERS

1. Conduct a taste test of sugar and its substitutes. What do your taste buds tell you? Do you prefer foods with sugar substitutes or the real thing?

2. Have a class discussion on the safety of aspartame. To fuel the debate, read the FDA’s report.

http://www.fda.gov/Food/FoodIngredientsPackaging/ FoodAdditives/ucm208580.htm

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4.8 End-of-Chapter Exercises

IT ’S YOUR TURN

1. List four functions of carbohydrates in the body. 2. Count the carbohydrates you consume in a day by following the steps for

carbohydrate counting. Is your intake within the recommended range? 3. Determine your daily fiber intake and whether your diet supplies the

amount of fiber recommended to promote health and prevent disease.

APPLY IT

1. Conduct a dietary assessment of the GI of foods in three of your dinners. To aid in this process peruse the website, http://www.gilisting.com/. Plan a dinner menu that balances the GI of the entire meal.

2. Conduct an experiment in the classroom that evaluates the sweetness and tastefulness of sugar substitutes. Try them in pure form by putting a small amount on your finger. Record the results from you and your classmates and make a sweetness and taste comparison chart.

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EXPAND YOUR KNOWLEDGE

1. Design a Thanksgiving feast with at least ten items that help balance the GI of the meal.

2. Draw a flow chart that incorporates the concept of negative feedback in the regulation of blood glucose levels.

3. Visit the website of the CDC (http://apps.nccd.cdc.gov/DDTSTRS/ default.aspx) and record the estimates of obesity, physical inactivity, and Type 2 diabetes in the county you live in. Make a list of five ways to curb the trends of obesity, physical inactivity, and Type 2 diabetes in your county.

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Chapter 5

Lipids

Big Idea

Get your dose of omega-3 fats for good health.

In the 1920s, anthropologist Vilhjalmur Stefansson lived with and studied a group of Inuit. The Inuit were fishers and hunters, primarily of sea mammals such as whales, walruses, and seals. They consumed a high-protein, high-fat diet. In fact, the Inuit consumed an average of 75 percent of their daily energy intake from fat.Patricia Gadsby, “The Inuit Paradox,” Discover, 1 October 2004. http://discovermagazine.com/2004/oct/inuit-paradox/article_print. Stefansson’s research focused on the fact that the Inuit diet had no adverse effects on either their health or his own.Lieb, C. W. “The Effects of an Exclusive Long-Continued Meat Diet.” JAMA 87, no. 1 (1926): 25–26. doi:10.1001/jama.1926.02680010025006

These findings were supported by a later study in 1972, when the Greenland Inuit first caught the attention of Dr. H. O. Bang from Aalborg University in Denmark. He noted that although the Inuit consumed massive amounts of fatty ocean fish, which are packed with omega-3s, none of the Inuit tested showed signs of heart disease. In addition, there was significantly less evidence of joint disease and skin disease than found in Western countries. Further research led Bang and his associate, Dyerberg, to conclude that the omega-3 fatty acids (docosahexaenoic acid, or DHA, and eicosapentaenoic acid, or EPA) present in the diet offer significant health

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benefits:Bang, H.O. and J. Dyerberg. “Fatty Acid Composition of the Plasma Lipids in Greenland Eskimos.” Am J Clin Nutr 28 (1975): 958–66.

• Heart disease. Further research supports Bang and Dyerberg’s finding and shows DHA and EPA to be beneficial to heart health and human development. EPA and DHA tend to reduce blood pressure, prevent blood-clot formation (thereby reducing the risk of stroke), and protect against irregular heartbeats.

• Inflammation and autoimmune diseases. According to research published in the Journal of the American College of Nutrition, animal experiments and clinical intervention studies indicate that omega-3 fatty acids have anti-inflammatory properties.Sears, B. “Anti- Inflammatory Diets for Obesity and Diabetes.” J Am Coll Nutr 21 (2008). The low incidence of autoimmune and inflammatory disorders such as psoriasis, asthma, and Type 1 diabetes and the complete absence of multiple sclerosis has been observed and studied in the Inuit population in Greenland.Brzezinski, A. “Review.” Gastroenterol Hepatol 3, no. 10 (2007): 787–88. http://www.ncbi.nlm.nih.gov/pmc/articles/ PMC3104160/. Subsequent studies concur with these findings and it is believed that omega-3 fats play an important role in the prevention and treatment of coronary artery disease, high blood pressure, arthritis, other inflammatory and autoimmune disorders, and cancer.Simopoulos, A. “Omega-3 Fatty Acids in Inflammation and Autoimmune Diseases.” J Am Coll Nutr 21, no. 6 (2002): 495–505. http://www.jacn.org/content/21/6/495.full.

• Brain health. Omega-3 fats play an important role in maintaining mental health and are crucial for brain function. Omega-3 fatty acids may provide benefits such as expanding learning and memory capacities. Early evidence suggests that the consumption of omega-3 fats is essential for synaptic transmission in the brain. Furthermore, omega-3 fats seem to be most effective when obtained from foods rather than from supplements.

You Decide

What sources of omega-3 fatty acids would you include in your diet and why?

As you read further, you will learn the different types of fats, their essential roles in the body, and the potential health consequences and benefits of diets rich in

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particular lipids. You will be better equipped to decide the best way to get your nutritional punch from various fats in your diet.

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5.1 What Are Lipids?

LEARNING OBJECTIVE

1. Explain the role of lipids in overall health.

Lipids are important fats that serve different roles in the human body. A common misconception is that fat is simply fattening. However, fat is probably the reason we are all here. Throughout history, there have been many instances when food was scarce. Our ability to store excess caloric energy as fat for future usage allowed us to continue as a species during these times of famine. So, normal fat reserves are a signal that metabolic processes are efficient and a person is healthy.

Lipids are a family of organic compounds that are mostly insoluble in water. Composed of fats and oils, lipids are molecules that yield high energy and have a chemical composition mainly of carbon, hydrogen, and oxygen. Lipids perform three primary biological functions within the body: they serve as structural components of cell membranes, function as energy storehouses, and function as important signaling molecules.

The three main types of lipids are triacylglycerols, phospholipids, and sterols. Triacylglycerols (also known as triglycerides) make up more than 95 percent of lipids in the diet and are commonly found in fried foods, vegetable oil, butter, whole milk, cheese, cream cheese, and some meats. Naturally occurring triacylglycerols are found in many foods, including avocados, olives, corn, and nuts. We commonly call the triacylglycerols in our food “fats” and “oils.” Fats are lipids that are solid at room temperature, whereas oils are liquid. As with most fats, triacylglycerols do not dissolve in water. The terms fats, oils, and triacylglycerols are discretionary and can be used interchangeably. In this chapter when we use the word fat, we are referring to triacylglycerols.

Phospholipids1 make up only about 2 percent of dietary lipids. They are water- soluble and are found in both plants and animals. Phospholipids are crucial for building the protective barrier, or membrane, around your body’s cells. In fact, phospholipids are synthesized in the body to form cell and organelle membranes. In blood and body fluids, phospholipids form structures in which fat is enclosed and transported throughout the bloodstream.

1. The second most common of the three basic lipids. Similar to triacylglycerols, phospholipids have an acid containing phosphorus in place of one of the fatty acids. These lipids appear in all cell membranes.

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Sterols are the least common type of lipid. Cholesterol is perhaps the best well- known sterol. Though cholesterol has a notorious reputation, the body gets only a small amount of its cholesterol through food—the body produces most of it. Cholesterol is an important component of the cell membrane and is required for the synthesis of sex hormones, vitamin D, and bile salts.

Later in this chapter, we will examine each of these lipids in more detail and discover how their different structures function to keep your body working.

The Functions of Lipids in the Body Storing Energy

The excess energy from the food we eat is digested and incorporated into adipose tissue2, or fatty tissue. Most of the energy required by the human body is provided by carbohydrates and lipids. As discussed in Chapter 4 “Carbohydrates”, glucose is stored in the body as glycogen. While glycogen provides a ready source of energy, lipids primarily function as an energy reserve. As you may recall, glycogen is quite bulky with heavy water content, thus the body cannot store too much for long.

2. Fatty tissue in the body that consists of masses of fat- storing cells.

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Alternatively, fats are packed together tightly without water and store far greater amounts of energy in a reduced space. A fat gram is densely concentrated with energy—it contains more than double the amount of energy than a gram of carbohydrate. Energy is needed to power the muscles for all the physical work and play an average person or child engages in. For instance, the stored energy in muscles propels an athlete down the track, spurs a dancer’s legs to showcase the latest fancy steps, and keeps all the moving parts of the body functioning smoothly.

Unlike other body cells that can store fat in limited supplies, fat cells are specialized for fat storage and are able to expand almost indefinitely in size. An overabundance of adipose tissue can result in undue stress on the body and can be detrimental to your health. A serious impact of excess fat is the accumulation of too much cholesterol3 in the arterial wall, which can thicken the walls of arteries and lead to cardiovascular disease4. Thus, while some body fat is critical to our survival and good health, in large quantities it can be a deterrent to maintaining good health.

Regulating and Signaling

Triacylglycerols5 control the body’s internal climate, maintaining constant temperature. Those who don’t have enough fat in their bodies tend to feel cold sooner, are often fatigued, and have pressure sores on their skin from fatty acid deficiency. Triacylglycerols also help the body produce and regulate hormones. For example, adipose tissue secretes the hormone leptin, which regulates appetite. In the reproductive system, fatty acids are required for proper reproductive health; women who lack proper amounts may stop menstruating and become infertile. Omega-3 and omega-6 essential fatty acids help regulate cholesterol and blood clotting and control inflammation in the joints, tissues, and bloodstream. Fats also play important functional roles in sustaining nerve impulse transmission, memory storage, and tissue structure. More specifically in the brain, lipids are focal to brain activity in structure and in function. They help form nerve cell membranes, insulate neurons, and facilitate the signaling of electrical impulses throughout the brain.

3. An important component of the cell membrane. Required for the synthesis of sex hormones, vitamin D, and bile salts.

4. A disease of the heart or blood vessels.

5. The most common of the three basic classes of lipids and the main form fat takes in both diet and the human body. A triacylglycerol is made up of three molecules of fatty acids and one molecule of glycerol.

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Lipids serve as signaling molecules; they are catalysts of electrical impulse activity within the brain. Common Lipids by Lmaps is available under a Creative Commons Attribution-ShareAlike 3.0 Unported license.

Insulating and Protecting

Did you know that up to 30 percent of body weight is comprised of fat tissue? Some of this is made up of visceral fat or adipose tissue surrounding delicate organs. Vital organs such as the heart, kidneys, and liver are protected by visceral fat. The composition of the brain is outstandingly 60 percent fat, demonstrating the major structural role that fat serves within the body. You may be most familiar with subcutaneous fat, or fat underneath the skin. This blanket layer of tissue insulates the body from extreme temperatures and helps keep the internal climate under control. It pads our hands and buttocks and prevents friction, as these areas frequently come in contact with hard surfaces. It also gives the body the extra padding required when engaging in physically demanding activities such as ice- or roller skating, horseback riding, or snowboarding.

Aiding Digestion and Increasing Bioavailability

The dietary fats in the foods we eat break down in our digestive systems and begin the transport of precious micronutrients. By carrying fat-soluble nutrients through the digestive process, intestinal absorption is improved. This improved absorption is also known as increased bioavailability6. Fat-soluble nutrients are especially important for good health and exhibit a variety of functions. Vitamins A, D, E, and K—the fat-soluble vitamins—are mainly found in foods containing fat. Some fat- soluble vitamins (such as vitamin A) are also found in naturally fat-free foods such as green leafy vegetables, carrots, and broccoli. These vitamins are best absorbed when combined with foods containing fat. Fats also increase the bioavailability of compounds known as phytochemicals7, which are plant constituents such as lycopene (found in tomatoes) and beta-carotene (found in carrots). Phytochemicals are believed to promote health and well-being. As a result, eating tomatoes with olive oil or salad dressing will facilitate lycopene absorption. Other essential nutrients, such as essential fatty acids, are constituents of the fats themselves and serve as building blocks of a cell.

6. Refers to the proportion of nutrients that are absorbed or become available in the bloodstream.

7. Nonessential plant compounds considered to have a beneficial impact on human health.

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Note that removing the lipid elements from food also takes away the food’s fat- soluble vitamin content. When products such as grain and dairy are processed, these essential nutrients are lost. Manufacturers replace these nutrients through a process called enrichment.

Tools for Change

Remember, fat-soluble nutrients require fat for effective absorption. For your next snack, look for foods that contain vitamins A, D, E, and K. Do these foods also contain fat that will help you absorb them? If not, think of ways to add a bit of healthy fat to aid in their absorption. (For more details on healthy fat, refer to Section 5.4 “Understanding Blood Cholesterol” of this chapter.)

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The Role of Lipids in Food High Energy Source

Fat-rich foods naturally have a high caloric density. Foods that are high in fat contain more calories than foods high in protein or carbohydrates. As a result, high-fat foods are a convenient source of energy. For example, 1 gram of fat or oil provides 9 kilocalories of energy, compared with 4 kilocalories found in 1 gram of carbohydrate or protein. Depending on the level of physical activity and on nutritional needs, fat requirements vary greatly from person to person. When energy needs are high, the body welcomes the high- caloric density of fats. For instance, infants and growing children require proper amounts of fat to support normal growth and development. If an infant or child is given a low-fat diet for an extended period, growth and development will not progress normally. Other individuals with high-energy needs are athletes, people who have physically demanding jobs, and those recuperating from illness.

When the body has used all of its calories from carbohydrates (this can occur after just twenty minutes of exercise), it initiates fat usage. A professional swimmer must consume large amounts of food energy to meet the demands of swimming long distances, so eating fat-rich foods makes sense. In contrast, if a person who leads a sedentary lifestyle eats the same high-density fat foods, they will intake more fat calories than their body requires within just a few bites. Use caution—consumption of calories over and beyond energy requirements is a contributing factor to obesity.

Smell and Taste

Fat contains dissolved compounds that contribute to mouth-watering aromas and flavors. Fat also adds texture to food. Baked foods are supple and moist. Frying foods locks in flavor and lessens cooking time. How long does it take you to recall the smell of your favorite food cooking? What would a meal be without that savory aroma to delight your senses and heighten your preparedness for eating a meal?

Fat plays another valuable role in nutrition. Fat contributes to satiety8, or the sensation of fullness. When fatty foods are swallowed the body responds by enabling the processes controlling digestion to retard the movement of food along the digestive tract, thus promoting an overall sense of fullness. Oftentimes before the feeling of fullness arrives, people overindulge in fat-rich foods, finding the delectable taste irresistible. Indeed, the very things that make fat-rich foods attractive also make them a hindrance to maintaining a healthful diet.

8. The feeling of being satisfied or full.

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Tools for Change

While fats provide delicious smells, tastes, and textures to our foods, they also provide numerous calories. To allow your body to experience the satiety effect of the fat before you overindulge, try savoring rich foods. Eating slowly will allow you to both fully enjoy the experience and be sated with a smaller portion. Remember to take your time. Drink water in between bites or eat a lower fat food before and after a higher fat food. The lower-fat foods will provide bulk, but fewer calories.

KEY TAKEAWAYS

• Lipids include triacylglycerols, phospholipids, and sterols. • Triacylglycerols, the most common lipid, comprise most body fat and

are described as fats and oils in food. • Excess energy from food is stored as adipose tissue in the body. • Fats are critical for maintaining body temperature, cushioning vital

organs, regulating hormones, transmitting nerve impulses, and storing memory.

• Lipids transport fat-soluble nutrients and phytochemicals and promote bioavailability of these compounds.

• Fat is a convenient source of energy for people with high-energy requirements.

• Fat provides double the energy per gram than protein or carbohydrates, enhances the smell and flavor of food, and promotes satiety.

DISCUSSION STARTERS

1. Discuss the role of lipids in our diet and their critical functions in the body.

2. Explain the importance of fats to the bioavailability of other nutrients. 3. Discuss the role of fats as an energy source for the body.

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5.2 How Lipids Work

LEARNING OBJECTIVES

1. Explain how the structure of each lipid impacts its function as it relates to health and disease.

2. Compare and contrast the structure of the following types of fats: triacylglycerols (monounsaturated, polyunsaturated, omega-3, and omega-6), phospholipids, and sterols.

3. Explain how the fatty acids you consume relate to the fatty-acid composition of your body fat.

Lipids are unique organic compounds, each serving key roles and performing specific functions within the body. As we discuss the various types of lipids (triacylglycerols, phospholipids, and sterols) in further detail, we will compare their structures and functions and examine their impact on human health.

Triacylglycerols Structure and Functions

Triacylglycerols are the main form of lipid found in the body and in the diet. Fatty acids and glycerol are the building blocks of triacylglycerols. Glycerol is a thick, smooth, syrupy compound that is often used in the food industry. To form a triacylglycerol, a glycerol molecule is joined by three fatty acid chains. Triacylglycerols contain varying mixtures of fatty acids.

Fatty Acids

Fatty acids determine if the compound is solid or liquid at room temperature. Fatty acids9 consist of a carboxylic acid (−OOH) group on one end of a carbon chain and a methyl group (−CH3) on the other end. Fatty acids can differ from one another in two important ways—carbon chain length and degree of saturation.

It’s All in the Chain

Fatty acids have different chain lengths and different compositions. Foods have fatty acids with chain lengths between four and twenty-four carbons and most of them contain an even number of carbon atoms. When the carbon chain length is shorter, the melting point of the fatty acid becomes lower—and the fatty acid becomes more liquid.

9. An organic compound that contains a carboxylic acid (−COOH) group at one end and a methyl group at the other (−CH3).

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Degrees of Saturation

Fatty acid chains are held together by carbon atoms that attach to each other and to hydrogen atoms. The term saturation refers to whether or not a fatty acid chain is filled (or “saturated”) to capacity with hydrogen atoms. If each available carbon bond holds a hydrogen atom we call this a saturated fatty acid10 chain. All carbon atoms in such a fatty acid chain are bonded with single bonds. Sometimes the chain has a place where hydrogen atoms are missing. This is referred to as the point of unsaturation11.

When one or more bonds between carbon atoms are a double bond (C=C), that fatty acid is called an unsaturated fatty acid12, as it has one or more points of

10. A fatty acid that contains the maximum number of hydrogen atoms with no points of unsaturation.

11. The place on a molecule where additional hydrogen atoms can attach.

12. A fatty acid that is missing hydrogen atoms with one or more point of unsaturation.

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unsaturation. Any fatty acid that has only one double bond is a monounsaturated fatty acid13, an example of which is olive oil (75 percent of its fat is monounsaturated). Monounsaturated fats help regulate blood cholesterol levels, thereby reducing the risk for heart disease and stroke. A polyunsaturated fatty acid14 is a fatty acid with two or more double bonds or two or more points of unsaturation. Soybean oil contains high amounts of polyunsaturated fatty acids. Both monounsaturated fats and polyunsaturated fats provide nutrition that is essential for normal cell development and healthy skin.

Foods that have a high percentage of saturated fatty acids tend to be solid at room temperature. Examples of these are fats found in chocolate (stearic acid, an eighteen-carbon saturated fatty acid is a primary component) and meat. Foods rich in unsaturated fatty acids, such as olive oil (oleic acid, an eighteen-carbon unsaturated fatty acid, is a major component) tend to be liquid at room temperature. Flaxseed oil is rich in alpha-linolenic acid, which is an unsaturated fatty acid and becomes a thin liquid at room temperature.

Knowing the connection between chain length, degree of saturation, and the state of the fatty acid (solid or liquid) is important for making food choices. If you decide to limit or redirect your intake of fat products, then choosing unsaturated fat is more beneficial than choosing a saturated fat. This choice is easy enough to make because unsaturated fats tend to be liquid at room temperature (for example, olive oil) whereas saturated fats tend to be solid at room temperature (for example, butter). Avocados are rich in unsaturated fats. Most vegetable and fish oils contain high quantities of polyunsaturated fats. Olive oil and canola oil are also rich in monounsaturated fats. Conversely, tropical oils are an exception to this rule in that they are liquid at room temperature yet high in saturated fat. Palm oil (often used in food processing) is highly saturated and has been proven to raise blood cholesterol. Shortening, margarine, and commercially prepared products (in general) report to use only vegetable-derived fats in their processing. But even so, much of the fat they use may be in the saturated and trans fat categories.

Cis or Trans Fatty Acids?

The introduction of a carbon double bond in a carbon chain, as in an unsaturated fatty acid, can result in different structures for the same fatty acid composition. When the hydrogen atoms are bonded to the same side of the carbon chain, it is called a cis fatty acid15. Because the hydrogen atoms are on the same side, the carbon chain has a bent structure. Naturally occurring fatty acids usually have a cis configuration.

13. A fatty acid that contains one point of unsaturation.

14. A fatty acid that contains two or more points of unsaturation.

15. A fatty acid with the hydrogen atoms bonded to the same side of the carbon chain.

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In a trans fatty acid16, the hydrogen atoms are attached on opposite sides of the carbon chain. Unlike cis fatty acids, most trans fatty acids are not found naturally in foods, but are a result of a process called hydrogenation. Hydrogenation is the process of adding hydrogen to the carbon double bonds, thus making the fatty acid saturated (or less unsaturated, in the case of partial hydrogenation). This is how vegetable oils are converted into semisolid fats for use in the manufacturing process.

According to the ongoing Harvard Nurses Health Study, trans fatty acids have been associated with increased risk for coronary heart disease because of the way they negatively impact blood cholesterol levels.Harvard School of Public Health. “It’s Time to End the Low-Fat Myth.” Introduction to “Fats and Cholesterol: Out with the Bad, In with the Good” in The Nutrition Source. http://www.hsph.harvard.edu/ nutritionsource/what-should-you-eat/fats-full-story/#references.

Interestingly, some naturally occurring trans fats do not pose the same health risks as their artificially engineered counterparts. These trans fats are found in ruminant animals such as cows, sheep, and goats, resulting in trans fatty acids being present in our meat, milk, and other dairy product supply. Reports from the US Department of Agriculture (USDA) indicate that these trans fats comprise 15 to 20 percent of the total trans-fat intake in our diet. While we know that trans fats are not exactly

16. A fatty acid that has hydrogens attached on opposite sides of the carbon chain.

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harmless, it seems that any negative effect naturally occurring trans fats have are counteracted by the presence of other fatty acid molecules in these animal products, which work to promote human health.

Nonessential and Essential Fatty Acids

Fatty acids are vital for the normal operation of all body systems. The circulatory system, respiratory system, integumentary system, immune system, brain, and other organs require fatty acids for proper function. The body is capable of synthesizing most of the fatty acids it needs from food. These fatty acids are known as nonessential fatty acids17. However, there are some fatty acids that the body cannot synthesize and these are called essential fatty acids18. It is important to note that nonessential fatty acids doesn’t mean unimportant; the classification is based solely on the ability of the body to synthesize the fatty acid.

Essential fatty acids must be obtained from food. They fall into two categories—omega-3 and omega-6. The 3 and 6 refer to the position of the first carbon double bond and the omega refers to the methyl end of the chain. Omega-3 and omega-6 fatty acids are precursors to important compounds called eicosanoids19. Eicosanoids are powerful hormones that control many other hormones and important body functions, such as the central nervous system and the immune system. Eicosanoids derived from omega-6 fatty acids are known to increase blood pressure, immune response, and inflammation. In contrast, eicosanoids derived from omega-3 fatty acids are known to have heart-healthy effects. Given the contrasting effects of the omega-3 and omega-6 fatty acids, a proper dietary balance between the two must be achieved to ensure optimal health benefits.

Essential fatty acids play an important role in the life and death of cardiac cells, immune system function, and blood pressure regulation. Docosahexaenoic acid (DHA)20 is an omega-3 essential fatty acid shown to play important roles in synaptic transmission in the brain during fetal development.

Some excellent sources of omega-3 and omega-6 essential fatty acids are fish, flaxseed oil, hemp, walnuts, and leafy vegetables. Because these essential fatty acids are easily accessible, essential fatty acid deficiency is extremely rare.

17. A fatty acid that can be synthesized by the body.

18. A fatty acid that the body cannot synthesize and must be supplied through the diet.

19. Compounds derived from polyunsaturated fatty acids that control several body functions.

20. An omega-3 fatty acid that is especially important for brain growth and development in infants.

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Tools for Change

It is important to strike a proper balance between omega-3 and omega-6 fats in your diet. Research suggests that a diet that is too high in omega-6 fats distorts the balance of proinflammatory agents, promoting chronic inflammation and causing the potential for health problems such as asthma, arthritis, allergies, or diabetes. Omega-6 fats compete with omega-3 fats for enzymes and will actually replace omega-3 fats. The typical western diet is characterized by an excessive consumption of foods high in omega-6 fatty acids. To gain proper balance between the two, increase your omega-3 fat intake by eating more fatty fish or other sources of omega-3 fatty acids at least two times per week.

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Fatty-Acid Composition in the Diet and in the Body

The fatty-acid profile of the diet directly correlates to the tissue lipid profile of the body. It may not solely be the quantity of dietary fat that matters. More directly, the type of dietary fat ingested has been shown to affect body weight, composition, and metabolism. The fatty acids consumed are often incorporated into the triacylglycerols within the body. Evidence confirms that saturated fatty acids are linked to higher rates of weight retention when compared to other types of fatty acids. Alternatively, the fatty acids found in fish oil are proven to reduce the rate of weight gain as compared to other fatty acids.Mori, T. “Dietary fish oil upregulates intestinal lipid metabolism and reduces body weight gain in C57BL/6J mice.” J Nutr. 2007 Dec;137(12):2629-34. http://www.ncbi.nlm.nih.gov/pubmed/18029475

Phospholipids

Like triacylglycerols, phospholipids have a glycerol backbone. But unlike triacylglycerols, phospholipids are diglycerides (two fatty-acid molecules attached to the glycerol backbone) while their third fatty-acid chain has a phosphate group coupled with a nitrogen-containing group. This unique structure makes phospholipids water soluble. Phospholipids are what we call amphiphilic21—the fatty-acid sides are hydrophobic (dislike water) and the phosphate group is hydrophilic (likes water).

In the body phospholipids bind together to form cell membranes. The amphiphilic nature of phospholipids governs their function as components of cell membranes. The phospholipids form a double layer in cell membranes, thus effectively protecting the inside of the cell from the outside environment while at the same time allowing for transport of fat and water through the membrane.

Phospholipids are ideal emulsifiers22 that can keep oil and water mixed. Emulsions are mixtures of two liquids that do not mix. Without emulsifiers, the fat and water content would be somewhat separate within food. Lecithin (phosphatidylcholine), found in egg yolk, honey, and mustard, is a popular food emulsifier. Mayonnaise demonstrates lecithin’s ability to blend vinegar and oil to create the stable, spreadable condiment that so many enjoy. Food emulsifiers play an important role in making the appearance of food appetizing. Adding emulsifiers to sauces and creams not only enhances their appearance but also increases their freshness.

21. A compound that has both water-loving and fat-loving properties.

22. Compound that allow two immiscible liquids to combine so that no separation occurs.

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Lecithin’s crucial role within the body is clear, because it is present in every cell throughout the body; 28 percent of brain matter is composed of lecithin and 66 percent of the fat in the liver is lecithin. Many people attribute health-promoting properties to lecithin, such as its ability to lower blood cholesterol and aid with weight loss. There are several lecithin supplements on the market broadcasting these claims. However, as the body can make most phospholipids, it is not necessary to consume them in a pill. The body makes all of the lecithin that it needs.

Sterols

Sterols have a very different structure from triacylglycerols and phospholipids. Most sterols do not contain any fatty acids but rather multiring structures. They are complex molecules that contain interlinking rings of carbon atoms, with side chains of carbon, hydrogen, and oxygen attached. Cholesterol is the best-known sterol because of its role in heart disease. It forms a large part of the plaque that narrows the arteries in atherosclerosis. In stark contrast, cholesterol does have specific beneficial functions to perform in the body. Like phospholipids, cholesterol is present in all body cells as it is an important substance in cell membrane structure. Approximately 25 percent of cholesterol in the body is localized in brain tissue. Cholesterol is used in the body to make a number of important things, including vitamin D, glucocorticoids, and the sex hormones, progesterone, testosterone, and estrogens. Notably, the sterols found in plants resemble cholesterol in structure. However, plant sterols inhibit cholesterol absorption in the human body, which can contribute to lower cholesterol levels.

Although cholesterol is preceded by its infamous reputation, it is clearly a vital substance in the body that poses a concern only when there is excess accumulation of it in the blood. Like lecithin, the body can synthesize cholesterol.

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KEY TAKEAWAYS

• Three fatty acids combine with one glycerol to make a triacylglycerol, the body’s storage form of fat.

• The carbon chain in fatty acids can be saturated (filled with hydrogen), monounsaturated (with one point of unsaturation and possessing one carbon-carbon double bond), or polyunsaturated (with more than one point of unsaturation and possessing two or more double-carbon bonds)

• The structure and length of a fatty acid determines whether it is solid or liquid at room temperature.

• Essential fatty acids cannot be synthesized by the body and must be included in the diet. Omega-3 and omega-6 fatty acids have opposing functions and must be consumed in proper balance to promote health.

• Fatty acids in food influence the composition of fatty acids in the body. • Phospholipids are diglycerides with a phosphate-nitrogen group in place

of the third fatty-acid chain. They are ideal emulsifiers as they keep oil and water mixed.

• Sterols contain a multiring structure. Cholesterol serves important body functions such as vitamin D and hormone synthesis and is important in cell membrane and brain structure.

DISCUSSION STARTERS

1. List the oils, snacks, spreads, or sauces in your home. Do they contain saturated or unsaturated fatty acids?

2. Name the characteristic that differentiates a triacylglycerol from a phospholipid. Describe the properties of phospholipids. Discuss their role in forming cell membranes. Explain their role as an emulsifier.

3. Think about your favorite restaurant and the food you like to order there. What type of fatty acids does a typical meal that you eat there have? Discuss the health benefits and possible drawbacks. What foods would you add to enhance your meal? What foods should you consider avoiding?

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5.3 Digestion and Absorption of Lipids

LEARNING OBJECTIVES

1. Summarize the steps in lipid digestion and absorption. 2. Explain how lipids are used for energy and stored in the body.

Lipids are large molecules and generally are not water-soluble. Like carbohydrates and protein, lipids are broken into small components for absorption. Since most of our digestive enzymes are water-based, how does the body break down fat and make it available for the various functions it must perform in the human body?

From the Mouth to the Stomach

The first step in the digestion of triacylglycerols and phospholipids begins in the mouth as lipids encounter saliva. Next, the physical action of chewing coupled with the action of emulsifiers enables the digestive enzymes to do their tasks. The enzyme lingual lipase23, along with a small amount of phospholipid as an emulsifier, initiates the process of digestion. These actions cause the fats to become more accessible to the digestive enzymes. As a result, the fats become tiny droplets and separate from the watery components.

23. An enzyme responsible for the breakdown of triacylglycerols and phospholipids.

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In the stomach, gastric lipase starts to break down triacylglycerols into diglycerides24 and fatty acids. Within two to four hours after eating a meal, roughly 30 percent of the triacylglycerols are converted to diglycerides and fatty acids. The stomach’s churning and contractions help to disperse the fat molecules, while the diglycerides derived in this process act as further emulsifiers. However, even amid all of this activity, very little fat digestion occurs in the stomach.

Going to the Bloodstream

As stomach contents enter the small intestine, the digestive system sets out to manage a small hurdle, namely, to combine the separated fats with its own watery fluids. The solution to this hurdle is bile25. Bile contains bile salts, lecithin, and substances derived from cholesterol so it acts as an emulsifier. It attracts and holds on to fat while it is simultaneously attracted to and held on to by water. Emulsification increases the surface area of lipids over a thousand-fold, making them more accessible to the digestive enzymes.

Once the stomach contents have been emulsified, fat-breaking enzymes work on the triacylglycerols and diglycerides to sever fatty acids from their glycerol

24. A product of lipid digestion, consisting of a glycerol molecule that has two fatty acids attached.

25. A substance secreted by the liver that aids in the absorption and digestion of fats.

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foundations. As pancreatic lipase enters the small intestine, it breaks down the fats into free fatty acids and monoglycerides26. Yet again, another hurdle presents itself. How will the fats pass through the watery layer of mucous that coats the absorptive lining of the digestive tract? As before, the answer is bile. Bile salts envelop the fatty acids and monoglycerides to form micelles. Micelles have a fatty acid core with a water-soluble exterior. This allows efficient transportation to the intestinal microvillus. Here, the fat components are released and disseminated into the cells of the digestive tract lining.

Just as lipids require special handling in the digestive tract to move within a water- based environment, they require similar handling to travel in the bloodstream. Inside the intestinal cells, the monoglycerides and fatty acids reassemble themselves into triacylglycerols. Triacylglycerols, cholesterol, and phospholipids form lipoproteins27 when joined with a protein carrier. Lipoproteins have an inner core that is primarily made up of triacylglycerols and cholesterol esters (a cholesterol ester is a cholesterol linked to a fatty acid). The outer envelope is made of phospholipids interspersed with proteins and cholesterol. Together they form a chylomicron28, which is a large lipoprotein that now enters the lymphatic system and will soon be released into the bloodstream via the jugular vein in the neck. Chylomicrons transport food fats perfectly through the body’s water-based environment to specific destinations such as the liver and other body tissues.

Cholesterols are poorly absorbed when compared to phospholipids and triacylglycerols. Cholesterol absorption is aided by an increase in dietary fat components and is hindered by high fiber content. This is the reason that a high

26. A product of lipid digestion, consisting of a glycerol molecule with one fatty acid attached.

27. Proteins that contains a lipid which serves to transport fat through blood and lymph.

28. Chylomicron clusters form when lipids are combined with carrier proteins in the cells of the intestinal lining. Chylomicron is a vehicle of transport for fats throughout the watery environment of the body to the liver and other tissues.

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intake of fiber is recommended to decrease blood cholesterol. Foods high in fiber such as fresh fruits, vegetables, and oats can bind bile salts and cholesterol, preventing their absorption and carrying them out of the colon.

If fats are not absorbed properly as is seen in some medical conditions, a person’s stool will contain high amounts of fat. If fat malabsorption persists the condition is known as steatorrhea. Steatorrhea can result from diseases that affect absorption, such as Crohn’s disease and cystic fibrosis.

The Truth about Storing and Using Body Fat

Before the prepackaged food industry, fitness centers, and weight-loss programs, our ancestors worked hard to even locate a meal. They made plans, not for losing those last ten pounds to fit into a bathing suit for vacation, but rather for finding food. Today, this is why we can go long periods without eating, whether we are sick with a vanished appetite, our physical activity level has increased, or there is simply no food available. Our bodies reserve fuel for a rainy day.

One way the body stores fat was previously touched upon in Chapter 4 “Carbohydrates”. The body transforms carbohydrates into glycogen that is in turn stored in the muscles for energy. When the muscles reach their capacity for glycogen storage, the excess is returned to the liver, where it is converted into triacylglycerols and then stored as fat.

In a similar manner, much of the triacylglycerols the body receives from food is transported to fat storehouses within the body if not used for producing energy. The chylomicrons are responsible for shuttling the triacylglycerols to various locations such as the muscles, breasts, external layers under the skin, and internal fat layers of the abdomen, thighs, and buttocks where they are stored by the body in adipose tissue for future use. How is this accomplished? Recall that chylomicrons are large lipoproteins that contain a triacylglycerol and fatty-acid core. Capillary walls contain an enzyme called lipoprotein-lipase that dismantles the triacylglycerols in the lipoproteins into fatty acids and glycerol, thus enabling these to enter into the adipose cells. Once inside the adipose cells, the fatty acids and glycerol are reassembled into triacylglycerols and stored for later use. Muscle cells may also take up the fatty acids and use them for muscular work and generating energy. When a person’s energy requirements exceed the amount of available fuel presented from a recent meal or extended physical activity has exhausted glycogen energy reserves, fat reserves are retrieved for energy utilization.

As the body calls for additional energy, the adipose tissue responds by dismantling its triacylglycerols and dispensing glycerol and fatty acids directly into the blood.

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Upon receipt of these substances the energy-hungry cells break them down further into tiny fragments. These fragments go through a series of chemical reactions that yield energy, carbon dioxide, and water.

KEY TAKEAWAYS

• In the stomach fat is separated from other food substances. In the small intestines bile emulsifies fats while enzymes digest them. The intestinal cells absorb the fats.

• Long-chain fatty acids form a large lipoprotein structure called a chylomicron that transports fats through the lymph system.

• Chylomicrons are formed in the intestinal cells and carry lipids from the digestive tract into circulation.

• Short- and medium-fatty chains can be absorbed directly into the bloodstream from the intestinal microvillus because they are water- soluble.

• Cholesterol absorption is hindered by foods high in fiber. • When energy supplies are low the body utilizes its stored fat reserves for

energy.

DISCUSSION STARTERS

1. Explain the role of emulsifiers in fat digestion. 2. Name the part of the digestive system where most fat digestion and

absorption occurs. 3. Describe the role of bile salts in the digestion of triacylglycerols and

phospholipids. 4. Define chylomicron. 5. Explain how fiber-rich foods affect cholesterol absorption. 6. Discuss the body’s processes for using energy.

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5.4 Understanding Blood Cholesterol

LEARNING OBJECTIVES

1. Compare and contrast the roles of LDLs and HDLs in your body. 2. Explain the purpose of a blood lipid profile and identify healthy ranges.

You may have heard of the abbreviations LDL and HDL with respect to heart health. These abbreviations refer to low-density lipoprotein (LDL) and high-density lipoprotein (HDL), respectively. Lipoproteins are characterized by size, density, and composition. As the size of the lipoprotein increases, the density decreases. This means that HDL is smaller than LDL. Why are they referred to as “good” and “bad” cholesterol? What should you know about these lipoproteins?

Major Lipoproteins

Recall that chylomicrons are transporters of fats throughout the watery environment within the body. After about ten hours of circulating throughout the body, chylomicrons gradually release their triacylglycerols until all that is left of their composition is cholesterol-rich remnants. These remnants are used as raw materials by the liver to formulate specific lipoproteins. Following is a list of the various lipoproteins and their functions:

• VLDLs29. Very low-density lipoproteins are made in the liver from remnants of chylomicrons and transport triacylglycerols from the liver to various tissues in the body. As the VLDLs travel through the circulatory system, the lipoprotein lipase strips the VLDL of triacylglycerols. As triacylglycerol removal persists, the VLDLs become intermediate-density lipoproteins.

• IDLs30. Intermediate-density lipoproteins transport a variety of fats and cholesterol in the bloodstream and are a little under half triacylglycerol in composition. While travelling in the bloodstream, cholesterol is gained from other lipoproteins while circulating enzymes strip its phospholipid component. When IDLs return to the liver, they are transformed into low-density lipoprotein.

• LDLs31. As low-density lipoproteins are commonly known as the “bad cholesterol” it is imperative that we understand their function in the body so as to make healthy dietary and lifestyle choices. LDLs carry cholesterol and other lipids from the liver to tissue throughout the

29. Very low-density lipoproteins formed in the liver from the remains of the chylomicron.

30. Intermediate-density lipoproteins transport a variety of fats and cholesterol in the bloodstream and are a little under half triacylglycerol in composition.

31. Low-density lipoproteins are also known as “bad cholesterol.” It contains higher concentrations of triacylglycerols and lower concentrations of protein and is responsible for delivering cholesterol to the body’s tissues.

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body. LDLs are comprised of very small amounts of triacylglycerols, and house over 50 percent cholesterol and cholesterol esters. How does the body receive the lipids contained therein? As the LDLs deliver cholesterol and other lipids to the cells, each cell’s surface has receptor systems specifically designed to bind with LDLs. Circulating LDLs in the bloodstream bind to these LDL receptors and are consumed. Once inside the cell, the LDL is taken apart and its cholesterol is released. In liver cells these receptor systems aid in controlling blood cholesterol levels as they bind the LDLs. A deficiency of these LDL binding mechanisms will leave a high quantity of cholesterol traveling in the bloodstream, which can lead to heart disease or atherosclerosis. Diets rich in saturated fats will prohibit the LDL receptors. Thus, LDL receptors are critical for regulating cholesterol levels.

• HDLs32. High-density lipoproteins are responsible for carrying cholesterol out of the bloodstream and into the liver, where it is either reused or removed from the body with bile. HDLs have a very large protein composition coupled with low cholesterol content (20 to 30 percent) compared to the other lipoproteins. Hence, these high-density lipoproteins are commonly called “good cholesterol.”

Contrasting LDL and HDL

Heart attack and atherosclerosis are conditions often caused by cholesterol that has accumulated and thickened in the walls of arteries. HDLs and LDLs are directly connected to these life-threatening ailments. By comparing and contrasting the roles each of these lipoproteins serves in the health of heart and blood vessels, you will be able to construct and evaluate a plan of action for your personal health. Consider the following lipoprotein facts:

• LDL/HDL composition. LDL is approximately 25 percent protein and 75 percent cholesterol and other fats. LDL is bigger (yet lighter) and richer in cholesterol than HDL. HDL is 50 percent protein and 50 percent cholesterol and other fats. HDL is smaller, more dense, and richer in protein.

• LDL/HDL function. LDLs carry cholesterol into cells for normal usage, but LDLs can also deposit cholesterol into the walls of blood vessels, which can lead to harmful disease. HDLs scavenge excess cholesterol from the cells, tissues, and blood vessels and deliver these back to the liver, where these are either reused or excreted.

• LDL/HDL and inflammation. LDLs carry lipids that are proinflammatory and may contribute to heart disease. HDLs transport lipids that are anti-inflammatory and may reduce the occurrence of heart disease.

32. High-density lipoproteins are also known as “good cholesterol.” It contains the maximum percentage of protein and a lower percentage of cholesterol and collects and transports excess cholesterol, returning it to the liver for reuse or excretion.

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• LDL/HDL warnings. High LDL values warn of increased health risks for heart disease, while high HDL values indicate a reduced risk for heart disease.

• Oxidized LDL. LDLs become more dangerous when oxidized. Oxidation33 is defined as the loss of electrons between two substances via a chemical reaction. If an LDL oxidation occurs, the oxidized LDL is left unstable. Oxidized LDL can speed up the process of plaque formation in the arteries. It is believed to hasten the deposition of cholesterol into the arterial walls and to induce a chronic inflammatory effect throughout the body’s vast network of vessels. This activity promotes atherosclerosis and significantly increases risks for heart attack or stroke.

Blood Cholesterol Recommendations

For healthy total blood cholesterol, the desired range you would want to maintain is under 200 mg/dL. More specifically, when looking at individual lipid profiles, a low amount of LDL and a high amount of HDL prevents excess buildup of cholesterol in the arteries and wards off potential health hazards. An LDL level of less than 100 milligrams per deciliter is ideal while an LDL level above 160 milligrams per deciliter would be considered high. In contrast, a low value of HDL is a telltale sign that a person is living with major risks for disease. Values of less than 40 milligrams per deciliter for men and 50 milligrams per deciliter for women mark a risk factor for developing heart disease. In short, elevated LDL blood lipid profiles indicate an increased risk of heart attack, while elevated HDL blood lipid profiles indicate a reduced risk.

The University of Maryland Medical Center reports that omega-3 fatty acids promote lower total cholesterol and lower triacylglycerols in people with high cholesterol.University of Maryland Medical Center. “Omega-3 fatty acids.” http://www.umm.edu/altmed/articles/omega-3-000316.htm It is suggested that people consume omega-3 fatty acids such as alpha-linolenic acid in their diets regularly. Polyunsaturated fatty acids are especially beneficial to consume because they both lower LDL and elevate HDL, thus contributing to healthy blood cholesterol levels. The study also reveals that saturated and trans fatty acids serve as catalysts for the increase of LDL cholesterol. Additionally, trans fatty acids raise HDL levels, which can impact negatively on total blood cholesterol.33. The interaction between

oxygen molecules and all the different substances they may contact. Can be more precisely defined as the loss of at least one electron when two or more substances interact and these substances may or may not include oxygen.

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Tools for Change

Being conscious of the need to reduce cholesterol means limiting the consumption of saturated fats and trans fats. Remember that saturated fats found in some meat, whole-fat dairy products, and tropical oils elevate your total cholesterol. Trans fats, such as the ones often found in margarines, processed cookies, pastries, crackers, fried foods, and snack foods also elevate your cholesterol levels. Read and select from the following suggestions as you plan ahead:

Soluble fiber reduces cholesterol absorption in the bloodstream. Try eating more oatmeal, oat bran, kidney beans, apples, pears, citrus fruits, barley, and prunes.

1. Fatty fish are heart-healthy due to high levels of omega-3 fatty acids that reduce inflammation and lower cholesterol levels. Consume mackerel, lake trout, herring, sardines, tuna, salmon, and halibut. Grilling or baking is best to avoid unhealthy trans fats that could be added from frying oil.

2. Walnuts, almonds, peanuts, hazelnuts, pecans, some pine nuts, and pistachios all contain high levels of unsaturated fatty acids that aid in lowering LDL. Make sure the nuts are raw and unsalted. Avoid sugary or salty nuts. One ounce each day is a good amount.

3. Olive oil contains a strong mix of antioxidants and monounsaturated fat, and may lower LDL while leaving HDL intact. Two tablespoons per day in place of less healthy saturated fats may contribute to these heart-healthy effects without adding extra calories. Extra virgin olive oil promises a greater effect, as the oil is minimally processed and contains more heart-healthy antioxidants.

Testing Your Lipid Profile

The danger of consuming foods rich in cholesterol and saturated and trans fats cannot be overemphasized. Regular testing can provide the foreknowledge necessary to take action to help prevent any life-threatening events.

Current guidelines recommend testing for anyone over age twenty. If there is family history of high cholesterol, your healthcare provider may suggest a test

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sooner than this. Testing calls for a blood sample to be drawn after nine to twelve hours of fasting for an accurate reading. (By this time, most of the fats ingested from the previous meal have circulated through the body and the concentration of lipoproteins in the blood will have stabilized.)

According to the National Institutes of Health (NIH), the following total cholesterol values are used to target treatment:National Heart, Lung, and Blood Institute, National Institutes of Health. “High Blood Cholesterol: What You Need to Know.” NIH Publication No. 05-3290. (Revised June 2005). Section 2.01. http://www.nhlbi.nih.gov/health/public/heart/chol/wyntk.htm.

• Desirable. Under 200 milligrams per deciliter • Borderline high. 200–239 milligrams per deciliter • High risk. 240 milligrams per deciliter and up

According to the NIH, the following desired values are used to measure an overall lipid profile:

• LDL. Less than 160 milligrams per deciliter (if you have heart disease or diabetes, less than 100 milligrams per deciliter)

• HDL. Greater than 40–60 milligrams per deciliter • Triacylglycerols. 10–150 milligrams per deciliter • VLDL. 2–38 milligrams per deciliter

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KEY TAKEAWAYS

• Some of the major lipoproteins are VLDL, IDL, LDL, and HDL. • VLDL delivers triacylglycerols and other lipids to the body’s tissues and

slowly becomes IDL. The liver uses IDL to create LDL, the main transporter of cholesterol.

• LDL, or “bad” cholesterol, has low protein composition and high cholesterol content. High levels of LDL have been shown to increase the risks for heart disease.

• HDL or “good’’ cholesterol has a larger proportion of protein and a small cholesterol composition. HDL scavenges excess cholesterol and returns it to the liver for reuse or disposal. A high level of HDL reduces the risk for heart disease.

• It is important to maintain a healthy lipid profile with values as recommended by the NIH in order to minimize the risk of heart disease. Consuming omega-3 fatty acids can help maintain a healthy blood lipid profile.

DISCUSSION STARTERS

1. Summarize the roles of LDL and HDL. Explain why LDL is termed “bad” cholesterol and why HDL is termed “good” cholesterol.

2. Explain oxidation and how it affects LDL and contributes to heart disease.

3. Describe the procedure and blood test for testing your lipid profile. 4. Recall the desired lipid values set out by the NIH. Identify the desired

total cholesterol, LDL, HDL, VLDL, and triacylglycerol values. 5. How has learning this information affected your motivation to eat a

more healthy diet?

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5.5 Balancing Your Diet with Lipids

LEARNING OBJECTIVES

1. Describe the current recommended intake levels for lipids. 2. Recognize sources of saturated and unsaturated fats, essential fatty

acids, and trans fats. 3. Discuss the functions of essential fatty acids, such as omega-3, and

where to find them in foods.

You may reason that if some fats are healthier than other fats, why not consume as much healthy fat as desired? Remember, everything in moderation. As we review the established guidelines for daily fat intake, the importance of balancing fat consumption with proper fat sources will be explained.

Recommended Fat Intake

The acceptable macronutrient distribution range (AMDR) from the Dietary Reference Intake Committee for adult fat consumption is as follows:Institute of Medicine. “Dietary Reference Intakes: Macronutrients.” Accessed October 5, 2012. http://www.iom.edu/~/media/Files/Activity%20Files/Nutrition/DRIs/DRI _Macronutrients.pdf

• Fat calories should be limited to 20–35 percent of total calories with most fats coming from polyunsaturated and monounsaturated fats, such as those found in fish, nuts, and vegetable oils.

• Consume fewer than 10 percent of calories from saturated fats. Some studies suggest that lowering the saturated fat content to less than 7 percent can further reduce the risk of heart disease.

• Keep the consumption of trans fats (any food label that reads hydrogenated or partially hydrogenated oil) to a minimum, less than 1 percent of calories.

• Think lean and low-fat when selecting meat, poultry, milk, and milk products.

The current AMDR for child and adolescent fat consumption (for children over four) are as follows:

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• For children between ages four and eighteen years, between 25 and 35 percent of caloric intake should be from fat.

• For all age groups, most fats should come from polyunsaturated and monounsaturated fats such as fish, nuts, and vegetable oils.

Identifying Sources of Fat

Population-based studies of American diets have shown that intake of saturated fat is more excessive than intake of trans fat and cholesterol. Saturated fat is a prominent source of fat for most people as it is so easily found in animal fats, tropical oils such as coconut and palm oil, and full-fat dairy products. Oftentimes the fat in the diet of an average young person comes from foods such as cheese, pizza, cookies, chips, desserts, and animal meats such as chicken, burgers, sausages, and hot dogs. To aim for healthier dietary choices, the American Heart Association (AHA) recommends choosing lean meats and vegetable alternatives, choosing dairy products with low fat content, and minimizing the intake of trans fats. The AHA guidelines also recommend consuming fish, especially oily fish, at least twice per week.American Heart Association. “Frequently Asked Questions About Fish.” http://www.heart.org/HEARTORG/General/Frequently-Asked-Questions-About- Fish _UCM_306451_Article.jsp. These more appropriate dietary choices will allow for enjoyment of a wide variety of foods while providing the body with the recommended levels of fat from healthier sources. Evaluate the following sources of fat in your overall dietary pattern:

• Monounsaturated fat. This type of fat is found in plant oils. Common sources are nuts (almonds, cashews, pecans, peanuts, and walnuts) and nut products, avocados, extra virgin olive oil, sesame oil, high oleic safflower oil, sunflower oil, and canola oil.

• Polyunsaturated fat. This type of fat is found mainly in plant-based foods, oils, and fish. Common sources are nuts (walnuts, hazel nuts, pecans, almonds, and peanuts), soybean oil, corn oil, safflower oil, flaxseed oil, canola oil, and fish (trout, herring, and salmon).

• Saturated fat. This fat is found in animal products, dairy products, palm and coconut oils, and cocoa butter. Limit these products to less than 10 percent of your overall dietary fat consumption.

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• Trans fatty acids. Stick margarines, fast foods, commercial baked goods, and some snack foods contain trans fats. Limit your consumption of these products to keep trans fats to less than 1 percent of your fat consumption.

• Omega-3 fatty acids (linolenic acid). Good sources of these are canola oil, flaxseed oil, soybean oil, olive oil, nuts, seeds, whole grains, legumes, and green leafy vegetables.

• DHA and EPA. Good sources of these are cod liver oil and fish such as tuna, herring, mackerel, salmon, and trout.

• Omega-6 fatty acids (linoleic acid). Eggs, poultry, most vegetable oils, wheat germ oil, whole grains, baked goods, and cereals contain these fatty acids. Omega-6 fatty acids are present abundantly in nuts and seeds such as flaxseeds, sunflower seeds, sesame seeds, and watermelon seeds.

Omega-3 and Omega-6 Fatty Acids

Recall that the body requires fatty acids and is adept at synthesizing the majority of these from fat, protein, and carbohydrate. However, when we say essential fatty acid we are referring to the two fatty acids that the body cannot create on its own, namely, linolenic acid34 and linoleic acid35.

• Omega-3 Fatty Acids. At the helm of the omega-3 fatty acid family is linolenic acid. From this fatty acid, the body can make eicosapentaenoic acid (EPA)36 and docosahexaenoic acid (DHA)37. Linolenic acid is found in nuts, seeds, whole grains, legumes, and vegetable oil such as soybean, canola, and flaxseed. EPA and DHA are found abundantly in fatty fish.

• Omega-6 Fatty Acids. At the helm of the omega-6 fatty acid family is linoleic acid. Like linolenic acid, the body uses linoleic acid to make other important substances such as arachidonic acid (ARA)38 that is used to make eicosanoids. Recall that eicosanoids perform critical roles in the body as they affect a broad spectrum of functions. The word eicosanoid originates from the Greek word eicosa, meaning twenty, because this hormone is derived from ARA that is twenty carbon atoms in length. Eicosanoids affect the synthesis of all other body hormones and control all body systems, such as the central nervous system and the immune system. Among the many functions eicosanoids serve in the body, their primary function is to regulate inflammation. Without these hormones the body would not be able to heal wounds, fight infections, or fight off illness each time a foreign germ presented itself. Eicosanoids work together with the body’s immune and inflammation

34. An omega-3 fatty acid that is essential for human health.

35. An omega-6 fatty acid that is essential for human health.

36. An omega-3 fatty acid made from linolenic acid, found in fish.

37. An omega-3 fatty acid that is especially important for brain growth and development in infants.

38. An omega-6 essential fatty acid that is a precursor to the synthesis of eicosanoids.

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processes to play a major role in several important body functions, such as circulation, respiration, and muscle movement.

Attain the Omega-3 and Omega-6 Balance

As our food choices evolve, the sources of omega-6 fatty acids in our diets are increasing at a much faster rate than sources of omega-3 fatty acids. Omega-3s are plentiful in diets of nonprocessed foods where grazing animals and foraging chickens roam free, eating grass, clover, alfalfa, and grass-dwelling insects. In contrast, today’s western diets are bombarded with sources of omega-6. For example, we have oils derived from seeds and nuts and from the meat of animals that are fed grain. Vegetable oils used in fast-food preparations, most snack-foods, cookies, crackers, and sweet treats are also loaded with omega-6 fatty acids. Also, our bodies synthesize eicosanoids from omega-6 fatty acids and these tend to increase inflammation, blood clotting, and cell proliferation, while the hormones synthesized from omega-3 fatty acids have just the opposite effect.

While omega-6 fatty acids are essential, they can be harmful when they are out of balance with omega-3 fatty acids. Omega-6 fats are required only in small quantities. Researchers believe that when omega-6 fats are out of balance with omega-3 fats in the diet they diminish the effects of omega-3 fats and their benefits. This imbalance may elevate the risks for allergies, arthritis, asthma, coronary heart disease, diabetes, and many types of cancer, autoimmunity, and neurodegenerative diseases, all of which are believed to originate from some form of inflammation in the body. The recommendations for the ratio of omega-3 to omega-6 fatty acids vary from 5:1 to 10:1.

What does this mean for you? If your diet is low in omega-3 fats to begin with, then most of your essential fatty acids are from omega-6s. Stop. Do not set up a proinflammatory environment. Attaining proper balance between omega-3 fatty acids and omega-6 fatty acids means learning to make healthy choices and replacing bad fats with good ones that promote health and well-being.

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KEY TAKEAWAYS

• The recommended fat intake for adults is 20–35 percent of your total caloric intake. Saturated fat must be less than 10 percent of your total caloric intake, and lowering this to 7 percent can further reduce the risks for heart disease. Trans fat should be less than 1 percent of total caloric intake.

• Nuts, seeds, whole grains, legumes, and vegetable oil such as soybean, canola, and flaxseed are excellent sources of monounsaturated and polyunsaturated fats.

• The polyunsaturated fatty acids linolenic and linoleic acids are used by the body to make substances that carry out many vital functions in the body.

• The omega-3 fatty-acid family includes linolenic acid, EPA, and DHA. The omega-6 fatty-acid family includes linoleic acid and ARA. DHA and ARA play crucial roles in brain and eye development. EPA and DHA found in fatty fish play important roles in inflammation reduction and disease prevention.

• Many people consume too many omega-6 fatty acids and not enough omega-3 fatty acids. Omega-3 fats and omega-6 fats are precursors to hormones that have opposing properties. A proper balance between both must be obtained to avoid health problems.

DISCUSSION STARTERS

1. State the recommended intake of total fat, as well as saturated versus unsaturated fat, in the diet.

2. List sources of monounsaturated and polyunsaturated fats. 3. Summarize the important functions of essential fatty acids in the human

body. 4. Explain why it is necessary to maintain a proper balance between

omega-3 fat and omega-6 fat intake. 5. Record a food diary for one week. What foods do you most often

consume? What type of fat dominates your diet? How can you alter your eating habits to promote better health? Outline steps you can take to replace saturated and trans fat in your diet.

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5.6 Lipids and the Food Industry

LEARNING OBJECTIVES

1. Discuss reasons oils are hydrogenated and describe this process. 2. Describe the health effects of trans fats.

What is the first thing that comes to mind when you read ingredients such as “partially hydrogenated oil” and “hydrogenated oil” on a food label? Do you think of heart disease, heart health, or atherosclerosis? Most people probably do not. As we uncover what hydrogenation is and why manufacturers use it, you will be better equipped to adhere to healthier dietary choices and promote your heart health.

Hydrogenation: The Good Gone Bad?

Food manufacturers are aware that fatty acids are susceptible to attack by oxygen molecules because their points of unsaturation render them vulnerable in this regard. When oxygen molecules attack these points of unsaturation the modified fatty acid becomes oxidized. The oxidation of fatty acids makes the oil rancid and gives the food prepared with it an unappetizing taste. Because oils can undergo oxidation when stored in open containers, they must be stored in airtight containers and possibly be refrigerated to minimize damage from oxidation. Hydrogenation poses a solution that food manufacturers prefer.

When lipids are subjected to hydrogenation, the molecular structure of the fat is altered. Hydrogenation is the process of adding hydrogen to unsaturated fatty-acid chains, so that the hydrogen atoms are connected to the points of saturation and results in a more saturated fatty acid. Liquid oils that once contained more unsaturated fatty acids become semisolid or solid (upon complete hydrogenation) and behave like saturated fats. Oils initially contain polyunsaturated fatty acids. When the process of hydrogenation is not complete, for example, not all carbon double bonds have been saturated the end result is a partially hydrogenated oil. The resulting oil is not fully solid. Total hydrogenation makes the oil very hard and virtually unusable. Some newer products are now using fully hydrogenated oil combined with nonhydrogenated vegetable oils to create a usable fat.

Manufacturers favor hydrogenation as a way to prevent oxidation of oils and ensure longer shelf life. Partially hydrogenated vegetable oils are used in the fast food and processed food industries because they impart the desired texture and crispness to

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baked and fried foods. Partially hydrogenated vegetable oils are more resistant to breakdown from extremely hot cooking temperatures. Because hydrogenated oils have a high smoking point39 they are very well suited for frying. In addition, processed vegetable oils are cheaper than fats obtained from animal sources, making them a popular choice for the food industry.

Trans fatty acids occur in small amounts in nature, mostly in dairy products. However, the trans fats that are used by the food industry are produced from the hydrogenation process. Trans fats are a result of the partial hydrogenation of unsaturated fatty acids, which cause them to have a trans configuration, rather than the naturally occurring cis configuration.

Health Implications of Trans Fats

No trans fats! Zero trans fats! We see these advertisements on a regular basis. So widespread is the concern over the issue that restaurants, food manufacturers, and even fast-food establishments proudly tout either the absence or the reduction of these fats within their products. Amid the growing awareness that trans fats may not be good for you, let’s get right to the heart of the matter. Why are trans fats so bad?

Processing naturally occurring fats to modify their texture from liquid to semisolid and solid forms results in the development of trans fats, which have been linked to an increased risk for heart disease. Trans fats are used in many processed foods such as cookies, cakes, chips, doughnuts, and snack foods to give them their crispy texture and increased shelf life. However, because trans fats can behave like saturated fats, the body processes them as if they were saturated fats. Consuming large amounts of trans fats has been associated with tissue inflammation throughout the body, insulin resistance in some people, weight gain, and digestive troubles. In addition, the hydrogenation process robs the person of the benefits of consuming the original oil because hydrogenation destroys omega-3 and omega-6 fatty acids. The AHA states that, like saturated fats, trans fats raise LDL “bad cholesterol,” but unlike saturated fats, trans fats lower HDL “good cholesterol.” The AHA advises limiting trans-fat consumption to less than 1 percent.

How can you benefit from this information? When selecting your foods, steer clear of anything that says “hydrogenated,” “fractionally hydrogenated,” or “partially hydrogenated,” and read food labels in the following categories carefully:

• cookies, crackers, cakes, muffins, pie crusts, pizza dough, and breads • stick margarines and vegetable shortening • premixed cake mixes, pancake mixes, and drink mixes

39. The temperature at which fat gives off a pungent blue gas.

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• fried foods and hard taco shells • snack foods (such as chips), candy, and frozen dinners

Choose brands that don’t use trans fats and that are low in saturated fats.

Dietary-Fat Substitutes

In response to the rising awareness and concern over the consumption of trans fat, various fat replacers have been developed. Fat substitutes aim to mimic the richness, taste, and smooth feel of fat without the same caloric content as fat. The carbohydrate-based replacers tend to bind water and thus dilute calories. Fat substitutes can also be made from proteins (for example, egg whites and milk whey). However, these are not very stable and are affected by changes in temperature, hence their usefulness is somewhat limited.

Tools for Change

One classic cinnamon roll can have 5 grams of trans fat, which is quite high for a single snack. Foods such as pastries, frozen bakery goods, cookies, chips, popcorn, and crackers contain trans fat and often have their nutrient contents listed for a very small serving size—much smaller than what people normally consume—which can easily lead you to eat many “servings.” Labeling laws allow foods containing trans fat to be labeled “trans-fat free” if there are fewer than 0.5 grams per serving. This makes it possible to eat too much trans fat when you think you’re not eating any at all because it is labeled trans-fat free.

Always review the label for trans fat per serving. Check the ingredient list, especially the first three to four ingredients, for telltale signs of hydrogenated fat such as partially or fractionated hydrogenated oil. The higher up the words “partially hydrogenated oil” are on the list of ingredients, the more trans fat the product contains.

Measure out one serving and eat one serving only. An even better choice would be to eat a fruit or vegetable. There are no trans fats and the serving size is more reasonable for similar calories. Fruits and vegetables are packed with water, fiber, and many vitamins, minerals, phytonutrients, and antioxidants. At restaurants be aware that phrases such as “cooked in vegetable oil” might mean hydrogenated vegetable oil, and therefore trans fat.

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KEY TAKEAWAYS

• Hydrogenation is the process of adding hydrogen to the points of unsaturation in unsaturated fatty acid chains. The resulting oil is very hard and unusable. Partial hydrogenation is the process of adding hydrogen to some of the points of unsaturation in unsaturated fatty acid chains. This produces oils that are more spreadable and usable in food products.

• Food manufacturers favor the use of hydrogenated oils because they do not succumb to oxidative damage, they increase the shelf life of food products, and they have a high smoking point.

• Fat replacers mimic fat but do not have the same chemical configuration as fat. Therefore the body does not process these the same way it would a naturally occurring fat. Fat substitutes such as Olestra have produced symptoms of fat malabsorption in some people.

DISCUSSION STARTERS

1. Describe how trans fatty acids are created. Explain the drawbacks of consuming this type of fat and its impact on human health.

2. Make a list of the foods in your kitchen. Read each food label. List all of the food items that contain trans fat. Recall the recommendation that trans fat be less that 1 percent of your fat intake. About what percentage of your diet is currently trans fat? Do you see a need to adjust your trans fat intake?

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5.7 Lipids and Disease

LEARNING OBJECTIVE

1. Describe how saturated fat and cholesterol intake can impact health.

Because heart disease, cancer, and stroke are the three leading causes of death in the United States, it is critical to address dietary and lifestyle choices that will ultimately decrease risk factors for these diseases. According to the US Department of Health and Human Services (HHS), the following risk factors are controllable: high blood pressure, high cholesterol, cigarette smoking, diabetes, poor diet, physical inactivity, being overweight, and obesity.

In light of that, we present the following informational tips to help you define, evaluate, and implement healthy dietary choices to last a lifetime. The amount and the type of fat that composes a person’s dietary profile will have a profound effect upon the way fat and cholesterol is metabolized in the body.

Watch Out for Saturated Fat and Cholesterol

In proper amounts, cholesterol is a compound used by the body to sustain many important body functions. In excess, cholesterol is harmful if it accumulates in the structures of the body’s vast network of blood vessels. High blood LDL and low blood HDL are major indicators of blood cholesterol risk. The largest influence on blood cholesterol levels rests in the mix of saturated fat and trans fat in the diet. According to the Harvard School of Public Health, for every extra 2 percent of calories from trans fat consumed per day—about the amount found in a midsize order of French fries at a fast-food establishment—the risk of coronary heart disease increases by 23 percent.Harvard School of Public Health. “Fats and Cholesterol: Out with the Bad, In with the Good.” Section 2.02. http://www.hsph.harvard.edu/nutritionsource/what-should-you -eat/fats-full- story/. A buildup of cholesterol in the blood can lead to brittle blood vessels and a blockage of blood flow to the affected area.

How saturated is the fat in your diet? Is it really necessary to eat saturated fat when the body makes all the saturated fat that it needs? Saturated fats should fall into the “bad” category—the body does not demand this kind of fat and it is proven to be a forerunner of cardiovascular disease. In the United States and other developed countries, populations acquire their saturated fat content mostly from meat,

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seafood, poultry (with skin consumed), and whole-milk dairy products (cheese, milk, and ice cream). Some plant foods are also high in saturated fats, including coconut oil, palm oil, and palm kernel oil.

Food Cholesterol’s Effect on Blood Cholesterol

Dietary cholesterol does have a small impact on overall blood cholesterol levels, but not as much as some people may think. The average American female consumes 237 milligrams of dietary cholesterol per day and for males the figure is slightly higher—about 358 milligrams. The USDA dietary guidelines suggest a daily limit intake of cholesterol not to exceed 300 milligrams for healthy people and 200 milligrams for those who may be suffering from high cholesterol. Most people display little response to normal dietary cholesterol intake as the body responds by halting its own synthesis of the substance in favor of using the cholesterol obtained through food. Genetic factors may also influence the way a person’s body modifies cholesterol.

A Prelude to Disease

If left unchecked, improper dietary fat consumption can lead down a path to severe health problems. An increased level of lipids, triacylglycerols, and cholesterol in the blood is called hyperlipidemia. Hyperlipidemia40 is inclusive of several conditions but more commonly refers to high cholesterol and triacylglycerol levels. When blood lipid levels are high, any number of adverse health problems may ensue. Consider the following:

• Cardiovascular disease. According to the AHA, cardiovascular disease encompasses a variety of problems, many of which are related to the process of atherosclerosis. Over time the arteries thicken and harden with plaque buildup, causing restricted or at times low or no blood flow to selected areas of the body.

• Heart attack. A heart attack happens when blood flow to a section of the heart is cut off due to a blood clot. Many have survived heart attacks and go on to return to their lives and enjoy many more years of life on this earth. However, dietary and lifestyle changes must be implemented to prevent further attacks.

• Ischemic stroke. The most common type of stroke in the United States, ischemic stroke, occurs when a blood vessel in the brain or leading to the brain becomes blocked, again usually from a blood clot. If part of the brain suffers lack of blood flow and/or oxygen for three minutes or longer, brain cells will start to die.

• Congestive heart failure. Sometimes referred to as heart failure, this condition indicates that the heart is not pumping blood as well as it

40. A term that refers to any number of conditions characterized by excessive amounts of fat in the blood.

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should. The heart is still working but it is not meeting the body’s demand for blood and oxygen. If left unchecked, it can progress to further levels of malfunction.

• Arrhythmia. This is an abnormal rhythm of the heart. The heart may beat above one hundred beats per minute (known as tachycardia) or below sixty beats per minute (known as bradychardia), or the beats are not regular. The heart may not be able to pump enough volume of blood to meet the body’s needs.

• Heart valve problems. Stenosis is a condition wherein the heart valves become compromised in their ability to open wide enough to allow proper blood flow. When the heart valves do not close tightly and blood begins to leak between chambers, this is called regurgitation. When valves bulge or prolapse back into the upper chamber, this condition is called mitral valve prolapse.

• Obesity. Obesity is defined as the excessive accumulation of body fat. According to US Surgeon General Richard Carmona, obesity is the fastest growing cause of death in America. The HHS reports that the number of adolescents who are overweight has tripled since 1980 and the prevalence of the disease among younger children has doubled.US Department of Health and Human Services. “Childhood Obesity.” Accessed October 5, 2012. http://aspe.hhs.gov/health/reports/ child_obesity/. Obesity has been linked to increased risks of developing diabetes and heart disease. To help combat this problem important dietary changes are necessary. Reducing the type and amount of carbohydrates and sugar consumed daily is critical. Limiting the intake of saturated fats and trans fats, increasing physical activity, and eating fewer calories are all equally important in this fight against obesity.

What You Can Do

Remember that saturated fats are found in large amounts in foods of animal origin. They should be limited within the diet. Polyunsaturated fats are generally obtained from nonanimal sources. While they are beneficial for lowering bad cholesterol they also lower good cholesterol. They are better for you than saturated fats but are not to be consumed in excess. Monounsaturated fats are of plant origin and are found in most nuts, seeds, seed oils, olive oil, canola oil, and legumes. Monounsaturated fats are excellent because they not only lower bad cholesterol, but also they elevate the good cholesterol. Replace current dietary fats with an increased intake of monounsaturated fats.

Choose whole-grain and high-fiber foods. Reduced risk for cardiovascular disease has been associated with diets that are high in whole grains and fiber. Fiber also slows down cholesterol absorption. The AHA recommends that at least half of daily

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grain intake should originate from whole grains. The Adequate Intake value for fiber is 14 grams per 1,000 kilocalories. These amounts are based upon the amount of fiber that has been shown to reduce cardiovascular risk.

Do not be sedentary. Get more exercise on a regular basis. Increasing your energy expenditure by just twenty minutes of physical activity at least three times per week will improve your overall health. Physical exercise can help you manage or prevent high blood pressure and blood cholesterol levels. Regular activity raises HDL while at the same time decreases triacylglycerols and plaque buildup in the arteries. Calories are burned consistently, making it easier to lose and manage weight. Circulation will improve, the body will be better oxygenated, and the heart and blood vessels will function more efficiently.

KEY TAKEAWAYS

• Food cholesterol does not affect blood cholesterol as much as some people think. The main causes of unfavorable blood cholesterol values come from an overconsumption of saturated fats and trans fats.

• An increased intake of lipids is associated with heart disease, obesity, cardiovascular disease, and other problems.

• Making dietary choices that limit the intake of saturated and trans fats to the recommended levels, replacing saturated and trans fats with monounsaturated and polyunsaturated fats, increasing physical activity, and cessation of smoking can reduce the risk of developing heart disease and other ailments.

DISCUSSION STARTERS

1. Explain why saturated fats and trans fats contribute to unfavorable blood cholesterol levels.

2. Discuss some of the diseases that can result from an unhealthy lipid profile for an extended period of time.

3. List the types of fat that will help you achieve a healthy blood lipid profile. List the sources of these fats.

4. Evaluate your personal dietary and lifestyle habits. Identify key areas where you need to improve. Construct an overall plan of diet and lifestyle choices that you implement to help you reach healthy goals.

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5.8 A Personal Choice about Lipids

LEARNING OBJECTIVE

1. Discuss ways to decrease saturated fat and cholesterol intake and increase unsaturated fat intake in your diet.

A Guide to Making Sense of Dietary Fat

On your next trip to the grocery store prepare yourself to read all food labels carefully and to seriously consider everything that goes into your shopping cart. Create a shopping list and divide your list into columns for “Best,” “Better,” “Good,” “Least Desirable,” and “Infrequent Foods.” As you refine your sense of dietary fat, here are key points to bear in mind:

• Shopping for groceries. Don’t be bombarded with gratuitous grams of saturated fats and empty grams of trans fats. Read and decipher food labels carefully so that you know exactly what types of fat a food item contains and how much fat it will contribute to your overall fat intake. For snacks and daily eating, gravitate toward foods that are lowest in or absent of harmful trans fats. Restrict other foods to occasional usage based upon their fat content. For example, if selecting prepared foods, choose the ones without high-fat sauces in favor of adding your own flavorings. If selecting precooked meats, avoid those that are fried, coated, or prepared in high-fat sauces. A popular and healthy precooked meat food choice is the rotisserie chicken that most supermarkets carry. When selecting meats be aware of the need to compare different cuts—notice their fat content, color, and marbling. Higher-fat meats tend to have whiter fat marbled throughout. Choose lean cuts and white meat as these are lower in saturated fat. Always choose plenty of fresh fruits, vegetables, nuts, and seeds, as their phytosterols are a good competitor for cholesterol. Keep a collection of nuts in your freezer that can be added to your salads, stir-fry, one-dish foods, soups, desserts, and yogurts.

• Appearance. Saturated and trans fats are not good for you and must be placed in your “Least Desirable” column because they increase cholesterol levels and put you at risk for heart disease. Monounsaturated and polyunsaturated fats are better choices to replace these undesirable fats. The key in identifying the “Best” or “Better” fats from the “Least Desirable” fats while you shop is based

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upon appearance. When choosing fats remember that saturated fats and trans fats are solid at room temperature; think of butter. Monounsaturated and polyunsaturated fats are liquid at room temperature; think of vegetable oil.

• Stay away from trans fats. There is no amount of trans fats that are good for human health. Try to eliminate as much of these fats as possible from your food selections. Avoid commercially baked goods and fast foods. Make these your “Infrequent Foods.”

• Choose unsaturated fats. Fatty fish, walnuts, flaxseeds, flaxseed oil, and canola oil all have good health benefits and should be on the “Best,” “Better,” and “Good” fat lists. They each provide essential omega-3 fatty acids necessary for overall body health. To derive the most benefit from including these foods, do not add them to an existing diet full of fat. Use these to replace the “Least Desirable” fats that are being removed from the diet. Be careful of exposing fats and oils to heat, light, and oxygen as they can be easily damaged. Exercise caution when heating oils. Polyunsaturated fats are the most fragile and lose beneficial properties when exposed to heat. For proper storage and freshness, place your oils in opaque containers and keep refrigerated. Do not use any oil if it has a bitter smell or taste.

• Limit saturated fat intake. Reduce red meat consumption, processed meats, and whole-fat dairy products. A good replacement for red meat could be beans (black beans are very high in protein), nuts, poultry, and fish whenever possible. To reduce full-fat dairy items try their low- fat or nonfat counterparts such as mozzarella cheese.

• Low fat does not equal healthy. Remember, a fat-free label does not provide you with a license to consume all the calories you desire. There will be consequences to your weight and your overall health. Common replacements for fat in many fat-free foods are refined carbohydrates, sugar, and calories. Too much of these ingredients can also cause health problems. Choose and consume wisely.

Tools for Change

As a delicious alternative to red meat, try preparing and eating at least one meal each week using beans. For interesting ideas and tips, visit http://www.swbeans.com.

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Helpful Suggestions

Keep the following in mind as you strive toward a healthier diet:

• A “better-fat” diet will successfully support weight loss. With the obesity rates in the United States more than tripling since 1980, it is interesting to note that this figure has presented itself and increased at a time when “low fat” advertising runs rampant throughout the food supply. While cutting “Least Desirable” fat calories are vital to weight loss, remember that “Better” fats are filling and just a handful of nuts can curb an appetite to prevent overeating.

• Consume omega-3 fats each day. For optimal health and disease prevention include a moderate serving of fish, walnuts, ground flaxseeds, flaxseed oil, or soybean oil in your diet every day.

• Limit cholesterol-rich foods. The following foods should be limited from the diet in order to reduce blood cholesterol: chicken livers, beef, pork, fast foods, pastries, butter, cheese, and ice cream.

• How much saturated fat is too much? Your goal is to keep your intake of saturated fat to no more than 10 percent of your total dietary calories on a daily basis. Thus, it is important to learn to reduce the intake of foods high in saturated fat. High-fat foods can be consumed but they must fall within the overall goal for a person’s fat allowance for the day.

• Home cooking. Limit the use of saturated fats in home preparation of meals. Instead of butter try spreads made from unsaturated oils such as canola or olive oils and the use of cooking sprays. Couple this with the use of herbs and spices to add flavor. Avoid using high-fat meat gravies, cheese, and cream sauces. Limit adding extras to foods such as butter on a baked potato. Use nonfat sour cream instead. Grill, bake, stir-fry, roast, or bake your foods. Never fry in solid fats such as butter or shortening. Marinate foods to be grilled in fruit juices and herbs. Instead of relying upon commercial salad dressings, learn to make your own top-quality dressing from cold-pressed olive oil, flaxseed oil, or sesame oil.

• Make sure the fat is flavorful. Adding flavor to food is what makes the eating experience enjoyable. Why not choose unsaturated fats and oils that have strong flavors? In this way you will add good flavor to your meals but use less fat in the process. Some examples are sesame oil, peanut oil, and peanut butter. Replace less flavorful cheeses with small amounts of strongly flavored cheeses such as romano, parmesan, and asiago.

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Now that you have gained a wealth of information and food for thought to enable you to make changes to your dietary pattern we hope that your desire to pursue a healthier lifestyle has been solidified. While we realize that making grand strides in this direction may be awkward at first, even the smallest of accomplishments can produce noticeable results that will spur you on and perhaps spark the interest of friends and family to join you in this health crusade.

Becoming aware of the need to limit your total fat intake will facilitate your ability to make better choices. In turn, making better dietary choices requires gaining knowledge. As you understand that your food choices not only impact your personal physical health but also the delicate balance of our ecosystem, we are confident that you will successfully adapt to the dynamics of the ever-changing global food supply. Remember, the food choices you make today will benefit you tomorrow and into the years to come.

KEY TAKEAWAYS

• To reduce saturated fat in your diet, eat less red and processed meat and more fish and chicken. Choose lean cuts of meat and white meat portions. Bake, broil, or grill instead of fry. Avoid deep-fried foods, cheeses, and creamy cheese sauces. Remove the skin from chicken and remove as much fat from meat as possible. Choose low-fat milk and lower fat cheeses, such as mozzarella, where possible. Use liquid vegetable oils such as olive oil or canola oil instead of shortening or butter.

• In order to reduce blood cholesterol, restrict the consumption of eggs, chicken livers, beef, pork, shrimp, crustaceans, fast foods, pastries, butter, cheese, and ice cream.

• To gain the most benefit from reducing your saturated fat intake, substitute unsaturated fats in the place of saturated fats and trans fats. Do not add unsaturated fats to an already fatty diet. Fill your plate with plant-based foods and use the foods containing fat more as an accompaniment.

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DISCUSSION STARTERS

1. Think of at least three ways to reduce, substitute, and eliminate from your diet foods that are higher in less-desirable fat. List some foods that you will add to your diet that will add bulk and help satisfy your need to eat, but do not contain the calories in fat-rich foods.

2. Make a list of your favorite snack foods. Then make a listing of the fat content in each. Decide what snack foods you should reduce or eliminate from your diet. Think of at least two replacement foods for these snacks. Tell what benefit these replacement foods will have on your overall health.

3. Make a list of all the common foods you eat that contain trans fats. Looking ahead, develop a plan of action for you to slowly eliminate as much of these fats from your diet as possible. What substitutes will you add in their place? How will you cut out trans fats from your diet?

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5.9 End-of-Chapter Exercises

IT ’S YOUR TURN

1. Provide examples of three foods that are rich in unsaturated fats. 2. Assume you are reluctant to eat fish. Name three other sources of

omega-3 fats. 3. Your friend tends to feel cold a lot of the time, is often tired, and has

developed sores on her skin. Based on the content in this chapter, identify a nutritional reason for this condition.

4. Explain the role of lipids in your overall health.

APPLY IT

1. Make a chart of the three main types of lipids, their specific functions in the body, and where they are found.

2. Diagram the steps in lipid digestion and absorption. 3. Create a blood lipid profile with healthy ranges.

EXPAND YOUR KNOWLEDGE

1. You’re making a concerted effort to begin eating more foods that will promote good health. Turn your attention to omega-3 fatty acids. What will you incorporate into your diet?

2. Obesity rates in the United States have more than tripled since 1980. At the same time, “low fat” advertising is all over the news. How would you explain this?

3. Review and analyze the Cholesterol Risk Chart on the following site: http://heartriskonline.com/CholesterolChart.htm. Check with three members of your family or close friends. Where do they “fit” into this chart?

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Chapter 6

Proteins

Big Idea

Protein is best used for vital body functions—eat just enough for your lifestyle needs.

Some dieters use protein bars as a prime part of their diet, with the hopes of slimming their waistlines. Exercise cafes serve protein shakes to many of their patrons, who drink them for building muscle and enhancing exercise recovery. Some people have stopped eating meat and feel the need to use protein supplements to ensure they are getting their required protein intake each day. After all, protein is a vital constituent of all organs in the body and is required to synthesize hormones, enzymes, and a variety of molecules. It is no wonder that so many people are preoccupied with optimizing their dietary protein intake. Dieters, athletes, physically active people, and vegetarians may worry that they lack protein in their diet, and that they need to consume more from protein bars, shakes, or supplements to perform better and optimize health. This chapter will help address these concerns. First, let us take a look at vegetarian diets.

There are different types of vegetarians, but a common theme is that vegetarians do not eat meat. Four common forms of vegetarianism are:

1. Lacto-ovo vegetarian. This is the most common form. This type of vegetarian eats eggs and dairy.

2. Lacto-vegetarian. This type of vegetarian eats dairy products but not eggs.

3. Ovo-vegetarian. This type of vegetarian eats eggs but not dairy products.

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4. Vegan. This type of vegetarian does not eat dairy, eggs, or any type of animal product or by-product.

People choose a vegetarian diet for various reasons, including religious doctrines, health concerns, ecological and animal welfare concerns, or simply because they dislike the taste of meat. Vegetarianism has been practiced for centuries. In the fourth century BC, great thinkers such as Pythagoras and Plato promoted vegetarian diets in their natural philosophies. Ancient Olympians were placed on vegetarian diets one month prior to the Olympic Games.

Gladiators were tough men who fought violently against each other during games sponsored by the Roman Empire’s upper class political rulers. In 1993, archaeologists uncovered a gladiator burial ground not far from the Temple of Artemis. To their surprise, forensic analysis of the gladiators’ bones revealed that they consumed a vegetarian diet. This information matches other historical accounts that gladiators ate a diet rich in barley and dried fruits. Hulled barley is a very nutritious whole grain; it is a complete protein source, containing more than 20 grams of protein and all nine essential amino acids in a one-cup serving.

Although the great philosophers, ancient Olympic athletes, and Roman gladiators saw vegetarianism as a means of maintaining optimal health, it took a while for the vegetarian dietary pattern to catch on in America. In 1987, John Robbins wrote Diet for a New America and popularized the vegan diet first introduced by Jay Dinshah in the United States in 1960. In the early 1990s, Dr. John McDougall wrote a series of books that promoted vegan dietary regimens to ward off chronic disease. Also during the 1990s, scientific evidence accumulated that supported that diets consisting of too much red meat were linked to chronic disease. This prompted many health organizations, such as the Academy of Nutrition and Dietetics (AND) and the American Heart Association (AHA), to issue statements endorsing the health benefits of vegetarian diets. These statements can be read at http://www.eatright.org/about/content.aspx?id=8357 and http://bit.ly/O2VQkC.

The US federal government was unable to ignore the health benefits of plant-based diets any longer, and consequently released the 2010 Dietary Guidelines in which Americans were challenged to eat a more plant-based diet. Moreover, the Dietary Guidelines advisory committee stated, “In prospective studies of adults, compared to nonvegetarian eating patterns, vegetarian-style eating patterns have been associated with improved health outcomes—lower levels of obesity, a reduced risk of cardiovascular disease, and lower total mortality.”

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You Decide

What are the best sources of protein and how much protein do I need to eat to have a healthy diet?

Whether you choose to consume protein from animal- or plant-derived products, an important factor to consider is the entire nutrient package of the food. What other fats, nutrients, additives, or preservatives come with the protein source? Red meat is a popular choice for protein, but it contains high amounts of saturated fat. Fish is another good protein choice, and it provides much less saturated fat than other meats, in addition to more healthy fats. Some plant-based sources of protein contain high amounts of protein per serving with just under one gram of less desirable fat in addition to good amounts of healthy fats. As you read through this chapter you will learn how to choose the best protein sources to support your health.

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6.1 Defining Protein

LEARNING OBJECTIVES

1. Categorize the different types of amino acids. 2. Describe how protein differs in structure from carbohydrates and lipids.

Protein makes up approximately 20 percent of the human body and is present in every single cell. The word protein is a Greek word, meaning “of utmost importance.” Proteins are called the workhorses of life as they provide the body with structure and perform a vast array of functions. You can stand, walk, run, skate, swim, and more because of your protein-rich muscles. Protein is necessary for proper immune system function, digestion, and hair and nail growth, and is involved in numerous other body functions. In fact, it is estimated that more than one hundred thousand different proteins exist within the human body. In this chapter you will learn about the components of protein, the important roles that protein serves within the body, how the body uses protein, the risks and consequences associated with too much or too little protein, and where to find healthy sources of it in your diet.

What Is Protein?

Proteins1, simply put, are macromolecules composed of amino acids. Amino acids2 are commonly called protein’s building blocks. Proteins are crucial for the nourishment, renewal, and continuance of life. Proteins contain the elements carbon, hydrogen, and oxygen just as carbohydrates and lipids do, but proteins are the only macronutrient that contains nitrogen. In each amino acid the elements are arranged into a specific conformation around a carbon center. Each amino acid consists of a central carbon atom connected to a side chain, a hydrogen, a nitrogen- containing amino group, a carboxylic acid group—hence the name “amino acid.” Amino acids differ from each other by which specific side chain is bonded to the carbon center.

1. Macromolecules composed of monomeric subunits, called amino acids.

2. Simple monomers composed of the elements carbon, oxygen, hydrogen, and nitrogen.

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It’s All in the Side Chain

The side chain of an amino acid, sometimes called the “R” group, can be as simple as one hydrogen bonded to the carbon center, or as complex as a six-carbon ring bonded to the carbon center. Although each side chain of the twenty amino acids is unique, there are some chemical likenesses among them. Therefore, they can be classified into four different groups. These are nonpolar, polar, acidic, and basic.

• Nonpolar amino acids. Nonpolar amino acids3 include alanine (Ala), leucine (Leu), isoleucine (Ile), proline (Pro), tryptophan (Trp), valine (Val), phenylalanine (Phe), and methionine (Met). The side chains of these amino acids are long carbon chains or carbon rings, making them bulky. They are hydrophobic, meaning they repel water.

• Polar amino acids. Polar amino acids4 are glycine (Gly), serine (Ser), threonine (Thr), cysteine (Cys), tyrosine (Tyr), asparagine (Asn), and glutamine (Gln). The side chains of polar amino acids make them hydrophilic, meaning they are water-soluble.

• Acidic amino acids. Acidic amino acids5 are negatively charged, hydrophilic amino acids and include aspartic acid (Asp) and glutamic acid (Glu).

• Basic amino acids. Basic amino acids6 are positively charged, hydrophilic amino acids and include lysine (Lys), arginine (Arg), and histidine (His).

3. Hydrophobic amino acids with side groups that are long or bulky.

4. Hydrophilic amino acids that are not charged.

5. Hydrophilic amino acids that are negatively charged.

6. Hydrophilic amino acids that are positively charged.

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Essential and Nonessential Amino Acids

Amino acids are further classified based on nutritional aspects. Recall that there are twenty different amino acids, and we require all of them to make the many different proteins found throughout the body. Eleven of these are called nonessential amino acids7 because the body can synthesize them. However, nine of the amino acids are called essential amino acids8 because we cannot synthesize them either at all or in sufficient amounts. These must be obtained from the diet. Sometimes during infancy, growth, and in diseased states the body cannot synthesize enough of some of the nonessential amino acids and more of them are required in the diet. These types of amino acids are called conditionally essential amino acids9. The nutritional value of a protein is dependent on what amino acids it contains and in what quantities.

7. Amino acids that are made in the human body.

8. Amino acids that are not made by humans and must be obtained from the diet.

9. Amino acids that become essential during certain times in life, such as child growth.

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The Many Different Types of Proteins

As discussed, there are over one hundred thousand different proteins in the human body. Different proteins are produced because there are twenty types of naturally occurring amino acids that are combined in unique sequences. Additionally, proteins come in many different sizes. The hormone insulin, which regulates blood glucose, is composed of only fifty-one amino acids; whereas collagen, a protein that acts like glue between cells, consists of more than one thousand amino acids. Titin is the largest known protein. It accounts for the elasticity of muscles, and consists of more than twenty-five thousand amino acids! The abundant variations of proteins are due to the unending number of amino acid sequences that can be formed. To compare how so many different proteins can be designed from only twenty amino acids, think about music. All of the music that exists in the world has been derived from a basic set of seven notes C, D, E, F, G, A, B and variations thereof. As a result, there is a vast array of music and songs all composed of specific sequences from these basic musical notes. Similarly, the twenty amino acids can be linked together in an extraordinary number of sequences, much more than are possible for the seven musical notes to create songs. As a result, there are enormous variations and potential amino acid sequences that can be created. For example, if an amino acid sequence for a protein is 104 amino acids long the possible combinations of amino acid sequences is equal to 20104, which is 2 followed by 135 zeros!

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Building Proteins with Amino Acids

The building of a protein consists of a complex series of chemical reactions that can be summarized into three basic steps: transcription10, translation11, and protein folding12. The first step in constructing a protein is the transcription (copying) of the genetic information in double-stranded deoxyribonucleic acid (DNA) into the single-stranded, messenger macromolecule ribonucleic acid (RNA). RNA is chemically similar to DNA, but has two differences; one is that its backbone uses the sugar ribose and not deoxyribose; and two, it contains the nucleotide base uracil, and not thymidine. The RNA that is transcribed from a given piece of DNA contains the same information as that DNA, but it is now in a form that can be read by the cellular protein manufacturer known as the ribosome. Next, the RNA instructs the cells to gather all the necessary amino acids and add them to the growing protein chain in a very specific order. This process is referred to as translation. The decoding of genetic information to synthesize a protein is the central foundation of modern biology.

10. Process of copying DNA into messenger RNA.

11. Process of decoding messenger RNA and synthesizing a protein.

12. A sequence of amino acids transforms into its dictated shape.

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During translation each amino acid is connected to the next amino acid by a special chemical bond called a peptide bond13. The peptide bond forms between the carboxylic acid group of one amino acid and the amino group of another, releasing a molecule of water. The third step in protein production involves folding it into its correct shape. Specific amino acid sequences contain all the information necessary to spontaneously fold into a particular shape. A change in the amino acid sequence will cause a change in protein shape. Each protein in the human body differs in its amino acid sequence and consequently, its shape. The newly synthesized protein is structured to perform a particular function in a cell. A protein made with an incorrectly placed amino acid may not function properly and this can sometimes cause disease.

Protein Organization

Protein’s structure enables it to perform a variety of functions. Proteins are similar to carbohydrates and lipids in that they are polymers of simple repeating units; however, proteins are much more structurally complex. In contrast to carbohydrates, which have identical repeating units, proteins are made up of amino acids that are different from one another. Furthermore, a protein is organized into four different structural levels. The first level is the one-dimensional sequence of amino acids that are held together by peptide bonds. Carbohydrates and lipids also are one-dimensional sequences of their respective monomers, which may be branched, coiled, fibrous, or globular, but their conformation is much more random and is not organized by their sequence of monomers. In contrast, the two- dimensional level of protein structure is dependent on the chemical interactions between amino acids, which cause the protein to fold into a specific shape, such as a

13. The chemical bond that connects amino acids in a sequence.

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helix (like a coiled spring) or sheet. The third level of protein structure is three- dimensional. As the different side chains of amino acids chemically interact, they either repel or attract each other, resulting in the coiled structure. Thus, the specific sequence of amino acids in a protein directs the protein to fold into a specific, organized shape. The fourth level of structure (also known as its “quaternary” structure) is achieved when protein fragments called peptides combine to make one larger functional protein. The protein hemoglobin is an example of a protein that has quaternary structure. It is composed of four peptides that bond together to form a functional oxygen carrier. A protein’s structure also influences its nutritional quality. Large fibrous protein structures are more difficult to digest than smaller proteins and some, such as keratin, are indigestible. Because digestion of some fibrous proteins is incomplete, not all of the amino acids are absorbed and available for the body to utilize, thereby decreasing their nutritional value.

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KEY TAKEAWAYS

• Amino acids differ chemically in the molecular composition of their side chains, but they do have some similarities. They are grouped into four different types: nonpolar, polar, acidic, and basic.

• Amino acids are also categorized based upon their nutritional aspects. Some are nonessential in the diet because the body can synthesize them, and some are essential in the diet because the body cannot make them.

• Proteins are polymers of amino acid monomers held together by peptide bonds. They are built in three steps; transcription, translation, and folding.

• Proteins have up to four different levels of structure, making them much more complex than carbohydrates or lipids.

DISCUSSION STARTERS

1. There are over four thousand diseases caused by incorrectly built protein. Find out more about how one incorrectly placed amino acid causes the disease sickle cell anemia by watching this animation.

http://www.dnalc.org/resources/3d/17-sickle-cell.html. 2. Why do you think protein-building diseases are rare? In every cell in

your body over ten million ribosomes are at work constructing millions of proteins every minute. What can you say about the body’s amazing track record in correctly building proteins?

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6.2 The Role of Proteins in Foods: Cooking and Denaturation

LEARNING OBJECTIVE

1. Explain the process of denaturation and its consequences. Give an example.

In addition to having many vital functions within the body, proteins perform different roles in our foods by adding certain functional qualities to them. Protein provides food with structure and texture and enables water retention. For example, proteins foam when agitated. (Picture whisking egg whites to make angel food cake. The foam bubbles are what give the angel food cake its airy texture.) Yogurt is another good example of proteins providing texture. Milk proteins called caseins coagulate, increasing yogurt’s thickness. Cooked proteins add some color to foods as the amino group binds with carbohydrates and produces a brown pigment. Eggs are between 10 and 15 percent protein by weight. Most cake recipes use eggs because the egg proteins help bind all the other ingredients together into a uniform cake batter. The proteins aggregate into a network during mixing and baking that gives cake structure.

Protein Denaturation: Unraveling the Fold

When a cake is baked, the proteins are denatured. Denaturation14 refers to the physical changes that take place in a protein exposed to abnormal conditions in the environment. Heat, acid, high salt concentrations, alcohol, and mechanical agitation can cause proteins to denature. When a protein denatures, its complicated folded structure unravels, and it becomes just a long strand of amino acids again. Weak chemical forces that

hold tertiary and secondary protein structures together are broken when a protein is exposed to unnatural conditions. Because proteins’ function is dependent on their shape, denatured proteins are no longer functional. During cooking the applied heat causes proteins to vibrate. This destroys the weak bonds holding proteins in their complex shape (though this does not happen to the stronger peptide bonds). The unraveled protein strands then stick together, forming an aggregate (or network).14. The physical changes that takeplace in a protein when it is

exposed to abnormal conditions in the environment.

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KEY TAKEAWAYS

• Proteins provide food not only with nutrition, but also with structure and texture.

• When a protein denatures, its complicated structure unfolds into a strand of amino acids.

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DISCUSSION STARTERS

1. Gelatin is a mixture of collagen proteins. How does gelatin add texture and structure to foods? Conduct an experiment by making some Jell-O™ using different methods of denaturation and discuss what happens to the texture and structure.

a. Make the first batch of Jell-O™ following the directions. Does it set?

b. Next, make up the Jell-O™, but replace hot water with cold. Does it set?

c. Instead of adding hot water, add 2 teaspoons of salt and only cold water. Does it set?

d. Take the first batch (that is now set) and either whisk it by hand or use an electric mixer. What happens?

2. If pouring salt on a live slug produces a puddle of goo, how is it possible to cook snails with salt and get a delicious dish?

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6.3 Protein Digestion and Absorption

LEARNING OBJECTIVE

1. Discuss how proteins are digested and absorbed by our bodies.

How do the proteins from foods, denatured or not, get processed into amino acids that cells can use to make new proteins? When you eat food the body’s digestive system breaks down the protein into the individual amino acids, which are absorbed and used by cells to build other proteins and a few other macromolecules, such as DNA. We discussed the process of food digestion in depth in Chapter 3 “Nutrition and the Human Body”, but now let’s follow the specific path that proteins take down the gastrointestinal tract and into the circulatory system. Eggs are a good dietary source of protein and will be used as our example to describe the path of proteins in the processes of digestion and absorption. One egg, whether raw, hard-boiled, scrambled, or fried, supplies about six grams of protein.

From the Mouth to the Stomach

Unless you are eating it raw, the first step in egg digestion (or any other protein food) involves chewing. The teeth begin the mechanical breakdown of the large egg pieces into smaller pieces that can be swallowed. The salivary glands provide some saliva to aid swallowing and the passage of the partially mashed egg through the esophagus. The mashed egg pieces enter the stomach through the esophageal sphincter. The stomach releases gastric juices containing hydrochloric acid15 and the enzyme, pepsin16, which initiate the breakdown of the protein. The acidity of the stomach facilitates the unfolding of the proteins that still retain part of their three-dimensional structure after cooking and helps break down the protein aggregates formed during cooking. Pepsin, which is secreted by the cells that line the stomach, dismantles the protein chains into smaller and smaller fragments. Egg proteins are large globular molecules and their chemical breakdown requires time and mixing. The powerful mechanical stomach contractions churn the partially digested protein into a more uniform mixture, which, you may recall from Chapter 3 “Nutrition and the Human Body”, is called chyme. Protein digestion in the stomach takes a longer time than carbohydrate digestion, but a shorter time than

15. Secreted by stomach cells; aids in the chemical breakdown of proteins.

16. An enzyme secreted by stomach cells. It breaks the peptide bonds between amino acids, producing much shorter protein fragments.

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fat digestion. Eating a high-protein meal increases the amount of time required to sufficiently break down the meal in the stomach. Food remains in the stomach longer, making you feel full longer.

From the Stomach to the Small Intestine

The stomach empties the chyme containing the broken down egg pieces into the small intestine, where the majority of protein digestion occurs. The pancreas secretes digestive juice that contains more enzymes that further break down the protein fragments. The two major pancreatic enzymes that digest proteins are chymotrypsin and trypsin. The cells that line the small intestine release additional enzymes that finally break apart the smaller protein fragments into the individual amino acids. The muscle contractions of the small intestine mix and propel the digested proteins to the absorption sites. In the lower parts of the small intestine, the amino acids are transported from the intestinal lumen through the intestinal cells to the blood. This movement of individual amino acids requires special transport proteins and the cellular energy molecule, adenosine triphosphate (ATP). Once the amino acids are in the blood, they are transported to the liver. As with other macronutrients, the liver is the checkpoint for amino acid distribution and any further breakdown of amino acids, which is very minimal. Recall that amino acids contain nitrogen, so further catabolism of amino acids releases nitrogen- containing ammonia. Because ammonia is toxic, the liver transforms it into urea, which is then transported to the kidney and excreted in the urine. Urea is a molecule that contains two nitrogens and is highly soluble in water. This makes it a good choice for transporting excess nitrogen out of the body. Because amino acids are building blocks that the body reserves in order to synthesize other proteins, more than 90 percent of the protein ingested does not get broken down further than the amino acid monomers.

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Amino Acids Are Recycled

Just as some plastics can be recycled to make new products, amino acids are recycled to make new proteins. All cells in the body continually break down proteins and build new ones, a process referred to as protein turnover17. Every day over 250 grams of protein in your body are dismantled and 250 grams of new protein are built. To form these new proteins, amino acids from food and those from protein destruction are placed into a “pool.” Though it is not a literal pool, when an amino acid is required to build another protein it can be acquired from the additional amino acids that exist within the body. Amino acids are used not only to build proteins, but also to build other biological molecules containing nitrogen, such as DNA and RNA, and to some extent to produce energy. It is critical to maintain amino acid levels within this cellular pool by consuming high-quality proteins in the diet, or the amino acids needed for building new proteins will be obtained by increasing protein destruction from other tissues within the body, especially muscle. This amino acid pool is less than one percent of total body- protein content. Thus, the body does not store protein as it does with carbohydrates (as glycogen in the muscles and liver) and lipids (as triglycerides in adipose tissue).

17. The processes of continually breaking down proteins and building new ones.

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KEY TAKEAWAYS

• Mechanical digestion of protein begins in the mouth and continues in the stomach and small intestine.

• Chemical digestion of protein begins in the stomach and ends in the small intestine.

• The body recycles amino acids to make more proteins.

DISCUSSION STARTERS

1. The next time you eat an egg, imagine it moving down the gastrointestinal tract and visualize what is happening to the proteins it contains. Does the amount of work required to digest a protein seem to be too much? How much energy does it take just to digest protein?

2. Why is it important to recycle amino acids?

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6.4 Protein’s Functions in the Body

LEARNING OBJECTIVE

1. List protein’s functions in the body.

Proteins are the “workhorses” of the body and participate in many bodily functions. As you may recall, proteins come in all sizes and shapes and each is specifically structured for its particular function.

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Collagen: A strong protein made up of three intertwined peptides. Collagen Triple Helix by Vossman is available under a Creative Commons Attribution- ShareAlike 3.0 Unported license.

Structure and Motion

More than one hundred different structural proteins have been discovered in the human body, but the most abundant by far is collagen, which makes up about 6 percent of total body weight. Collagen makes up 30 percent of bone tissue and comprises large amounts of tendons, ligaments, cartilage, skin, and muscle. Collagen18 is a strong, fibrous protein made up of mostly glycine and proline amino acids. Within its quaternary structure three protein strands twist around each other like a rope and then these collagen ropes overlap with others. This highly ordered structure is even stronger than steel fibers of the same size. Collagen makes bones strong, but flexible. Collagen fibers in the skin’s dermis provide it with structure, and the accompanying elastin19 protein fibrils make it flexible. Pinch the skin on your hand and then let go; the collagen and elastin proteins in skin allow it to go back to its original shape. Smooth-muscle cells that secrete collagen and elastin proteins surround blood vessels, providing the vessels with structure and the ability to stretch back after blood is pumped through them. Another strong, fibrous protein is keratin20, which is what skin, hair, and nails are made of.

The closely packed collagen fibrils in tendons and ligaments allow for synchronous mechanical movements of bones and muscle and the ability of these tissues to spring back after a movement is complete. Move your fingers and watch the synchrony of your knuckle movements. In order to move, muscles must contract. The contractile parts of muscles are the proteins actin21 and myosin22. When these proteins are stimulated by a nerve impulse they slide across each other, causing a shortening of the muscle cell. Upon stimulation, multiple muscle cells shorten at the same time, resulting in muscle contraction.

18. The most abundant protein in the human body. It is a strong fibrous rope that plays a role in structure, motion, protection, and tissue repair and regeneration.

19. A fibrous protein that allows connective tissues, such as skin and tendons, to stretch back into their original shape.

20. A fibrous protein that provides skin, hair, and nails with structure.

21. A contractile protein in muscle cells.

22. A contractile protein in muscle cells.

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Enzymes

Although proteins are found in the greatest amounts in connective tissues such as bone, their most extraordinary function is as enzymes. Enzymes23 are proteins that conduct specific chemical reactions. An enzyme’s job is to provide a site for a chemical reaction and to lower the amount of energy and time it takes for that chemical reaction to happen (this is known as “catalysis”). On average, more than one hundred chemical reactions occur in cells every single second and most of them require enzymes. The liver alone contains over one thousand enzyme systems. Enzymes are specific and will use only particular substrates that fit into their active site, similar to the way a lock can be opened only with a specific key. Nearly every chemical reaction requires a specific enzyme. Fortunately, an enzyme can fulfill its role as a catalyst over and over again, although eventually it is destroyed and rebuilt. All bodily functions, including the breakdown of nutrients in the stomach and small intestine, the transformation of nutrients into molecules a cell can use, and building all macromolecules, including protein itself, involve enzymes.

23. Proteins that conduct a specific chemical reaction in order to transform substrates into a product.

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Hormones

Proteins are responsible for hormone synthesis. Recall from Chapter 3 “Nutrition and the Human Body” that hormones are the chemical messages produced by the endocrine glands. When an endocrine gland is stimulated, it releases a hormone. The hormone is then transported in the blood to its target cell, where it communicates a message to initiate a specific reaction or cellular process. For instance, after you eat a meal, your blood glucose levels rise. In response to the increased blood glucose, the pancreas releases the hormone insulin. Insulin tells the cells of the body that glucose is available and to take it up from the blood and store it or use it for making energy or building macromolecules. A major function of hormones is to turn enzymes on and off, so some proteins can even regulate the actions of other proteins. While not all hormones are made from proteins, many of them are.

Fluid and Acid-Base Balance

Proper protein intake enables the basic biological processes of the body to maintain the status quo in a changing environment. Fluid balance refers to maintaining the distribution of water in the body. If too much water in the blood suddenly moves into a tissue, the results are swelling and, potentially, cell death. Water always flows from an area of high concentration to one of a low concentration. As a result, water moves toward areas that have higher concentrations of other solutes, such as proteins and glucose. To keep the water evenly distributed between blood and cells, proteins continuously circulate at high concentrations in the blood. The most abundant protein in blood is the butterfly-shaped protein known as albumin24. Albumin’s presence in the blood makes the protein concentration in the blood similar to that in cells. Therefore, fluid exchange between the blood and cells is not in the extreme, but rather is minimized to preserve the status quo.

24. A butterfly-shaped protein that plays a role in fluid balance, acid-base balance, and the transport of biological molecules.

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The butterfly-shaped protein, albumin, has many functions in the body including maintaining fluid and acid-base balance and transporting molecules.

PDB by Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute comprises public domain material worldwide.

Protein is also essential in maintaining proper pH balance (the measure of how acidic or basic a substance is) in the blood. Blood pH is maintained between 7.35 and 7.45, which is slightly basic. Even a slight change in blood pH can affect body functions. Recall that acidic conditions can cause protein denaturation, which stops proteins from functioning. The body has several systems that hold the blood pH within the normal range to prevent this from happening. One of these is the circulating albumin. Albumin is slightly acidic, and because it is negatively charged it balances the many positively charged molecules, such as hydrogen protons (H+), calcium, potassium, and magnesium which are also circulating in the blood. Albumin acts as a buffer against abrupt changes in the concentrations of these molecules, thereby balancing blood pH and maintaining the status quo. The protein hemoglobin also participates in acid-base balance by binding hydrogen protons.

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Transport

Figure 6.6

Molecules move in and out of cells through transport proteins, which are either channels or carriers.

Scheme Facilitated Diffusion in Cell Membrane by Mariana Ruiz Villarreal comprises public domain material worldwide.

Albumin and hemoglobin also play a role in molecular transport. Albumin chemically binds to hormones, fatty acids, some vitamins, essential minerals, and drugs, and transports them throughout the circulatory system. Each red blood cell contains millions of hemoglobin molecules that bind oxygen in the lungs and transport it to all the tissues in the body. A cell’s plasma membrane is usually not permeable to large polar molecules, so to get the required nutrients and molecules into the cell many transport proteins exist in the cell membrane. Some of these proteins are channels that allow particular molecules to move in and out of cells. Others act as one-way taxis and require energy to function (Figure 6.6).

Protection

Earlier we discussed that the strong collagen fibers in skin provide it with structure and support. The skin’s dense network of collagen fibers also serves as a barricade against harmful substances. The immune system’s attack and destroy functions are dependent on enzymes and antibodies, which are also proteins. An enzyme called lysozyme25 is secreted in the saliva and attacks the walls of bacteria, causing them to rupture. Certain proteins circulating in the blood can be directed to build a molecular knife25. A protein that is an enzyme

that destroys bacteria.

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that stabs the cellular membranes of foreign invaders. The antibodies26 secreted by the white blood cells survey the entire circulatory system looking for harmful bacteria and viruses to surround and destroy. Antibodies also trigger other factors in the immune system to seek and destroy unwanted intruders.

Wound Healing and Tissue Regeneration

Proteins are involved in all aspects of wound healing, a process that takes place in three phases: inflammatory, proliferative, and remodeling. For example, if you were sewing and pricked your finger with a needle, your flesh would turn red and become inflamed. Within a few seconds bleeding would stop. The healing process begins with proteins such as bradykinin, which dilate blood vessels at the site of injury. An additional protein called fibrin helps to secure platelets that form a clot to stop the bleeding. Next, in the proliferative phase, cells move in and mend the injured tissue by installing newly made collagen fibers. The collagen fibers help pull the wound edges together. In the remodeling phase, more collagen is deposited, forming a scar. Scar tissue is only about 80 percent as functional as normal uninjured tissue. If a diet is insufficient in protein, the process of wound healing is markedly slowed.

While wound healing takes place only after an injury is sustained, a different process called tissue regeneration is ongoing in the body. The main difference between wound healing and tissue regeneration is in the process of regenerating an exact structural and functional copy of the lost tissue. Thus, old, dying tissue is not replaced with scar tissue but with brand new, fully functional tissue. Some cells (such as skin, hair, nails, and intestinal cells) have a very high rate of regeneration, while others, (such as heart-muscle cells and nerve cells) do not regenerate at any appreciable levels. Tissue regeneration is the creation of new cells (cell division), which requires many different proteins including enzymes that synthesize RNA and proteins, transport proteins, hormones, and collagen. In a hair follicle, cells divide and a hair grows in length. Hair growth averages 1 centimeter per month and fingernails about 1 centimeter every one hundred days. The cells lining the

26. A protein that protects against unwanted intruders.

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intestine regenerate every three to five days. Protein-inadequate diets impair tissue regeneration, causing many health problems including impairment of nutrient digestion and absorption and, most visibly, hair and nail growth.

Energy Production

Some of the amino acids in proteins can be disassembled and used to make energy. Only about 10 percent of dietary proteins are catabolized each day to make cellular energy. The liver is able to break down amino acids to the carbon skeleton, which can then be fed into the citric acid cycle. This is similar to the way that glucose is used to make ATP. If a person’s diet does not contain enough carbohydrates and fats their body will use more amino acids to make energy, which compromises the synthesis of new proteins and destroys muscle proteins. Alternatively, if a person’s diet contains more protein than the body needs, the extra amino acids will be broken down and transformed into fat.

KEY TAKEAWAYS

• The many shapes and sizes of proteins allow them to perform a vast array of functions, including: acting as enzymes and hormones, and providing for fluid and acid-base balance, transport, protection, wound healing and tissue regeneration, and energy production.

• Without adequate intake of protein containing all the essential amino acids, all protein functions will be impaired.

DISCUSSION STARTER

1. Given protein’s critical roles in the immune system, what do you think might occur more frequently in a person whose diet is protein deficient?

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6.5 Diseases Involving Proteins

LEARNING OBJECTIVE

1. Identify the potential health risks associated with abnormal protein levels in the diet.

As you may recall, moderation refers to having the proper amount of a nutrient—having neither too little nor too much. A healthy diet incorporates all nutrients in moderation. Low protein intake has several health consequences, and a severe lack of protein in the diet eventually causes death. Although severe protein deficiency is a rare occurrence in children and adults in the United States, it is estimated that more than half of the elderly in nursing homes are protein-deficient. The Acceptable Macronutrient Distribution Range (AMDR) for protein for adults is between 10 and 35 percent of kilocalories, which is a fairly wide range. The percent of protein in the diet that is associated with malnutrition and its health consequences is less than 10 percent, but this is often accompanied by deficiencies in calories and other micronutrients. There is some scientific evidence that shows that people with diets low in animal protein (< 8 percent of caloric intake), who get adequate protein from plant-based foods instead, may actually have improved health and increased longevity. On the other hand, diets rich in animal-derived protein (> 30 percent of caloric intake) are associated with increased early mortality, kidney and liver malfunction, cardiovascular disease, colon cancer, and osteoporosis. In this section we will discuss the health consequences of protein intake that is either too low to support life’s processes or too high, thereby increasing the risk of chronic disease. In the last section of this chapter, we will discuss in more detail the personal choices you can make to optimize your health by consuming the right amount of high-quality protein.

Health Consequences of Protein Deficiency

Although severe protein deficiency is rare in the developed world, it is a leading cause of death in children in many poor, underdeveloped countries. There are two main syndromes associated with protein deficiencies: Kwashiorkor and Marasmus. Kwashiorkor27 affects millions of children worldwide. When it was first described in 1935, more than 90 percent of children with Kwashiorkor died. Although the associated mortality is slightly lower now, most children still die after the initiation of treatment. The name Kwashiorkor comes from a language in Ghana and means, “rejected one.” The syndrome was named because it occured most commonly in children who had recently been weaned from the breast, usually because another

27. A syndrome of severe protein and micronutrient deficiency, characterized by swelling (edema) of the feet and abdomen, poor skin health, growth retardation, low muscle mass, and liver malfunction.

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child had just been born. Subsequently the child was fed watery porridge made from low-protein grains, which accounts for the low protein intake. Kwashiorkor is characterized by swelling (edema) of the feet and abdomen, poor skin health, growth retardation, low muscle mass, and liver malfunction. Recall that one of protein’s functional roles in the body is fluid balance. Diets extremely low in protein do not provide enough amino acids for the synthesis of albumin. One of the functions of albumin is to hold water in the blood vessels, so having lower concentrations of blood albumin results in water moving out of the blood vessels and into tissues, causing swelling. The primary symptoms of Kwashiorkor include not only swelling, but also diarrhea, fatigue, peeling skin, and irritability. Severe protein deficiency in addition to other micronutrient deficiencies, such as folate (vitamin B9), iodine, iron, and vitamin C all contribute to the many health manifestations of this syndrome.

Children and adults with marasmus28 neither have enough protein in their diets nor do they take in enough calories. Marasmus affects mostly children below the age of one in poor countries. Body weights of children with Marasmus may be up to 80 percent less than that of a normal child of the same age. Marasmus is a Greek word, meaning “starvation.” The syndrome affects more than fifty million children under age five worldwide. It is characterized by an extreme emaciated appearance, poor skin health, and growth retardation. The symptoms are acute fatigue, hunger, and diarrhea.

Kwashiorkor and marasmus often coexist as a combined syndrome termed marasmic kwashiorkor29. Children with the combined syndrome have variable amounts of edema and the characterizations and symptoms of marasmus. Although organ system function is compromised by undernutrition, the ultimate cause of death is usually infection. Undernutrition is intricately linked with suppression of the immune system at multiple levels, so undernourished children commonly die from severe diarrhea and/or pneumonia resulting from bacterial or viral infection. The United Nations Children’s Fund (UNICEF), the most prominent agency with the mission of changing the world to improve children’s lives, reports that undernutrition causes at least one-third of deaths of young children. As of 2008, the prevalence of children under age five who were underweight was 26 percent. The percentage of underweight children has declined less than 5 percent in the last eighteen years despite the Millenium

28. A syndrome of severe protein and energy deficiency, characterized by emaciation, poor skin health, and growth retardation.

29. The combined syndrome of severe protein and energy deficiency, characterized by variable edema, emaciation, poor skin health, and growth retardation.

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Development Goal of halving the proportion of people who suffer from hunger by the year 2015.

Interactive 6.2

If you are interested in finding out more about world hunger and what is being done about it, visit the UNICEF website.

http://www.childinfo.org/index.html

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Health Consequences of Too Much Protein in the Diet

An explicit definition of a high-protein diet has not yet been developed by the Food and Nutrition Board of the Institute of Medicine (IOM), but typically diets high in protein are considered as those that derive more than 30 percent of calories from protein. Many people follow high-protein diets because marketers tout protein’s ability to stimulate weight loss. It is true that following high-protein diets increases weight loss in some people. However the number of individuals that remain on this type of diet is low and many people who try the diet and stop regain the weight they had lost. Additionally, there is a scientific hypothesis that there may be health consequences of remaining on high-protein diets for the long-term, but clinical trials are ongoing or scheduled to examine this hypothesis further. As the high- protein diet trend arose so did the intensely debated issue of whether there are any health consequences of eating too much protein. Observational studies conducted in the general population suggest diets high in animal protein, specifically those in which the primary protein source is red meat, are linked to a higher risk for kidney stones, kidney disease, liver malfunction, colorectal cancer, and osteoporosis. However, diets that include lots of red meat are also high in saturated fat and cholesterol and sometimes linked to unhealthy lifestyles, so it is difficult to conclude that the high protein content is the culprit.

High protein diets appear to only increase the progression of kidney disease and liver malfunction in people who already have kidney or liver malfunction, and not to cause these problems. However, the prevalence of kidney disorders is relatively high and underdiagnosed. In regard to colon cancer, an assessment of more than ten studies performed around the world published in the June 2011 issue of PLoS purports that a high intake of red meat and processed meat is associated with a significant increase in colon cancer risk.Chan, D. S., et al. “Red and Processed Meat and Colorectal Cancer Incidence: Meta-Analysis of Prospective Studies.” PLoS One 6, no. 6 (2011): e20456. doi: 10.1371/journal.pone.0020456. Although there are a few ideas, the exact mechanism of how proteins, specifically those in red and processed meats, causes colon cancer is not known and requires further study.

Some scientists hypothesize that high-protein diets may accelerate bone-tissue loss because under some conditions the acids in protein block absorption of calcium in the gut, and, once in the blood, amino acids promote calcium loss from bone; however even these effects have not been consistently observed in scientific studies. Results from the Nurse’s Health Study suggest that women who eat more than 95 grams of protein each day have a 20 percent higher risk for wrist fracture.Harvard School of Public Health. “Protein: The Bottom Line.” The Nutrition Source. © 2012 The President and Fellows of Harvard University. http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/protein/., Barzel, U. S. and L. K. Massey. “Excess Dietary Protein Can Adversely Affect Bone.” J

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Nutr 128, no. 6 (June 1, 1998): 1051–53. http://jn.nutrition.org/content/128/6/ 1051.long. Other studies have not produced consistent results. The scientific data on high protein diets and increased risk for osteoporosis remains highly controversial and more research is needed to come to any conclusions about the association between the two.St. Jeor, S. T. et al. “Dietary Protein and Weight Reduction: A Statement for Healthcare Professionals from the Nutrition Committee of the Council on Nutrition, Physical Activity, and Metabolism of the American Heart Association.” Circulation 104 (2001): 1869–74.

High-protein diets can restrict other essential nutrients. The AHA states that “High- protein diets are not recommended because they restrict healthful foods that provide essential nutrients and do not provide the variety of foods needed to adequately meet nutritional needs. Individuals who follow these diets are therefore at risk for compromised vitamin and mineral intake, as well as potential cardiac, renal, bone, and liver abnormalities overall.”St. Jeor, S. T. et al. “Dietary Protein and Weight Reduction: A Statement for Healthcare Professionals from the Nutrition Committee of the Council on Nutrition, Physical Activity, and Metabolism of the American Heart Association.” Circulation 104 (2001): 1869–74.

As with any nutrient, protein must be eaten in proper amounts. Moderation and variety are key strategies to achieving a healthy diet and need to be considered when optimizing protein intake. While the scientific community continues its debate about the particulars regarding the health consequences of too much protein in the diet, you may be wondering just how much protein you should consume to be healthy. Read on to find out more about calculating your dietary protein recommendations, dietary protein sources, and personal choices about protein.

KEY TAKEAWAYS

• Protein deficiency syndromes are a leading cause of death in children under the age of five in poor, underdeveloped countries. Protein deficiency can cause swelling, fatigue, skin problems, irritability, muscle wasting, and eventual death from infection.

• The long-term health consequences of high-protein diets have not been adequately studied.

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DISCUSSION STARTER

1. What are some diet changes you can make that are better, more sustainable, and easier to follow for the rest of your life than a high- protein diet?

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LEARNING OBJECTIVES

1. Calculate your Recommended Dietary Allowance for protein. 2. Plan a one-day diet for each of the following: vegetarian, lacto-ovo

vegetarian, and vegan. For each, calculate nutrient intake, then assess for adequacy, balance, and variety.

3. Decide whether to take protein or amino acid supplements based on nutrition science studies.

We have discussed what proteins are, how they are made, how they are digested and absorbed, the many functions of proteins in the body, and the consequences of having too little or too much protein in the diet. This section will provide you with information on how to determine the recommended amount of protein for you, and your many choices in designing an optimal diet with high-quality protein sources.

How Much Protein Does a Person Need in Their Diet?

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Protein Input = Protein Used by the Body + Protein Excreted

The appropriate amount of protein in a person’s diet is that which maintains a balance between what is taken in and what is used. The RDAs for protein were determined by assessing nitrogen balance30. Nitrogen is one of the four basic elements contained in all amino acids. When proteins are broken down and amino acids are catabolized, nitrogen is released. Remember that when the liver breaks down amino acids, it produces ammonia, which is rapidly converted to nontoxic, nitrogen-containing urea, which is then transported to the kidneys for excretion. Most nitrogen is lost as urea in the urine, but urea is also excreted in the feces. Proteins are also lost in sweat and as hair and nails grow. The RDA, therefore, is the amount of protein a person should consume in their diet to balance the amount of protein used up and lost from the body. For healthy adults, this amount of protein was determined to be 0.8 grams of protein per kilogram of body weight. You can calculate your exact recommended protein intake per day based on your weight by using the following equation:

(Weight in lbs. ÷ 2.2 kg/lb) × 0.8 g/kg

Note that if a person is overweight, the amount of dietary protein recommended can be overestimated.

The IOM used data from multiple studies that determined nitrogen balance in people of different age groups to calculate the RDA for protein. A person is said to be in nitrogen balance when the nitrogen input equals the amount of nitrogen used and excreted. A person is in negative nitrogen balance when the amount of excreted nitrogen is greater than that consumed, meaning that the body is breaking down more protein to meet its demands. This state of imbalance can occur in people who have certain diseases, such as cancer or muscular dystrophy. Someone who has a low-protein diet may also be in negative nitrogen balance as they are taking in less protein than what they actually need. Positive nitrogen balance occurs when a person excretes less nitrogen than what is taken in by the diet, such

30. When the amount of protein input into the body equals the amount used up and excreted.

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as during child growth or pregnancy. At these times the body requires more protein to build new tissues, so more of what gets consumed gets used up and less nitrogen is excreted. A person healing from a severe wound may also be in positive nitrogen balance because protein is being used up to repair tissues.

Dietary Sources of Protein

The protein food group consists of foods made from meat, seafood, poultry, eggs, soy, beans, peas, and seeds. According to the Harvard School of Public Health, “animal protein and vegetable protein probably have the same effects on health. It’s the protein package that’s likely to make a difference.”Harvard School of Public Health. “Protein: The Bottom Line.” The Nutrition Source. © 2012 The President and Fellows of Harvard University. http://www.hsph.harvard.edu/nutritionsource/ what-should-you-eat/protein/. Simply put, different protein sources differ in their additional components, so it is necessary to pay attention to the whole nutrient “package.” Protein-rich animal-based foods commonly have high amounts of B vitamins, vitamin E, iron, magnesium, and zinc. Seafood often contains healthy fats,

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and plant sources of protein contain a high amount of fiber. Some animal-based protein-rich foods have an unhealthy amount of saturated fat and cholesterol. When choosing your dietary sources of protein, take note of the other nutrients and also the nonnutrients, such as cholesterol, dyes, and preservatives, in order to make good selections that will benefit your health. For instance, a hamburger patty made from 80 percent lean meat contains 22 grams of protein, 5.7 grams of saturated fat, and 77 milligrams of cholesterol. A burger made from 95 percent lean meat also contains 22 grams of protein, but has 2.3 grams of saturated fat and 60 milligrams of cholesterol. A cup of boiled soybeans contains 29 grams of protein, 2.2 grams of saturated fat, and no cholesterol. For more comparisons of protein-rich foods, see Table 6.3 “Sources of Dietary Protein”. To find out the complete nutrient package of different foods, visit the US Department of Agriculture (USDA) website listed in Note 6.55 “Interactive 6.3”.

Table 6.3 Sources of Dietary Protein

Food Protein Content(g) Saturated Fat

(g) Cholesterol

(mg) Calories

Hamburger patty 3 oz. (80% lean) 22.0 5.7 77 230

Hamburger patty 3 oz. (95% lean) 22.0 2.3 60 139

Top sirloin 3 oz. 25.8 2.0 76 158

Beef chuck 3 oz. (lean, trimmed) 22.2 1.8 51 135

Pork loin 3 oz. 24.3 3.0 69 178

Pork ribs (country style, 1 piece) 56.4 22.2 222 790

Chicken breast (roasted, 1 c.) 43.4 1.4 119 231

Chicken thigh (roasted, 1 thigh) 13.5 1.6 49 109

Chicken leg (roasted, 1 leg) 29.6 4.2 105 264

Salmon 3 oz. 18.8 2.1 54 175

Tilapia 3 oz. 22.2 0.8 48 109

Halibut 3 oz. 22.7 0.4 35 119

Shrimp 3 oz. 17.8 0.2 166 84

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Food Protein Content(g) Saturated Fat

(g) Cholesterol

(mg) Calories

Shrimp (breaded, fried, 6–8 pcs.) 18.9 5.4 200 454

Tuna 3 oz. (canned) 21.7 0.2 26 99

Soybeans 1 c. (boiled) 29.0 2.2 0 298

Lentils 1 c. (boiled) 17.9 0.1 0 226

Kidney beans 1 c. (canned) 13.5 0.2 0 215

Sunflower seeds 1 c. 9.6 2.0 0 269

Interactive 6.3

This interactive USDA tool allows you to enter the foods you eat (with serving size) and find out the whole nutrient package.

http://www.ars.usda.gov/Services/docs.htm?docid=17032

The USDA provides some tips for choosing your dietary protein sources. Their motto is, “Go Lean with Protein” (see Note 6.56 “Interactive 6.4”). The overall suggestion is to eat a variety of protein-rich foods to benefit health. The USDA recommends lean meats, such as round steaks, top sirloin, extra lean ground beef, pork loin, and skinless chicken. Additionally, a person should consume 8 ounces of cooked seafood every week (typically as two 4-ounce servings) to assure they are getting the healthy omega-3 fatty acids that have been linked to a lower risk for heart disease. Another tip is choosing to eat beans, peas, or soy products as a main dish. Some of the menu choices include chili with kidney and pinto beans, hummus on pita bread, and black bean enchiladas. You could also enjoy nuts in a variety of ways. You can put them on a salad, in a stir-fry, or use them as a topping for steamed vegetables in place of meat or cheese. If you do not eat meat, the USDA has much more information on how to get all the protein you need from a plant-based diet. When choosing the best protein-rich foods to eat, pay attention to the whole nutrient package and remember to select from a variety of protein sources to get all the other essential micronutrients.

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Interactive 6.4

The USDA manages the website choosemyplate.gov. The site provides a lot of tips and information about protein-rich foods.

http://www.choosemyplate.gov/food-groups/protein-foods.html

Tools for Change

Try some new, healthy, protein-rich food recipes by visiting the Harvard School of Public Health website, http://hvrd.me/OJRkpV. You will find recipes for foods such as spicy lemongrass tofu with Asian basil, fish Creole, and spicy chicken kebabs.

Protein Quality

While protein is contained in a wide variety of foods, it differs in quality. High- quality protein contains all the essential amino acids in the proportions needed by the human body. The amino acid profile of different foods is therefore one component of protein quality. Foods that contain some of the essential amino acids are called incomplete protein sources31, while those that contain all nine essential amino acids are called complete protein sources32, or high-quality protein sources. Foods that are complete protein sources include animal foods such as milk, cheese, eggs, fish, poultry, and meat, and a few plant foods, such as soy and quinoa. The only animal-based protein that is not complete is gelatin, which consists of the protein, collagen.

31. Foods that contain some of the essential amino acids.

32. Foods that contain all nine of the essential amino acids.

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Most plant-based foods are deficient in at least one essential amino acid and therefore are incomplete protein sources. For example, grains are usually deficient in the amino acid lysine, and legumes do not contain methionine or tryptophan. Because grains and legumes are not deficient in the same amino acids they can complement each other in a diet. Incomplete protein foods are called complementary foods33 because when consumed in tandem they contain all nine essential amino acids at adequate levels. Complementary protein sources do not have to be consumed at the same time—as long as they are consumed within the same day, you will meet your protein needs.

33. A combination of foods that when consumed together (though not necessarily at the same time) contain all nine essential amino acids at adequate levels.

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Tools for Change

Explore some ethnic grocery markets to find new high-protein foods for your diet and/or experiment with the much cheaper plant-based protein sources. See Table 6.4 “Complementing Protein Sources the Vegan Way” for complementing protein sources the vegan way.

Table 6.4 Complementing Protein Sources the Vegan Way

Foods Lacking Amino Acids ComplementaryFood Complementary Menu

Legumes Methionine, tryptophan Grains, nuts, andseeds Hummus and whole-wheat pita

Grains Lysine, isoleucine,threonine Legumes Cornbread and kidney bean chili

Nuts and seeds Lysine, isoleucine Legumes Stir-fried tofu with cashews

The second component of protein quality is digestibility, as not all protein sources are equally digested. In general, animal-based proteins are completely broken down during the process of digestion, whereas plant-based proteins are not. This is because some proteins are contained in the plant’s fibrous cell walls and these pass through the digestive tract unabsorbed by the body.

Protein Digestibility Corrected Amino Acid Score (PDCAAS)

The PDCAAS is a method adopted by the US Food and Drug Administration (FDA) to determine a food’s protein quality. It is calculated using a formula that incorporates the total amount of amino acids in the food and the amount of protein in the food that is actually digested by humans. The food’s protein quality is then ranked against the foods highest in protein quality. Milk protein, egg whites, whey, and soy all have a ranking of one, the highest ranking. Other foods’ ranks are listed in Table 6.5 “PDCAAS of Various Foods”.

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Table 6.5 PDCAAS of Various Foods

Food PDCAAS*

Milk protein 1.00

Egg white 1.00

Whey 1.00

Soy protein 1.00

Beef 0.92

Soybeans 0.91

Chickpeas 0.78

Fruits 0.76

Vegetables 0.73

Legumes 0.70

Cereals 0.59

Whole wheat 0.42

*1 is the highest rank, 0 is the lowest

Protein Needs: Special Considerations

Some groups may need to examine how to meet their protein needs more closely than others. We will take a closer look at the special protein considerations for vegetarians, the elderly, and athletes.

Vegetarians and Vegans

People who follow variations of the vegetarian diet and consume eggs and/or dairy products can easily meet their protein requirements by consuming adequate amounts of these foods. Vegetarians and vegans can also attain their recommended protein intakes if they give a little more attention to high-quality plant-based protein sources. However, when following a vegetarian diet, the amino acid lysine can be challenging to acquire. Grains, nuts, and seeds are lysine-poor foods, but tofu, soy, quinoa, and pistachios are all good sources of lysine. Following a vegetarian diet and getting the recommended protein intake is also made a little more difficult because the digestibility of plant-based protein sources is lower than the digestibility of animal-based protein.

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To begin planning a more plant-based diet, start by finding out which types of food you want to eat and in what amounts you should eat them to ensure that you get the protein you need. The Dietary Guidelines Advisory Committee (DGAC) has analyzed how three different, plant-based dietary patterns can meet the recommended dietary guidelines for all nutrients.Jacobs, D. R. et al. “Food, Plant Food, and Vegetarian Diets in the US Dietary Guidelines: Conclusions of an Expert Panel.” Am J Clin Nutr 89, no. 5 (2009). http://ajcn.nutrition.org/content/89/5/ 1549S.short. The diets are defined in the following manner:

• Plant-based. Fifty percent of protein is obtained from plant foods. • Lacto-ovo vegetarian. All animal products except eggs and dairy are

eliminated. • Vegan. All animal products are eliminated.

These diets are analyzed and compared to the more common dietary pattern of Americans, which is referred to as the USDA Base Diet. The percentages of foods in the different groups are the proportions consumed by the population, so that, on average, Americans obtain 44.6 percent of their foods in the meat and beans group from meats. If you choose to follow a lacto-ovo vegetarian diet, the meats, poultry, and fish can be replaced by consuming a higher percentage of soy products, nuts, seeds, dry beans, and peas. As an aside, the DGAC notes that these dietary patterns may not exactly align with the typical diet patterns of people in the United States. However, they do say that they can be adapted as a guide to develop a more plant- based diet that does not significantly affect nutrient adequacy.

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From these analyses the DGAC concluded that the plant-based, lacto-ovo vegetarian, and vegan diets do not significantly affect nutrient adequacy. Additionally, the DGAC states that people who choose to obtain proteins solely from plants should include foods fortified with vitamins B12, D, and calcium. Other nutrients of concern may be omega-3 fatty acids and choline. Two large observational studies with thousands of participants demonstrated that in comparison to regular meat-eaters, people who followed a vegetarian diet had a significantly decreased risk of dying from heart disease or cancer.Lindbloom, E. “Long-Term Benefits of a Vegetarian Diet.” Am Fam Physician 79, no. 7 (April 1, 2009): 541–42. http://www.aafp.org/afp/ 2009/0401/p541.html.

Interactive 6.5

To read the full report on nutrient adequacy of plant-based, lacto-ovo vegetarian, and vegan diets, go to the link to the Dietary Guidelines below, which takes you directly to appendix E-3.3. This document provides details on the actual amounts in ounces and cups of various food groups required to eat each day in order to meet the dietary guidelines.

http://1.usa.gov/ML3M8D

Tools for Change

Make a sustainable choice to go meatless more than once a week. To get some ideas on how to expand your dietary choices, visit the Eating Well website, which has a twenty-eight-day vegetarian meal plan that meets the US dietary guidelines. http://www.eatingwell.com/nutrition_health/ weight_loss_diet_plans/diet_meal_plans /vegetarian_meal_plan

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The Elderly

As we age, muscle mass gradually declines. This is a process referred to as sarcopenia34. A person is sarcopenic when their amount of muscle tissue is significantly lower than the average value for a healthy person of the same age. A significantly lower muscle mass is associated with weakness, movement disorders, and a generally poor quality of life. It is estimated that about half the US population of men and women above the age of eighty are sarcopenic. A review published in the September 2010 issue of Clinical Intervention in Aging demonstrates that higher intakes (1.2 to 1.5 grams per kilogram of weight per day) of high-quality protein may prevent aging adults from becoming sarcopenic.Waters, D. L. et al. “Advantages of Dietary, Exercise-Related, and Therapeutic Interventions to Prevent and Treat Sarcopenia in Adult Patients: An Update.” Clin Interv Aging 5 (September 7, 2010): 259–70. http://www.ncbi.nlm.nih.gov/pmc/articles/ PMC2938033/?tool=pubmed Currently, the RDA for protein for elderly persons is the same as that for the rest of the adult population, but several clinical trials are ongoing and are focused on determining the amount of protein in the diet that prevents the significant loss of muscle mass specifically in older adults.

Athletes

Muscle tissue is rich in protein composition and has a very high turnover rate. During exercise, especially when it is performed for longer than two to three hours, muscle tissue is broken down and some of the amino acids are catabolized to fuel muscle contraction. To avert excessive borrowing of amino acids from muscle tissue to synthesize energy during prolonged exercise, protein needs to be obtained from the diet. Intense exercise, such as strength training, stresses muscle tissue so that afterward, the body adapts by building bigger, stronger, and healthier muscle tissue. The body requires protein postexercise to accomplish this. The IOM does not set different RDAs for protein intakes for athletes, but the AND, the American College of Sports Medicine, and Dietitians of Canada have the following position statements:

• “Nitrogen balance studies suggest that dietary protein intake necessary to support nitrogen balance in endurance athletes ranges from 1.2 to 1.4 grams per kilogram of body weight per day.”

• “Recommended protein intakes for strength-trained athletes range from approximately 1.2 to 1.7grams per kilogram of weight per day.”American College of Sports Medicine, Academy of Nutrition and Dietetics, and Dietitians of Canada. “Joint Position Statement: Nutrition and Athletic Performance.” Med Sci Sports Exerc 41, no. 3 (March 2009). doi: 10.1249/MSS.0b013e31890eb86.

34. The age-related decline in muscle mass.

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An endurance athlete who weighs 170 pounds should take in 93 to 108 grams of protein per day ((170 ÷ 2.2) × 1.2 and (170 ÷ 2.2) × 1.4). On a 3,000-kilocalorie diet, that amount is between 12 and 14 percent of total kilocalories and within the AMDR. There is general scientific agreement that endurance and strength athletes should consume protein from high-quality sources, such as dairy, eggs, lean meats, or soy; however eating an excessive amount of protein at one time does not further stimulate muscle-protein synthesis. Nutrition experts also recommend that athletes consume some protein within one hour after exercise to enhance muscle tissue repair during the recovery phase, but some carbohydrates and water should be consumed as well. The recommended ratio from nutrition experts for exercise-recovery foods is 4 grams of carbohydrates to 1 gram of protein.

In response to hard training, a person’s body also adapts by becoming more efficient in metabolizing nutrient fuels both for energy production and building macromolecules. However, this raises another question: if athletes are more efficient at using protein, is it necessary to take in more protein from dietary sources than the average person? There are two scientific schools of thought on this matter. One side believes athletes need more protein and the other thinks the protein requirements of athletes are the same as for nonathletes. There is scientific evidence to support both sides of this debate. The consensus of both sides is that few people exercise at the intensity that makes this debate relevant. It is good to remember that the increased protein intake recommended by the AND, American College of Sports Medicine, and Dietitians of Canada still lies within the AMDR for protein.

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Interactive 6.6

Visit “Nutrition 101, Eating for Exercise and Sports.” This USDA site contains a wealth of nutritional information for active people.

http://1.usa.gov/ML3RJj

Protein Supplements

Protein supplements include powders made from compounds such as whey or soy and amino acids that either come as a powder or in capsules. We have noted that the protein requirements for most people, even those that are active, is not high. Is taking protein supplements ever justified, then? Neither protein nor amino acid supplements have been scientifically proven to improve exercise performance or increase strength. In addition, the average American already consumes more protein than is required. Despite these facts, many highly physically active individuals use protein or amino acid supplements. According to the AND, American College of Sports Medicine, and Dietitians of Canada, “the current evidence indicates that protein and amino acid supplements are no more or no less effective than food when energy is adequate for gaining lean body mass.”American College of Sports Medicine, Academy of Nutrition and Dietetics, and Dietitians of Canada. “Joint Position Statement: Nutrition and Athletic Performance.” Med Sci Sports Exerc 41, no. 3 (March 2009). doi: 10.1249/MSS.0b013e31890eb86. Branched-chain amino acids, such as leucine, are often touted as a way to build muscle tissue and enhance athletic performance. Despite these marketing claims, a review in the June 2005 issue of The Journal of Nutrition shows that most studies that evaluated a variety of exercise types failed to show any performance-enhancing effects of taking branched-chain amino acids.Gleeson, M. “Interrelationship between Physical Activity and Branched-Chain Amino Acids.” J Nutr 135, no. 6, supplement (June 1, 2005): 1591S–5S. http://jn.nutrition.org/content/135/6/1591S.long. Moreover, the author of this review claims that high-quality protein foods are a better and cheaper source for branched-chain amino acids and says that a chicken breast (100 grams) contains the equivalent of seven times the amount of branched-chain amino acids as one supplement tablet. This means if you are interested in enhancing exercise performance or building muscle, you do not need to support the $20 billion supplement industry.

Although the evidence for protein and amino acid supplements impacting athletic performance is lacking, there is some scientific evidence that supports consuming

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high-quality dairy proteins, such as casein and whey, and soy proteins positively influences muscle recovery in response to hard training. If you choose to buy a bucket of whey protein, use it to make a protein shake after an intense workout and do not add more than what is required to obtain 20 to 25 grams of protein. As always, choosing high-quality protein foods will help you build muscle and not empty your wallet as much as buying supplements. Moreover, relying on supplements for extra protein instead of food will not provide you with any of the other essential nutrients. The bottom line is that whether you are an endurance athlete or strength athlete, or just someone who takes Zumba classes, there is very little need to put your money into commercially sold protein and amino acid supplements. The evidence to show that they are superior to regular food in enhancing exercise performance is not sufficient.

What about the numerous protein shakes and protein bars on the market? Are they a good source of dietary protein? Do they help you build muscle or lose weight as marketers claim? These are not such a bad idea for an endurance or strength athlete who has little time to fix a nutritious exercise-recovery snack. However, before you ingest any supplement, do your homework. Read the label, be selective, and don’t use them to replace meals, but rather as exercise-recovery snacks now and then. Some protein bars have a high amount of carbohydrates from added sugars and are not actually the best source for protein, especially if you are not an athlete. Protein bars are nutritionally designed to restore carbohydrates and protein after endurance or strength training; therefore they are not good meal replacements. If you want a low-cost alternative after an intense workout, make yourself a peanut butter sandwich on whole-grain bread and add some sliced banana for less than fifty cents. Supermarket and healthfood-store shelves offer an extraordinary number of high-protein shake mixes. While the carbohydrate count is lower now in some of these products than a few years ago, they still contain added fats and sugars. They also cost, on average, more than two dollars per can. If you want more nutritional bang for your buck, make your own shakes from whole foods. Use the AMDRs for macronutrients as a guide to fill up the blender. Your homemade shake can now replace some of the whole foods on your breakfast, lunch, or dinner plate. Unless you are an endurance or strength athlete and consume commercially sold protein bars and shakes only postexercise, these products are not a good dietary source of protein.

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Proteins in a Nutshell

Proteins are long chains of amino acids folded into precise structures that determine their functions, which are in the tens of thousands. They are the primary construction materials of the body serving as building blocks for bone, skin, hair, muscle, hormones, and antibodies. Without them we cannot breakdown or build macromolecules, grow, or heal from a wound. Eat proteins in moderation, at least 10 percent of the calories you take in and not more than 35 percent. Too little protein impairs bodily functions and too much can lead to chronic disease. Proteins are in a variety of foods. More complete sources are in animal-based foods, but choose those low in saturated fat and cholesterol. Some plant-based foods are also complete protein sources and don’t add much to your saturated fat or cholesterol intake. Incomplete protein sources can easily be combined in the daily diet and provide all of the essential amino acids at adequate levels. Growing children and the elderly need to ensure they get enough protein in their diet to help build and maintain muscle strength. Even if you’re a hardcore athlete, get your proteins from nutrient-dense foods as you need more than just protein to power up for an event. Nuts are one nutrient-dense food with a whole lot of protein. One ounce of pistachios, which is about fifty nuts, has the same amount of protein as an egg and contains a lot of vitamins, minerals, healthy polyunsaturated fats, and antioxidants. Moreover, the FDA says that eating one ounce of nuts per day can lower your risk for heart disease. Can you be a hardcore athlete and a vegetarian? Many Olympians are vegetarians: figure skater Charlene Wong, sprinter Leroy Burrell, hurdler Edwin Moses, and Carl Lewis, who won ten medals (nine of them gold) in track and field. The analysis of vegetarian diets by the DGAC did not find that they were inadequate in any nutrients, but did state that people who obtain proteins solely from plants should make sure they consume foods with vitamin B12, vitamin D, calcium, omega-3 fatty acids, and choline. Iron and zinc may also be of concern especially for female athletes. Being a vegetarian athlete requires that you pay more attention to what you eat, however this is also a true statement for all athletes. For an exhaustive list that provides the protein, calcium, cholesterol, fat, and fiber content, as well as the number of calories, of numerous foods, go to the website, http://www.soystache.com/protein.htm.

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Getting All the Nutrients You Need—The Plant-Based Way

Below are five ways to assure you are getting all the nutrients you need while working toward a more plant-based diet;

1. Get your protein from foods such as soybeans, tofu, tempeh, lentils, and beans, beans, and more beans. Many of these foods are high in zinc too.

2. Eat foods fortified with vitamins B12 and D and calcium. Some examples are soy milk and fortified cereals.

3. Get enough iron in your diet by eating kidney beans, lentils, whole- grain cereals, and leafy green vegetables.

4. To increase iron absorption, eat foods with vitamin C at the same time.

5. Don’t forget that carbohydrates and fats are required in your diet too, especially if you are training. Eat whole-grain breads, cereals, and pastas. For fats, eat an avocado, add some olive oil to a salad or stir-fry, or spread some peanut or cashew butter on a bran muffin.

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KEY TAKEAWAYS

• The RDA set for protein for adults is 0.8 grams per kilogram of body weight and represents the amount of protein in the diet required to balance the protein that is used up by the body and that is excreted.

• The protein foods group consists of foods made from meat, seafood, poultry, eggs, soy, beans, peas, and seeds.

• By determining a food’s amino acid content and the amount of protein that is actually digested and absorbed we can determine that food’s protein quality.

• Most animal-based proteins are complete protein sources and most plant-based proteins are incomplete protein sources. The exceptions are soy, which is a plant-based complete protein source, and gelatin, which is an incomplete animal-based protein source.

• A vegan’s protein needs are slightly higher because of the lower digestibility of plant-based sources. The elderly may require more protein in their diets to prevent significant muscle wasting. There is debate on whether athletes require more proteins in their diet.

• Protein and amino acid supplements do not enhance exercise performance and do not promote a gain in muscle mass any more so than protein from foods.

• Unless you are an endurance or strength athlete, commercially sold protein bars and shakes are not a good dietary source of protein.

DISCUSSION STARTERS

1. What is the consensus in your class on how easy it is to follow a more plant-based diet?

2. Even though high-protein diets may not cause significant health problems in healthy people, are they a sustainable option for losing weight? What are the consequences to the environment of consuming more and not less animal-based sources of protein?

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6.7 End-of-Chapter Exercises

IT ’S YOUR TURN

1. Calculate your daily protein requirements. 2. List ten of your favorite protein-rich foods and find out the actual

protein contents using the USDA National Nutrient Database, http://www.ars.usda.gov/Services/docs.htm?docid=8964. How easy is it for you to get all the protein you need? Are there some protein-rich food choices that you need to replace with a lower saturated fat alternative?

3. Design a more plant-based menu for a day that you are willing to follow. Make sure it is balanced and has variety. Give examples of the micronutrients (other than protein) the foods contain in appreciable amounts.

APPLY IT

1. In class or at home, use two inexpensive cake mixes. Make one without adding eggs and the other by following the recipe correctly. Bake them and summarize the differences in taste, texture, and structure.

2. Create a recipe for a shake made from your favorite whole foods that has the macronutrients in their recommended ranges. Also list the different micronutrients in your shake. Now that you know the shake is of good nutritional value, conduct a taste test on your friends or family.

3. Read these articles about nutrition in the future http://www.nature.com/nature/journal/v468/n7327_supp/full/ 468S21a.html and http://www.nature.com/nature/journal/v468/ n7327_supp/full/468S10a.html.

4. Summarize three basic points about how tailoring the diet can reduce the risk for chronic disease.

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EXPAND YOUR KNOWLEDGE

1. Take a trip to a nearby ethnic market and either write down the names of certain foods or purchase a few interesting ones. At home, use the USDA National Nutrient Database to find out the protein contents and other nutrients in the new food items. If you cannot find values for these new foods, try these websites: http://many-calories.com/, http://www.myfitnesspal.com/nutrition-facts-calories/chinese-food and http://caloriecount.about.com/calories-ethnic-foods-ic3500.

2. Plan a menu for one week that is completely plant-based. Look up the whole nutrient package for the items in your menu by visiting the website, http://www.ars.usda.gov/Services/docs.htm?docid=17032. Follow your diet plan. Record some basic health parameters, such as blood pressure and body weight, before and after following your menu plan. Assess how you feel in general after following the diet. Are you less tired or more? Are you irritable or happy? Did you exercise with more intensity or less?

3. Seafood is a good source of high-quality protein. The DGAC has assessed the nutrient adequacy of diets high in seafood. Read the following document and plan a weekly menu where you consume at least 8 ounces of seafood. http://1.usa.gov/OXdk2X

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Chapter 7

Nutrients Important to Fluid and Electrolyte Balance

Big Idea

Heed your thirst and drink up, but drink mostly water.

Maintaining the right level of water in your body is crucial to survival, as either too little or too much water in your body will result in less-than-optimal functioning. One mechanism to help ensure the body maintains water balance is thirst. Thirst is the result of your body’s physiology telling your brain to initiate the thought to take a drink. Sensory proteins detect when your mouth is dry, your blood volume too low, or blood electrolyte concentrations too high and send signals to the brain stimulating the conscious feeling to drink.

In the summer of 1965, the assistant football coach of the University of Florida Gators requested scientists affiliated with the university study why the withering heat of Florida caused so many heat-related illnesses in football players and provide a solution to increase athletic performance and recovery post-training or game. The discovery was that inadequate replenishment of fluids, carbohydrates, and electrolytes was the reason for the “wilting” of their football players. Based on

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Drinking Water Filter Singapore by Priyanka Sharma comprises public domain material worldwide.

their research, the scientists concocted a drink for the football players containing water, carbohydrates, and electrolytes and called it “Gatorade.” In the next football season the Gators were nine and two and won the Orange Bowl. The Gators’ success launched the sports-drink industry, which is now a multibillion-dollar industry that is still dominated by Gatorade.

The latest National Health and Nutrition Examination Survey, covering the period from 2005 to 2008, reports that about 50 percent of Americans consume sugary drinks daily.Ogden, C. et al. “Consumption of Sugar Drinks in the United States, 2005–2008.” Centers for Disease Control and Prevention. NCHS Data Brief, no. 71 (August 2011). http://www.cdc.gov/nchs/data/databriefs/db71.htm. Excess consumption of sugary soft drinks have been scientifically proven to increase the risk for dental caries, obesity, Type 2 diabetes, and cardiovascular disease. In addition to sugary soft drinks, beverages containing added sugars include fruit drinks, sports drinks, energy drinks and sweetened bottled waters. In Chapter 4 “Carbohydrates” we considered in detail the effects of sugary soft drinks on health. In this chapter we will consider sports drinks. Sports drinks are designed to rehydrate the body after excessive fluid depletion. Electrolytes in particular promote normal rehydration to prevent fatigue during physical exertion. Are they a good choice for achieving the recommended fluid intake? Are they performance and endurance enhancers like they claim? Who should drink them?

Typically, eight ounces of a sports drink provides between fifty and eighty calories and 14 to 17 grams of carbohydrate, mostly in the form of simple sugars. Sodium and potassium are the most commonly included electrolytes in sports drinks, with the levels of these in sports drinks being highly variable. The American College of Sports Medicine says a sports drink should contain 125 milligrams of sodium per 8 ounces as it is helpful in replenishing some of the sodium lost in sweat and promotes fluid uptake in the small intestine, improving hydration.

You Decide

Are there better beverage options than sugary soft drinks and sports drinks to satisfy your thirst?

In this chapter we will consider the importance of maintaining fluid and electrolyte balance in the human body, the functions of water and electrolytes in the body, the consequences of getting too much or too little of water and electrolytes, the best dietary sources of these nutrients, and healthier beverage choices. After reading

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this chapter you will know what to look for in sports drinks and will be able to select the best products to keep hydrated.

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7.1 Overview of Fluid and Electrolyte Balance

LEARNING OBJECTIVE

1. Define osmosis.

A human body is made up of mostly water. An adult consists of about 37 to 42 liters of water, or about eighty pounds. Fortunately, humans have compartmentalized tissues; otherwise we might just look like a water balloon! Newborns are approximately 70 percent water. Adult males typically are composed of about 60 percent water and females are about 55 percent water. (This gender difference reflects the differences in body-fat content, since body fat is practically water-free. This also means that if a person gains weight in the form of fat the percentage of total body water content declines.) As we age total body water content also diminishes so that by the time we are in our eighties the percent of water in our bodies has decreased to around 45 percent. Does the loss in body water play a role in the aging process? Alas, no one knows. But, we do know that dehydration accelerates the aging process whereas keeping hydrated decreases headaches, muscle aches, and kidney stones. Additionally a study conducted at the Fred Hutchinson Cancer Research Center in Seattle found that women who drank more than five glasses of water each day had a significantly decreased risk for developing colon cancer.Shannon J. E. et al. “Relationship of Food Groups and Water Intake to Colon Cancer Risk.” Cancer Epidemiol Biomarkers Prev 5, no. 7 (1996): 495–502. http://cebp.aacrjournals.org/content/5/7/495.long.

Fluid and Electrolyte Balance

Although water makes up the largest percentage of body volume, it is not actually pure water but rather a mixture of cells, proteins, glucose, lipoproteins, electrolytes, and other substances. Electrolytes1 are substances that, when dissolved in water, disassociate into charged ions. Positively charged electrolytes are called cations and negatively charged electrolytes are called anions. For example, in water sodium chloride (the chemical name for table salt) dissasociates into sodium cations (Na+) and chloride anions (Cl−). Solutes2 refers to all dissolved substances in a fluid, which may be charged, such as sodium (Na+), or uncharged, such as glucose. In the human body, water and solutes are distributed into two compartments: inside cells, called intracellular, and outside cells, called extracellular. The extracellular water compartment is subdivided into the spaces between cells (interstitial), blood plasma, and other bodily fluids (such as cerebrospinal fluid which surrounds and protects the brain and spinal cord). The

1. Substances that when dissolved in water disassociate into charged ions.

2. Any dissolved substances in a fluid.

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composition of solutes differs between the fluid compartments. For instance, more protein is inside cells than outside and more chloride anions exist outside of cells than inside.

Osmoregulation

One of the essential homeostatic functions of the body is to maintain fluid balance and the differences in solute composition between cells and their surrounding environment. Osmoregulation3 is the control of fluid balance and composition in the body. The processes involved keep fluids from becoming too dilute or too concentrated. Fluid compartments are separated by selectively permeable membranes, which allow some things, such as water, to move through while other substances require special transport proteins, channels, and often energy. The movement of water between fluid compartments happens by osmosis4, which is simply the movement of water through a selectively permeable membrane from an area where it is highly concentrated to an area where it is not so concentrated. Water is never transported actively; that is, it never takes energy for water to move between compartments. Although cells do not directly control water movement, they do control movement of electrolytes and other solutes and thus indirectly regulate water movement by controlling where there will be regions of high and low concentrations.

Cells maintain their water volume at a constant level, but the composition of solutes in a cell is in a continuous state of flux. This is because cells are bringing nutrients in, metabolizing them, and disposing of waste products. To maintain water balance a cell controls the movement of electrolytes to keep the total number of dissolved particles, called osmolality5 the same inside and outside (Figure 7.1). The total number of dissolved substances is the same inside and outside a cell, but the composition of the fluids differs between compartments. For example, sodium exists in extracellular fluid at fourteen times the concentration as compared to that inside a cell.

3. The scientific term that refers to the control of fluid balance and composition in the body.

4. The movement of water through a selectively permeable membrane from an area where it is highly concentrated to an area where it is not as concentrated.

5. The total number of dissolved particles in a solvent, such as water.

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Figure 7.1

Cells maintain water volume by actively controlling electrolyte concentrations.

Osmotic Flow Isotonic by Blausen.com staff, from the Wikiversity Journal of Medicine, is available under a Creative Commons Attribution 3.0 Unported license. Osmotic Flow Hypotonic by Blausen.com staff, from the Wikiversity Journal of Medicine, is available under a Creative Commons Attribution 3.0 Unported license. Osmotic Flow Hypertonic by Blausen.com staff, from the Wikiversity Journal of Medicine, is available under a Creative Commons Attribution 3.0 Unported license.

If a cell is placed in a solution that contains fewer dissolved particles (known as a hypotonic solution) than the cell itself, water moves into the more concentrated cell, causing it to swell (Figure 7.1). Alternatively, if a cell is placed in a solution that is more concentrated (known as a hypertonic solution) water moves from inside the cell to the outside, causing it to shrink. Cells keep their water volume constant by pumping electrolytes in and out in an effort to balance the concentrations of dissolved particles on either side of their membranes. When a solution contains an equal concentration of dissolved particles on either side of the membrane, it is known as an isotonic solution.

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KEY TAKEAWAYS

• A human body is mostly water. • Movement of water is regulated by controlling the movement of

electrolytes between fluid compartments. • While water makes up the largest percentage of body volume it is not

pure water but a mixture of water, cells, proteins, glucose, lipoproteins, electrolytes and other substances.

• In the human body water and solutes are distributed into two compartments; inside cells, called intracellular, and outside cells, called extracellular.

• One of the essential homeostatic functions, called osmoregulation of the body is to maintain fluid balance and the differences in composition between fluid compartments.

• The movement of water between fluid compartments happens by the process of osmosis.

• Water is never transported actively; that is, it never takes special proteins and energy for water to move between compartments, it simply flows from an area of high concentration to an area where its concentration is lower.

• Under normal circumstances, a cell maintains its water volume at a constant level, but the composition of solutes in a cell is in a continuous state of flux.

• To maintain water balance a cell controls the movement of electrolytes to keep the total number of dissolved particles the same inside and outside.

DISCUSSION STARTERS

1. If the membrane surrounding a cell was permeable to sodium what would happen to the concentration of sodium inside and outside a cell?

2. Discuss why maintaining fluid homeostasis is a dynamic process.

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Water is the foundation of all life—the surface of the earth is 70 percent water; the volume of water in humans is about 60 percent. Earth by WikiImages comprises public domain material worldwide.

7.2 Water’s Importance to Vitality

LEARNING OBJECTIVE

1. Describe the four major functions of water in the human body.

You get up in the morning, flush wastes down the toilet, take a shower, brush your teeth, drink, eat, drive, wash the grime from your windshield, get to work, and drink coffee. Next to a fountain you eat lunch and down it with a glass of water, you use the toilet again and again, drive home, prepare dinner, etc. Add all the ways you use water every day and you still will not come close to the countless uses water has in the human body. Of all the nutrients, water is the most critical as its absence proves lethal within a few days. Organisms have adapted numerous mechanisms for water conservation. Water uses in the human body can be loosely categorized into four basic functions: transportation vehicle, medium for chemical reactions, lubricant/shock absorber, and temperature regulator.

Water As a Transportation Vehicle

Water is called the “universal solvent” because more substances dissolve in it than any other fluid. Molecules dissolve in water because of the hydrogen and oxygen molecules ability to loosely bond with other molecules. Molecules of water (H2O) surround substances, suspending them in a sea of water molecules. The solvent action of water allows for substances to be more readily transported. A pile of undissolved salt would be difficult to move throughout tissues, as would a bubble of gas or a glob of fat. Blood, the primary transport fluid in the body is about 78 percent water. Dissolved substances in blood include proteins, lipoproteins, glucose, electrolytes, and metabolic waste products, such as carbon dioxide and urea, all of which are either dissolved in the watery surrounding of blood to be transported to cells to support basic functions or are removed from cells to prevent waste build-up and toxicity. Blood is not just the primary vehicle of transport in the body, but also as a fluid tissue blood structurally supports blood vessels that would collapse in its absence. Similarly, the brain is 75 percent water, with the water in the brain providing structure.

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Water As a Medium for Chemical Reactions

Water is required for even the most basic chemical reactions. In Chapter 6 “Proteins” you learned that enzymes are proteins and proteins fold into their functional shape based on how their amino-acid sequences react with water. Once formed, enzymes must conduct their specific chemical reactions in a medium, which in all organisms is water. Water is an ideal medium for chemical reactions as it can store a large amount of heat, is electrically neutral, and has a pH of 7.0, meaning it is not acidic or basic. Additionally, water is involved in many enzymatic reactions as an agent to break bonds or, by its removal from a molecule, to form bonds.

Water As a Lubricant/Shock Absorber

Many may view the slimy products of a sneeze as gross, but sneezing is essential for removing irritants and could not take place without water. Mucus, which is not only essential to discharge nasal irritants, but also required for breathing, transportation of nutrients along the gastrointestinal tract, and elimination of waste materials through the rectum is composed of more than 90 percent water. Mucus is a front-line defense against injury and foreign invaders. It protects tissues from irritants, entraps pathogens, and contains immune-system cells that destroy pathogens. Water is the main component of the lubricating fluid between joints and eases the movement of articulated bones.

The aqueous and vitreous humors, which are fluids that fill the extra space in the eyes and the cerebrospinal fluid surrounding the brain and spinal cord are primarily water and buffer these organs against sudden changes in the environment. Watery fluids surrounding organs provide both chemical and mechanical protection. Just two weeks after fertilization water fills the amniotic sac in a pregnant woman providing a cushion of protection for the developing embryo.

Water As a Temperature Regulator

Another homeostatic function of the body, termed thermoregulation6 is to balance heat gain with heat loss and body water plays an important role in accomplishing this. Human life is supported within a narrow range of temperature, with the temperature set point of the body being 98.6°F (37°C). Too low or too high of a temperature causes enzymes to stop functioning and metabolism is haulted. At 82.4°F (28°C) muscle failure occurs and hypothermia sets in. At the opposite extreme of 111.2°F (44°C) the central nervous system fails and death results. Water is good at storing heat, an attribute referred to as heat capacity7 and thus helps maintain the temperature set point of the body despite changes in the surrounding environment.

6. The balance of heat gain with heat loss in the body.

7. The capability of a substance to store heat.

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There are several mechanisms in place that move body water from place to place as a method to distribute heat in the body and equalize body temperature. The hypothalamus in the brain is the thermoregulatory center. The hypothalamus contains special protein sensors that detect blood temperature. The skin also contains temperature sensors that respond quickly to changes in immediate surroundings. In response to cold sensors in the skin, a neural signal is sent to the hypothalamus, which then sends a signal to smooth muscle tissue surrounding blood vessels causing them to constrict and reduce blood flow. This reduces heat lost to the environment. The hypothalamus also sends signals to muscles to erect hairs and shiver and to endocrine glands like the thyroid to secrete hormones capable of ramping up metabolism. These actions increase heat conservation and stimulate its production in the body in response to cooling temperatures.

When body temperature rises, as what occurs during exercise, the hypothalamus detects an increase in blood temperature. In response, the hypothalamus sends a

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signal to the smooth muscle of blood vessels causing them to dilate so that more blood flows to the body’s periphery. Once on the skin, extra heat exits the body via perspiration (sweat), which is 98 to 99 percent water. Water on the skin’s surface evaporates, a process that takes energy and results in the loss of heat, thereby cooling the body. Perspiration is a process that intertwines temperature homeostasis with fluid and electrolyte homeostasis. Water and electrolytes lost in sweat need to be replenished in order to maintain fluid and electrolyte balance. In Section 7.3 “Regulation of Water Balance”, we will explain the physiological mechanisms that are involved in maintaining fluid and electrolyte balance in the body.

KEY TAKEAWAYS

• Uses of water in the human body can be loosely categorized into four basic functions: transportation vehicle, medium for chemical reactions, lubricant/shock absorber, and temperature regulator.

• Water has been termed the “universal solvent” because more substances dissolve in it than any other fluid. Water is essential to form enzymes and serves as a medium for chemical reactions. Water as a component of body fluids acts as a lubricant and shock absorber.

• Water is good at storing heat and buffers the body against extreme variations in temperature.

• There are several mechanisms that move body water from place to place as a method of heat distribution and temperature equalization.

DISCUSSION STARTERS

1. Refer back to Chapter 5 “Lipids” of this book and discuss why lipids are coated with proteins, forming chylomicrons, prior to absorption.

2. Why do your fingers turn white in the cold?

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7.3 Regulation of Water Balance

LEARNING OBJECTIVES

1. Discuss the physiological events that trigger the thirst mechanism. 2. Describe two mechanisms by which the body controls urine output.

As you eat a bite of food, the salivary glands secrete saliva. As the food enters your stomach, gastric juice is secreted. As it enters the small intestine, pancreatic juice is secreted. Each of these fluids contains a great deal of water. How is that water replaced in these organs? What happens to the water now in the intestines? In a day there is an exchange of about 10 liters of water among the body’s organs. The osmoregulation of this exchange involves complex communication between the brain, kidneys, and endocrine system. A homeostatic goal for a cell, a tissue, an organ, and an entire organism is to balance water output with water input.

Regulation of Daily Water Input

Total water ouput per day averages 2.5 liters. This must be balanced with water input. Our tissues produce around 300 milliliters of water per day through metabolic processes. The remainder of water output must be balanced by drinking fluids and eating solid foods. The average fluid consumption per day is 1.5 liters, and water gained from solid foods approximates 700 milliliters.

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Dietary Gain of Water

The Food and Nutrition Board of the Institute of Medicine (IOM) has set the Adequate Intake (AI) for water for adult males at 3.7 liters (15.6 cups) and at 2.7 liters (11 cups) for adult females.Institute of Medicine Panel on Dietary Reference Intakes for Electrolytes and Water. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. (Washington, D.C.: National Academies Press, 2005). http://www.nap.edu/openbook.php?record_id=10925&page=73. These intakes are higher than the average intake of 2.2 liters. It is important to note that the AI for water includes water from all dietary sources; that is, water coming from food as well as beverages. People are not expected to consume 15.6 or 11 cups of pure water per day. In America, approximately 20 percent of dietary water comes from solid foods.

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There is some debate over the amount of water required to maintain health because there is no consistent scientific evidence proving that drinking a particular amount of water improves health or reduces the risk of disease. In fact, kidney-stone prevention seems to be the only premise for water-consumption recommendations. You may be surprised to find out that the commonly held belief that people need to drink eight 8-ounce glasses of water per day isn’t an official recommendation and isn’t based on any scientific evidence! The amount of water/fluids a person should consume every day is actually variable and should be based on the climate a person lives in, as well as their age, physical activity level, and kidney function. No maximum for water intake has been set.

Thirst Mechanism: Why Do We Drink?

Thirst8 is an osmoregulatory mechanism to increase water input. The thirst mechanism is activated in response to changes in water volume in the blood, but is even more sensitive to changes in blood osmolality. Blood osmolality is primarily

8. An osmoregulatory mechanism to increase water input.

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driven by the concentration of sodium cations. The urge to drink results from a complex interplay of hormones and neuronal responses that coordinate to increase water input and contribute toward fluid balance and composition in the body. The “thirst center” is contained within the hypothalamus, a portion of the brain that lies just above the brain stem. In older people the thirst mechanism is not as responsive and as we age there is a higher risk for dehydration. Thirst happens in the following sequence of physiological events:

1. Receptor proteins in the kidney, heart, and hypothalamus detect decreased fluid volume or increased sodium concentration in the blood.

2. Hormonal and neural messages are relayed to the brain’s thirst center in the hypothalamus.

3. The hypothalamus sends neural signals to higher sensory areas in the cortex of the brain, stimulating the conscious thought to drink.

4. Fluids are consumed. 5. Receptors in the mouth and stomach detect mechanical movements

involved with fluid ingestion. 6. Neural signals are sent to the brain and the thirst mechanism is shut

off.

The physiological control of thirst is the back-up mechanism to increase water input. Fluid intake is controlled primarily by conscious eating and drinking habits dependent on social and cultural influences. For example, you might have a habit of drinking a glass of orange juice and eating a bowl of cereal every morning before school or work. Most American adolescents have a daily habit of soft-drink consumption. Soft-drink consumption is influenced by demographics, access to soft drinks, social impacts, and personal behavior.

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Regulation of Daily Water Output

Figure 7.4 Kidneys

A primary function of the kidneys is to filter blood and remove wastes. They play a major role in fluid and electrolyte balance.

Kidney Anatomy by Blausen.com staff, from the Wikiversity Journal of Medicine, is available under a Creative Commons Attribution 3.0 Unported license.

As stated, daily water output averages 2.5 liters. There are two types of outputs. The first type is insensible water loss, meaning we are unaware of it. The body loses about 400 milliliters of its daily water output through exhalation. Another 500 milliliters is lost through our skin. The second type of output is sensible water loss, meaning we are aware of it. Urine accounts for about 1,500 milliliters of water output, and feces account for roughly 100 milliliters of water output. Regulating urine output is a primary function of the kidneys, and involves communication with the brain and endocrine system.

The Kidneys Detect Blood Volume

The kidneys are two bean-shaped organs, each about the size of a fist and located on either side of the spine just below the rib cage (Figure 7.4 “Kidneys”). The kidneys filter about 190 liters of blood and produce (on average) 1.5 liters of urine per day. Urine is mostly water, but it also contains electrolytes and waste products, such as

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urea. The amount of water filtered from the blood and excreted as urine is dependent on the amount of water in, and the electrolyte composition of, blood.

Kidneys have protein sensors that detect blood volume from the pressure, or stretch, in the blood vessels of the kidneys. When blood volume is low, kidney cells detect decreased pressure and secrete the enzyme, renin. Renin travels in the blood and cleaves another protein into the active hormone, angiotensin. Angiotensin targets three different organs (the adrenal glands, the hypothalamus, and the muscle tissue surrounding the arteries) to rapidly restore blood volume and, consequently, pressure.

First, angiotensin travels to the outer perimeter of the adrenal glands and stimulates release of the hormone aldosterone. Aldosterone travels back to the kidneys and stimulates the sodium-potassium pump. As a result of the pump’s work, the blood reabsorbs the sodium from the liquid that has already been filtered by the kidneys. Water follows sodium into the blood by osmosis, resulting in less water in the urine and restored fluid balance and composition of blood.

Next, angiotensin travels to the hypothalamus where it stimulates the thirst mechanism and the release of antidiuretic hormone. Antidiuretic hormone travels back to the kidneys where it increases water reabsorption.

Lastly, angiotensin targets smooth muscle tissue surrounding arteries, causing them to contract (narrow) the blood vessels, which assists in elevating blood pressure.

The Hypothalamus Detects Blood Osmolality

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Osmoreceptors (specialized protein receptors) in the hypothalamus detect sodium concentration in the blood. In response to a high sodium level, the hypothalamus activates the thirst mechanism and concurrently stimulates the release of antidiuretic hormone. Thus, it is not only kidneys that stimulate antidiuretic- hormone release, but also the hypothalamus. This dual control of antidiuretic hormone release allows for the body to respond to both decreased blood volume and increased blood osmolality.

The Adrenal Glands Detect Blood Osmolality

Cells in the adrenal glands sense when sodium levels are low, and when potassium levels are high, in the blood. In response to either stimulus, they release aldosterone. Therefore, aldosterone is released in response to angiotensin stimulation and is also controlled by blood electrolyte concentrations. In either case, aldosterone communicates the same message, which is to increase sodium reabsorption and consequently water reabsorption. In exchange, potassium is excreted.

The mechanisms involved in regulating water input and output are intertwined with those controlling electrolyte balance. In a healthy individual, this multilevel coordinated control of fluid and electrolyte levels in the body ensures homeostasis. However, in a person with heart failure, the crosstalk between organs can have dire consequences. Heart failure results in a decrease in blood output from the heart, which lowers blood pressure. In response to the lower blood pressure the kidneys release renin, leading to the release of antidiuretic hormone. Antidiuretic hormone acts on the kidneys and increases water reabsorption, thereby increasing blood volume and pressure. This makes the heart work harder and exacerbates the heart condition. To block this response, people with heart failure are treated with drugs that block the kidneys’ compensatory response. Diuretics are drugs that act either by inhibiting the actions of antidiuretic hormone or by promoting sodium excretion in the urine. This increases water output and blood pressure is reduced. Diuretics, along with other drugs, are useful in treating heart failure and in decreasing blood pressure in people with hypertension.

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KEY TAKEAWAYS

• A homeostatic goal for a cell, tissue, organ, and entire organism is to balance water ouptut with water input. The amount of water a person should consume everyday is variable and should be based on the climate a person lives in, as well as their age, physical activity level, and kidney function.

• Thirst results from a complex interaction of hormones and neuronal responses that coordinate to achieve fluid balance and composition in the body. Thirst is triggered by either a decrease in blood volume or an increase in blood osmolality.

• Other mechanisms by which body water balance is maintained are aimed at controlling the water volume of urine. The amount of water filtered from the blood and excreted as urine is dependent upon the amount of water in blood and the electrolyte composition of blood.

• The regulation of water output involves complex communication between the kidneys, hypothalamus, and endocrine glands.

DISCUSSION STARTERS

1. Why do people urinate more often when it is cold outside? 2. Discuss the signs you first detect when you are thirsty.

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7.4 Electrolytes Important for Fluid Balance

LEARNING OBJECTIVE

1. Explain the role of the electrolytes sodium, potassium, and chloride in fluid balance.

Cells are about 75 percent water and blood plasma is about 95 percent water. Why then, does the water not flow from blood plasma to cells? The maintenance of the unequal volumes of water between fluid compartments is achieved by balancing the force of water (hydrostatic pressure) against the force of all dissolved substances. Concentration9 means the amount of particles in a set volume of water. (Recall that individual solutes can differ in concentration between the intracellular and extracellular fluids, but the total concentration of all dissolved substances is equal.)

The force driving the water movement through the selectively permeable membrane is the higher solute concentration on the one side. Solutes at different concentrations on either side of a selectively permeable membrane exert a force, called osmotic pressure10. The higher concentration of solutes on one side compared to the other of the U-tube exerts osmotic pressure, pulling the water to a higher volume on the side of the U-tube containing more dissolved particles. When the osmotic pressure is equal to the pressure of the water on the selectively permeable membrane, net water movement stops (though it still diffuses back and forth at an equal rate).

One equation exemplifying equal concentrations but different volumes is the following

5 grams of glucose in 1 liter = 10 grams of glucose in 2 liters (5g/L = 5g/L)

The differences in concentrations of particular substances provide concentration gradients that cells can use to perform work. A concentration gradient is a form of potential energy, like water above a dam. When water falls through a dam the potential energy is changed to moving energy (kinetic), that in turn is captured by turbines. Similarly, when an electrolyte at higher concentration in the extracellular fluid is transported into a cell, the potential energy is harnessed and used to perform work.

9. The amount of particles in a set volume of water.

10. The force exerted by solutes at different concentrations on either side of a selectively permeable membrane.

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Cells are constantly transporting nutrients in and wastes out. How is the concentration of solutes maintained if they are in a state of flux? This is where electrolytes come into play. The cell (or more specifically the numerous sodium- potassium pumps in its membrane) continuously pumps sodium ions out to establish a chemical gradient. The transport protein, called the glucose symporter, uses the sodium gradient to power glucose movement into the cell. Sodium and glucose both move into the cell. Water passively follows the sodium. To restore balance, the sodium-potassium pump transfers sodium back to the extracellular fluid and water follows (see Note 7.26 “Interactive 7.1”). Every cycle of the sodium- potassium pump involves the movement of three sodium ions out of a cell, in exchange for two potassium ions into a cell. To maintain charge neutrality on the outside of cells every sodium cation is followed by a chloride anion. Every cycle of the pump costs one molecule of ATP (adenosine triphosphate). The constant work of the sodium-potassium pump maintains the solute equilibrium and consequently, water distribution between intracellular and extracellular fluids.

The unequal movement of the positively charged sodium and potassium ions makes intracellular fluid more negatively charged than the extracellular fluid. This charge gradient is another source of energy that a cell uses to perform work. You will soon learn that this charge gradient and the sodium-potassium pump are also essential for nerve conduction and muscle contraction. The many functions of the sodium- potassium pump in the body account for approximately a quarter of total resting energy expenditure.

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Sodium

Sodium, is vital not only for maintaining fluid balance but also for many other essential functions. In contrast to many minerals, sodium absorption in the small intestine is extremely efficient and in a healthy individual all excess sodium is excreted by the kidneys. In fact, very little sodium is required in the diet (about 200 milligrams) because the kidneys actively reabsorb sodium. Kidney reabsorption of sodium is hormonally controlled, allowing for a relatively constant sodium concentration in the blood.

Other Functions of Sodium in the Body

The second notable function of sodium is in nerve impulse transmission. Nerve impulse transmission results from the transport of sodium cations into a nerve cell, which creates a charge difference (or voltage) between the nerve cell and its extracellular environment. Similar to how a current moves along a wire, a sodium current moves along a nerve cell. Stimulating a muscle contraction also involves the movement of sodium ions as well as other ion movements. For a muscle to contract, a nerve impulse travels to a muscle. The movement of the sodium current in the nerve communicates to the muscle by releasing the neurotransmitter, acetylcholine. Acetylcholine signals sodium channels in the muscle to open and sodium rushes in, creating another current that travels along the muscle eventually

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culminating in contraction. In both the nerve cell and the muscle cell, the sodium that went in during a stimulus now has to be moved out by the sodium-potassium pump.

Sodium is essential for nutrient absorption in the small intestine and also for nutrient reabsorption in the kidney. Amino acids, glucose, and water must make their way from the small intestine to the blood. To do so they pass through intestinal cells on their way to the blood. The transport of nutrients through intestinal cells is facilitated by the sodium-potassium pump, which by moving sodium out of the cell, creates a higher sodium concentration outside of the cell (requiring ATP).

Sodium Imbalances

Sweating is a homeostatic mechanism for maintaining body temperature, which influences fluid and electrolyte balance. Sweat is mostly water but also contains some electrolytes, mostly sodium and chloride. Under normal environmental conditions (i.e., not hot, humid days) water and sodium loss through sweat is negligible, but is highly variable among individuals. It is estimated that sixty minutes of high-intensity physical activity, like playing a game of tennis, can produce approximately one liter of sweat; however the amount of sweat produced is highly dependent on environmental conditions. A liter of sweat typically contains between 1 and 2 grams of sodium and therefore exercising for multiple hours can result in a high amount of sodium loss in some people. Additionally, hard labor can produce substantial sodium loss through sweat. In either case, the lost sodium is easily replaced in the next snack or meal.

In athletes hyponatremia, or a low blood-sodium level, is not so much the result of excessive sodium loss in sweat, but rather drinking too much water. The excess water dilutes the sodium concentration in blood. Illnesses causing vomiting, sweating, and diarrhea may also cause hyponatremia. The symptoms of hyponatremia, also called water intoxication since it is often the root cause, include nausea, muscle cramps, confusion, dizziness, and in severe cases, coma and death. The physiological events that occur in water intoxication are the following:

1. Excessive sodium loss and/or water intake. 2. Sodium levels fall in blood and in the fluid between cells. 3. Water moves to where solutes are more concentrated (i.e. into cells). 4. Cells swell. 5. Symptoms, including nausea, muscle cramps, confusion, dizziness, and

in severe cases, coma and death result.

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Hyponatremia in endurance athletes (such as marathon runners) can be avoided by drinking the correct amount of water, which is about 1 cup every twenty minutes during the event. Sports drinks are better at restoring fluid and blood-glucose levels than replacing electrolytes. During an endurance event you would be better off drinking water and eating an energy bar that contains sugars, proteins, and electrolytes. The American College of Sports Medicine suggests if you are exercising for longer than one hour you eat one high carbohydrate (25–40 grams) per hour of exercise along with ample water. Convertino, V. A. et al. “American College of Sports Medicine Position Stand. Exercise and Fluid Replacement.” US National Library of Medicine, National Institutes of Health. Medicine and Science in Sports and Exercise 28, no. 1 (January 1996): i–vii. http://www.ncbi.nlm.nih.gov/pubmed/9303999. Watch out for the fat content, as sometimes energy bars contain a hefty dose. If you’re not exercising over an hour at high intensity, you can skip the sports drinks, but not the water. For those who do not exercise or do so at low to moderate intensity, sports drinks are another source of extra calories, sugar, and salt.

Needs and Dietary Sources of Sodium

The IOM has set an AI level for sodium for healthy adults between the ages of nineteen and fifty at 1.5 grams (1,500 milligrams). Table salt is approximately 40 percent sodium and 60 percent chloride. As a reference point, only ⅔ teaspoon of salt is needed in the diet to meet the AI for sodium. The AI takes into account the amount of sodium lost in sweat during recommended physical activity levels and additionally provides for the sufficient intake of other nutrients, such as chloride, meaning that to get all the other nutrients in our diet, we have to allow for a higher intake of sodium. The Tolerable Upper Intake Level (UL) for sodium is 2.3 grams per day for adults. (Just over 1 teaspoon of salt contains the 2.3 grams of sodium recommended). The UL is considered appropriate for healthy individuals but not those with hypertension (high blood pressure). The IOM estimates that greater than 95 percent of men and 75 percent of women in America consume salt in excess of the UL. Many scientific studies demonstrate that reducing salt intake prevents hypertension, is helpful in reducing blood pressure after hypertension is diagnosed, and reduces the risk for cardiovascular disease. The IOM recommends that people over fifty, African Americans, diabetics, and those with chronic kidney disease should consume no more than 1.5 grams of sodium per day. The American Heart Association (AHA) states that all Americans, not just those listed, should consume less than 1.5 grams of sodium per day to prevent cardiovascular disease. The AHA recommends this

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because millions of people have risk factors for hypertension and there is scientific evidence supporting that lower-sodium diets are preventive against hypertension.

Food Sources for Sodium

Most sodium in the typical American diet comes from processed and prepared foods. Manufacturers add salt to foods to improve texture and flavor, and also as a preservative. The amount of salt in similar food products varies widely. Some foods, such as meat, poultry, and dairy foods, contain naturally-occurring sodium. For example, one cup of low-fat milk contains 107 milligrams of sodium. Naturally- occurring sodium accounts for less than 12 percent of dietary intake in a typical diet.

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Table 7.3 Sodium Contents of Selected Foods

Food Group Serving Size Sodium (mg)

Breads, all types 1 oz. 95–210

Rice Chex cereal 1 ¼ c. 292

Raisin Bran cereal 1 c. 362

Granola bar 1 bar 83

Frozen pizza, plain, cheese 4 oz. 450–1200

Frozen vegetables, all types ½ c. 2–160

Salad dressing, regular fat, all types 2 Tbsp. 110–505

Salsa 2 Tbsp. 150–240

Soup (tomato), reconstituted 8 oz. 700–1260

Tomato juice 8 oz. (~1 c.) 340–1040

Potato chips 1 oz. (28.4 g) 120–180

Tortilla chips 1 oz. (28.4 g) 105–160

Pretzels 1 oz. (28.4 g) 290–560

Potato 1 medium 1–5

Pork 3 oz. 59

Chicken (½ breast) 69

Chicken fast food dinner 2243

Chicken noodle soup 1 c. 1107

Ham 3 oz. 1114

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Food Group Serving Size Sodium (mg)

Dill pickle 1 928

Sweet pickle 1 128

Soy sauce 1 Tbsp. 1029

Corn on cob 1 ear 1

Canned corn 1 c. 384

Baked beans, canned 1 c. 856

Hot dog 1 639

Burger, fast-food 1 990

Catsup 1 Tbsp. 156

Steak 3 oz. 55

Canned tuna 3 oz. 384

Fresh tuna 3 oz. 50

Dry-roasted peanuts 1 c. 986

Cheddar cheese 1 oz. 176

American cheese 1 oz. 406

Tap water 8 oz. 12

Interactive 7.2

To find out the sodium content of other foods visit the USDA National Nutrient Database for Standard Reference, Release 17.

http://www.nal.usda.gov/fnic/foodcomp/Data/SR17/wtrank/sr17a307.pdf.

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The Nutrition Facts panel displays the amount of sodium (in milligrams) per serving of the food in question. Food additives are often high in sodium, for example, monosodium glutamate (MSG) contains 12 percent sodium. Additionally, baking soda, baking powder, disodium phosphate, sodium alginate, and sodium nitrate or nitrite contain a significant proportion of sodium. When you see a food’s Nutrition Facts label, you can check the ingredients list to identify the source of the added sodium. Various claims about the sodium content in foods must be in accordance with Food and Drug Administration (FDA) regulations.

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Tools for Change

To decrease your sodium intake, become a salt-savvy shopper by reading the labels and ingredients lists of processed foods and choosing those lower in salt. Even better, stay away from processed foods and control the seasoning of your foods. Eating a diet with less salty foods diminishes salt cravings so you may need to try a lower sodium diet for a week or two before you will be satisfied with the less salty food.

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Salt Substitutes

For those with hypertension or those looking for a way to decrease salt use, using a salt substitute for food preparation is one option. However, many salt substitutes still contain sodium, just in lesser amounts than table salt. Also, remember that most salt in the diet is not from table-salt use, but from processed foods. Salt substitutes often replace the sodium with potassium. People with kidney disorders often have problems getting rid of excess potassium in the diet and are advised to avoid salt substitutes containing potassium. People with liver disorders should also avoid salt substitutes containing potassium because their treatment is often accompanied by potassium dysregulation.

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Alternative Seasonings

Table salt may seem an essential ingredient of good food, but there are others that provide alternative taste and zest to your foods.

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Tools for Change

Do you think many alternative spices are too expensive? Spices are much cheaper in bulk, and many grocery stores and ethnic markets carry them in this way. For example, when purchased in bulk, cumin is, on average, only one dollar per ounce, a quantity that takes many meals to exhaust.

Chloride

Chloride is the primary anion in extracellular fluid. In addition to passively following sodium, chloride has its own protein channels that reside in cell

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membranes. These protein channels are especially abundant in the gastrointestinal tract, pancreas, and lungs.

Chloride’s Role in Fluid Balance

Chloride aids in fluid balance mainly because it follows sodium in order to maintain charge neutrality. Chloride channels also play a role in regulating fluid secretion, such as pancreatic juice into the small intestine and the flow of water into mucus. Fluid secretion and mucus are important for many of life’s processes. Their importance is exemplified in the signs and symptoms of the genetic disease, cystic fibrosis.

Cystic Fibrosis

Cystic fibrosis, or CF, is one of the most prevalent inherited diseases in people of European descent. It is caused by a mutation in a protein that transports chloride ions out of the cell. CF’s signs and symptoms include salty skin, poor digestion and absorption (leading to poor growth), sticky mucus accumulation in the lungs (causing increased susceptibility to respiratory infections), liver damage, and infertility.

When chloride channels do not transport chloride out of cells, the following signs and symptoms of CF become apparent:

1. Salty skin. Defective chloride channels in the sweat glands cause excess release of chloride, which sodium then follows into the sweat.

2. Poor digestion and growth. Defective chloride channels in the pancreas cause pancreatic juices to thicken. As a result of the thickening, the release of pancreatic juices is slowed and nutrient digestion is compromised.

3. Respiratory infection. Defective chloride channels in the lungs cause thickened mucus. The mucus then traps bacteria.

4. Liver damage. Defective chloride channels in the gall bladder cause thickened gall-bladder secretions. The gall-bladder ducts then become blocked, leading to liver damage.

5. Infertility. Defective chloride channels in male and female reproductive organs can result in impaired sperm transport and viscous mucus in the cervix, respectively.

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Other Functions of Chloride

Chloride has several other functions in the body, most importantly in acid-base balance. Blood pH is maintained in a narrow range and the number of positively charged substances is equal to the number of negatively charged substances. Proteins, such as albumin, as well as bicarbonate ions and chloride ions, are negatively charged and aid in maintaining blood pH. Hydrochloric acid (a gastric acid composed of chlorine and hydrogen) aids in digestion and also prevents the growth of unwanted microbes in the stomach. Immune-system cells require chloride, and red blood cells use chloride anions to remove carbon dioxide from the body.

Chloride Imbalances

Low dietary intake of chloride and more often diarrhea can cause low blood levels of chloride. Symptoms typically are similar to those of hyponatremia and include weakness, nausea, and headache. Excess chloride in the blood is rare with no characteristic signs or symptoms.

Needs and Dietary Sources of Chloride

Most chloride in the diet comes from salt. (Salt is 60 percent chloride.) A teaspoon of salt equals 5.6 grams, with each teaspoon of salt containing 3.4 grams of chloride and 2.2 grams of sodium. The chloride AI for adults, set by the IOM, is 2.3 grams. Therefore just ⅔ teaspoon of table salt per day is sufficient for chloride as well as sodium.

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Other Dietary Sources of Chloride

Chloride has dietary sources other than table salt, namely as another form of salt— potassium chloride. Dietary sources of chloride are: all foods containing sodium chloride, as well as tomatoes, lettuce, olives, celery, rye, whole-grain foods, and seafood. Although many salt substitutes are sodium-free, they may still contain chloride.

Bioavailability

In the small intestine, the elements of sodium chloride split into sodium cations and chloride anions. Chloride follows the sodium ion into intestinal cells passively, making chloride absorption quite efficient. When chloride exists as a potassium salt, it is also well absorbed. Other mineral salts, such as magnesium chloride, are not absorbed as well, but bioavailability still remains high.

Potassium

Potassium is the most abundant positively charged ion inside of cells. Ninety percent of potassium exists in intracellular fluid, with about 10 percent in extracellular fluid, and only 1 percent in blood plasma. As with sodium, potassium levels in the blood are strictly regulated. The hormone aldosterone is what primarily controls potassium levels, but other hormones (such as insulin) also play a role. When potassium levels in the blood increase, the adrenal glands release aldosterone. The aldosterone acts on the collecting ducts of kidneys, where it stimulates an increase in the number of sodium-potassium pumps. Sodium is then reabsorbed and more potassium is excreted. Because potassium is required for maintaining sodium levels, and hence fluid balance, about 200 milligrams of potassium are lost from the body every day.

Other Functions of Potassium in the Body

Nerve impulse involves not only sodium, but also potassium. A nerve impulse moves along a nerve via the movement of sodium ions into the cell. To end the impulse,

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potassium ions rush out of the nerve cell, thereby decreasing the positive charge inside the nerve cell. This diminishes the stimulus. To restore the original concentrations of ions between the intracellular and extracellular fluid, the sodium-potassium pump transfers sodium ions out in exchange for potassium ions in. On completion of the restored ion concentrations, a nerve cell is now ready to receive the next impulse. Similarly, in muscle cells potassium is involved in restoring the normal membrane potential and ending the muscle contraction. Potassium also is involved in protein synthesis, energy metabolism, and platelet function, and acts as a buffer in blood, playing a role in acid-base balance.

Imbalances of Potassium

Insufficient potassium levels in the body (hypokalemia) can be caused by a low dietary intake of potassium or by high sodium intakes, but more commonly it results from medications that increase water excretion, mainly diuretics. The signs and symptoms of hypokalemia are related to the functions of potassium in nerve cells and consequently skeletal and smooth-muscle contraction. The signs and symptoms include muscle weakness and cramps, respiratory distress, and constipation. Severe potassium depletion can cause the heart to have abnormal contractions and can even be fatal. High levels of potassium in the blood, or hyperkalemia, also affects the heart. It is a silent condition as it often displays no signs or symptoms. Extremely high levels of potassium in the blood disrupt the electrical impulses that stimulate the heart and can cause the heart to stop. Hyperkalemia is usually the result of kidney dysfunction.

Needs and Dietary Sources of Potassium

The IOM based their AIs for potassium on the levels associated with a decrease in blood pressure, a reduction in salt sensitivity, and a minimal risk of kidney stones. For adult male and females above the age of nineteen, the adequate intake for potassium is 4.7 grams per day.

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Food Sources for Potassium

Fruits and vegetables that contain high amounts of potassium are spinach, lettuce, broccoli, peas, tomatoes, potatoes, bananas, apples and apricots. Whole grains and seeds, certain fish (such as salmon, cod, and flounder), and meats are also high in potassium. The Dietary Approaches to Stop Hypertension (DASH diet) emphasizes potassium-rich foods and will be discussed in greater detail in the next section.

Bioavailability

Greater than 90 percent of dietary potassium is absorbed in the small intestine. Although highly bioavailable, potassium is a very soluble mineral and easily lost during cooking and processing of foods. Fresh and frozen foods are better sources of potassium than canned.

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KEY TAKEAWAYS

• The maintenance of water volume between fluid compartments is achieved by keeping the concentration of all dissolved substances between the compartments the same.

• Individual solutes are at different concentrations between fluid compartments, providing a mechanism by which to control water movement.

• Sodium is the primary regulator of water balance and plays important roles in nerve transmission, muscle contraction, and nutrient absorption and reabsorption.

• Most sodium in the typical American diet comes from processed and prepared foods.

• Chloride aids in fluid balance by helping to maintain charge neutrality. Chloride channels also play a role in regulating fluid secretion, such as the flow of pancreatic juice into the small intestine and the flow of water into mucus.

• Potassium is the most abundant positively charged ion inside of cells, and similar to sodium, potassium levels in the blood are under strict regulatory control. Potassium is the exchanged cation for sodium and helps maintain fluid balance.

DISCUSSION STARTERS

1. Why might high sodium intake cause depletion of potassium in the body?

2. Read the following article from ScienceDaily and discuss why salt is so prevalent in the diet.

http://www.sciencedaily.com/releases/2009/03/ 090310152329.htm

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7.5 Consequences of Deficiency or Excess

LEARNING OBJECTIVES

1. Summarize the following fluid and electrolyte imbalance disorders: dehydration, water intoxication, heat stroke, and hypertension.

2. Describe the DASH diet and state its benefits.

As with all nutrients, having too much or too little water has health consequences. Excessive water intake can dilute the levels of critical electrolytes in the blood. Water intoxication is rare, however when it does happen, it can be deadly. On the other hand, having too little water in the body is common. In fact, diarrhea-induced dehydration is the number-one cause of early-childhood death world-wide. In this section we will discuss subtle changes in electrolytes that compromise health on a chronic basis.

High-Hydration Status: Water Intoxication/Hyponatremia

Water intoxication mainly affects athletes who overhydrate. Water intoxication is extremely rare, primarily because healthy kidneys are capable of excreting up to one liter of excess water per hour. Overhydration was unfortunately demonstrated in 2007 by Jennifer Strange, who drank six liters of water in three hours while competing in a “Hold Your Wee for a Wii” radio contest. Afterward she complained of a headache, vomited, and died.

Low-Hydration Status: Dehydration

Dehydration11 refers to water loss from the body without adequate replacement. It can result from either water loss or electrolyte imbalance, or, most commonly, both. Dehydration can be caused by prolonged physical activity without adequate water intake, heat exposure, excessive weight loss, vomiting, diarrhea, blood loss, infectious diseases, malnutrition, electrolyte imbalances, and very high glucose levels. Physiologically, dehydration decreases blood volume. The water in cells moves into the blood to compensate for the low blood-volume, and cells shrink. Signs and symptoms of dehydration include thirst, dizziness, fainting, headaches, low blood-pressure, fatigue, low to no urine output, and, in extreme cases, loss of consciousness and death. Signs and symptoms are usually noticeable after about 2 percent of total body water is lost.

11. Water loss from the body without adequate replacement.

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Chronic dehydration is linked to higher incidences of some diseases. There is strong evidence that low-hydration status increases the risk for kidney stones and exercise-induced asthma. There is also some scientific evidence that chronic dehydration increases the risk for kidney disease, heart disease, and the development of hyperglycemia in people with diabetes. Older people often suffer from chronic dehydration as their thirst mechanism is no longer as sensitive as it used to be.

Heat Stroke

Heat stroke is a life-threatening condition that occurs when the body temperature is greater than 105.1°F (40.6°C). It is the result of the body being unable to sufficiently cool itself by thermoregulatory mechanisms. Dehydration is a primary cause of heat stroke as there are not enough fluids in the body to maintain adequate sweat production, and cooling of the body is impaired. Signs and symptoms are dry skin (absence of sweating), dizziness, trouble breathing, rapid pulse, confusion, agitation, seizures, coma, and possibly death. Dehydration may be preceded by heat exhaustion, which is characterized by heavy sweating, rapid breathing, and fast pulse. The elderly, infants, and athletes are the most at risk for heat stroke.

Hypertension

Blood pressure12 is the force of moving blood against arterial walls. It is reported as the systolic pressure over the diastolic pressure, which is the greatest and least pressure on an artery that occurs with each heart beat. The force of blood against an artery is measured with a device called a sphygmomanometer. The results are recorded in millimeters of mercury, or mmHg. A desirable blood pressure ranges between 90/60 and 120/80 mmHg. Hypertension13 is the scientific term for high blood pressure and defined as a sustained blood pressure of 140/90 mmHg or greater. Hypertension is a risk factor for cardiovascular disease, and reducing blood pressure has been found to decrease the risk of dying from a heart attack or stroke. The Centers for Disease Control and Prevention (CDC) reported that in 2007–2008 approximately 33 percent of Americans were hypertensive.Centers for Disease Control and Prevention. “FastStats—Hypertension.” Accessed October 2, 2011. http://www.cdc.gov/nchs/fastats/hyprtens.htm. The percentage of people with hypertension increases to over 60 percent in people over the age of sixty.

12. The force of moving blood against arterial walls. It is reported as the systolic pressure over the diastolic pressure, which is the greatest and least pressure on an artery that occurs with each heartbeat.

13. The scientific term for high blood pressure and equivalent to a sustained blood pressure of 140/90 mmHg or greater.

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Blood pressure is measured with a cuff, also known as a sphygmomanometer, that measures blood pressure in millimeters of mercury, or mmHg. Blood Pressure comprises public domain material from the Centers for Disease Control and Prevention.

There has been much debate about the role sodium plays in hypertension. In the latter 1980s and early 1990s the largest epidemiological study evaluating the relationship of dietary sodium intake with blood pressure, called INTERSALT, was completed and then went through further analyses.Intersalt Cooperative Research Group. “Intersalt: An International Study of Electrolyte Excretion and Blood Pressure. Results for 24 Hour Urinary Sodium and Potassium Excretion.” BMJ 297, no. 6644 (1988): 319–28. http://www.ncbi.nlm.nih.gov/pmc/articles/ PMC1834069/., Elliott, P. et al. “Intersalt Revisited: Further Analyses of 24 Hour Sodium Excretion and Blood Pressure within and across Populations.” BMJ 312, no. 7041 (1996): 1249–53. http://www.ncbi.nlm.nih.gov/ pubmed/8634612. More than ten thousand men and women from thirty-two countries participated in the study. The study concluded that a higher sodium intake is linked to an increase in blood pressure. A more recent study, involving over twelve thousand US citizens, concluded that a higher sodium-to-potassium intake is linked to higher cardiovascular mortality and all-causes mortality.Yang Q. et al. “Sodium and Potassium Intake and Mortality among US Adults: Prospective Data from the Third National Health and Nutrition Examination Survey.” Arch Intern Med 171, no. 13 (2011): 1183–91. doi: 10.1001/archinternmed.2011.257. The DASH-Sodium trial was a clinical trial which evaluated the effects of a specified eating plan with or without reduced sodium intake. The DASH diet is an eating plan that is low in saturated fat, cholesterol, and total fat. Fruits, vegetables, low-fat dairy foods, whole-grain foods, fish, poultry, and nuts are emphasized while red meats, sweets, and sugar-containing beverages are mostly avoided. (To find out more about the DASH eating plan see Note 7.37 “Interactive 7.3”.) In this study, people on the low- sodium (1500 milligrams per day) DASH diet had mean systolic blood pressures that were 7.1 mmHg lower than people without hypertension not on the DASH diet. The effect on blood pressure was greatest in participants with hypertension at the beginning of the study who followed the DASH diet. Their systolic blood pressures were, on average, 11.5 mmHg lower than participants with hypertension on the control diet.Sacks, F. M. et al. “Effects on Blood Pressure of Reduced Dietary Sodium and the Dietary Approaches to Stop Hypertension (DASH) Diet.” N Engl J Med 344, no. 1 (2001): 3–10. http://www.ncbi.nlm.nih.gov/pubmed/11136953. Following the DASH diet not only reduces sodium intake, but also increases potassium, calcium, and magnesium intake. All of these electrolytes have a positive effect on blood pressure, although the mechanisms by which they reduce blood pressure are largely unknown.

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While some other large studies have demonstrated little or no significant relationship between sodium intake and blood pressure, the weight of scientific evidence demonstrating low-sodium diets as effective preventative and treatment measures against hypertension led the US government to pass a focus on salt within the Consolidated Appropriations Act of 2008. A part of this act tasked the CDC, under guidance from the IOM, to make recommendations for Americans to reduce dietary sodium intake. This task is ongoing and involves “studying government approaches (regulatory and legislative actions), food supply approaches (new product development, food reformulation), and information/education strategies for the public and professionals.”Jane E. Henney, Christine L. Taylor, and Caitlin S. Boon, eds., Strategies to Reduce Sodium Intake in the United States, by Committee on Strategies to Reduce Sodium Intake, Institute of Medicine (Washington, D.C.: National Academies Press, 2010): 19. http://www.nap.edu/ openbook.php?record_id=12818&page= 19#p2001bcf59960019001.

Interactive 7.3

The National Heart, Lung, and Blood Institute has prepared an informative fact sheet on the DASH diet.

http://www.nhlbi.nih.gov/health/public/heart/hbp/dash/new_dash.pdf.

Use the food-group charts to help design a daily menu that follows the DASH eating plan.

Salt Sensitivity

High dietary intake of sodium is one risk factor for hypertension and contributes to high blood pressure in many people. However, studies have shown that not everyone’s blood pressure is affected by lowering sodium intake. About 10 to 20 percent of the population is considered to be salt-sensitive, meaning their blood pressure is affected by salt intake. Genetics, race, gender, weight, and physical activity level are determinants of salt sensitivity. African Americans, women, and overweight individuals are more salt-sensitive than others. Also, if hypertension runs in a person’s family, that person is more likely to be salt-sensitive. Because reducing dietary salt intake will not work for everyone with hypertension or a risk for developing the condition, there are many opponents of reducing dietary salt intake at the national level. Among such opponents is the Salt Institute, a nonprofit trade organization that states, “No evidence demonstrates that current salt intake

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levels lead to worse health outcomes such as more heart attacks or higher cardiovascular mortality.”The Salt Institute. “Salt and Health.” © 2011 Salt Institute. Accessed October 2, 2011. http://www.saltinstitute.org/Issues-in-focus/ Food-salt-health.

KEY TAKEAWAYS

• Dehydration decreases blood volume. Dehydration is a primary cause of heat stroke.

• Chronic dehydration is linked to higher incidences of some diseases. • Hypertension is a risk factor for cardiovascular disease and reducing

blood pressure has been found to decrease the risk of dying from a heart attack or stroke. Many large studies suggest that high sodium intake is linked to an increase in blood pressure.

• The Dietary Approaches to Stop Hypertension (DASH)-Sodium trial concluded that sodium intake is effective in decreasing blood pressure.

• About 10 to 20 percent of the population is considered to be salt- sensitive. Genetics, race, gender, body weight and physical activity level are determinants of salt sensitivity.

DISCUSSION STARTER

1. Does salt restriction need to be a public policy? Compare it to having a public policy on water intake to prevent dehydration in children during school-sponsored sports events.

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7.6 Water Concerns

LEARNING OBJECTIVES

1. List sources of fluid intake. 2. Learn to examine beverage labels carefully and determine nutritional

adequacy. 3. Describe the major shifts in beverage consumption in the United States

and identify the potential related health problems.

At this point you have learned how critical water is to support human life, how it is distributed and moved in the body, how fluid balance and composition is maintained, and the recommended amount of fluids a person should consume daily. In America you have a choice of thousands of different beverages. Which should you choose to receive the most health benefit and achieve your recommended fluid intake?

Reading the Label

Most beverages marketed in the United States have a Nutrition Facts panel and ingredients list, but some, such as coffee (for home consumption), beer, and wine, do not. As with foods, beverages that are nutrient-dense are the better choices, with the exception of plain water, which contains few to no other nutrients. Beverages do not make you full; they satiate your thirst. Therefore, the fewer calories in a beverage the better it is for avoiding weight gain.

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Beverage Consumption in the United States

According to the Beverage Marketing Corporation, in the United States in 2010 Americans consumed 29,325 millions of gallons of refreshment beverages including soft drinks, coffee, tea, sports drinks, energy drinks14, fruit drinks, and bottled water.Beverage Marketing Corporation. “US Liquid Refreshment Beverage Market Increased by 1.2% in 2010, Beverage Marketing Corporation Reports.” Accessed March 17, 2011. http://www.beveragemarketing.com/?section=pressreleases. As in the past, carbonated soft drinks remained the largest category of consumed14. Beverages containing

extremely high levels of caffeine, which can augment the effects of the drug.

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beverages. In recent decades total caloric consumption has increased in the United States and is largely attributed to increased consumption of snacks and caloric beverages. People between the ages of nineteen and thirty-nine obtain 10 percent of their total energy intake from soft drinks.The Beverage Panel, University of North Carolina, Chapel Hill. “Beverage Intake in the United States.” Accessed October 2, 2011. http://www.cpc.unc.edu/projects/beverage. In all age groups the consumption of total beverages provides, on average, 21 percent of daily caloric intake. This is 7 percent higher than the IOM acceptable caloric intake from beverages. Moreover, the high intakes of soft drinks and sugary beverages displace the intake of more nutrient-dense beverages, such as low-fat milk.

Scientific studies have demonstrated that while all beverages are capable of satisfying thirst they do not make you feel full, or satiated. This means that drinking a calorie-containing beverage with a meal only provides more calories, as it won’t be offset by eating less food. The Beverage Panel of the University of North Carolina, Chapel Hill has taken on the challenge of scientifically evaluating the health benefits and risks of beverage groups and providing recommendations for beverage groups. In regards to soft drinks and fruit drinks, The Beverage Panel states that they increase energy intake, are not satiating, and that there is little if any reduction in other foods to compensate for the excess calories. All of these factors contribute to increased energy intake and obesity. Beverage Marketing Corporation. “US Liquid Refreshment Beverage Market Increased by 1.2% in 2010, Beverage Marketing Corporation Reports.” Accessed March 17, 2011.

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http://www.beveragemarketing.com/?section=pressreleases. The Beverage Panel recommends an even lower intake of calories from beverages than IOM—10 percent or less of total caloric intake.

Sources of Drinking Water

The Beverage Panel recommends that women drink at least 32 ounces and men drink at least 48 ounces of water daily. In 1974, the US federal government enacted The Safe Drinking Water Act with the intention of providing the American public with safe drinking water. This act requires the Environmental Protection Agency (EPA) to set water-quality standards and assure that the 150,000-plus public water systems in the country adhere to the standards. About 15 percent of Americans obtain drinking water from private wells, which are not subject to EPA standards.

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For more information on the health risks of and the maintenance of private wells visit the EPA website.

http://water.epa.gov/drink/info/well/index.cfm

Producing water safe for drinking involves some or all of the following processes: screening out large objects, removing excess calcium carbonate from hard water sources, flocculation, which adds a precipitating agent to remove solid particles, clarification, sedimentation, filtration, and disinfection These processes aim to remove unhealthy substances and produce high-quality, colorless, odorless, good- tasting water .

Most drinking water is disinfected by the process of chlorination, which involves adding chlorine compounds to the water. Chlorination is cheap and effective at killing bacteria. However, it is less effective at removing protozoa, such as Giardia lamblia. Chlorine-resistant protozoa and viruses are instead removed by extensive filtration methods. In the decades immediately following the implementation of water chlorination and disinfection methods in this country, water-borne illnesses, such as cholera and typhoid fever, essentially disappeared in the United States. In fact, the treatment of drinking water is touted as one of the top public-health achievements of the last century.

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Chlorine reaction with inadequately filtered water can result in the formation of potentially harmful substances. Some of these chlorinated compounds, when present at extremely high levels, have been shown to cause cancer in studies conducted in rodents. In addition to many other contaminants, the EPA has set maximum contaminant levels (legal threshold limits) for these chlorinated compounds in water, in order to guard against disease risk. The oversight of public water systems in this country is not perfect and water-borne illnesses are significantly underreported; however, there are far fewer cases of water-borne illnesses than those attributed to food-borne illnesses that have occurred in the recent past.

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For a full list of contaminants regulated by the EPA view the tables on the EPA website.

http://water.epa.gov/drink/contaminants/index.cfm

Hard versus Soft Water

The characteristics of hard water are attributed to higher concentration of calcium and magnesium salts. Hard water is prevalent in the mountain and central time zones and in the Midwestern United States. Hard water is characterized by a calcium carbonate concentration of at least 60 milligrams per liter. Higher concentrations of cations in hard water make it difficult to get soap to lather and clean effectively. Also, the cations precipitate as salts in pipes, dishes, and industrial equipment and can reduce the palatability of drinking water. The average dietary contribution of calcium and magnesium from water ranges between 5 and 20 percent.World Health Organization. “Hardness in Drinking Water.” © 2011. http://www.who.int/water_sanitation_health/dwq/chemicals/hardness.pdf The World Health Organization states that there is no convincing evidence that consumption of hard water adversely affects human health.World Health Organization. “Hardness in Drinking Water.” © 2011. http://www.who.int/ water_sanitation_health/dwq/chemicals/hardness.pdf On the contrary, there is some evidence from observational studies that consuming hard water is inversely associated with the incidence of some chronic diseases, including cardiovascular disease and some cancers, although the studies have not been consistent and often have multiple confounding variables.

Soft water is produced primarily by running water through a resin system which exchanges sodium cations for calcium and magnesium ions. Treating exceptionally hard waters can significantly increase the sodium concentration in drinking water. The practical benefits of soft water are that soap scum no longer makes dishes and bathrooms dingy, clothes are softer, and there is less of a toll on household and industrial equipment. On the other hand, the increased sodium in soft water can make it taste worse and potentially exacerbate health problems such as hypertension, especially in salt-sensitive populations. Soft water can be treated by a process called “reverse osmosis,” which removes the sodium ions. These filtration systems can be purchased for home use, although their cost is a bit high.

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The consumption of bottled water in the United States creates a mound of plastic waste.

Bales of PET Bottles by Michal Maňas is available under a Creative Commons Attribution 3.0 Unported license.

Is Bottled Water a Better Beverage Choice than Tap Water?

Bottled water is not regulated by the EPA but by FDA. For bottled water, the FDA adheres to the same quality standards as those set by the EPA for tap water. Therefore, the contaminant levels set by the EPA for tap water are not different for bottled water; although there is much less testing, monitoring, and oversight of bottled water in comparison to tap water. Similar to tap water the source and treatment of bottled water determines its taste and quality. Depending on where you live, tap water can be a dietary source of minerals (such as calcium and magnesium), but remember that food rather than water serves as a more prominent dietary source of these minerals.

Distilled and purified bottled waters have had all minerals removed during processing, but not all bottled waters have had minerals removed. Mineral waters, sparkling waters, and Artesian waters are examples of bottled waters that contain some minerals, but they are more expensive. Tap water in the United States costs, on average, much less than one cent per gallon, while bottled water is upwards of three dollars per gallon. Moreover, bottled water uses more resources and produces more waste in comparison to tap water. Iowa State University reports that in the United States alone, the making of plastic bottles for bottled water consumption uses more than 1.5 million barrels of oil every year, which is more than the fuel required for one hundred thousand cars.Iowa State University. “Bottled Water, Know the Facts.” Accessed October 2, 2011. http://www.extension.iastate.edu/ publications/pm1813.pdf.

Soda, seltzer, and tonic waters are not considered bottled waters and are classified as soft drinks by the FDA. Recently, flavored and nutrient-added water beverages have arrived on the market and are regulated by the FDA in accordance with regulation of bottled waters.

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What Is Bisphenol A and Is It a Health Hazard?

Bisphenol A (BPA) is a chemical added to plastics, mostly polycarbonate (which is used to make bottled water containers), and to epoxy resins (which are used to line metal-based containers, such as those used for packaging infant formulas). It has been utilized for these purposes and many others since the 1940s. Most studies evaluating toxicity of BPA demonstrate it does not cause adverse health effects to humans at the levels it exists in for beverage and food containers. However, in January of 2010 the FDA issued an update on BPA uses in the food industry.US Food and Drug Administration. “Update on Bisphenol A (BPA) for Use in Food Contact Applications.” Last updated March 30, 2012. http://www.fda.gov/NewsEvents/ PublicHealthFocus/ucm197739.htm. This update reports that the FDA, along with the IOM and the National Toxicology Program, “have some concern about the potential effects of BPA on the brain, behavior, and prostate gland in fetuses, infants, and young children.”US Food and Drug Administration. “Update on Bisphenol A (BPA) for Use in Food Contact Applications.” Last updated March 30,

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2012. To address these potential health concerns studies are currently being conducted to further evaluate the risk of adverse health effects associated with exposure to low levels of BPA. In the interim the FDA is taking steps to reduce human exposure to BPA. Many bottled water companies have switched to “BPA- free” plastic containers.

Tools for Change

Make a more sustainable choice and enjoy a glass of water from the tap right in your home.

Save some money, reduce your exposure to BPA, and be more sustainable in your water consumption by drinking more tap water than bottled water. If your tap water has a bad smell or taste, purchase a home water filter. If you still prefer bottled water, do not buy purified water. Also, buy larger volumes of bottled water with less packaging and use a reusable bottle for drinking, or better yet try a water glass from the kitchen cupboard. If you have questions on the safety of your tap water, visit the website of the municipality in which you live. They are required by law to provide this information to the public.

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KEY TAKEAWAYS

• Beverages do not make you full rather, they satiate your thirst. Therefore, the fewer calories in a beverage, the better it is for avoiding weight gain.

• In all age groups the consumption of total beverages provides, on average, 21 percent of daily caloric intake. This is 7 percent higher than the IOM acceptable caloric intake from beverages, and 11 percent higher than that recommended by The Beverage Panel.

• In 1974, the US federal government enacted The Safe Drinking Water Act in order to help provide the American public with safe drinking water.

• In the decades immediately following the implementation of water chlorination and disinfection methods, water-borne illnesses, such as cholera and typhoid fever, essentially disappeared in the United States. In fact, the treatment of drinking water is touted as one of the top public-health achievements of the last century.

• There is some evidence from observational studies that consuming hard water is inversely associated with the incidence of some chronic diseases, including cardiovascular disease and some cancers.

• Bottled water is not regulated by the EPA but by the FDA. The contaminant levels set by the EPA for tap water are not different for bottled water, but there is much less testing, monitoring, and oversight of bottled water in comparison to tap water.

DISCUSSION STARTERS

1. What is your favorite bottled water? Look up its source and treatment and compare your information with others in your class.

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7.7 Popular Beverage Choices

LEARNING OBJECTIVES

1. Explain the impacts of excessive alcohol intake (both acutely and chronically) on health.

2. Discuss the scientific evidence about caffeine and human health.

In this last section we will discuss three beverage types in particular: alcohol, caffeinated drinks, and sports drinks. We will examine the effects of these beverages upon fluid levels and nutrition within the body so that you will be better able to make wise decisions about your beverage choices.

Alcohol

Alcohol is both a beverage providing some sustenance and a drug. For thousands of years, alcohol has been consumed in a medicinal, celebratory, and ritualistic manner. It is drunk in just about every country and often in excessive amounts. Alcohol is a psychoactive drug. A psychoactive drug15 is any substance that crosses the blood-brain barrier primarily affecting the functioning of the brain, be it altering mood, thinking, memory, motor control, or behavior. Alcohols16 in chemistry refer to a group of similar organic compounds, but in beverages the only alcohol consumed is ethanol.

The Behavioral Risk Factor Surveillance System survey reported that more than half of the adult US population drank alcohol in the past thirty days.Centers for Disease Control and Prevention. “Alcohol and Public Health.” Last updated March 5, 2012. http://www.cdc.gov/alcohol/. Of the total population who drank alcohol, approximately 5 percent drank heavily, while 15 percent binge drank. Binge drinking (as defined by the National Institute on Alcohol Abuse and Alcoholism) is when men consume five or more drinks, and when women consume four or more drinks, in two hours or less.Centers for Disease Control and Prevention. “Alcohol and Public Health.” Last updated March 5, 2012. http://www.cdc.gov/alcohol/. Alcohol in excess is detrimental to health; however since its beginnings it has been suspected and promoted as a benefit to the body and mind when consumed in moderation. In the United States, the Dietary Guidelines define moderate alcohol intake as no more than one drink per day for women and no more than two drinks per day for men.US Department of Agriculture and US Department of Health and Human Services. “Alcoholic Beverages.” In Dietary Guidelines for Americans 2005.

15. Any substance that crosses the blood-brain barrier and affects the brain’s functioning.

16. In chemistry, alcohols refer to a group of similar organic compounds, but in beverages the only alcohol consumed is ethanol.

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(Washington D. C.: US Department of Health and Human Services and US Department of Agriculture, 2005). http://www.health.gov/DIETARYGUIDELINES/ dga2005/document/html/chapter9.htm. Although drunkenness has pervaded many cultures, drinking in moderation has long been a mantra of multiple cultures with access to alcohol.

More than 90 percent of ingested alcohol is metabolized in the liver. The remaining amount stays in the blood and is eventually excreted through the breath (which is how Breathalyzers work), urine, saliva, and sweat. The blood alcohol concentration (BAC)17 is measured in milligrams percent, comparing units of alcohol to units of blood. BAC is a measurement used legally to assess intoxication and the impairment and ability to perform certain activities, as in driving a car. As a general rule, the liver can metabolize one standard drink (defined as 12 ounces of beer, 5 ounces of wine, or 1 ½ ounces of hard liquor) per hour. Drinking more than this, or more quickly, will cause BAC to rise to potentially unsafe levels. Table 7.12 “Mental and Physical Effects of Different BAC Levels” summarizes the mental and physical effects associated with different BAC levels.

Table 7.12 Mental and Physical Effects of Different BAC Levels

BAC Percent Typical Effects

0.02 Some loss of judgment, altered mood, relaxation, increased body warmth

0.05 Exaggerated behavior, impaired judgment, may have some loss of muscle control(focusing eyes), usually good feeling, lowered alertness, release of inhibition

0.08 Poor muscle coordination (balance, speech, vision, reaction time), difficultydetecting danger, and impaired judgment, self-control, reasoning, and memory

0.10 Clear deterioration of muscle control and reaction time, slurred speech, poorcoordination, slowed thinking

0.15 Far less muscle control than normal, major loss of balance, vomiting

In addition to the one drink per hour guideline, the rate at which an individual’s BAC rises is affected by the following factors:

• Sex (A woman’s BAC will rise more quickly than a man’s.) • Weight (BAC will rise more slowly for heavier people.) • Genetics • Length of time as a heavy drinker • Type of alcohol consumed

17. A measurement of the level of alcohol in the blood stream, in terms of percentages; used to determine if an individual is legally intoxicated and driving while impaired.

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• Amount of alcohol consumed • Consumption rate • Consumption before or after a meal (food in the stomach slows

absorption) • Mixture (carbonated mixers speed absorption) • Medications may increase the bioavailability of alcohol.

Giving the liver enough time to fully metabolize the ingested alcohol is the only effective way to avoid alcohol toxicity. Drinking coffee or taking a shower will not help. The legal limit for intoxication is a BAC of 0.08. Taking into account the rate at which the liver metabolizes alcohol after drinking stops, and the alcohol excretion rate, it takes at least five hours for a legally intoxicated person to achieve sobriety.

Health Benefits of Moderate Alcohol Intake

In contrast to excessive alcohol intake, moderate alcohol intake has been shown to provide health benefits. The data is most convincing for preventing heart disease in middle-aged and older people. A review of twenty-nine studies concluded that moderate alcohol intake reduces the risk of coronary heart disease by about 30 percent in comparison to those who do not consume alcohol. Ronksley, P. E. et al. “Association of Alcohol Consumption with Selected Cardiovascular Disease Outcomes: A Systematic Review and Meta- Analysis.” BMJ 342, no. d671 (2011). doi: 10.1136/ bmj.d671. Several other studies demonstrate that moderate alcohol consumption reduces the incidences of stroke and heart attack, and also death caused by cardiovascular and heart disease. The drop in risk for these adverse events ranges between percent. Moreover, there is some scientific evidence that moderate alcohol intake reduces the risk for metabolic syndrome, Type 2 diabetes, and gallstones. In addition to providing some health benefits, moderate alcohol intake has long served as a digestive aid and a source of comfort and relaxation, and it induces social interaction, thereby benefiting all aspects of the health triangle. It has not been clearly demonstrated that moderate alcohol consumption benefits younger populations, and the risks of any alcohol consumption do not outweigh the benefits for pregnant women, those who are taking medications that interact with alcohol, and those who are unable to drink in moderation.

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Health Consequences of Alcohol Abuse

Distilled spirits have exceptionally few nutrients, but beer and wine do provide some nutrients, vitamins, minerals, and beneficial plant chemicals along with calories. A typical beer is 150 kilocalories, a glass of wine contains approximately 80 kilocalories, and an ounce of hard liquor (without mixer) is around 65 kilocalories. Alcoholic drinks in excess contribute to weight gain by substantially increasing caloric intake. However, alcohol displays its two-faced character again in its effects on body weight, making many scientific studies contradictory. Multiple studies show high intakes of hard liquor are linked to weight gain, although this may be the result of the regular consumption of hard liquor with sugary soft drinks, juices, and other mixers. On the other hand drinking beer and, even more so, red wine, is not consistently linked to weight gain and in some studies actually decreases weight gain. The contradictory results of scientific studies that have examined the association of alcohol intake with body weight are partly due to the fact that alcohol contributes calories to the diet, but when drunk in excess reduces the secretion of pancreatic juice and damages the lining of the gastrointestinal system, impairing nutrient digestion and absorption. The impaired digestion and absorption of nutrients in alcoholics contributes to their characteristic “skinniness” and multiple associated micronutrient deficiencies. The most common macronutrient deficiency among alcoholics is water, as it is excreted in excess. Commonly associated micronutrient deficiencies include thiamine, pyridoxine, folate, vitamin A, magnesium, calcium, and zinc. Furthermore, alcoholics typically replace calories from alcohol with those of nutritious foods, sometimes getting 50 percent or more of their daily caloric intake from alcoholic beverages.

Effects of Alcohol Abuse on the Brain

Alcohol can adversely affect nearly every area of the brain. When BAC rises, the central nervous system is depressed. Alcohol disrupts the way nerve cells communicate with each other by interfering with receptors on certain cells. The immediate impact of alcohol on the brain can be seen in the awkwardly displayed symptoms of confusion, blurred vision, slurred speech, and other signs of intoxication. These symptoms will go away once drinking stops, but abusive alcohol consumption over time can lead to long-lasting damage to the brain and nervous system. This is because alcohol and its metabolic byproducts kill brain cells. Excessive alcohol intake has the following effects on specific areas of the brain:

1. Medulla. This area controls automatic functions, such as heart rate. When alcohol first limits its functioning, people feel sleepy. With greater BAC levels, unconsciousness, comas, and death can result.

2. Cerebellum. This is where conscious movement is coordinated. With too much alcohol, balance and motor skills are impaired.

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Figure 7.10 Liver Cirrhosis

Excessive alcohol consumption causes the destruction of liver cells. In an attempt to repair itself, the liver initiates an inflammatory and reparation process causing scar tissue to form. In the liver’s attempt to replace the dead cells, surviving liver cells multiply. The result is clusters of newly formed liver cells, also called regenerative nodules, within the scar tissue. This state is called cirrhosis of the liver.

Liver Cirrhosis by Blausen Medical is available under a Creative Commons Attribution-ShareAlike 4.0 International license.

3. Cerebral cortex. Senses and thoughts are processed here, and this is where action is initiated. When BAC levels increase, the ability to think, exercise good judgment, and feel pain decrease.

4. Hypothalamus and pituitary gland. Alcohol increases sexual desire but decreases sexual performance. It also prompts signals which increase urine production.

5. Limbic system. When alcohol affects this area, individuals may become very emotional and lose memory function.

Effects of Alcohol Abuse on the Liver

According to the CDC, 14,406 Americans died from alcohol-related liver diseases in 2007. Although not every alcoholic or heavy drinker will die from liver problems, the liver is one of the body’s main filtering organs and is severely stressed by alcohol abuse. The term Alcoholic Liver Disease (ALD)18 is used to describe liver problems linked to excessive alcohol intake. ALD can be progressive, with individuals first suffering from a fatty liver and going on to develop cirrhosis. It is also possible to have different forms of ALD at the same time.

The three most common forms of ALD are:

• Fatty liver. A rather benign disorder that develops after excessive alcohol consumption; however it can progress to more fatal diseases. Fatty liver is reversible if alcohol use is brought under control.

• Alcoholic hepatitis. The symptoms of this alcohol-induced liver inflammation are a swollen liver, abdominal pain, nausea, fever, jaundice, and vomiting. Although linked to alcohol use, even people who drink moderately can sometimes develop this condition, and not all alcohol abusers do. If a person stops drinking alcohol, the liver damage can be reversed. But if they continue, cirrhosis may develop and death can result.

• Cirrhosis. This serious and sometimes fatal form of ALD develops when liver cells die and form scar tissue, which blocks blood flow and causes wastes and toxins to build up in the system. Strictly speaking, cirrhosis cannot be cured. It can, however,

18. Liver problems linked to excessive alcohol intake including fatty liver, alcoholic hepatitis, and cirrhosis.

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be stopped with medical treatment and complications can be managed if the individual stops drinking, and many do survive. Not all cases of cirrhosis are strictly due to alcoholism, and not all alcoholics develop the disease. Symptoms of cirrhosis include the buildup of abdominal fluid (ascites), abdominal pain, fever, thirst, confusion, and fatigue.

The Reality

Alcohol is a diuretic that results in dehydration. It suppresses the release of antidiuretic hormone and less water is reabsorbed and more is excreted. Drinking alcohol in excess can lead to a “hangover,” of which the majority of symptoms are the direct result of dehydration.

Caffeine

Caffeine19 is a chemical called xanthine found in the seeds, leaves, and fruit of many plants, where it acts as a natural pesticide. It is the most widely consumed psychoactive substance and is such an important part of many people’s lives that they might not even think of it as a drug. Up to 90 percent of adults around the world use it on a daily basis. According to both the FDA and the American Medical Association the moderate use of caffeine is “generally recognized as safe.” It is considered a legal psychoactive drug and, for the most part, is completely unregulated.

Typical Doses and Dietary Sources

What is a “moderate intake” of caffeine? Caffeine intakes are described in the following manner:

• Low–moderate intake. 130–300 milligrams per day • Moderate intake. 200–300 milligrams per day • High intake. 400 or more milligrams per day

The average caffeine consumption for American adults is considered moderate at 280 milligrams per day, although it is not uncommon for people to consume up to 600 milligrams per day. This works out to almost 4 ½ cups of coffee per day. The bitter taste of caffeine is palatable for many and coffee is the most readily available source of it, accounting for 70 percent of daily caffeine consumption. The second readily available source of caffeine is soft drinks, delivering 16 percent of daily

19. A chemical called xanthine found in the seeds, leaves, and fruit of many plants, where it acts as a natural pesticide. It is the most widely consumed psychoactive substance.

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caffeine. (In this case, the bitter caffeine taste is usually masked by a large amount of added sugar.) Tea is the third common source of caffeine, at 12 percent.

Just how much caffeine is there in a cup of coffee? It varies. The caffeine content of an average cup of coffee can range from 102 to 200 milligrams, and the range for tea is 40 to 120 milligrams. When estimating your total caffeine consumption remember its not only in beverages, but also some foods and medicine.

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Health Benefits

The most renowned effects of caffeine on the body are increased alertness and delay of fatigue and sleep. How does caffeine stimulate the brain? Caffeine is chemically similar to a chemical in our brains (adenosine). Caffeine interacts with adenosine’s specific protein receptor. It blocks the actions of the adenosine, and affects the levels of signaling molecules in the brain, leading to an increase in energy metabolism. At the molecular level, caffeine stimulates the brain, increasing alertness and causing a delay of fatigue and sleep. At high doses caffeine stimulates the motor cortex of the brain and interferes with the sleep-wake cycle, causing side effects such as shakiness, anxiety, and insomnia. People’s sensitivity to the adverse effects of caffeine varies and some people develop side effects at much lower doses. The many effects caffeine has on the brain do not diminish with habitual drinking of caffeinated beverages.

Tools for Change

Consuming caffeine in the evening and in the middle of the night will help keep you awake to study for an exam, but it will not enhance your performance on the next day’s test if you do not get enough sleep. Drink caffeinated beverages in moderation at any time of the day or evening to increase alertness (if you are not sensitive to caffeine’s adverse effects), but get the recommended amount of sleep.

It is important to note that caffeine has some effects on health that are either promoted or masked by the other beneficial chemicals found in coffee and tea. This means that when assessing the benefits and consequences of your caffeine intake, you must take into account how much caffeine in your diet comes from coffee and tea versus how much you obtain from soft drinks.

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There is a good amount of scientific evidence supporting that higher consumption of caffeine, mostly in the form of coffee, substantially reduces the risk for developing Type 2 diabetes and Parkinson’s disease. There is a lesser amount of evidence suggesting increased coffee consumption lowers the risk of heart attacks in both men and women, and strokes in women. In smaller population studies, decaffeinated coffee sometimes performs as well as caffeinated coffee, bringing up the hypothesis that there are beneficial chemicals in coffee other than caffeine that play larger roles in the health benefits of coffee. A review of fifteen epidemiological studies in The Journal of the American Medical Association proposes that habitual coffee consumption reduces the risk of Type 2 diabetes. van Dam, R. M., PhD and F. B. Hu, M.D., PhD “Coffee Consumption and Risk of Type 2 Diabetes: A Systematic Review.” JAMA 294, no. 1 (2005): 97–104. doi: 10.1001/ jama.294.1.97. The risk reduction was 35 percent for those who consumed greater than 6–7 cups of coffee per day and was 28 percent for those who consumed 4–5 cups daily. These groups were compared with people who consumed less than 2 cups of coffer per day. Parkinson’s disease is an illness of the central nervous system causing many disorders of movement. Research scientists in Hawaii found an inverse relationship between caffeine intake and the incidence of Parkinson’s disease. In fact, men who did not consume coffee had a five times more likely chance of Parkinson’s disease than men who consumed more than 3 cups of coffee daily.Ross, G. W. et al. “Association of Coffee and Caffeine Intake with the Risk of Parkinson’s Disease.” JAMA 283, no. 20 (2000): 2674–79. doi: 10.1001/ jama.283.20.2674. In this study other caffeine sources, such as soft drinks and tea, were also associated with a reduced risk of Parkinson’s disease. A review of several studies, published in the Journal of Alzheimer’s Disease, has reaffirmed that caffeine intake may reduce the risk of Parkinson’s disease in both men and women.Costa, J. et al. “Caffeine Exposure and the Risk of Parkinson’s Disease: A Systematic Review and Meta-Analysis of Observational Studies.” J Alzheimers Dis 20 (2010). Supplement 1: S221–38. http://www.ncbi.nlm.nih.gov/pubmed/20182023. This review also took into consideration caffeine obtained from dietary sources other than caffeine, though the data on these is not as extensive or as strong as for coffee. There is also some scientific evidence that drinking coffee is linked to a much lower risk for dementia and Alzheimer’s disease.Patil, H., C. J. Lavie, J. H. O’Keefe. “Cuppa Joe: Friend or Foe? Effects of Chronic Coffee Consumption on Cardiovascular and Brain Health.” Missouri Medical 108, no. 6 (November–December 2011): 431–8. http://www.ncbi.nlm.nih.gov/pubmed/22338737.

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Health Consequences

The acute adverse health effects of caffeine ingestion are anxiety, shakiness, and sleep deprivation. On a more chronic basis, some scientific reports suggest that higher caffeine intake is linked to negative effects on heart health and increased cardiovascular disease; although at this point most data suggests caffeine does not significantly increase either. A comprehensive review published in the American Journal of Clinical Nutrition reports that caffeine induces a modest increase in blood pressure lasting less than three hours in people with hypertension, but there is no evidence that habitual coffee consumption increases blood pressure long-term or increases the risk for cardiovascular disease.Mesas, A. E. et al. “The Effect of Coffee on Blood Pressure and Cardiovascular Disease in Hypertensive Individuals: A Systematic Review and Meta-Analysis.” Am J Clin Nutr 94, no. 4 (2011): 1113–26. http://www.ncbi.nlm.nih.gov/pubmed/21880846. There is no good evidence that chronic caffeine exposure increases blood pressure chronically in people without hypertension.

Some have hypothesized that caffeine elevates calcium excretion and therefore could potentially harm bones. The scientific consensus at this time is that caffeine minimally affects calcium levels and intake is not associated with any increased risk for osteoporosis or the incidence of fractures in most women. Although the effect of caffeine on calcium excretion is small, postmenopausal women with risk factors for osteoporosis may want to make sure their dietary caffeine intake is low or moderate and not excessive.

The Caffeine Myth

A diuretic refers to any substance that elevates the normal urine output above that of drinking water. Caffeinated beverages are commonly believed to be dehydrating due to their diuretic effect, but results from scientific studies do not support that caffeinated beverages increase urine output more so than water. This does not mean that consuming caffeinated beverages does not affect urine output, but rather that it does not increase urine output more than water does. Thus, caffeinated beverages are considered a source of hydration similar to water.

Sports Drinks

Scientific studies under certain circumstances show that consuming sports drinks (instead of plain water) during high-intensity exercise lasting longer than one hour significantly enhances endurance, and some evidence indicates it additionally enhances performance. There is no consistent evidence that drinking sports drinks instead of plain water enhances endurance or performance in individuals exercising less than one hour and at low to moderate intensities. A well-concocted sports

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drink contains sugar, water, and sodium in the correct proportions so that hydration is optimized. The sugar is helpful in maintaining blood-glucose levels needed to fuel muscles, the water keeps an athlete hydrated, and the sodium enhances fluid absorption and replaces some of that lost in sweat. The American College of Sports Medicine states that the goal of drinking fluids during exercise is to prevent dehydration, which compromises performance and endurance.

The primary source of water loss during intense physical activity is sweat. Perspiration rates are variable and dependent on many factors including body composition, humidity, temperature, and type of exercise. The hydration goal for obtaining optimal endurance and performance is to replace what is lost, not to over-hydrate. A person’s sweating rate can be approximated by measuring weight before and after exercise—the difference in weight will be the amount of water weight you lost.

The primary electrolyte lost in sweat is sodium. One liter of sweat can contain between 1,000–2,000 milligrams of sodium. Potassium, magnesium, and calcium are also lost, but in much lower amounts. If you are exercising at high intensity for greater than ninety minutes, it is important to replace sodium as well as water. This can be partly accomplished by consuming a sports drink. The highest content of sodium in commercial sports drinks is approximately 450 milligrams per liter and thus will not replace all lost sodium unless a person drinks several liters. This is NOT recommended, as water intoxication not only compromises performance, but may also be deadly. The sodium in sports drinks enhances fluid absorption so that rehydration is more efficiently accomplished. If you are not exercising for more than ninety minutes at a high intensity, dietary intake of sodium and other electrolytes should be sufficient for replacing lost electrolytes.

Who Needs Sports Drinks?

Children and adult athletes exercising for more than one hour at high-intensity (tennis, rowing, rugby, soccer, etc.) may benefit endurance-wise and possibly performance-wise from consuming a sports drink rather than water. However, consuming sports drinks provides no benefit over water to endurance, performance, or exercise recovery for those exercising less than an hour. In fact, as with all other sugary drinks containing few to no nutrients, they are only another source of calories. Drinking sports drinks when you are doing no exercise at all is not recommended.

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Sports Drink Alternatives

Instead of a sports drink, you can replenish lost fluids and obtain energy and electrolytes during exercise by drinking plain water and eating a sports bar or snack that contains carbohydrates, protein, and electrolytes. Postexercise, low-fat milk has been scientifically shown to be just as effective as a sports drink as a rehydration beverage and it is more nutrient-dense, containing carbohydrates, protein, and electrolytes, in addition to other vitamins.

The Bottom Line

Sports drinks consumed in excess by athletes or used by non-athletes simply are another source of added sugars, and thus extra calories, in the diet and provide no performance, exercise recovery or health benefit.

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KEY TAKEAWAYS

• Alcohol in excess is detrimental to health; in moderation, however, it is promoted as a benefit to the body and mind. The US Dietary Guidelines define moderate alcohol intake as no more than one drink per day for women and no more than two drinks per day for men.

• Moderate intake of alcohol has been shown in multiple scientific studies to provide health benefits, including reducing the risks of heart disease, cardiovascular disease, metabolic syndrome, Type 2 diabetes, and gallstones.

• The most renowned effects of caffeine on the body are increased alertness and delay of fatigue and sleep. At high doses, caffeine stimulates the motor cortex of the brain and interferes with the sleep- wake cycle, causing side effects such as shakiness, anxiety, and insomnia.

• There is a good amount of scientific evidence supporting that higher consumption of caffeine, mostly in the form of coffee, substantially reduces the risk for developing Type 2 diabetes and Parkinson’s disease. There is a lesser amount of evidence suggesting increased coffee consumption lowers the risk of heart attacks in both men and women and strokes in women. According to both the FDA and the American Medical Association, the moderate use of caffeine is “generally recognized as safe.”

• For most physically active individuals, water is the best hydration source. For endurance athletes, there is increased need of glucose as well as fluid. The body needs healthy foods and beverages, not supplements, to regain electrolytes lost through sweat.

DISCUSSION STARTERS

1. Late nights seem to be part of college life, and with many students working while going to school, early mornings can be part of the equation, too. How much do you and most people you know sleep? How much caffeine do you use? Have you ever suffered from the ill effects of caffeine?

2. How big a problem is the over-consumption of energy drinks at your school? What might be some of the ramifications to learning?

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7.8 End-of-Chapter Exercises

IT ’S YOUR TURN

1. Make a flow chart of the physiological events that trigger thirst. 2. Calculate your sodium intake in a day. Is it lower, average, or higher

than the recommended intake? 3. Tear the labels off of, or bring in the whole can or bottle of, your

favorite beverages. Make a chart of the fluid amount, calories, and nutrients in each beverage.

APPLY IT

1. Make a list of ten things you do that use water and then another of ten things the body does with water.

2. Calculate your daily sodium intake for a week. Is your daily intake lower, average, or higher than the recommended intake? How does it vary during the week?

3. Perform an experiment in class by conducting a taste-test of tap water and bottled waters. Make a chart of the results.

EXPAND YOUR KNOWLEDGE

1. Diagram two physiological mechanisms that regulate water output. 2. Read this article and summarize in a paragraph if it is or is not the time

to “end the war on salt.” (http://www.scientificamerican.com/ article.cfm?id=its-time-to-end-the-war-on-salt). Can you find a reference that disputes the conclusions of this article?

3. Visit the website of The Beverage Panel and review how they used the knowledge of health and nutrition to set recommendations for particular beverages (http://www.cpc.unc.edu/projects/beverage/ panel_recommendations).

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Chapter 8

Nutrients Important As Antioxidants

Big Idea

Eating foods such as fruits, vegetables, herbs, and spices that are high in antioxidants can help prevent cell damage and promote health.

Government trickery and greed are a big part of the history of the woody, bittersweet nutmeg people sprinkle in their eggnog and add to their pumpkin pie.

Arabs originally controlled the lucrative nutmeg trade. Run Island, part of the Banda archipelago in the Maluku province of Indonesia, and (for a while) the sole source of nutmeg, remained a well-kept secret under their control. Then, in 1521, the Portuguese conquered the southern region of Malay in Indonesia and discovered the island.

Control of this nutmeg source switched hands rapidly from this point on. Although the Portuguese claimed ownership for a moment, the Spaniards were quick to take over. In the seventeenth century, the Dutch East India Company invaded the Band Islands. They then ran plantation estates on Run Island and actively patrolled the sea in war vessels to discourage the stealing of seeds from Myristica fragrans. They went so far as to track the movement of pigeons and other animals that might unwittingly transport the seeds elsewhere, and they burned any trees found off of Run Island.

The battles over Run Island had one important motivation: money. Trade was lucrative in the seventeenth century because nutmeg was valued as a curative for stomach ailments, as an aphrodisiac, and as a healer of the liver. The spice even had a reputation for curing the plague, which might have worked—wearing a clove of it

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around the neck may have deterred fleas and other disease carriers. Buyers were also well aware of nutmeg’s hallucinogenic properties and used it in high doses as a psychoactive drug. Its price was astronomically high and kept so by the Dutch, who burned their own nutmeg warehouses down to assure the laws of supply and demand did not lower the spice’s value.

During the Napoleanic wars, while the Dutch were battling the French, the British slipped onto Run Island, stole Myristica fragras seeds, and successfully grew the tree on plantations on the island of Grenada. Today, Grenada, also known as the “Isle of Spice,” produces about one-third of the world’s supply, which is why its flag boasts a clove of nutmeg.

Our ancestors were probably right to value nutmeg for its curative properties. While it does not actually cure disease outright, nutmeg contains a variety of antioxidants, including phenolic compounds, lignans, and eugenol. Foods rich in antioxidants have been touted as preventative and curative, and some believe they delay certain aspects of the aging process. While we are no longer fighting over nutmeg’s production and sale, we are waging a fierce debate about the lack of scientific proof of these believed benefits.

The “antioxidant hypothesis”—the educated guess that antioxidant chemicals protect against chronic disease—has existed for decades. Despite thousands of studies conducted on the health benefits of particular antioxidants, there is little evidence supporting the idea that they singularly prevent disease, reduce the effects of aging, or promote health. It is the combination of antioxidants, phytochemicals, and nutrient-rich foods that achieves these end goals.

Nutmeg has been shown in animal and laboratory studies to act as an antimicrobial, antifungal, and anti-inflammatory agent. It has protected against liver damage and stimulated male sexual activity in rats. However, none of these effects has been scientifically shown to occur in humans. On the other hand, nutmeg has proven effective as a psychoactive drug when taken in high doses.

In this chapter, you will learn there is no miracle food or supplement. The debate over the nutmeg’s effectiveness as an antioxidant—and over the effects of antioxidants in general—is proof of this. You will also learn that plant chemicals can affect the body in many different ways, depending on the type of chemical and the dosage. Different antioxidants are believed to have different functions, and those functions are sometimes interdependent or dependent on the amount of nutrient-rich foods you eat.

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You Decide

Will you increase your intake of antioxidant- and nutrient-rich foods to improve health and reduce the risk of chronic disease? Why and how?

“Shall I not have intelligence with the earth? Am I not partly leaves and vegetable mould myself?”

– Henry David Thoreau (July 12, 1817–May 6, 1862)

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8.1 Generation of Free Radicals in the Body

LEARNING OBJECTIVES

1. Describe how free radicals are generated in the body. 2. Explain oxidative stress and what diseases it is associated with.

In mainstream advertising you may have heard that antioxidants can extend your life by preventing disease and slowing the aging process. But what are antioxidants? And how do they work in the body? Is there any truth to the marketers’ claims? Are there better sources than supplements for antioxidants? After reading this chapter you will be able to answer these questions, and your new knowledge will assist you in making dietary decisions to optimize your health.

Keep in mind as you read there is no scientific evidence that antioxidants singularly provide bodily benefits, but there is evidence that certain benefits are achieved by ingesting antioxidants as part of a balanced, healthy, nutrient-rich diet. This is to say antioxidants may go a long way toward preventing damage, but other nutrients are necessary to repair damage and sustain health. No one chemical acts alone!

The Atom

Before we can talk about the nutritional value of antioxidants we must review a few chemistry basics, starting with the atom. Cells are the basic building blocks of life, but atoms1 are the basic building blocks of all matter, living and nonliving.

The structural elements of an atom are protons (positively charged), neutrons (no charge), and electrons (negatively charged). Protons and neutrons are contained in the dense nucleus of the atom; the nucleus thus has a positive charge. Because opposites attract, electrons are attracted to this nucleus and move around it in the electron cloud.

Electrons contain energy, and this energy is stored within the charge and movement of electrons and the bonds atoms make with one another. However, this energy is not always stable, depending on the number of electrons within an atom.

Atoms are more stable when their electrons orbit in pairs. An atom with an odd number of electrons must have an unpaired electron. In most cases, these unpaired

1. The basic building blocks of all matter, living and nonliving.

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electrons are used to create chemical bonds. A chemical bond is the attractive force between atoms and contains potential energy. By bonding, electrons find pairs and chemicals become part of a molecule.

Bond formation and bond breaking are chemical reactions that involve the movement of electrons between atoms. These chemical reactions occur continuously in the body and many of them will be discussed in more detail in Chapter 10 “Nutrients Important for Metabolism and Blood Function”.

In Chapter 3 “Nutrition and the Human Body” we reviewed how glucose breaks down into water and carbon dioxide as part of cellular respiration. The energy released by breaking those bonds is used to form molecules of adenosine triphosphate (ATP). Recall how during this process electrons are extracted from glucose in a stepwise manner and transferred to other molecules. Occasionally electrons “escape” and, instead of completing the cellular respiration cycle, are transferred to an oxygen molecule. Oxygen (a molecule with two atoms) with one unpaired electron is known as superoxide.

Atoms and molecules such as superoxide that have unpaired electrons are called free radicals2; those containing oxygen are more specifically referred to as reactive oxygen species3. The unpaired electron in free radicals destabilizes them, making them highly reactive. Other reactive oxygen species include hydrogen peroxide and the hydroxyl radical.

The reactivity of free radicals is what poses a threat to macromolecules such as DNA, RNA, proteins, and fatty acids. Free radicals can cause chain reactions that ultimately damage cells. For example, a superoxide molecule may react with a fatty acid and steal one of its electrons. The fatty acid then becomes a free radical that can react with another fatty acid nearby. As this chain reaction continues, the permeability and fluidity of cell membranes changes, proteins in cell membranes experience decreased activity, and receptor proteins undergo changes in structure that either alter or stop their function. If receptor proteins designed to react to insulin levels undergo a structural change it can negatively effect glucose uptake.

Free radical reactions can continue unchecked unless stopped by a defense mechanism.

2. Highly reactive atoms with unpaired electrons.

3. Molecules containing oxygen that have unpaired electrons and are highly reactive.

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The Body’s Defense

Free radical development is unavoidable, but human bodies have adapted by setting up and maintaining defense mechanisms that reduce their impact. The body’s two major defense systems are free radical detoxifying enzymes and antioxidant chemicals.

Free radical detoxifying enzyme systems are responsible for protecting the insides of cells from free radical damage. An antioxidant4 is any molecule that can block free radicals from stealing electrons; antioxidants act both inside and outside of cells.

Free Radical Detoxifying Enzymes

The three major enzyme systems and the chemical reactions they catalyze are:

1. Superoxide Dismutases (SOD). These enzymes have either a manganese, copper, or zinc cofactor, which is essential for their free radical detoxifying activity. During SOD-mediated enzymatic catalysis, two superoxides are converted into hydrogen peroxide and oxygen. Hydrogen peroxide (H2O2) is still considered a reactive oxygen species, but it is markedly less reactive than a superoxide. SOD enzymes are one of the fastest enzymes known, and they are also inducible, meaning that the higher their exposure to superoxides the greater their number and detoxifying activity.

2. Catalase. This enzyme contains iron as a cofactor and converts hydrogen peroxide to water and oxygen, thereby finishing the detoxification reaction started by SOD. In cells, catalase enzymes are found in high numbers and continuously patrol for hydrogen peroxide molecules. Catalase is highly efficient and is capable of destroying millions of hydrogen peroxide molecules per second.

3. Glutathione Peroxidases. The majority of enzymes within this family are dependent on the micronutrient selenium. Similar to catalase, these enzymes convert hydrogen peroxide to water and oxygen.

Antioxidant Chemicals

Antioxidants are broadly classified as either hydrophilic (water soluble) or hydrophobic (lipid soluble) chemicals, and this classification determines where they act in the body. Hydrophilic antioxidants act in the cytosol of cells or in4. Any molecule that can block

free radicals from stealing electrons.

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extracellular fluids such as blood; hydrophobic antioxidants are largely responsible for protecting cell membranes from free radical damage.

The body can synthesize some antioxidants, but others must be obtained from the diet.

Antioxidant Chemicals the Body Synthesizes

There are two antioxidant chemicals that the body synthesizes. They are:

1. Glutathione. This molecule is composed of three amino acids and is found in high concentrations in cells. The cysteine amino acid of glutathione contains a sulfur group that can donate an electron to a free radical, thereby stabilizing it. After glutathione has lost its electron, it is regenerated enzymatically so that it can perform its antioxidant function once again.

2. Uric Acid. This molecule is a metabolic intermediate in the breakdown of nucleotides such as adenine, which is found in DNA and RNA, among other macromolecules. It circulates at high concentrations in the blood and disables circulating free radicals. However, uric acid is a good example of the adage “it’s the dose that makes the poison” because high concentrations in the blood can cause gout, a painful joint disorder.

Antioxidant Chemicals Obtained from the Diet

There are many different antioxidants in food, including selenium, which is one of the major antioxidants. However, the antioxidants you may be the most familiar with are vitamins. The “big three” vitamin antioxidants are vitamins E, A, and C, although it may be that they are called the “big three” only because they are the most studied.

Table 8.1 Some Antioxidants Obtained from Diet and Their Related Functions

Antioxidant Functions Attributed to Antioxidant Capacity

Vitamin A Protects cellular membranes, prevents glutathione depletion, maintains freeradical detoxifying enzyme systems, reduces inflammation

Vitamin E Protects cellular membranes, prevents glutathione depletion

Vitamin C Protects DNA, RNA, proteins, and lipids, aids in regenerating vitamin E

Carotenoids Free radical scavengers

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Antioxidant Functions Attributed to Antioxidant Capacity

Lipoic acid Free radical scavenger, aids in regeneration of vitamins C and E

Phenolic acids Free radical scavengers, protect cellular membranes

Selenium Cofactor of free radical detoxifying enzymes, maintains glutathione levels,aids in regeneration of vitamins C and E

The Body’s Offense

While our bodies have acquired multiple defenses against free radicals, we also use free radicals to support its functions. For example, the immune system uses the cell-damaging properties of free radicals to kill pathogens. First, immune cells engulf an invader (such as a bacterium), then they expose it to free radicals such as hydrogen peroxide, which destroys its membrane. The invader is thus neutralized.

Scientific studies also suggest hydrogen peroxide acts as a signaling molecule that calls immune cells to injury sites, meaning free radicals may aid with tissue repair when you get cut.

Free radicals are necessary for many other bodily functions as well. The thyroid gland synthesizes its own hydrogen peroxide, which is required for the production of thyroid hormone. Reactive oxygen species and reactive nitrogen species, which are free radicals containing nitrogen, have been found to interact with proteins in cells to produce signaling molecules. The free radical nitric oxide has been found to help dilate blood vessels and act as a chemical messenger in the brain.

By acting as signaling molecules, free radicals are involved in the control of their own synthesis, stress responses, regulation of cell growth and death, and metabolism.

Sources of Free Radicals in the Environment

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Substances and energy sources from the environment can add to or accelerate the production of free radicals within the body. Exposure to excessive sunlight, ozone, smoke, heavy metals, ionizing radiation, asbestos, and other toxic chemicals increase the amount of free radicals in the body. They do so by being free radicals themselves or by adding energy that provokes electrons to move between atoms. Excessive exposure to environmental sources of free radicals can contribute to disease by overwhelming the free radical detoxifying systems and those processes involved in repairing oxidative damage.

Oxidative Stress

Oxidative stress5 refers to an imbalance in any cell, tissue, or organ between the amount of free radicals and the capabilities of the detoxifying and repair systems. Sustained oxidative damage results only under conditions of oxidative stress—when the detoxifying and repair systems are insufficient. Free radical-induced damage, when left unrepaired, destroys lipids, proteins, RNA, and DNA, and can contribute to disease. Oxidative stress has been implicated as a contributing factor to cancer, atherosclerosis (hardening of arteries), arthritis, diabetes, kidney disease, Alzheimer’s disease, Parkinson’s disease, schizophrenia, bipolar disorder, emphysema, and cataracts.

Aging is a process that is genetically determined but modulated by factors in the environment. In the process of aging, tissue function declines. The idea that oxidative stress is the primary contributor to age-related tissue decline has been around for decades, and it is true that tissues accumulate free radical-induced damage as we age. Recent scientific evidence slightly modifies this theory by suggesting oxidative stress is not the initial trigger for age-related decline of tissues; it is suggested that the true culprit is progressive dysfunction of metabolic processes, which leads to increases in free radical production, thus influencing the stress response of tissues as they age.

5. An imbalance in any cell, tissue, or organ between the amount of free radicals and the capablilities of its detoxifying and repair systems.

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KEY TAKEAWAYS

• Free radicals, unstable molecules with unpaired electrons, are an unavoidable byproduct of cellular metabolism.

• Free radicals can steal electrons from lipids, proteins, RNA, and DNA, causing them damage.

• The body has defenses against free radicals—free radical detoxifying enzymes and antioxidant chemicals.

• The body can synthesize some antioxidant molecules, but many are obtained from the diet.

• The body sometimes uses free radicals for beneficial functions such as killing pathogens and regulating cell growth and death.

• Oxidative stress is an imbalance between free radical production and detoxification and repair systems. It also plays an integral role in the development of many chronic diseases and in age-related decline of tissues.

• Excessive sunlight, ozone, smoke, heavy metals, radiation, asbestos, and other toxic chemicals increase the amount of free radicals in the body and can accelerate the progression of diseases in which oxidative stress is a contributing cause.

DISCUSSION STARTER

1. What are some ways you can prevent exposure to environmental factors that increase free radical production in your body?

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8.2 Antioxidant Micronutrients

LEARNING OBJECTIVES

1. List the antioxidant nutrients. 2. Give examples of the best food sources of antioxidant nutrients. 3. Name some phytochemicals and their health benefits as backed by

scientific evidence.

The market is flooded with advertisements for “super antioxidant” supplements teeming with molecules that block free radical production, stimulate the immune system, prevent cancer, and reduce the signs of aging. Based on the antioxidant- supplement industry’s success, the general public appears to believe these health claims. However, these claims are not backed by scientific evidence; rather, there is some evidence suggesting supplements can actually cause harm.

While scientists have found evidence supporting the consumption of antioxidant- rich foods as a method of reducing the risk of chronic disease, there is no “miracle cure;” no pill or supplement alone can provide the same benefits as a healthy diet. Remember, it is the combination of antioxidants and other nutrients in healthy foods that is beneficial.

In this section, we will review how particular antioxidants function in the body, learn how they work together to protect the body against free radicals, and explore the best nutrient-rich dietary sources of antioxidants.

Antioxidant Vitamins

One dietary source of antioxidants is vitamins. In our discussion of antioxidant vitamins, we will focus on vitamins E, C, and A.

Vitamin E Functions and Health Benefits

Vitamin E is actually eight chemically similar substances, of which alpha-tocopherol appears to be the most potent antioxidant. Alpha-tocopherol and vitamin E’s other constituents are fat-soluble and primarily responsible for protecting cell membranes against lipid destruction caused by free radicals.

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After alpha-tocopherol interacts with a free radical it is no longer capable of acting as an antioxidant unless it is enzymatically regenerated. Vitamin C helps to regenerate some of the alpha-tocopherol, but the remainder is eliminated from the body. Therefore, to maintain vitamin E levels, you ingest it as part of your diet.

In addition to its antioxidant functions, vitamin E, mainly as alpha-tocopherol, can change the functions of proteins in cells, plays a role in the operations of the immune system, enhances the dilation of blood vessels, and inhibits blood clot formation. Despite vitamin E’s numerous beneficial functions when taken in recommended amounts, large studies do not support the idea that taking higher doses of this vitamin will increase its power to prevent or reduce disease risk.Goodman, M., Bostlick RM, Kucuk O, Jones DP. 2011. Clinical trials of antioxidants as cancer prevention agents: past, present, and future. Free Radic Biol Med. 51(5): 1068–84., McGinley C, Shafat A. Donnelly AE. 2009. Does antioxidant vitamin supplementation protect against muscle damage. Sports Med. 39(12): 1011–32.

Cardiovascular Disease

Recall from Chapter 5 “Lipids” that low-density lipoproteins (LDLs) transport cholesterol and other lipids from the liver to the rest of the body. LDLs are often referred to as “bad cholesterol,” as an elevation in their levels in the blood is a risk factor for cardiovascular disease. Oxidation of the lipids and proteins in LDLs causes them to stick to the walls of arteries and this contributes to the development of fatty streaks and, eventually, plaque, which hardens the arteries. Hardening of the arteries, called atherosclerosis6 can lead to a heart attack.

Vitamin E reduces the oxidation of LDLs, and it was therefore hypothesized that vitamin E supplements would protect against atherosclerosis. However, large clinical trials have not consistently found evidence to support this hypothesis. In fact, in the “Women’s Angiographic Vitamin and Estrogen Study,” postmenopausal women who took 400 international units (264 milligrams) of vitamin E and 500 milligrams of vitamin C twice per day had higher death rates from all causes.Waters, D.D. et al. “Effects of Hormone Replacement Therapy and Antioxidant Vitamin Supplements on Coronary Atherosclerosis in Postmenopausal Women: A Randomized Controlled Trial.” JAMA 288, no. 19 (2002): 2432–40. doi: 10.1001/jama.288.19.2432

Other studies have not confirmed the association between increased vitamin E intake from supplements and increased mortality. There is more consistent evidence from observational studies that a higher intake of vitamin E from foods is linked to a decreased risk of dying from a heart attack.

6. A progressive hardening of the arteries that can lead to a heart attack.

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Cancer

The large clinical trials that evaluated whether there was a link between vitamin E and cardiovascular disease risk also looked at cancer risk. These trials, called the HOPE-TOO Trial and Women’s Health Study, did not find that vitamin E at doses of 400 international units (264 milligrams) per day or 600 international units (396 milligrams) every other day reduced the risk of developing any form of cancer.HOPE and HOPE-TOO Trial Investigators. “Effects of Long-Term Vitamin E Supplementation on Cardiovascular Events and Cancer.” JAMA 293 (2005):1338–47. http://jama.ama-assn.org/content/293/11/1338.long., Lee, I-M., et al. “Vitamin E in the Primary Prevention of Cardiovascular Disease and Cancer: The Women’s Health Study.” JAMA 294 (2005): 56–65. http://jama.ama-assn.org/content/294/1/56.long.

Eye Conditions

Oxidative stress plays a role in age-related loss of vision, called macular degeneration. Age-related macular degeneration (AMD)7 primarily occurs in people over age fifty and is the progressive loss of central vision resulting from damage to the center of the retina, referred to as the macula. There are two forms of AMD, dry and wet, with wet being the more severe form.

In the dry form, deposits form in the macula; the deposits may or may not directly impair vision, at least in the early stages of the disease. In the wet form, abnormal blood vessel growth in the macula causes vision loss. Clinical trials evaluating the effects of vitamin E supplements on AMD and cataracts (clouding of the lens of an eye) did not consistently observe a decreased risk for either. However, scientists do believe vitamin E in combination with other antioxidants such as zinc and copper may slow the progression of macular degeneration in people with early-stage disease.

Dementia

The brain’s high glucose consumption makes it more vulnerable than other organs to oxidative stress. Oxidative stress has been implicated as a major contributing factor to dementia and Alzheimer’s disease. Some studies suggest vitamin E supplements delay the progression of Alzheimer’s disease and cognitive decline, but again, not all of the studies confirm the relationship. A recent study with over five thousand participants published in the July 2010 issue of the Archives of Neurology demonstrated that people with the highest intakes of dietary vitamin E were 25 percent less likely to develop dementia than those with the lowest intakes of vitamin E.Devore, E. E. et al. “Dietary Antioxidants and Long-Term Risk of Dementia.” Arch Neurol 67, no.7 (2010): 819–25. http://www.ncbi.nlm.nih.gov/pmc/ articles/PMC2923546/?tool=pubmed. More studies are needed to better assess the

7. The progressive loss of central vision resulting from damage to the center of the retina, referred to as the macula.

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dose and dietary requirements of vitamin E and, for that matter, whether other antioxidants lower the risk of dementia, a disease that not only devestates the mind, but also puts a substantial burden on loved ones, caretakers, and society in general.

Dietary Reference Intakes for Vitamin E

The RDAs are based on scientific evidence that these levels of vitamin E in the diet prevent conditions associated with vitamin E deficiency, which are rare (signs and symptoms of such conditions are not always evident) but are primarily the result of nerve degeneration. People with malabsorption disorders, such as Crohn’s disease or cystic fibrosis, and babies born prematurely, are at higher risk for vitamin E deficiency.

Fat in the diet is required for vitamin E absorption as it is packaged into lipid-rich chylomicrons in intestinal cells and transported to the liver. The liver stores some of the vitamin E or packages it into lipoproteins, which deliver it to cells.

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Add some nuts to your salad and make your own dressing to get a healthy dietary dose of vitamin E.

Ding’s Cooking by Oleg Sidorenko is available under a Creative Commons Attribution 2.0 Generic license.

Vitamin E supplements often contain more than 400 international units, which is almost twenty times the RDA. The UL for vitamin E is set at 1,500 international units for adults. There is some evidence that taking vitamin E supplements at high doses has negative effects on health. As mentioned, vitamin E inhibits blood clotting and a few clinical trials have found that people taking vitamin E supplements have an increased risk of stroke. In contrast to vitamin E from supplements, there is no evidence that consuming foods containing vitamin E compromises health.

Dietary Sources of Vitamin E

Vitamin E is found in many foods, especially those higher in fat, such as nuts and oils. Some spices, such as paprika and red chili pepper, and herbs, such as oregano, basil, cumin, and thyme, also contain vitamin E. (Keep in mind spices and herbs are commonly used in small amounts in cooking and therefore are a lesser source of dietary vitamin E.)

Tools for Change

To increase your dietary intake of vitamin E from plant-based foods try a spinach salad with tomatoes and sunflower seeds, and add a dressing made with sunflower oil, oregano, and basil.

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Vitamin C Functions and Health Benefits

Vitamin C, also commonly called ascorbic acid, is a water-soluble micronutrient essential in the diet for humans, although most other mammals can readily synthesize it. Vitamin C’s ability to easily donate electrons makes it a highly effective antioxidant. It is effective in scavenging reactive oxygen species, reactive nitrogen species, and many other free radicals. It protects lipids both by disabling free radicals and by aiding in the regeneration of vitamin E.

In addition to its role as an antioxidant, vitamin C is a required part of several enzymes involved in the synthesis of collagen, signaling molecules in the brain, some hormones, and amino acids. Vitamin C levels in the body are affected by the amount in the diet, which influences how much is absorbed and how much the kidney allows to be excreted, such that the higher the intake, the more vitamin C is excreted. Vitamin C is not stored in any significant amount in the body, but once it has reduced a free radical, it is very effectively regenerated and therefore it can exist in the body as a functioning antioxidant for many weeks.

Cardiovascular Disease

Vitamin C’s ability to prevent disease has been debated for many years. Overall, higher dietary intakes of vitamin C (via food intake, not supplements), are linked to decreased disease risk. A review of multiple studies published in the April 2009 issue of the Archives of Internal Medicine concludes there is moderate scientific

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evidence supporting the idea that higher dietary vitamin C intakes are correlated with reduced cardiovascular disease risk, but there is insufficient evidence to conclude that taking vitamin C supplements influences cardiovascular disease risk.Mente, A., et al. “A Systematic Review of the Evidence Supporting a Causal Link between Dietary Factors and Coronary Heart Disease.” Arch Intern Med 169, no.7 (2009): 659–69. http://archinte.ama-assn.org/cgi/content/full/169/7/659.

Vitamin C levels in the body have been shown to correlate well with fruit and vegetable intake, and higher plasma vitamin C levels are linked to reduced risk of some chronic diseases. In a study involving over twenty thousand participants, people with the highest levels of circulating vitamin C had a 42 percent decreased risk for having a stroke.Myint, P.K. et al. “Plasma Vitamin C Concentrations Predict Risk of Incident Stroke Over 10 Y[ears] in 20,649 Participants of the European Prospective Investigation into Cancer, Norfolk Prospective Population Study.” Am J Clin Nutr 87, no.1 (2008): 64–69. http://www.ajcn.org/content/87/1/64.long.

Cancer

There is some evidence that a higher vitamin C intake is linked to a reduced risk of cancers of the mouth, throat, esophagus, stomach, colon, and lung, but not all studies confirm this is true. As with the studies on cardiovascular disease, the reduced risk of cancer is the result of eating foods rich in vitamin C, such as fruits and vegetables, not from taking vitamin C supplements. In these studies, the specific protective effects of vitamin C cannot be separated from the many other beneficial chemicals in fruits and vegetables.

Immunity

Vitamin C does have several roles in the immune system, and many people increase vitamin C intake either from diet or supplements when they have a cold. Many others take vitamin C supplements routinely to prevent colds. Contrary to this popular practice, however, there is no good evidence that vitamin C prevents a cold. A review of more than fifty years of studies published in 2004 in the Cochrane Database of Systematic Reviews concludes that taking vitamin C routinely does not prevent colds in most people, but it does slightly reduce cold severity and duration. Moreover, taking megadoses (up to 4 grams per day) at the onset of a cold provides no benefits.Douglas, R.M. et al. “Vitamin C for Preventing and Treating the Common Cold.” Cochrane Database of Systematic Reviews 4 (2004): CD000980. http://www.ncbi.nlm.nih.gov/pubmed/15495002?dopt=Abstract.

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Gout is a disease caused by elevated circulating levels of uric acid and is characterized by recurrent attacks of tender, hot, and painful joints. There is some evidence that a higher intake of vitamin C reduces the risk of gout.

Dietary Reference Intakes for Vitamin C

The classic condition associated with vitamin C deficiency is scurvy. The signs and symptoms of scurvy include skin disorders, bleeding gums, painful joints, weakness, depression, and increased susceptibility to infections. Scurvy is prevented by having an Adequate Intake of fruits and vegetables rich in vitamin C.

They are considered adequate to prevent scurvy. Vitamin C’s effectiveness as a free radical scavenger motivated the Institute of Medicine (IOM) to increase the RDA for smokers by 35 milligrams, as tobacco smoke is an environmental and behavioral contributor to free radicals in the body.

High doses of vitamin C have been reported to cause numerous problems, but the only consistently shown side effects are gastrointestinal upset and diarrhea. To prevent these discomforts the IOM has set a UL for adults at 2,000 milligrams per day (greater than twenty times the RDA).

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At very high doses in combination with iron, vitamin C has sometimes been found to increase oxidative stress, reaffirming that getting your antioxidants from foods is better than getting them from supplements, as that helps regulate your intake levels. There is some evidence that taking vitamin C supplements at high doses increases the likelihood of developing kidney stones, however, this effect is most often observed in people that already have multiple risk factors for kidney stones.

Dietary Sources of Vitamin C

Citrus fruits are great sources of vitamin C and so are many vegetables. In fact, British sailors in the past were often referred to as “limeys” as they carried sacks of limes onto ships to prevent scurvy. Vitamin C is not found in significant amounts in animal-based foods.

Because vitamin C is water soluble, it leaches away from foods considerably during cooking, freezing, thawing, and canning. Up to 50 percent of vitamin C can be boiled away. Therefore, to maximize vitamin C intake from foods, you should eat fruits and vegetables raw or lightly steamed.

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Vitamin A Functions and Health Benefits

Vitamin A is a generic term for a group of similar compounds called retinoids. Retinol is the form of vitamin A found in animal-derived foods, and it is converted in the body to the biologically active forms of vitamin A: retinal and retinoic acid (thus retinol is sometimes referred to as “preformed vitamin A”). About 10 percent of plant-derived carotenoids, including beta-carotene, can be converted in the body to retinoids and are another source of functional vitamin A. The retinoids are aptly named as their most notable function is in the retina of the eye where they aid in vision, particularly in seeing under low-light conditions. This is why night blindness is the most definitive sign of vitamin A deficiency.

Like vitamin E, vitamin A is fat-soluble and is packaged into chylomicrons in small intestine mucosal cells, and then transported to the liver. The liver stores and exports vitamin A as needed; it is released into the blood bound to a retinol-binding protein, which transports it to cells.

Vitamin A has several important functions in the body, including maintaining vision and a healthy immune system. Many of vitamin A’s functions in the body are similar to the functions of hormones (for example, vitamin A can interact with DNA, causing a change in protein function). Vitamin A assists in maintaining healthy skin and the linings and coverings of tissues; it also regulates growth and development. As an antioxidant, vitamin A protects cellular membranes, helps in maintaining glutathione levels, and influences the amount and activity of enzymes that detoxify free radicals.

Vision

Retinol that is circulating in the blood is taken up by cells in the retina, where it is converted to retinal and is used as part of the pigment rhodopsin, which is involved in the eye’s ability to see under low light conditions. A deficiency in vitamin A thus results in less rhodopsin and a decrease in the detection of low-level light, a condition referred to as nightblindness.

Insufficient intake of dietary vitamin A over time can also cause complete vision loss. In fact, vitamin A deficiency is the number one cause of preventable blindness worldwide. Vitamin A not only supports the vision function of eyes but also maintains the coverings and linings of the eyes. Vitamin A deficiency can lead to

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the dysfunction of the linings and coverings of the eye, causing dryness of the eyes, a condition called xerophthalmia. This condition can progress, causing ulceration of the cornea and eventually blindness.

Immunity

The common occurrence of advanced xerophthalmia in children who died from infectious diseases led scientists to hypothesize that supplementing vitamin A in the diet for children with xerophthalmia might reduce disease-related mortality. In Asia in the late 1980s, targeted populations of children were administered vitamin A supplements, and the death rates from measles and diarrhea declined by up to 50 percent. Vitamin A supplementation in these deficient populations did not reduce the number of children who contracted these diseases, but it did decrease the severity of the diseases so that they were no longer fatal. Soon after the results of these studies were communicated to the rest of the world, the World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF) commenced worldwide campaigns against vitamin A deficiency. UNICEF estimates that the distribution of over half a billion vitamin A capsules prevents 350,000 childhood deaths annually.Sommer, A. “Vitamin A Deficiency and Clinical Disease: An Historical Overview.” J Nutr 138 (2008):1835–39. http://jn.nutrition.org/content/ 138/10/1835.long.

In the twenty-first century, science has demonstrated that vitamin A greatly affects the immune system. What we are still lacking are clinical trials investigating the proper doses of vitamin A required to help ward off infectious disease and how large of an effect vitamin A supplementation has on populations that are not deficient in this vitamin. This brings up one of our common themes in this text—micronutrient deficiencies may contribute to the development, progression, and severity of a disease, but this does not mean that an increased intake of these micronutrients will solely prevent or cure disease. The effect, as usual, is cumulative and depends on the diet as a whole, among other things.

Growth and Development

Vitamin A acts similarly to some hormones in that it is able to change the amount of proteins in cells by interacting with DNA. This is the primary way that vitamin A affects growth and development. Vitamin A deficiency in children is linked to growth retardation; however, vitamin A deficiency is often accompanied by protein malnutrition and iron deficiency, thereby confounding the investigation of vitamin A’s specific effects on growth and development.

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In the fetal stages of life, vitamin A is important for limb, heart, eye, and ear development and in both deficiency and excess, vitamin A causes birth defects. Furthermore, both males and females require vitamin A in the diet to effectively reproduce.

Cancer

Vitamin A’s role in regulating cell growth and death, especially in tissues that line and cover organs, suggests it may be effective in treating certain cancers of the lung, neck, and liver. It has been shown in some observational studies that vitamin A-deficient populations have a higher risk for some cancers. However, vitamin A supplements have actually been found to increase the risk of lung cancer in people who are at high risk for the disease (i.e., smokers, exsmokers, workers exposed to asbestos). The Beta-Carotene and Retinol Efficacy Trial (CARET) involving over eighteen thousand participants who were at high risk for lung cancer found that people who took supplements containing very high doses of vitamin A (25,000 international units) and beta-carotene had a 28 percent higher incidence of lung cancer midway through the study, which was consequently stopped.Goodman, G.E. et al. “The Beta-Carotene and Retinol Efficacy Trial: Incidence of Lung Cancer and Cardiovascular Disease Mortality During 6-year Follow-up after Stopping Beta- Carotene and Retinol Supplements.” J Natl Cancer Inst 96, no. 23 (2004): 1743–50. http://jnci.oxfordjournals.org/content/96/23/1743.long.

Vitamin A supplementation is a relatively common practice in treating some types of cancer patients and is thought to improve the effectiveness of some anticancer drugs, but many oncologists (physicians who treat cancer patients) do not recommend this practice as vitamin A may actually inhibit the actions of some anticancer drugs.

Vitamin A Toxicity

Vitamin A toxicity, or hypervitaminosis A, is rare. Typically it requires you to ingest ten times the RDA of preformed vitamin A in the form of supplements (it would be hard to consume such high levels from a regular diet) for a substantial amount of time, although some people may be more susceptible to vitamin A toxicity at lower doses. The signs and symptoms of vitamin A toxicity include dry, itchy skin, loss of appetite, swelling of the brain, and joint pain. In severe cases, vitamin A toxicity may cause liver damage and coma.

Vitamin A is essential during pregnancy, but doses above 3,000 micrograms per day (10,000 international units) have been linked to an increased incidence of birth defects. Pregnant women should check the amount of vitamin A contained in any

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prenatal or pregnancy multivitamin she is taking to assure the amount is below the UL.

Dietary Reference Intakes for Vitamin A

There is more than one source of vitamin A in the diet. There is preformed vitamin A, which is abundant in many animal-derived foods, and there are carotenoids, which are found in high concentrations in vibrantly colored fruits and vegetables and some oils.

Some carotenoids are converted to retinol in the body by intestinal cells and liver cells. However, only miniscule amounts of certain carotenoids are converted to retinol, meaning fruits and vegetables are not necessarily good sources of vitamin A. Beta-carotene dissolved in oil is more readily converted to retinol; one-half of a microgram of beta-carotene is converted to retinol. Overall, the carotenoids do not have the same biological potency of preformed vitamin A, but as you will soon find out, they have other attributes that influence health, most notably their antioxidant activity.

The RDA for vitamin A includes all sources of vitamin A. The amount of vitamin A obtained from carotenoids—the retinol activity equivalent (RAE)—can be calculated. For example, 12 micrograms of fruit- or vegetable-based beta-carotene will yield 1 microgram of retinol, as mentioned.

The RDA for vitamin A is considered sufficient to support growth and development, reproduction, vision, and immune system function while maintaining adequate stores (good for four months) in the liver.

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Dietary Sources of Vitamin A

Preformed vitamin A is found only in foods from animals, with the liver being the richest source because that’s where vitamin A is stored. The dietary sources of carotenoids will be given in the following text.

Phytochemicals

Phytochemicals8 are chemicals in plants that may provide some health benefit. Carotenoids are one type of phytochemical. Phytochemicals also include indoles, lignans, phytoestrogens, stanols, saponins, terpenes, flavonoids, carotenoids, anthocyanidins, phenolic acids, and many more. They are found not only in fruits and vegetables, but also in grains, seeds, nuts, and legumes.

8. Chemicals in plants that may provide some health benefit.

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Many phytochemicals act as antioxidants, but they have several other functions, such as mimicking hormones, altering absorption of cholesterol, inhibiting inflammatory responses, and blocking the actions of certain enzymes.

Phytochemicals are present in small amounts in the food supply, and although thousands have been and are currently being scientifically studied, their health benefits remain largely unknown. Also largely unknown is their potential for toxicity, which could be substantial if taken in large amounts in the form of supplements. Moreover, phytochemicals often act in conjunction with each other and with micronutrients. Thus, supplementing with only a few may impair the functions of other phytochemicals or micronutrients. As with the antioxidant vitamins, it is the mixture and variety of phytochemicals in foods that are linked to health benefits.

Carotenoids Function and Health Benefits

Carotenoids are pigments synthesized by plants that give them their yellow, orange, and red color. Over six hundred carotenoids have been identified and, with just a few exceptions, all are found in the plant kingdom. There are two classes of carotenoids—the xanthophylls, which contain oxygen, and the carotenes, which do not.

In plants, carotenoids absorb light for use in photosynthesis and act as antioxidants. Beta-carotene, alpha-carotene, gamma-carotene, and beta-cryptoxanthin are converted to some extent to retinol in the body. The other carotenoids, such as lycopene, are not. Many biological actions of carotenoids are attributed to their antioxidant activity, but they likely act by other mechanisms, too.

Eye Conditions

Lutein, found in green leafy vegetables, and zeaxanthin, found in peppers, corn, and saffron, act as antioxidants in the retina of the eye and protect it from ultraviolet light damage. Diets high in these carotenoids are associated with a decreased risk of AMD, and there is good evidence that supplements containing these carotenoids also provide vision benefits. A review published in the August 2010 issue of Current Medical Research and Opinion concludes that supplementation with lutein and zeaxanthin reduces the incidence of AMD and cataracts.Barker II, F. M. “Dietary Supplementation: Effects on Visual Performance and Occurrence of AMD and Cataracts.” Curr Med Res Opin 26, no. 8 (2010): 2011–23. http://informahealthcare.com/doi/abs/10.1185/03007995.2010.494549.

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The data that supports that beta-carotene supplementation may delay the progression of AMD is more convincing when beta-carotene is taken in combination with other micronutrients. The Age-Related Eye Disease Study found that a supplement containing 500 milligrams of vitamin C, 400 international units of vitamin E, 15 milligrams of beta-carotene, 80 milligrams of zinc oxide, and 2 milligrams of copper as cupric oxide reduced the risk of progressing to advanced stages of AMD by 25 percent.Age-Related Eye Disease Study Research Group. “A Randomized, Placebo-Controlled, Clinical Trial of High-Dose Supplementation with Vitamins C and E, Beta-Carotene, and Zinc for Age-Related Macular Degeneration and Vision Loss.” Arch Ophthalmol 119, no. 10 (2001): 1417–36. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1462955/. This study did not find that the formulated supplement significantly prevented the onset of disease, only that it delayed its progression specifically in people with intermediate or advanced stage AMD. Studies are ongoing to determine if other antioxidant combinations actually protect against developing AMD at all.

Cardiovascular Disease

While some studies do associate a decreased risk for atherosclerosis with higher dietary intake of carotenoids, others do not. There is a large number of studies that show total carotenoid intake is associated with improvement in blood vessel function. A smaller number of studies show that intake of specific carotenoids, such as lycopene and alpha-carotene, are also associated with improved blood vessel function. The main problems associated with linking carotenoids to a decrease in cardiovascular disease risk, or any other disease for that matter, are that they are present in foods containing many other beneficial plant chemicals, and trials evaluating the effects of specific carotenoids in the form of supplements provide inconsistent and sometimes contradictory results.

Cancer

A higher intake of some carotenoids, but not others, is linked to decreased risks for some cancers. A review of two large studies (> 120,000 men and women) published in the October 2000 issue of The American Journal of Clinical Nutrition reports that there is no significant association between beta-carotene intake and lung cancer risk, but men and women with the highest intakes of total carotenoids had a more than 30 percent risk reduction for developing lung cancer.Michaud, D.S. et al. “Intake of Specific Carotenoids and Risk of Lung Cancer in 2 Prospective US Cohorts.” Am J Clin Nutr 72, no. 4 (2000): 990–97. http://www.ajcn.org/content/72/ 4/990.long. Other large studies conducted in Europe have confirmed the inverse relationship of total dietary carotenoid intake with lung cancer risk. There is some evidence that diets rich in lycopene, which is present in high concentrations in tomatoes, is linked to decreased prostate cancer risk, but it is not known if it is

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lycopene specifically or some other component in tomatoes that protects against prostate cancer.

Carotenoid Bioavailability and Dietary Sources

Carotenoids are not absorbed as well as vitamin A, but similar to vitamin A, they do require fat in the meal for absorption. In intestinal cells, carotenoids are packaged into the lipid-containing chylomicrons inside small intestine mucosal cells and then transported to the liver. In the liver, carotenoids are repackaged into lipoproteins, which transport them to cells.

In contrast to most micronutrients, carotenoid availability is actually increased by the cooking process because cooking, along with chopping and homogenizing, releases carotenoids from the plant matrix. Thus, eating a can of tomatoes provides more lycopene than eating a raw tomato. However, overcooking transforms some of the carotenoids into inactive products, and in general it is best to chop and lightly steam vegetables containing carotenoids to maximize their availability from foods. Cooking carotenoid-containing foods in oil also enhances the bioavailability of carotenoids.

In the United States, the most consumed carotenoids are alpha-carotene, beta-carotene, beta-cryptoxanthin, lycopene, lutein, and zeaxanthin.

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Interactive 8.1

Visit the USDA website and find out more about the carotenoid content of various foods.

http://www.ars.usda.gov/Services/docs.htm?docid=20958

Three Other Phytochemicals and Their Potential Health Benefits

Three classes of phytochemicals (other than carotenoids) are flavonoids, organosulfur compounds, and lignans. Their potential health benefits are discussed below.

Flavonoids

Flavonoids are a large class of chemicals including anthocyanidins (found in red, blue, and purple berries), flavanols (found in teas, chocolate, berries, apples, yellow onions, kale, and broccoli), and isoflavones (found in soy products). Flavonoids are very effective free radical scavengers, and there is some evidence that higher intakes of flavonoid-rich foods and/or beverages reduce the risk of cardiovascular disease, but this has not been consistently observed. Although flavonoids have been

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shown to reduce the incidence of some tumors in animals, similar studies in humans have been inconclusive.

Organosulfur Compounds

These compounds are predominantly found in garlic, but can also be found in onions and leeks. It’s suspected that the higher intake of garlic is the aspect of the Mediterranean diet that contributes to a decreased risk of cardiovascular disease. Animal and laboratory studies suggest the organosulfur compounds in garlic reduce cholesterol, are anti-inflammatory, stimulate the synthesis of glutathione, and cause death of cancer cells. There is some evidence in humans that garlic reduces cholesterol, but more recent studies did not confirm that the effect was signficant or sustained. A higher intake of garlic likely inhibits blood clot formation in humans.

Observational studies suggest diets high in organosulfur compounds decrease the risk of gastric and colorectal cancer. For other cancers, the data is less consistent.

Lignans

Lignans are a group of chemical compounds obtained from many food sources, including grains, nuts, seeds, fruits, and vegetables, and especially flax seed. Some lignans are also called phytoestrogens as they can mimic or inhibit some of the actions of the hormone estrogen in the body.

The antiestrogenic effect of some lignans suggests they may be helpful in treating hormone-dependent cancers, such as breast and ovarian cancers. However, studies are few and conflicting on whether eating foods high in lignans reduces breast or ovarian cancer.

In regard to cardiovascular disease risk, diets rich in whole grains are protective, but it remains unclear whether it is the lignans in whole grains that are responsible for the reduced risk. Whole grains contain many other beneficial phytochemicals, micronutrients, and fiber.

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Interactive 8.2

To discover more about phytochemicals, visit the website for the Micronutrient Information Center of the Linus Pauling Institute at Oregon State University.

http://lpi.oregonstate.edu/infocenter/phytochemicals.html

Other Dietary Sources of Beneficial Phytochemicals Herbs and Spices

These are the aromatic parts of plants, such as the leaves, seeds, pods, and berries. They are an additional dietary source of phytochemicals, and many have exceptional antioxidant capacity.

Throughout the ages, people have used spices and herbs not only for adding flavor to foods, but also as medicines. Curcumin, the principal component of tumeric, has been used for over two thousand years in India to treat a variety of ailments. As of 2011, over seventy clinical trials are investigating the health benefits of curcumin, which may include reducing cancer risk and delaying the progression of Alzheimer’s disease.

You learned in the beginning of this chapter that nutmeg comes from the dried seed kernel of Myristica fragrans and has been used as an antimicrobial, antifungal, and anti-inflammatory agent, and as a pain reliever. In high doses nutmeg acts similar to a psychoactive drug in that it causes euphoria, delusions, and hallucinations. According to a study conducted on over 3,100 foods, beverages, spices, herbs, and supplements, the spices and herbs were the dietary sources most rich in antioxidants (see Note 8.20 “Interactive 8.3”).

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Interactive 8.3

Read the article, “The Total Antioxidant Content of More than 3,100 Foods, Beverages, Spices, Herbs, and Supplements Used Worldwide,” published in the January 2010 issue of the Nutrition Journal. It is a useful source to find dietary sources of antioxidants.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2841576/?tool=pubmed

Tools for Change

Add some spice, flavor, and decoration to your food along with beneficial antioxidants and phytochemicals. Embracing cuisine rich in spices and herbs further enhances the health benefits of eating a diet rich in fruit and vegetables. Think spices are too hot for your palate? As little as half a teaspoon of cinnamon has been shown in scientific studies to provide health benefits, such as improving glucose homeostasis in people with Type 2 diabetes. Over fifteen clinical trials are now evaluating the effectiveness of cinnamon as a adjunct treatment for Type 2 diabetes and/or cardiovascular disease.

Tea

Tea is an aromatic beverage made from the dried parts of plants steeped in hot water. Its health benefits have been known for years, and as with coffee the benefits are not just physiological, but also mental and social. In folklore, teas are considered curatives of stomachache, diarrhea, and even the plague. In The Book of Tea, Okakura Kakuzo asserts that consuming a cup of tea provides “the adoration of the beautiful among the sordid facts of everyday existence.”Okakura Kakuzo. The Book of Tea. (Berlin, Germany: Dover Publications, 1964).

Teas can contain more than seven hundred different phytochemicals. Some of them may be beneficial and others may not be, as some reduce the dietary

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absorption of some micronutrients. The health claims of drinking tea—black, green, or red—number at least in the hundreds but remain mostly scientifically unsupported. There are a great number of studies showing that drinking tea is at least linked to a decreased risk of heart disease, cancer, and diabetes, but the exact phyotchemicals illiciting these health benefits are under intense scrutiny. Moreover, people who consume more tea are likely to drink fewer soft drinks and therefore, based on a “replacement theory,” have a reduced likelihood of having a chronic disease.

Antioxidant Minerals

In addition to the antioxidant vitamins and phytochemicals, several minerals have antioxidant function, including selenium, manganese, iron, copper, and zinc.

Selenium Functions and Health Benefits

Around twenty-five known proteins require selenium to function. Some are enzymes involved in detoxifying free radicals and include glutathione peroxidases and thioredoxin reductase. As an integral functioning part of these enzymes, selenium aids in the regeneration of glutathione and oxidized vitamin C. Selenium as part of glutathione peroxidase also protects lipids from free radicals, and, in doing so, spares vitamin E. This is just one example of how antioxidants work together to protect the body against free radical-induced damage.

Other functions of selenium-containing proteins include protecting endothelial cells that line tissues, converting the inactive thyroid hormone to the active form in cells, and mediating inflammatory and immune system responses.

Observational studies have demonstrated that selenium deficiency is linked to an increased risk of cancer. A review of forty-nine observational studies published in the May 2011 issue of the Cochrane Database of Systematic Reviews concludes that higher selenium exposure reduces overall cancer incidence by about 34 percent in men and 10 percent in women, but notes these studies had several limitations, including data quality, bias, and large differences among different studies.Dennert, G. et al. “Selenium for Preventing Cancer.” Cochrane Database of Systematic Reviews 5 (2011): CD005195. http://www.ncbi.nlm.nih.gov/pubmed/21563143. Additionally, this review states that there is no convincing evidence from six clinical trials that selenium supplements reduce cancer risk.

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Because of its role as a lipid protector, selenium has been suspected to prevent cardiovascular disease. In some observational studies, low levels of selenium are associated with a decreased risk of cardiovascular disease. However, other studies have not always confirmed this association and clinical trials are lacking.

Dietary Reference Intakes for Selenium

The IOM has set the RDAs for selenium based on the amount required to maximize the activity of glutathione peroxidases found in blood plasma. The RDAs for different age groups are listed in Table 8.9 “Dietary Reference Intakes for Selenium”.

Table 8.9 Dietary Reference Intakes for Selenium

Age Group RDA Males and Females mcg/day UL

Infants (0–6 months) 15* 45

Infants (7–12 months) 20* 65

Children (1–3 years) 20 90

Children (4–8 years) 30 150

Children (9–13 years) 40 280

Adolescents (14–18 years) 55 400

Adults (> 19 years) 55 400

*denotes Adequate Intake

Selenium at doses several thousand times the RDA can cause acute toxicity, and when ingested in gram quantities can be fatal. Chronic exposure to foods grown in soils containing high levels of selenium (significantly above the UL) can cause brittle hair and nails, gastrointestinal discomfort, skin rashes, halitosis, fatigue, and irritability. The IOM has set the UL for selenium for adults at 400 micrograms per day.

Dietary Sources of Selenium

Organ meats, muscle meats, and seafood have the highest selenium content. Plants do not require selenium, so the selenium content in fruits and vegetables is usually low. Animals fed grains from selenium-rich soils do contain some selenium. Grains and some nuts contain selenium when grown in selenium-containing soils.

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Manganese, Iron, Copper, and Zinc: Functions and Health Benefits

As with selenium, manganese, iron, copper, and zinc are essential cofactors for enzymes involved in detoxifying free radicals. In the proper doses they allow for optimal detoxification of free radicals. In excess and when not bound to proteins, manganese, iron, and copper actually accelerate the production of free radicals. This is an attribute of all antioxidants in general, although the effect is greater for certain antioxidants.

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Antioxidants can become pro-oxidants when the conditions are altered. Recall from Section 8.1 “Generation of Free Radicals in the Body” of this chapter that oxidative stress results from an imbalance in free radicals with their detoxifying and repair systems. Another factor that can cause oxidative stress is a high level of antioxidants, as some will revert to acting as pro-oxidants.

KEY TAKEAWAYS

• Health claims of antioxidant supplements are not backed by scientific evidence and there is some evidence suggesting they cause harm.

• Consuming antioxidant-rich foods is scientifically supported to reduce the risk of chronic diseases.

• Antioxidants have specific functions, and they can act in concert with each other to protect against free radicals.

• Some antioxidants are involved in the regeneration of other antioxidants.

• Many phytochemicals act as antioxidants, but they perform several other functions as well.

• Dietary antioxidants and phytochemicals in the proper doses are beneficial to health but can cause harm in excess.

DISCUSSION STARTERS

1. In regard to doses, discuss why it is better to obtain antioxidants from the diet and not from supplements. When might supplements be advantageous?

2. With more scientific evidence in hand, debate whether or not the supplement industry requires more regulation.

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8.3 The Whole Nutrient Package versus Disease

LEARNING OBJECTIVES

1. List some of the health-related conditions that might be mitigated by eating antioxidant- and phytochemical-rich foods regularly.

2. Explain the importance of eating a variety of fruits, vegetables, nuts, legumes, teas, and grains to obtain antioxidants and phytochemicals.

A healthy diet incorporating seven or more servings of fruits and vegetables has been shown in many scientific studies to reduce cardiovascular disease and overall deaths attributable to cancer. The WHO states that insufficient fruit and vegetable intake is linked to approximately 14 percent of gastrointestinal cancer deaths, about 11 percent of heart attack deaths, and 9 percent of stroke deaths globally.World Health Organization. “Global Strategies on Diet, Physical Activity, and Health.” Accessed September 30, 2011. http://www.who.int/dietphysicalactivity/fruit/en/ index.html. The WHO estimates that, overall, 2.7 million deaths could be avoided annually by increasing fruit and vegetable intake. These preventable deaths place an economic, social, and mental burden on society. This is why, in 2003, the WHO and the Food and Agricultural Organization of the United Nations launched a campaign to promote fruit and vegetable intake worldwide.

In the last section we reviewed the health benefits of particular antioxidants and phytochemicals obtained from fruits and vegetables and discovered that naturally incorporating them in the diet rather than taking supplements is best. Here we will consider the scientific evidence that diets rich in antioxidants actually lower chronic disease risk.

Antioxidant Variety in Food Provides Health Benefits

Not only has the several-billion-dollar supplement industry inundated us with FDA- unapproved health claims, but science is continously advancing and providing us

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with a multitude of promising health benefits from particular fruits, vegetables, teas, herbs, and spices. For instance, blueberries protect against cardiovascular disease, an apple or pear a day reduces stroke risk by over 52 percent, eating more carrots significantly reduces the risk of bladder cancer, drinking tea reduces cholesterol and helps glucose homeostasis, and cinnamon blocks infection and reduces the risk of some cancers. However, recall that science also tells us that no one nutrient alone is shown to provide these effects.

What micronutrient and phytochemical sources are best at protecting against chronic disease? All of them, together. Just as there is no wonder supplement or drug, there is no superior fruit, vegetable, spice, herb, or tea that protects against all diseases. A review in the July–August 2010 issue of Oxidative Medicine and Cellular Longevity concludes that the plant-food benefits to health are attributed to two main factors—that nutrients and phytochemicals are present at low concentrations in general, and that the complex mixtures of nutrients and phytochemicals provides additive and synergistic effects.Bouayed, J. and T. Bohn. “Exogenous Antioxidants—Double-Edged Swords in Cellular Redox State: Health Beneficial Effects at Physiologic Doses versus Deleterious Effects at High Doses.” Oxidative Medicine and Cellular Longevity 3, no. 4 (2010): 228–37. http://www.ncbi.nlm.nih.gov/ pmc/articles/PMC2952083/?tool=pubmed. In short, don’t overdo it with supplements and make sure you incorporate a wide variety of nutrients in your diet.

Eating a variety of fruits and vegetables rich in antioxidants and phytochemicals promotes health. Consider these diets:

• Mediterranean diet. Fresh fruit and vegetables are abundant in this diet, and the cultural identity of the diet involves multiple herbs and spices. Moreover, olive oil is the main source of fat. Fish and poultry are consumed in low amounts and red meat is consumed in very low amounts. An analysis of twelve studies involving over one million subjects published in the September 2008 issue of the British Medical Journal reports that people who followed the Mediterranean diet had a 9 percent decrease in overall deaths, a 9 percent decrease in cardiovascular death, a 6 percent decrease in cancer deaths, and a 13 percent reduced incidence of Parkinson’s disease and Alzheimer’s disease.Sofi, F. et al. “Adherence to Mediterranean Diet and Health Status: Meta-Analysis.” Br Med J 337 (2008): a1344. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2533524/. The authors of this study concluded that the Mediterranean diet is useful as a primary prevention against some major chronic diseases.

• Dietary Approaches to Stop Hypertension (DASH diet). Recall from Chapter 7 “Nutrients Important to Fluid and Electrolyte Balance” that

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the DASH diet is an eating plan that is low in saturated fat, cholesterol, and total fat. Fruits, vegetables, low-fat dairy foods, whole-grain foods, fish, poultry, and nuts are emphasized while red meats, sweets, and sugar-containing beverages are mostly avoided. Results from a follow- up study published in the December 2009 issue of the Journal of Human Hypertension suggest the low-sodium DASH diet reduces oxidative stress, which may have contributed to the improved blood vessel function observed in salt-sensitive people (between 10 to 20 percent of the population).Al-Solaiman, Y. et al. “Low-Sodium DASH Reduces Oxidative Stress and Improves Vascular Function in Salt-Sensitive Humans.” J Hum Hypertens 12 (2009): 826–35. http://www.ncbi.nlm.nih.gov/pmc/articles/ PMC2783838/?tool=pubmed.

• Diets high in fruits and vegetables. An analysis of The Nurses’ Health Study and the Health Professionals’ Follow-up Study reported that for every increased serving of fruits or vegetables per day, especially green leafy vegetables and vitamin C-rich fruits, there was a 4 percent lower risk for heart disease.Joshipura, K.J. et al. “The Effect of Fruit and Vegetable Intake on Risk for Coronary Heart Disease.” Ann Intern Med 134, no. 12 (2001): 1106–14. http://www.ncbi.nlm.nih.gov/pubmed/ 11412050.

Americans Typically Eat Fewer than the Recommended Servings of Fruits and Vegetables

An article in the January 2009 issue of the Medscape Journal of Medicine reports that fewer than one in ten Americans consumes the recommended amount of fruits and vegetables, which is between five and thirteen servings per day.Kimmons, J. et al. “Fruit and Vegetable Intake among Adolescents and Adults in the United States: Percentage Meeting Individualized Recommendations.” Medscape Journal of Medicine 11, no. 1 (2009): 26. http://www.ncbi.nlm.nih.gov/pmc/articles/ PMC2654704/?tool=pubmed. According to this study, the largest single contributor to fruit intake was orange juice, and potatoes were the dominant vegetable.

The USDA recommends that you fill half your plate with fruits and vegetables. The number of servings of fruits and vegetables that a person should consume every day is dependent on age, sex, and level of physical activity. For example, a forty-year- old male who exercises for sixty minutes per day should consume 2 cups of fruit and 3½ cups of vegetables, while a fifteen-year-old female who exercises for thirty minutes per day should consume 1½ cups of fruit and 2½ cups of vegetables. (One cup of a fruit or vegetable is equal to one banana, one small apple, twelve baby carrots, one orange, or one large sweet potato.) To find out the amount of fruits and

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vegetables the Centers for Disease Control and Prevention (CDC) recommends, see Note 8.25 “Interactive 8.4”.

Interactive 8.4

The CDC provides a fruit- and vegetable-intake calculator.

http://www.fruitsandveggiesmatter.gov/form.html

Improving Fruit and Vegetable Intake at Home and in Your Community

Eating more fruits and vegetables can make you think better, too. According to a study published in 2009 in the Journal of Alzheimer’s Disease, no matter your age, eating more fruits and vegetables improves your brain function.Polidori, M.C. et al. “High Fruit and Vegetable Intake Is Positively Correlated with Antioxidant Status and Cognitive Performance in Healthy Subjects.” Journal of Alzheimer’s Disease 17, no. 4 (2009): 921–7. http://www.ncbi.nlm.nih.gov/pubmed/19542607. Check out Note 8.26 “Interactive 8.5” for thirteen fun ways to increase your fruit and vegetable intake.

Interactive 8.5

Visit the University of Nebraska-Lincoln’s website to discover thirteen fun ways to increase your fruit and vegetable intake.

http://food.unl.edu/web/fnh/freezer-bags

For individually based strategies on how to stretch your fruit and vegetable budget see Note 8.27 “Interactive 8.6”.

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Interactive 8.6

The Department of Health and Human Services provides “30 Ways in 30 Days to Stretch Your Fruit and Vegetable Budget.”

http://www.fruitsandveggiesmatter.gov/downloads/Stretch_FV_Budget.pdf

Tools for Change

Accept the challenge of optimizing your fruit and vegetable intake. Make it easier on your wallet by choosing five of the thirty ways (Note 8.27 “Interactive 8.6”) to stretch your fruit and vegetable budget, and implement them in the next seven days.

The CDC has developed seven strategies to increase American’s intake of fruits and vegetables.Centers for Disease Control and Prevention. “The CDC Guide to Fruit and Vegetable Strategies to Increase Access, Availability, and Consumption.” March 2010. http://www.cdph.ca.gov/SiteCollectionDocuments/ StratstoIncreaseFruitVegConsumption.pdf.

1. Support local and state governments in the implementation of a Food Policy Council, which develops policies and programs that increase the availability of affordable fruits and vegetables.

2. In the food system, increase the availability and affordability of high- quality fruits and vegetables in underserved populations.

3. Promote farm-to-where-you-are programs, which is the delivery of regionally grown farm produce to community institutions, farmers markets, and individuals.

4. Encourage worksites, medical centers, universities, and other community and business establishments to serve more fruits and vegetables in cafeterias and onsite eateries.

5. Support schools in developing healthy food messages to students by incorporating activities such as gardening into curricula.

6. Encourage the development and support of community and home gardens.

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7. Have emergency food programs, including food banks and food rescue programs, increase their supply of fruits and vegetables.

The seven strategies developed by the CDC are based on the idea that improving access to and availability of fruits and vegetables will lead to an increase in their consumption.

KEY TAKEAWAYS

• Antioxidants and phytochemicals from fruits and vegetables are thought to reduce disease risk.

• Antioxidants and phytochemicals may be beneficial in low doses but not in high doses.

• Eat a variety of foods rich in micronutrient antioxidants and phytochemicals to promote health.

• Fewer than one in ten Americans consumes the recommended amount of fruits and vegetables, which is between five and thirteen servings per day.

• National and international campaigns aim to increase the intake of fruits and vegetables worldwide.

DISCUSSION STARTERS

1. Discuss the various strategies you use, or plan to use, to increase the amount of fruits and vegetables in your diet. Learn other interesting and fun ways to do so from your peers.

2. Share with your classmates your favorite spices, how you use them, and where you buy them.

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8.4 End-of-Chapter Exercises

IT ’S YOUR TURN

1. Use the fruit- and vegetable-intake calculator provided by the CDC to determine the amount of fruit and vegetables recommended for your diet, and then plan a menu for a day that incorporates the recommended amount of fruits and vegetables. http://www.fruitsandveggiesmatter.gov/form.html

2. The next time you’re at the grocery store, record the number, color, and names of the fruits and vegetables available. Draw a table of them, sorted by color. Write a brief statement on whether you have access to an affordable variety of fruits and vegetables.

3. Visit the website “Nutrition-and-You” and choose three herbs and/or spices to write a brief summary on, including the plant they come from, their potential health benefits, and how they are used in foods. http://www.nutrition-and-you.com/healthy_spices.html

APPLY IT

1. Visit the Oldways website at http://www.oldwayspt.org/mediterranean- diet-pyramid and construct a pyramid of the Mediterranean diet.

EXPAND YOUR KNOWLEDGE

1. Read the article, “Antioxidant Content of Whole-Grain Breakfast Cereals, Fruits, and Vegetables” in the Journal of the American College of Nutrition (http://www.jacn.org/content/19/suppl_3/312S.long) and summarize in a paragraph the unique phytochemical profile and antioxidant capacity of whole grains.

2. Find out how much fruit and vegetables cost by reviewing this document published by the USDA (http://www.ers.usda.gov/Publications/EIB71/ EIB71.pdf), and make a chart of the costs of your favorite fruits and vegetables.

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Chapter 9

Nutrients Important for Bone Health

Big Idea

Build peak bone mass during youth to preserve bone mass during aging.

Milk has been and will continue to be a key component in the diets of millions of people. During the agrarian age, people drank milk from the animals they raised. At the dawn of the twentieth century, nutritional science appeared on the scene and quickly acknowledged milk’s importance as a part of a balanced diet. For over one hundred years, several US government nutrition programs have highlighted milk’s value. How does milk get from a cow to your doorstep?

In the early nineteenth century raw milk was distributed in carelessly washed metal pails and was, at times, still warm from the cow when it reached its destination. If you got up too late to fetch your milk you received little of the coagulated cream on top. This distribution method did not suffice for the widespread delivery of fresh milk to the masses living in cities, thus milk and its preparation methods had to be changed in several ways. Consuming raw milk can be a potential health hazard as harmful bacteria such as Salmonella, E. coli, and Listeria may be present, all of which are known as culprits for many foodborne illnesses. Pasteurization, homogenization, fortification, and eventually packaging in plastic containers were developed to address distribution and food-safety issues.

In 1863, Louis Pasteur invented pasteurization. Pasteurization involves heating the milk to a high temperature (greater than 161 degrees Fahrenheit) for a short time (less than 20 seconds) and is an effective method of killing 99.999 percent of bacteria, molds, and yeast. Pasteurization was a welcome technology as it extended the shelf life of milk by about two to three weeks and destroyed infectious bacteria, such as those that caused diphtheria, typhoid fever, tuberculosis, and scarlet fever, thereby making milk safe to drink. Unfortunately, pasteurization also destroys vitamins, enzymes, and some beneficial bacteria. Milk may also be microfiltered, a process that pushes milk forcefully through ceramic filters that remove bacteria. Milk is homogenized so that it does not separate into butter-fat globules and milk

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fluid. During homogenization milk is emulsified under intense pressure as it is pumped through narrow tubes. Fat globules are broken into smaller ones and they do not recoagulate. The homogenization process, however, does not have a negative effect on the milk’s nutritional value or effectiveness.

Milk: An ever-changing product of the dairy industry.

Melkkarussell by Gunnar Richter is available under a Creative Commons Attribution-ShareAlike 3.0 Unported license. Hand Milking a Cow by D. Darian Smith is in the public domain.

The dairy industry has gone through many changes to increase milk production, quality, and distribution. As a result of pasteurization and to meet the health needs of the American population, a public-policy decision was made in 1933 to fortify milk with vitamin D to prevent childhood bone disease. More recently, changes include expanding the number of cows per herd, increasing milk production per cow by over six-fold, improving dairy cow nutrition and herd management practices, and advancing technologies that increase storage time and decrease bacterial contamination. How did milk production increase six-fold per cow? Most cows are Holsteins, bred with optimum genetics for producing milk. They are provided with the best nutrition, a dietary pattern taken from many scientific studies that provides optimal nutrients specifically for cows to make milk. Some people are concerned about the changes that were brought about by controversial methods, such as injecting dairy cows with bovine growth hormone. This increases milk production by about 15 percent, but also increases the risk of udder infection in the cows. As a result, antibiotics are widely used in the dairy industry. There is evidence linking widespread antibiotic use with the increase in the resistance of bacteria. This practice also decreases the effectiveness of antibiotics in humans.

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You Decide

How will you ensure that you are building strong bones and will be able to avoid detrimental bone loss in old age?

It is estimated that every three seconds around the globe, an osteoporotic fracture occurs. Over two hundred million women worldwide suffer from this disease.Kanis, J. A. WHO Technical Report, (University of Sheffield, United Kingdom, 2007): 66. Statistics also show that one in three women and one in five men over sixty will experience an osteoporotic fracture.European Foundation for Osteoporosis and National Osteoporosis Foundation. “Who Are Candidates for Prevention and Treatment for Osteoporosis?” Osteoporos Int 7, no. 1 (1997):Melton 3rd, L. J. et al. “Perspective. How Many Women Have Osteoporosis?” J Bone Miner Res 7 (1992): 1005.Kanis, J. A. et al. “Long-Term Risk of Osteoporotic Fracture.” Malmo Osteoporos Int 11 (2000): 669. How can you prepare yourself and fortify your bones against this disease? Milk is a ready and convenient source of calcium and vitamin D, but one glass of milk per day is not sufficient to provide adequate intake of these nutrients and many people have an allergy or intolerance to dairy products. Other good sources of calcium and vitamin D are soybeans, parsley, kale, salmon, broccoli, eggs, tuna, beans, and fortified products such as soymilk, rice milk, and almond milk. As you read this chapter you will learn the importance of building and preserving healthy bones through proper diet and exercise. Whatever you decide, know that your bone health will be affected by your dietary and lifestyle choices for years to come.

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9.1 Bone Structure and Function

LEARNING OBJECTIVE

1. Explain the process of bone remodeling and explain why bones are living tissues.

Your bones are stronger than reinforced concrete. Bone tissue is a composite of fibrous collagen1 strands that resemble the steel rebar in concrete and a hardened mineralized matrix that contains large amounts of calcium, just like concrete. But this is where the similarities end. Bone outperforms reinforced concrete by several orders of magnitude in compression and tension strength tests. Why? The microarchitecture of bone is complex and built to withstand extreme forces. Moreover, bone is a living tissue that is continuously breaking down and forming new bone to adapt to mechanical stresses.

Why Is the Skeletal System Important?

The human skeleton consists of 206 bones and other connective tissues called ligaments, tendons, and cartilage. Ligaments connect bones to other bones, tendons connect bones to muscles, and cartilage provides bones with more flexibility and acts as a cushion in the joints between bones. The skeleton’s many bones and connective tissues allow for multiple types of movement such as typing and running. The skeleton provides structural support and protection for all the other organ systems in the body. The skull, or cranium, is like a helmet and protects the eyes, ears, and brain. The ribs form a cage that surrounds and protects the lungs and heart. In addition to aiding in movement, protecting organs, and providing

1. A strong, fibrous protein made up of mostly glycine and proline amino acids.

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structural support, red and white blood cells and platelets are synthesized in bone marrow. Another vital function of bones is that they act as a storage depot for minerals such as calcium, phosphorous, and magnesium. Although bone tissue may look inactive at first glance, at the microscopic level you will find that bones are continuously breaking down and reforming. Bones also contain a complex network of canals, blood vessels, and nerves that allow for nutrient transport and communication with other organ systems.

The human skeleton contains 206 bones. It is divided into two main parts, the axial and appendicular.

Human Skeleton Front by Mariana Ruiz Villarreal is in the public domain.

Bone Anatomy and Structure

To optimize bone health through nutrition, it is important to understand bone anatomy. The skeleton is composed of two main parts, the axial and the appendicular parts. The axial skeleton consists of the skull, vertebral column, and rib cage, and is composed of eighty bones. The appendicular skeleton consists of the shoulder girdle, pelvic girdle, and upper and lower extremities and is composed of 126 bones. Bones are also categorized by size and shape. There are four types of

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bone: long bones, short bones, flat bones, and irregular bones. The longest bone in your body is the femur (or “thigh” bone), which extends from your hip to your knee. It is a long bone and functions to support your weight as you stand, walk, or run. Your wrist is composed of eight irregular-shaped bones, which allow for the intricate movements of your hands. Your twelve ribs on each side of your body are curved flat bones that protect your heart and lungs. Thus, the bones’ different sizes and shapes allow for their different functions.

Figure 9.1 The Arrangement of Bone Tissues

Bone is composed of organized living tissues.

Compact Spongy Bone comprises public domain material from the National Cancer Institute.

Bones are composed of approximately 65 percent inorganic material known as mineralized matrix. This mineralized matrix consists of mostly crystallized hydroxyapatite2. The bone’s hard crystal matrix of bone tissue gives it its rigid structure. The other 35 percent of bone is organic material, most of which is the fibrous protein, collagen. The collagen fibers are networked throughout bone tissue and provide it with flexibility and strength. The bones’ inorganic and organic materials are structured into two different tissue types. There is spongy bone, also called trabecular or cancellous bone3, and compact bone, also called cortical bone4 (Figure 9.1 “The Arrangement of Bone Tissues”). The two tissue types differ in their microarchitecture and porosity. Trabecular bone is 50 to 90 percent porous and appears as a lattice-like structure under the microscope. It is found at the ends of long bones, in the cores of vertebrae, and in the pelvis. Trabecular bone tissue makes up about 20 percent of the adult skeleton. The more dense cortical bone is

2. The primary crystal of bone formed from calcium and phosphorous.

3. Less dense bone with a lattice- like structure. Also called spongy bone.

4. Dense, strong bone that surrounds trabecular bone tissue. Also called compact bone.

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about 10 percent porous and it looks like many concentric circles, similar to the rings in a tree trunk, sandwiched together (Figure 9.2). Cortical bone tissue makes up approximately 80 percent of the adult skeleton. It surrounds all trabecular tissue and is the only bone tissue in the shafts of long bones.

Figure 9.2

The two basic tissue types of bones are trabecular and cortical. Trabecular (spongy) and cortical (compact) bone tissues differ in their microarchitecture and porosity.

Diagram of Compact Bone from Human Anatomy and Physiology by Openstax is available under a Creative Commons Attribution 3.0 Unported license. © Jul 30, 2014 OpenStax. Download for free at http://cnx.org/ contents/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@6.27

Bone tissue is arranged in an organized manner. A thin membrane, called the periosteum, surrounds the bone. It contains connective tissue with many blood vessels and nerves. Lying below the periosteum is the cortical bone. In some bones, the cortical bone surrounds the less-dense trabecular bone and the bone marrow lies within the trabecular bone, but not all bones contain trabecular tissue or marrow.

Bone Tissues and Cells, Modeling and Remodeling

Bone tissue contains many different cell types that constantly resize and reshape bones throughout growth and adulthood. Bone tissue cells include osteoprogenitor cells, osteoblasts, osteoclasts, and osteocytes. The osteoprogenitor cells are cells that have not matured yet. Once they are stimulated, some will become osteoblasts5, the bone builders, and others will become osteoclasts6, the cells that break bone down. Osteocytes7 are the most abundant cells in bone tissue. Osteocytes are star-shaped cells that are networked throughout the bone via their long cytoplasmic arms that allow for the exchange of nutrients and other factors from bones to the blood and lymph.

5. Cells that build new bone tissue.

6. Large cells that break down bone tissue.

7. Star-shaped cells that are the most abundant cell type in bone tissue.

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Bone Modeling and Remodeling

During infancy, childhood, and adolescence, bones are continuously growing and changing shape through two processes called growth (or ossification) and modeling. In fact, in the first year of life, almost 100 percent of the bone tissue in the skeleton is replaced. In the process of modeling, bone tissue is dismantled at one site and built up at a different site. In adulthood, our bones stop growing and modeling, but continue to go through a process of bone remodeling8. In the process of remodeling, bone tissue is degraded and built up at the same location. About 10 percent of bone tissue is remodeled each year in adults. Bones adapt their structure to the forces acting upon them, even in adulthood. This phenomenon is called Wolff’s law, which states that bones will develop a structure that is best able to resist the forces acting upon them. This is why exercising, especially when it involves weight-bearing activities, increases bone strength.

The first step in bone remodeling is osteocyte activation. Osteocytes detect changes in mechanical forces, calcium homeostasis, or hormone levels. In the second step, osteoclasts are recruited to the site of the degradation. Osteoclasts are large cells with a highly irregular ruffled membrane. These cells fuse tightly to the bone and secrete hydrogen ions, which acidify the local environment and dissolve the minerals in the bone tissue matrix. This process is called bone resorption9 and resembles pit excavation. Our bodies excavate pits in our bone tissue because bones act as storehouses for calcium and other minerals. Bones supply these minerals to other body tissues as the demand arises. Bone tissue also remodels when it breaks so that it can repair itself. Moreover, if you decide to train to run a marathon your bones will restructure themselves by remodeling to better able sustain the forces of their new function.

8. Process in which bone tissue is broken down and then rebuilt at the same location.

9. Process in which osteoclasts secrete hydrogen ions, which acidify the local environment and dissolve the minerals in the bone tissue matrix.

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After a certain amount of bone is excavated, the osteoclasts begin to die and bone resorption stops. In the third step of bone remodeling, the site is prepared for building. In this stage, sugars and proteins accumulate along the bone’s surface, forming a cement line which acts to form a strong bond between the old bone and the new bone that will be made. These first three steps take approximately two to three weeks to complete. In the last step of bone remodeling, osteoblasts lay down new osteoid tissue that fills up the cavities that were excavated during the resorption process. Osteoid10 is bone matrix tissue that is composed of proteins such as collagen and is not mineralized yet. To make collagen, vitamin C is required. A symptom of vitamin C deficiency (known as scurvy) is bone pain, which is caused by diminished bone remodeling. After the osteoid tissue is built up, the bone tissue begins to mineralize. The last step of bone remodeling continues for months, and for a much longer time afterward the mineralized bone is continuously packed in a more dense fashion.

10. Bone tissue that is not mineralized.

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Thus, we can say that bone is a living tissue that continually adapts itself to mechanical stress through the process of remodeling. For bone tissue to remodel certain nutrients such as calcium, phosphorus, magnesium, fluoride, vitamin D, and vitamin K are required.

KEY TAKEAWAYS

• The skeletal system aids in movement, provides support for and protects organs, synthesizes platelets and red and white blood cells, and serves as a storage depot for minerals, such as calcium.

• The skeleton is composed of connective tissues including bones, cartilage, tendons, and ligaments.

• Bones are made up of a periosteum that surrounds compact bone, which in turn surrounds trabecular bone. Bone marrow resides within the trabecular bone.

• Bone tissue cells are osteoprogenitor cells, osteoblasts, osteoclasts, and osteocytes.

• Bone is a living tissue that adapts to mechanical stress via the remodeling process.

• Bone remodeling is a multifaceted process involving four steps: osteocyte activation, osteoclast-mediated bone resorption, surface preparation, and osteoblast-mediated bone building.

• The bone remodeling process requires certain nutrients such as calcium, phosphorus, magnesium, fluoride, vitamin D, and vitamin K.

DISCUSSION STARTERS

1. Analyze the shape of some of your bones. Recognize the varying structure of different bones that allows for the performance of multiple functions. With a classmate, compare the shape of hand bones (that allow for fine articulated movements) to the shape of foot bones and toe bones (that allow more awkward movement). If you designed a bone system to grasp a doorknob or hang upside down, what would it look like? For inspiration, go to the web and look at bat bones, monkey bones, and human bones.

2. Why do you think it hurts when you hit your funny bone? Why are there no bones to protect the nerves?

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9.2 Bone Mineral Density Is an Indicator of Bone Health

LEARNING OBJECTIVE

1. Identify the tests used to measure bone mass.

Bone mineral density (BMD)11 is a measurement of the amount of calcified tissue in grams per centimeter squared of bone tissue. BMD can be thought of as the total amount of bone mass in a defined area. When BMD is high, bone strength will be great. Similar to measuring blood pressure to predict the risk of stroke, a BMD measurement can help predict the risk of bone fracture. The most common tool used to measure BMD is called dual energy X-ray absorptiometry (DEXA)12. During this procedure, a person lies on their back and a DEXA scanner passes two X- ray beams through their body. The amount of X-ray energy that passes through the bone is measured for both beams. The total amount of the X-ray energy that passes through a person varies depending on their bone thickness. Using this information and a defined area of bone, the amount of calcified tissue in grams per unit area (cm2) is calculated. Most often the DEXA scan focuses on measuring BMD in the hip and the spine. These measurements are then used as indicators of overall bone strength and health. DEXA is the cheapest and most accurate way to measure BMD. It also uses the lowest dose of radiation. Other methods of measuring BMD include quantitative computed tomography (QCT) and radiographic absorptiometry. People at risk for developing bone disease are advised to have a DEXA scan. We will discuss the many risk factors linked to an increased incidence of osteoporosis and the steps a person can take to prevent the disease from developing.

KEY TAKEAWAYS

• Bone-mineral density is a measurement of calcified bone tissue and positively correlates with overall bone health.

• DEXA is a clinical tool used to assess BMD.

11. Measurement of the amount of calcified tissue in grams per centimeter squared of bone tissue.

12. A procedure during which two X-ray beams pass through a person and calculate the amount of calcified tissue in grams per unit area of bone.

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9.3 Micronutrients Essential for Bone Health: Calcium and Vitamin D

LEARNING OBJECTIVES

1. List the four primary functions of calcium in the human body. 2. Identify the Dietary Reference Intake for calcium.

Calcium

The most abundant mineral in the body is calcium13, and greater than 99 percent of it is stored in bone tissue. Although only 1 percent of the calcium in the human body is found in the blood and soft tissues, it is here that it performs the most critical functions. Blood calcium levels are rigorously controlled so that if blood levels drop the body will rapidly respond by stimulating bone resorption, thereby releasing stored calcium into the blood. (This is discussed in further detail shortly.) Thus, bone tissue sacrifices its stored calcium to maintain blood calcium levels. This is why bone health is dependent on the intake of dietary calcium and also why blood levels of calcium do not always correspond to dietary intake.

Calcium’s Functional Roles

Calcium plays a role in a number of different functions in the body:

• Bone and tooth formation. The most well- known calcium function is to build and strengthen bones and teeth. Recall that when bone tissue first forms during the modeling or remodeling process, it is unhardened, protein-rich osteoid tissue. In the osteoblast-directed process of bone mineralization, calcium phosphates (salts) are deposited on the protein matrix. The calcium salts gradually crystallize into hydroxyapatite, which typically makes up about 65 percent of bone tissue. When your diet is calcium deficient, the mineral content of bone decreases causing it to become brittle and weak. Thus, increased

13. The most abundant mineral in mineralized bone tissue. Good dietary sources of calcium are dairy products and many vegetables with low oxalate content, such as kale, collard greens, and okra.

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calcium intake helps to increase the mineralized content of bone tissue. Greater mineralized bone tissue corresponds to a greater BMD, and to greater bone strength. The varying arrangements of the calcium-rich hydroxyapatite crystals on bone tissue’s protein matrix contribute to bone’s differing mechanical properties. In tooth enamel, hydroxyapatite crystals are densely packed, making it the most mineralized tissue (more than 95 percent) in the human body. Tooth enamel’s densely packed crystal architecture provides it with its incredible strength and durability. The mineralized bone tissue in human teeth is so incredibly strong that back molars can withstand bite forces exceeding four hundred pounds of pressure.

• Nerve impulse transmission. Calcium facilitates electrical impulse transmission from one nerve cell to another. Calcium binds to vesicles that contain neurotransmitters, causing a release into the neural synapses (junction between nerve cells). This allows the flow of ions in and out of nerve cells. If calcium is lacking, nerve-cell function will fail (see Note 9.30 “Interactive 9.1”).

• Muscle contraction. The flow of calcium ions along the muscle cell’s surface and the influx of calcium into the muscle cell are critical for muscle contraction. If calcium levels fall below a crucial range, the muscles can’t relax after contracting. The muscles become stiff, and involuntary twitching may ensue in a condition known as tetany.

• Clotting factors. When a blood vessel is injured and bleeding starts, it must be stopped or death may result. Clotting factors and platelets are continuously circulating in the blood in case of such an emergency. When an injury occurs, the damaged tissue releases specific factors that activate the circulating clotting factors and platelets. Some of the clotting factors require calcium for activation. If clotting factors weren’t activated blood clots would not form.

In addition to calcium’s four primary functions calcium has several other minor functions that are also critical for maintaining normal physiology. For example, without calcium, the hormone insulin could not be released from cells in the pancreas and glycogen could not be broken down in muscle cells and used to provide energy for muscle contraction.

Maintaining Calcium Levels

Because calcium performs such vital functions in the body, blood calcium level is closely regulated by the hormones parathyroid hormone (PTH)14, calcitriol15, and calcitonin16. Calcitriol is the active hormone produced from vitamin D. Parathyroid hormone and calcitriol act in a concert to increase calcium levels in the blood, while

14. Parathyroid hormone acts to increase calcium levels in the blood.

15. The active hormone produced by vitamin D that also helps to increase and regulate blood calcium levels.

16. This hormone has the opposite effect of calcitriol and parathyroid hormone and aids in the maintenance of blood calcium levels by decreasing the calcium level as necessary.

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calcitonin does the opposite and decreases blood calcium levels. These hormones maintain calcium levels in the blood in a range between 9 and 11 milligrams per deciliter.

Parathyroid Hormone

Four parathyroid glands, each the size of a grain of rice, can be found in the neck on the sides of the thyroid gland. PTH increases blood calcium levels via three different mechanisms (Figure 9.4). First, PTH stimulates the release of calcium stored in the bone. Second, PTH acts on kidney cells to increase calcium reabsorption and decrease its excretion in the urine. Third, PTH stimulates enzymes in the kidney that activate vitamin D to calcitriol. Calcitriol acts on intestinal cells and increases dietary calcium absorption. Thus, stored calcium is released, more calcium is absorbed from the diet, and less calcium is excreted, all of which increase calcium levels in the blood.

Figure 9.4

This is a typical negative feedback loop in which low calcium levels in the blood stimulate PTH release. PTH increases the movement of calcium from the bones, kidneys, and intestine to the blood with the help of activated vitamin D. The now higher calcium levels in the blood shut off further PTH release.

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Calcium Regulation by Mikael Häggström is in the public domain.

Calcitriol (1,25 Hydroxy-Vitamin D)

Calcitriol functions as a second hand to PTH. It not only increases calcium release from bone tissue, but also it increases the absorption of calcium in the small intestine and increases calcium reabsorption by the kidneys. Neither hormone will work unless accompanied by the other. Vitamin D regulates PTH secretion and PTH regulates vitamin D activation to calcitriol. Adequate levels of vitamin D allow for a balance of the calcium between what is released by bone tissue and what is incorporated into bone tissue, so that bone health is not compromised. Calcitriol and PTH function together to maintain calcium homeostasis.

Calcitonin

Calcitonin is a hormone secreted by certain cells in the thyroid gland in response to high calcium levels in the blood. In comparison to PTH and calcitriol, calcitonin plays a small role in regulating calcium levels on a day-to-day basis. This is because as calcium levels rise in the blood, calcium feedback inhibits PTH release and effectively shuts off the actions of PTH and calcitriol. This route of feedback inhibition helps prevent calcium’s further accumulation in the blood. At higher nonphysiological concentrations, calcitonin lowers blood calcium levels by increasing calcium excretion in the urine, preventing further absorption of calcium in the gut and by directly inhibiting bone resorption.

Other Health Benefits of Calcium in the Body

Besides forming and maintaining strong bones and teeth, calcium has been shown to have other health benefits for the body, including:

• Cancer. The National Cancer Institute reports that there is enough scientific evidence to conclude that higher intakes of calcium decrease colon cancer risk and may suppress the growth of polyps that often precipitate cancer. Although higher calcium consumption protects against colon cancer, some studies have looked at the relationship between calcium and prostate cancer and found higher intakes may increase the risk for prostate cancer; however the data is inconsistent and more studies are needed to confirm any negative association.

• Blood pressure. Multiple studies provide clear evidence that higher calcium consumption reduces blood pressure. A review of twenty-three observational studies concluded that for every 100 milligrams of

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calcium consumed daily, systolic blood pressure is reduced 0.34 millimeters of mercury (mmHg) and diastolic blood pressure is decreased by 0.15 mmHg.Birkett, N. J. “Comments on a Meta-Analysis of the Relation between Dietary Calcium Intake and Blood Pressure.” Am J Epidemiol 148, no. 3 (1998): 223–28. http://aje.oxfordjournals.org/ content/148/3/223.long. There is emerging evidence that higher calcium intakes prevent against other risk factors for cardiovascular disease, such as high cholesterol and obesity, but the scientific evidence is weak or inconclusive.

• Kidney stones. Another health benefit of a high-calcium diet is that it blocks kidney stone formation. Calcium inhibits the absorption of oxalate, a chemical in plants such as parsley and spinach, which is associated with an increased risk for developing kidney stones. Calcium’s protective effects on kidney stone formation occur only when you obtain calcium from dietary sources. Calcium supplements may actually increase the risk for kidney stones in susceptible people.

Calcium Needs, Sources, and Bioavailability Dietary Reference Intake for Calcium

The RDA is elevated to 1,300 milligrams per day during adolescence because this is the life stage with accelerated bone growth. Studies have shown that a higher intake of calcium during puberty increases the total amount of bone tissue that accumulates in a person. For women above age fifty and men older than seventy- one, the RDAs are also a bit higher for several reasons including that as we age, calcium absorption in the gut decreases, vitamin D3 activation is reduced, and maintaining adequate blood levels of calcium is important to prevent an acceleration of bone tissue loss (especially during menopause). Currently, the dietary intake of calcium for females above age nine is, on average, below the RDA for calcium. The Institute of Medicine (IOM) recommends that people do not consume over 2,500 milligrams per day of calcium as it may cause adverse effects in some people.

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In the typical American diet, calcium is obtained mostly from dairy products, primarily cheese. A slice of cheddar or Swiss cheese contains just over 200 milligrams of calcium. One cup of nonfat milk contains approximately 300 milligrams of calcium, which is about a third of the RDA for calcium for most adults. Foods fortified with calcium such as cereals, soy milk, and orange juice also provide one third or greater of the calcium RDA. Although the typical American diet relies mostly on dairy products for obtaining calcium, there are many other good nondairy sources of calcium (see Note 9.28 “Tools for Change” in Section 9.3 “Micronutrients Essential for Bone Health: Calcium and Vitamin D”. A food’s calcium content can be calculated from the percent daily value (percent DV) displayed on the Nutrition Facts panel (Figure 9.5 “How to Calculate Calcium in Milligrams from the Nutrition Facts Panel”). Since the RDA for calcium used to calculate the daily value (DV) is 1,000 milligrams, you multiply the percent DV by ten to arrive at the calcium content in milligrams for a serving of a particular food. It is important to note that most processed foods offer a poor source for this vital mineral as the refinement process strips away the nutrients in the food.

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Tools for Change

If you need to increase calcium intake, are a vegan, or have a food allergy to dairy products, it is helpful to know that there are several plant-based foods that are high in calcium. Broccoli, kale, mustard greens, and Brussel sprouts are excellent sources. One cup of these cooked vegetables provides between 100 and 180 milligrams of calcium. To increase the calcium content in your lunch and add some texture to your food, chop up some kale and put it on your sandwich or in your soup. For a list of nondairy sources that are high in calcium. Additionally, you can find the calcium content for thousands of foods by visiting the USDA National Nutrient Database (http://www.nal.usda.gov/ fnic/foodcomp/search/). When obtaining your calcium from a vegan diet, it is important to know that some plant-based foods significantly impair the absorption of calcium. These include spinach, Swiss chard, rhubarb, beets, cashews, and peanuts. With careful planning and good selections, you can ensure that you are getting enough calcium in your diet even if you do not drink milk or consume other dairy products.

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Figure 9.5 How to Calculate Calcium in Milligrams from the Nutrition Facts Panel

The percent DV of calcium is given on the Nutrition Facts panel. To convert this to milligrams (mg), multiply this number by ten. This is the amount of calcium in milligrams in one serving. This can be done this easily ONLY for calcium and not for other nutrients because the DV for calcium, based on the RDA for adults between the ages of nineteen and fifty, is equal to 1,000 milligrams. Nutrition Facts comprises public domain material from the Food and Drug Administration.

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Calcium Bioavailability

Bioavailability refers to the amount of a particular nutrient in foods that is actually absorbed in the intestine and not eliminated in the urine or feces. Simply put, the bioavailability of calcium is the amount that is on hand to perform its biological functions. In the small intestine, calcium absorption primarily takes place in the duodenum (first section of the small intestine) when intakes are low, but calcium is also absorbed passively in the jejunum and ileum (second and third sections of the small intestine), especially when intakes are higher. The body doesn’t completely absorb all the calcium in food. About 30 percent of calcium is absorbed from milk and other dairy products. Interestingly, the calcium in some vegetables such as kale, Brussel sprouts, and bok choy, is better absorbed by the body than are dairy

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products. The body absorbs approximately 50 percent of calcium from these plant- based sources.

Factors that Increase Calcium Bioavailability

Stomach acid releases calcium from foods and ionizes it to Ca++. Calcium must be in its ionized form to be absorbed in the small intestine. The greatest positive influence on calcium absorption comes from having an adequate intake of vitamin D. People deficient in vitamin D absorb less than 15 percent of calcium from the foods they eat. The hormone estrogen is another factor that enhances calcium bioavailability. Thus, as a woman ages and goes through menopause, during which estrogen levels fall, the amount of calcium absorbed decreases and the risk for bone disease increases. Some fibers, such as inulin, found in jicama, onions, and garlic, also promote calcium intestinal uptake.

Factors that Decrease Calcium Bioavailability

Chemicals that bind to calcium decrease its bioavailability. These negative effectors of calcium absorption include the oxalates in certain plants, the tannins in tea, phytates in nuts, seeds, and grains, and some fibers. Oxalates are found in high concentrations in spinach, parsley, cocoa, and beets. In general, the calcium bioavailability is inversely correlated to the oxalate content in foods. High-fiber, low-fat diets also decrease the amount of calcium absorbed, an effect likely related to how fiber and fat influence the amount of time food stays in the gut. Anything that causes diarrhea, including sicknesses, medications, and certain symptoms related to old age, decreases the transit time of calcium in the gut and therefore decreases calcium absorption. As we get older, stomach acidity sometimes decreases, diarrhea occurs more often, kidney function is impaired, and vitamin D absorption and activation is compromised, all of which contribute to a decrease in calcium bioavailability.

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Vitamin D

Figure 9.6 Vitamin D Food Sources

Vitamin D17 refers to a group of fat-soluble vitamins derived from cholesterol. Vitamins D2 and D3 are the only ones known to have biological actions in the human body. Although vitamin D3 is called a vitamin, the body can actually synthesize vitamin D3. When exposed to sunlight, a cholesterol precursor in the skin is transformed into vitamin D3. However, this is not the bioactive form of vitamin D. It first must be acted upon by enzymes in the liver and then transported to the kidney where vitamin D3 is finally transformed into the active hormone, calcitriol (1,25-dihydroxy vitamin D3) (Figure 9.7 “The Activation of Vitamin D to Calcitriol”). The skin synthesizes vitamin D when exposed to sunlight. In fact, for most people, more than 90 percent of their vitamin D3 comes from the casual exposure to the UVB rays in sunlight. Anything that reduces your exposure to the sun’s UVB rays decreases the amount of vitamin D3 your skin synthesizes. That would include long winters, your home’s altitude, whether you are wearing sunscreen, and the color of your skin (including tanned skin). Do you ever wonder

17. Both a vitamin and a hormone, vitamin D plays an essential role in maintaining calcium homeostasis. A deficiency in vitamin D compromises bone health.

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about an increased risk for skin cancer by spending too much time in the sun? Do not fret. Less than thirty minutes of sun exposure to the arms and legs will increase blood levels of vitamin D3 more than orally taking 10,000 IU (250 micrograms) of vitamin D3. However, it important to remember that the skin production of vitamin D3 is a regulated process, so too much sun does cause vitamin D toxicity.

Interactive 9.1

Vitamin D Production in the Body

Visit the University of North Carolina Gillings School of Global Public Health website to review the activation of vitamin D to calcitriol.

http://www.unc.edu/tlim/nutr240/?6

A person’s vitamin D status is determined by measuring 25-hydroxy vitamin D3 levels in the blood serum because it reflects both the vitamin D obtained from production in the skin and that from dietary sources. Measuring the active hormone, calcitriol, does not accurately reflect one’s vitamin D status because of its short half-life (six to twelve hours). The vast majority of nutrition experts consider a concentration of 25-hydroxy vitamin D3 in the blood serum less than 20 nanograms per millileter as an indicator of vitamin D deficiency. The IOM states that serum levels above 20 nanograms per milliliter are sufficient to maintain bone health in healthy individuals. Both nutrition experts and health advocates currently are debating what the optimal levels of vitamin D3 should be to take full advantage of all of its health benefits. Some advocates propose that serum levels of vitamin D3 above 40 nonograms per milliliter are optimal. To determine whether higher levels of vitamin D3 provide advantages in fighting diseases such as cancer, a large clinical trial called VITAL (Vitamin D and Omega-3 Trial) has been initiated at Brigham and Women’s Hospital and Harvard Medical School in Boston, Massachusetts. To remain updated on this trial, visit their website at http://www.vitalstudy.org/index.html.

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Figure 9.7 The Activation of Vitamin D to Calcitriol

Synthesis of Vitamin D from Human Anatomy and Physiology by Openstax is available under a Creative Commons Attribution 3.0 Unported license. © Jul 30, 2014 OpenStax. Download for free at http://cnx.org/contents/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@6.27.

Vitamin D’s Functional Role

As previously discussed, activated vitamin D3 (calcitriol) regulates blood calcium levels in concert with parathyroid hormone. In the absence of an adequate intake of vitamin D, less than 15 percent of calcium is absorbed from foods or supplements. The effects of calcitriol on calcium homeostasis are critical for bone health. A deficiency of vitamin D in children causes the bone disease nutritional rickets18. Rickets is very common among children in developing countries and is characterized by soft, weak, deformed bones that are exceptionally susceptible to fracture. In adults, vitamin D deficiency causes a similar disease called osteomalacia19, which is characterized by low BMD. Osteomalacia has the same symptoms and consequences as osteoporosis and often coexists with osteoporosis. Vitamin D deficiency is common, especially in the elderly population, dark-skinned populations, and in the many people who live in the northern latitudes where sunlight exposure is much decreased during the long winter season.

18. A childhood bone disease caused by a lack of vitamin D. It is characterized by soft, weak bones that are susceptible to fracture.

19. Similar to nutritional rickets, in adults this disease involves softening and weakening of the bones due to a lack of vitamin D or a problem metabolizing the vitamin.

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Observational studies have shown that people with low levels of vitamin D in their blood have lower BMD and an increased incidence of osteoporosis. In contrast, diets with high intakes of salmon, which contains a large amount of vitamin D, are linked with better bone health. A review of twelve clinical trials, published in the May 2005 issue of the Journal of the American Medical Association, concluded that oral vitamin D supplements at doses of 700–800 international units per day, with or without coadministration of calcium supplements, reduced the incidence of hip fracture by 26 percent and other nonvertebral fractures by 23 percent.“Fracture Prevention with Vitamin D Supplementation: A Meta-Analysis of Randomized Controlled Trials.” JAMA 293, no. 18 (2005): 2257–64. http://jama.ama-assn.org/content/293/ 18/2257.long. A reduction in fracture risk was not observed when people took vitamin D supplements at doses of 400 international units.

Vitamin D Needs and Sources Dietary Reference Intake for Vitamin D

For adults, the RDA is 600 international units, which is equivalent to 15 micrograms of vitamin D. The National Osteoporosis Foundation recommends slightly higher levels and that adults under age fifty get between 400 and 800 international units of vitamin D every day, and adults fifty and older get between 800 and 1,000 international units of vitamin D every day. According to the IOM, the tolerable upper intake level (UL) for vitamin D is 4,000 international units per day. Toxicity from excess vitamin D is rare, but certain diseases such as hyperparathyroidism, lymphoma, and tuberculosis make people more sensitive to the increases in calcium caused by high intakes of vitamin D.

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Vitamin D Bioavailability

There are few food sources of vitamin D. Oily fish, such as salmon, is one of the best. The amount of vitamin D obtained from one 3-ounce piece of salmon is greater than the recommended intake for one day. Many foods, including dairy products, orange juice, and cereals are now fortified with vitamin D. Most vitamin-D-fortified foods contain about 25 percent of the RDA for vitamin D per serving, but check the label. Many people are deficient in vitamin D as a result of the few dietary sources for this vitamin.

Other Health Benefits of Vitamin D in the Body

Many other health benefits have been linked to higher intakes of vitamin D, from decreased cardiovascular disease to the prevention of infection. Furthermore, evidence from laboratory studies conducted in cells, tissues, and animals suggest vitamin D prevents the growth of certain cancers, blocks inflammatory pathways, reverses atherosclerosis, increases insulin secretion, and blocks viral and bacterial infection and many other things. Vitamin D deficiency has been linked to an increased risk for autoimmune diseases. (Autoimmune diseases are those that result from an abnormal immune response targeted against the body’s own tissues.) An increased prevalence of the autoimmune diseases, rheumatoid arthritis, multiple sclerosis, and Type 1 diabetes has been observed in populations with inadequate vitamin D levels. Additionally, vitamin D deficiency is linked to an increased incidence of hypertension. Until the results come out from the VITAL study, the bulk of scientific evidence touting other health benefits of vitamin D is from laboratory and observational studies and requires confirmation in clinical intervention studies.

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KEY TAKEAWAYS

• Calcium is the most abundant mineral in the body and has four primary functions: making bones strong and healthy, facilitating nerve-to-nerve communication, stimulating muscle contraction, and activating blood- clotting factors. Other benefits of calcium in the body include decreasing blood pressure and preventing colon cancer.

• Calcium blood-levels are rigorously controlled by three hormones: PTH, calcitriol, and calcitonin.

• The DRI for calcium intake for adults averages from 1,000–1,200 milligrams per day.

• Only some of the calcium in food is absorbed by the body. Vitamin D and estrogen enhance the bioavailability of calcium in the body. Alternately, diets high in oxalates, some types of fiber, and diets low in fat decrease the bioavailability of calcium in the body.

• Vitamin D is essential for maintaining calcium levels in the body. Once activated to calcitriol, it acts in concert with PTH to keep blood levels of calcium constant, especially by enhancing its intestinal absorption. High levels of vitamin D in the blood promote bone health.

DISCUSSION STARTERS

1. Talk about some of the vital functions of calcium and vitamin D in the body. Why are these nutrients so important to health? What can you do to increase these vitamins in your diet?

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9.4 Other Essential Micronutrients for Bone Health: Phosphorous, Magnesium, Fluoride, and Vitamin K

LEARNING OBJECTIVES

1. Identify additional nutrients that are vital in maintaining bone health and state their primary role.

2. Identify food sources for each nutrient.

Bone tissue is greater than 70 percent inorganic material and as such, minerals are important for maintaining skeletal health. In addition to calcium, other minerals critical for bone health are phosphorus, magnesium, and fluoride. Vitamin K is also important to bone health. But that is not all—iron, copper, zinc, and vitamin C are also essential for the synthesis of collagen. Consuming too much or too little vitamin A affects bone health too, as it plays a role in osteoclast and osteoblast activities. The fact that there are many bone-friendly nutrients provides us with one more reason why it is better to eat a diet rich in many nutrients than take one particular supplement. In Table 9.4 “Micronutrients and Bone Health”, notice the important nutrients for bone health and good food sources for each.

Table 9.4 Micronutrients and Bone Health

Micronutrient Functional Role in Bone Health Food Sources

Calcium

• Component of mineralized bone

• Provides structure and microarchitecture

collards, mustard greens, kale, turnips, broccoli, beans, black molasses, and fortified juices, cereals, and milk.

Phosphorus

• Component of mineralized bone

• Provides structure and microarchitecture

non-genetically-modified soy, legumes, whole grains, dairy, nuts, and seeds

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Micronutrient Functional Role in Bone Health Food Sources

Magnesium

• Component of mineralized bone

• Provides structure and microarchitecture

whole grains and legumes, almonds, cashews, hazelnuts, beets, collards, and kelp

Fluoride

• Component of mineralized bone

• Provides structure and microarchitecture

• Stimulates new bone growth

fluoridated water, foods prepared in fluoridated water, seafood (because the ocean contains natural sodium flouride)

Vitamin D

• Critical for maintaining calcium levels

• Aids the absorption of calcium, promotes bone health

salmon, mackerel, tuna, sardines, mushrooms, cod liver oil, egg yolks, and fortified milk, yogurt, and cheese

Vitamin K • Stimulates boneremodeling kale, spinach, turnip, and other dark leafy vegetables

Boron • May enhance calcium

absorption and estrogen metabolism

avocado, nuts, peanut butter, green and orange vegetables, grapes, and raisins

Iron • Helps enzymes and

regulators function properly so the body

red meat, egg yolks, dark leafy vegetables, dried fruit, iron- fortified foods, beans, lentils, chick peas, liver, and artichoke

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Micronutrient Functional Role in Bone Health Food Sources

can form optimal bone structure for bone strength

Vitamin C

• Helps enzymes and regulators to function properly so the body can form optimal bone structure for bone strength

citrus fruits, tomatoes and tomato juice, potatoes, Brussel sprouts, cauliflower, broccoli, strawberries, cabbage, and spinach

Zinc

• Helps enzymes and regulators to function properly so the body can form optimal bone structure for bone strength

oysters, wheat germ, pumpkin seeds, squash, watermelon seeds, beans, sesame seeds, tahini, beef, lamb

Phosphorus’s Functional Role

Phosphorus20 is the second most abundant mineral in the human body. Eighty-five percent of it is housed in the skeleton. In addition to serving as a primary mineral in the skeleton, phosphorus in the form of phosphate is a component of the backbones of RNA and DNA, the cellular energy storing molecule, adenosine triphosphate (ATP), and phospholipids. Because phosphorus is present with calcium in mineralized bone, it is somewhat regulated in parallel to calcium. PTH and calcitriol stimulate bone resorption, increasing not only blood levels of calcium, but also blood phosphate levels. However, in contrast to the effect of PTH on calcium reabsorption by the kidney, PTH stimulates the renal excretion of phosphate so that it does not accumulate to toxic levels.

20. A mineral that makes up a substantial part of mineralized bone tissue. The dietary sources are meat, fish, and dairy products, as well as processed foods, and cola beverages.

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Dietary Reference Intake and Food Sources for Phosphorus

In comparison to calcium, most Americans are not at risk for having a phosphate deficiency. Phosphate is present in many foods popular in the American diet including meat, fish, dairy products, processed foods, and beverages. Phosphate is added to many foods because it acts as an emulsifying agent, prevents clumping, improves texture and taste, and extends shelf-life. The average intake of phosphorus in US adults ranges between 1,000 and 1,500 milligrams per day, well above the RDA of 700 milligrams per day. The UL set for phosphorous is 4,000 milligrams per day for adults and 3,000 milligrams per day for people over age seventy.

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Magnesium’s Functional Role

Approximately 60 percent of magnesium21 in the human body is stored in the skeleton, making up about 1 percent of mineralized bone tissue. Magnesium is not an integral part of the hydroxyapatite crystal, but it does reside on the surface of the crystal and helps maximize bone structure. Observational studies link magnesium deficiency with an increased risk for osteoporosis. A magnesium- deficient diet is associated with decreased levels of parathyroid hormone and the activation of vitamin D, which may lead to an impairment of bone remodeling. A study in nine hundred elderly women and men did show that higher dietary intakes of magnesium correlated to an increased BMD in the hip. Tucker, K. L. et al. “Potassium, Magnesium, and Fruit and Vegetable Intakes Are Associated with Greater Bone Mineral Density in Elderly Men and Women.” Am J ClinNutr 69, no. 4 (1999): 727–36. Only a few clinical trials have evaluated the effects of magnesium supplements on bone health and their results suggest some modest benefits on BMD.

In addition to participating in bone maintenance, magnesium has several other functions in the body. In every reaction involving the cellular energy molecule, ATP, magnesium is required. More than three hundred enzymatic reactions require magnesium. Magnesium plays a role in the synthesis of DNA and RNA, carbohydrates, and lipids, and is essential for nerve conduction and muscle contraction. Another health benefit of magnesium is that it may decrease blood pressure.

21. A mineral that is part of mineralized bone tissue. The dietary sources are meat, fish, dairy products, whole grains, nuts, chocolate, and coffee.

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Dietary Reference Intake and Food Sources for Magnesium

The RDAs for magnesium for adults between ages nineteen and thirty are 400 milligrams per day for males and 310 milligrams per day for females. For adults above age thirty, the RDA increases slightly to 420 milligrams per day for males and 320 milligrams for females.

Magnesium is part of the green pigment, chlorophyll, which is vital for photosynthesis in plants; therefore green leafy vegetables are a good dietary source for magnesium. Magnesium is also found in high concentrations in fish, dairy products, meats, whole grains, and nuts. Additionally chocolate, coffee, and hard water contain a good amount of magnesium. Most people in America do not fulfill the RDA for magnesium in their diets. Typically, Western diets lean toward a low fish intake and the unbalanced consumption of refined grains versus whole grains.

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Fluoride’s Functional Role

Fluoride22 is known mostly as the mineral that combats tooth decay. It assists in tooth and bone development and maintenance. Fluoride combats tooth decay via three mechanisms:

1. Blocking acid formation by bacteria 2. Preventing demineralization of teeth 3. Enhancing remineralization of destroyed enamel

Fluoride was first added to drinking water in 1945 in Grand Rapids, Michigan; now over 60 percent of the US population consumes fluoridated drinking water. The Centers for Disease Control and Prevention (CDC) has reported that fluoridation of water prevents, on average, 27 percent of cavities in children and between 20 and 40 percent of cavities in adults. The CDC considers water fluoridation one of the ten great public health achievements in the twentieth century.Centers for Disease Control. “10 Great Public Health Achievements in the 20th Century.” Morbidity and Mortality Weekly Report 48, no. 12 (April 2, 1999): 241–43. http://www.cdc.gov/about/ history/tengpha.htm. The optimal fluoride concentration in water to prevent tooth decay ranges between 0.7–1.2 milligrams per liter. Exposure to fluoride at three to five times this concentration before the growth of permanent teeth can cause fluorosis, which is the mottling and discoloring of the teeth.

Fluoride’s benefits to mineralized tissues of the teeth are well substantiated, but the effects of fluoride on bone are not as well known. Fluoride is currently being researched as a potential treatment for osteoporosis. The data are inconsistent on whether consuming fluoridated water reduces the incidence of osteoporosis and fracture risk. Fluoride does stimulate osteoblast bone building activity, and fluoride therapy in patients with osteoporosis has been shown to increase BMD. In general, it appears that at low doses, fluoride treatment increases BMD in people with osteoporosis and is more effective in increasing bone quality when the intakes of calcium and vitamin D are adequate. The Food and Drug Administration has not approved fluoride for the treatment of osteoporosis mainly because its benefits are not sufficiently known and it has several side effects including frequent stomach upset and joint pain. The doses of fluoride used to treat osteoporosis are much greater than that in fluoridated water.

Dietary Reference Intake and Food Sources for Fluoride

The IOM has given Adequate Intakes (AI) for fluoride, but has not yet developed RDAs. The AIs are based on the doses of fluoride shown to reduce the incidence of cavities, but not cause dental fluorosis. From infancy to adolescence, the AIs for

22. A mineral that blocks tooth decay and is part of mineralized bone tissue. The primary dietary source is fluoridated water.

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fluoride increase from 0.01 milligrams per day for ages less than six months to 2 milligrams per day for those between the ages of fourteen and eighteen. In adulthood, the AI for males is 4 milligrams per day and for females is 3 milligrams per day. The UL for young children is set at 1.3 and 2.2 milligrams per day for girls and boys, respectively. For adults, the UL is set at 10 milligrams per day. Greater than 70 percent of a person’s fluoride comes from drinking fluoridated water when they live in a community that fluoridates the drinking water. Other beverages with a high amount of fluoride include teas and grape juice. Solid foods do not contain a large amount of fluoride. Fluoride content in foods depends on whether it was grown in soils and water that contained fluoride or cooked with fluoridated water. Canned meats and fish that contain bones do contain some fluoride.

Vitamin K’s Functional Role

Vitamin K23 refers to a group of fat-soluble vitamins that are similar in chemical structure. They act as coenzymes and have long been known to play an essential role in blood coagulation. Without vitamin K, blood would not clot. Vitamin K is also required for maintaining bone health. It modifies the protein osteocalcin, which is involved in the bone remodeling process. All the functions of osteocalcin and the other vitamin K-dependent proteins in bone tissue are not well understood and are23. A vitamin that acts as acoenzyme that modifies

proteins important for bone health. The dietary sources are green vegetables such as broccoli, cabbage, kale, parsley, spinach, and lettuce.

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under intense study. Some studies do show that people who have diets low in vitamin K also have an increased risk for bone fractures.

Dietary Reference Intake and Food Sources for Vitamin K

The AI of vitamin K for adult females is 75 micrograms per day, and for males it is 120 micrograms per day. A UL for vitamin K has not been set. Vitamin K is present in many foods. It is found in highest concentrations in green vegetables such as broccoli, cabbage, kale, parsley, spinach, and lettuce. Additionally, vitamin K can be synthesized via bacteria in the large intestine. The exact amount of vitamin K synthesized by bacteria that is actually absorbed in the lower intestine is not known, but likely contributes less than 10 percent of the recommended intake. Newborns have low vitamin K stores and it takes time for the sterile newborn gut to acquire the good bacteria it needs to produce vitamin K. So, it has become a routine practice to inject newborns with a single intramuscular dose of vitamin K. This practice has basically eliminated vitamin K-dependent bleeding disorders in babies.

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KEY TAKEAWAYS

• Phosphorous is a primary mineral component of bone, is regulated in parallel with calcium, and in high amounts is detrimental to bone health.

• Magnesium helps keep bones strong. A deficiency in magnesium can compromise bone health.

• Fluoride combats tooth decay and benefits teeth and bones when present in the diet at the recommended intake.

• Vitamin K is a coenzyme that participates in the modification of proteins that act in bone tissues and promotes normal blood clotting.

DISCUSSION STARTERS

1. Discuss and plan a dinner menu that specifically contains bone-friendly foods. What are you going to serve? Be sure to include enough bone- friendly foods for the different types of vegetarians.

2. Discuss some of the functional roles that magnesium, phosphorous, fluoride, and vitamin K serve in the body. In the midst of a busy schedule, how can you ensure you are eating the right amount of foods to provide an adequate supply of these nutrients?

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9.5 Osteoporosis

LEARNING OBJECTIVE

1. Describe osteoporosis, including its notable characteristics.

There are several factors that lead to loss of bone quality during aging, including a reduction in hormone levels, decreased calcium absorption, and increased muscle deterioration. It is comparable to being charged with the task of maintaining and repairing the structure of your home without having all of the necessary materials to do so. However, you will learn that there are many ways to maximize your bone health at any age.

Osteoporosis24 is the excessive loss of bone over time. It leads to decreased bone strength and an increased susceptibility to bone fracture. The Office of the Surgeon General (OSG) reports that approximately ten million Americans over age fifty are living with osteoporosis, and an additional thirty-four million have osteopenia25, which is lower-than-normal bone mineral density.Office of the Surgeon General. “Bone Health and Osteoporosis: A Report of the Surgeon General.” October 2004. http://www.surgeongeneral.gov/library/bonehealth/chapter_1.html. Osteoporosis is a debilitating disease that markedly increases the risks of suffering from bone fractures. A fracture in the hip causes the most serious consequences—and approximately 20 percent of senior citizens who have one will die in the year after the injury. Osteoporosis affects more women than men, but men are also at risk for developing osteoporosis, especially after the age of seventy. These statistics may appear grim, but many organizations—including the National Osteoporosis Foundation and the OSG—are disseminating information to the public and to health-care professionals on ways to prevent the disease, while at the same time, science is advancing in the prevention and treatment of this disease.International Osteoporosis Foundation. “Facts and Statistics about Osteoporosis and Its Impact.” © 2012 International Osteoporosis Foundation. Accessed http://www.iofbonehealth.org/facts-and-statistics.html.

As previously discussed, bones grow and mineralize predominately during infancy, childhood, and puberty. During this time, bone growth exceeds bone loss. By age twenty, bone growth is fairly complete and only a small amount (about 10 percent) of bone mass accumulates in the third decade of life. By age thirty, bone mass is at its greatest in both men and women and then gradually declines after age forty. Bone mass refers to the total weight of bone tissue in the human body. The greatest

24. Excessive bone loss over time.

25. Lower than normal bone mass.

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quantity of bone tissue a person develops during his or her lifetime is called peak bone mass26. The decline in bone mass after age forty occurs because bone loss is greater than bone growth. On a cellular level, this means that the osteoclast- mediated bone degradation exceeds that of the bone building activity of osteoblasts. The increased bone degradation decreases the mineral content of bone tissue leading to a decrease in bone strength and increased fracture risk.

Osteoporosis is referred to as a silent disease, much like high blood pressure, because symptoms are rarely exhibited. A person with osteoporosis may not know he has the disease until he experiences a bone break or fracture. Detection and treatment of osteoporosis, before the occurrence of a fracture, can significantly improve the quality of life. To detect osteopenia or osteoporosis, BMD must be measured by the DEXA procedure. The results of a BMD scan are most often reported as T-scores. A T-score27 compares a person’s BMD to an averaged BMD of a healthy thirty-year-old population of the same sex. According to the World Health Organization, a T-score of −1.0 or above indicates normal BMD. A person with a T- score between −1.0 and −2.5 has a low BMD, which is a condition referred to as osteopenia. A person with a T-score of −2.5 or below is diagnosed with osteoporosis.National Osteoporosis Foundation. “Having A Bone Density Test.” © 2011. http://www.nof.org/node/42 This classification of T-scores is based on studies of white postmenopausal women and does not apply to premenopausal women, nonwhite postmenopausal women, or men.

Osteoporosis is categorized into two types that differ by the age of onset and what type of bone tissue is most severely deteriorated. Type 1 osteoporosis, also called postmenopausal osteoporosis, most often develops in women between the ages of fifty and seventy. Between the ages of forty-five and fifty, women go through menopause and their ovaries stop producing estrogen. Because estrogen plays a role in maintaining bone mass, its rapid decline during menopause accelerates bone loss. This occurs mainly as a result of increased osteoclast activity. The trabecular tissue is more severely affected because it contains more osteoclasts cells than cortical tissue. Type 1 osteoporosis is commonly characterized by wrist and spine fractures. Type 2 osteoporosis is also called senile osteoporosis and typically occurs after the age of seventy. It affects women twice as much as men and is most often associated with hip and spine fractures. In Type 2 osteoporosis, both the trabecular and cortical bone tissues are significantly affected. Not everybody develops osteoporosis as they age. Other factors, which will be discussed in Section 9.6 “Risk Factors for Osteoporosis” of this chapter, also contribute to the risk or likelihood of developing the disease.

During the course of both types of osteoporosis, BMD decreases and the bone tissue microarchitecture is compromised. Excessive bone resorption in the trabecular tissue increases the size of the holes in the lattice-like structure making it more

26. The greatest amount of bone mass that a person reaches during their lifetime.

27. Compares the patient’s BMD to the averaged BMD of a healthy thirty-year-old population of the same sex.

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porous and weaker. A disproportionate amount of resorption of the strong cortical bone causes it to become thinner. The deterioration of one or both types of bone tissue causes bones to weaken and, consequently, become more susceptible to fractures. The American Academy of Orthopaedic Surgeons reports that one in two women and one in five men older than sixty-five will experience a bone fracture caused by osteoporosis.American Academy of Orthopaedic Surgeons. “Osteoporosis.” © 1995–2012. Last reviewed August 2009. http://orthoinfo.aaos.org/ topic.cfm?topic=a00232.

Figure 9.8 Osteoporosis in Vertebrae

Osteoporosis is characterized by a gradual weakening of the bones, which leads to poor skeletal formation.

Osteoporosis by Blausen.com staff, from the Wikiversity Journal of Medicine, is available under a Creative Commons Attribution 3.0 Unported license. Osteoporosis Locations by Blausen Medical is available under a Creative Commons Attribution-ShareAlike 4.0 International license.

When the vertebral bone tissue is weakened, it can cause the spine to curve (Figure 9.8 “Osteoporosis in Vertebrae”). The increase in spine curvature not only causes pain, but also decreases a person’s height. Curvature of the upper spine produces what is called Dowager’s hump, also known as kyphosis. Severe upper-spine deformity can compress the chest cavity and cause difficulty breathing. It may also cause abdominal pain and loss of appetite because of the increased pressure on the abdomen.

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KEY TAKEAWAYS

• Bone mineral density (BMD) is an indicator of bone quality and correlates with bone strength.

• Excessive bone loss can lead to the development of osteopenia and eventually osteoporosis.

• Osteoporosis affects women more than men, but is a debilitating disease for either sex.

• Osteoporosis is often a silent disease that doesn’t manifest itself until a fracture is sustained.

DISCUSSION STARTERS

1. Discuss how bone microarchitecture is changed in people with osteoporosis. How do these structural changes increase the risk of having a bone fracture?

2. Go back to Section 9.1 “Bone Structure and Function” and review that bone is a living tissue that adapts to changes in mechanical forces. How might weight training help prevent a fracture in someone with osteoporosis?

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9.6 Risk Factors for Osteoporosis

LEARNING OBJECTIVE

1. Discuss risk factors for osteoporosis.

A risk factor28 is defined as a variable that is linked to an increased probability of developing a disease or adverse outcome. Recall that advanced age and being female increase the likelihood for developing osteoporosis. These factors present risks that should signal doctors and individuals to focus more attention on bone health, especially when the risk factors exist in combination. This is because not all risk factors for osteoporosis are out of your control. Risk factors such as age, gender, and race are biological risk factors, and are based on genetics that cannot be changed. By contrast, there are other risk factors that can be modified, such as physical activity, alcohol intake, and diet. The changeable risk factors for osteoporosis provide a mechanism to improve bone health even though some people may be genetically predisposed to the disease.

Nonmodifiable Risk Factors Age, Sex, Body Type, and Heredity

As noted previously, after age forty, bone mass declines due to bone breakdown exceeding bone building. Therefore, any person over the age of forty has an increased probability of developing osteoporosis in comparison to a younger person. As noted, starting out with more bone (a high peak bone mass) enables you to lose more bone during the aging process and not develop osteoporosis. Females, on average, have a lower peak bone mass in comparison to males and therefore can sustain less bone tissue loss than males before developing a low BMD. Similarly, people with small frames are also at higher risk for osteoporosis. Being of advanced age, being a woman, and having a small frame are all biological risk factors for osteoporosis. Other biological risk factors that are linked to an increased likelihood of developing osteoporosis are having low estrogen levels, or another endocrine disorder such as hyperthyroidism, having a family member with osteoporosis, and being Caucasian or Asian.

28. A variable that is linked to an increased probability of developing a disease or adverse outcome.

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Estrogen Level

Estrogen29 is the primary female reproductive hormone and it stimulates osteoblast-mediated bone building and reduces osteoclast activity. Any condition in which estrogen levels are reduced throughout a woman’s life decreases BMD and increases the risk for osteoporosis. By far the most profound effect on estrogen occurs during female menopause. Around the age of forty-five or fifty, women stop producing estrogen. The rapid decline in estrogen levels that occurs during menopause speeds up the bone resorptive process, and as a result the loss of bone tissue in menopausal women lasts for a period of five to ten years. Up to 3 percent of bone tissue is lost annually during menopause and therefore potentially 30 percent of peak bone mass can vanish during this time, leading to a substantial increase in risk for developing osteoporosis in postmenopausal women.

Medications

Some medications, most notably glucocorticoids (used to treat inflammatory disorders such as rheumatoid arthritis and asthma), are associated with an increased risk for osteoporosis. A side effect of glucocorticoids is that they stimulate bone resorption and decrease bone building. Other medications linked to an increased risk for osteoporosis are certain anticancer drugs, some antidiabetic drugs, and blood thinners.

Other Diseases

Diseases that predispose people to osteoporosis include those that disrupt nutrient absorption and retention, such as anorexia nervosa, chronic kidney disease, and Crohn’s disease; diseases that influence bone remodeling such as hyperthyroidism and diabetes; and diseases that are characterized by chronic inflammatory responses such as cancer, chronic obstructive pulmonary disease, and rheumatoid arthritis.

Modifiable Risk Factors Physical Inactivity

Bone is a living tissue, like muscle, that reacts to exercise by gaining strength. Physical inactivity lowers peak bone mass, decreases BMD at all ages, and is linked to an increase in fracture risk, especially in the elderly. Recall that mechanical stress increases bone remodeling and leads to increased bone strength and quality. Weight-bearing exercise puts mechanical stress on bones and therefore increases bone quality. The stimulation of new bone growth

29. Primary female reproductive hormone.

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occurs when a person participates in weight-bearing or resistance activities that force the body to work against gravity. Research has shown that this is an excellent way to activate osteoblasts to build more new bone. Conversely, physical inactivity lowers peak bone mass, decreases BMD at all ages, and is linked to an increase in fracture risk, especially in the elderly.

Being Underweight

Being underweight significantly increases the risk for developing osteoporosis. This is because people who are underweight often also have a smaller frame size and therefore have a lower peak bone mass. Maintaining a normal, healthy weight is important and acts as a form of weight-bearing exercise for the skeletal system as a person moves about. Additionally, inadequate nutrition negatively impacts peak bone mass and BMD. The most striking relationship between being underweight and bone health is seen in people with the psychiatric illness anorexia nervosa. Anorexia nervosa is strongly correlated with low peak bone mass and a low BMD. In fact, more than 50 percent of men and women who have this illness develop osteoporosis and sometimes it occurs very early in life.Mehler, P. S. and K. Weiner. “The Risk of Osteoporosis in Anorexia Nervosa.” Reprinted from Eating Disorders Recovery Today 1, no. 5 (Summer 2003). © 2003 Gurze Books. http://www.eatingdisordersreview.com/nl/nl_edt_1_5_2.html Women with anorexia nervosa are especially at risk because they not only have inadequate nutrition and low body weight, but also the illness is also associated with estrogen deficiency.

Smoking, Alcohol, and Caffeine

Smoking cigarettes has long been connected to a decrease in BMD and an increased risk for osteoporosis and fractures. However, because people who smoke are more likely to be physically inactive and have poor diets, it is difficult to determine whether smoking itself causes osteoporosis. What is more, smoking is linked to earlier menopause and therefore the increased risk for developing osteoporosis among female smokers may also be attributed, at least in part, to having stopped estrogen production at an earlier age. A review of several studies, published in the British Medical Journal in 1997, reports that in postmenopausal women who smoked, BMD was decreased an additional 2 percent for every ten-year increase in age and that these women had a substantial increase in the incidence of hip fractures.Law, M. R. and A.K. Hackshaw. “A Meta-Analysis of Cigarette Smoking, Bone Mineral Density and Risk of Hip Fracture: Recognition of a Major Effect.” Br Med J 315, no. 7112 (October 4, 1997): 841–6. http://www.ncbi.nlm.nih.gov/pubmed/9353503.

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Alcohol intake’s effect on bone health is less clear. In some studies, excessive alcohol consumption was found to be a risk factor for developing osteoporosis, but the results of other studies suggests consuming two drinks per day is actually associated with an increase in BMD and a decreased risk for developing osteoporosis. The International Osteoporosis Foundation states that consuming more than two alcoholic drinks per day is a risk factor for developing osteoporosis and sustaining a hip fracture in both men and women.International Osteoporosis Foundation. “New IOF Report Shows Smoking, Alcohol, Being Underweight, and Poor Nutrition Harm our Bones.” Accessed October 2011. http://www.iofbonehealth.org/news/news-detail.html?newsID=193. Moreover, excessive alcohol intake during adolescence and young adulthood has a more profound effect on BMD and osteoporosis risk than drinking too much alcohol later in life.

Some studies have found that, similar to alcohol intake, excessive caffeine consumption has been correlated to decreased BMD, but in other studies moderate caffeine consumption actually improves BMD. Overall, the evidence that caffeine consumption poses a risk for developing osteoporosis is scant, especially when calcium intake is sufficient. Some evidence suggests that carbonated soft drinks negatively affect BMD and increase fracture risk. Their effects, if any, on bone health are not attributed to caffeine content or carbonation. It is probable that any effects of the excessive consumption of soft drinks, caffeinated or not, on bone health can be attributed to the displacement of milk as a dietary source of calcium.

Nutrition

Ensuring adequate nutrition is a key component in maintaining bone health. Having low dietary intakes of calcium and vitamin D are strong risk factors for developing osteoporosis. Another key nutrient for bone health is protein. Remember that the protein collagen comprises almost one third of bone tissue. A diet inadequate in protein is a risk factor for osteoporosis. Multiple large observational studies have shown that diets high in protein increase BMD and reduce fracture risk and that diets low in protein correlate to decreased BMD and increased fracture risk. There has been some debate over whether diets super high in animal protein decrease bone quality by stimulating bone resorption and increasing calcium excretion in the urine. A review in the May 2008 issue of the American Journal of Clinical Nutrition concludes that there is more evidence that diets adequate in protein play a role in maximizing bone health and there is little consistent evidence that suggests high protein diets negatively affect bone health when calcium intake is adequate.Heaney, R. P. and D.K. Layman. “Amount and Type of Protein Influences Bone Health.” Am J Clin Nutr 87, no. 5 (2008): 1567S–70S. http://www.ajcn.org/ content/87/5/1567S.long

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KEY TAKEAWAYS

• Nonmodifiable risk factors for osteoporosis include: being female, being over age fifty, having a small frame, having an endocrine disorder, having a family member with the disease, and being Caucasian or Asian.

• The risk factors for osteoporosis that can be changed are: smoking, alcohol intake, physical inactivity, and poor nutrition.

• Dietary inadequacy, certain medications, and diseases increase the risk for developing osteoporosis.

DISCUSSION STARTER

1. Discuss why it is important for a person with more than one biological risk factor for osteoporosis to begin to manage their lifestyle early on to prevent the development of the disease.

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9.7 Osteoporosis Prevention and Treatment

LEARNING OBJECTIVES

1. Explain why it is important to build peak bone mass when you are young.

2. Identify the tests used to measure bone mass.

Although the symptoms of osteoporosis do not occur until old age, osteoporosis is referred to as a childhood disease with old-age consequences. Thus, preventing osteoporosis in old age begins with building strong bones when you are growing. Remember, the more bone mass a person has to start with, the greater the loss a person can withstand without developing osteopenia or osteoporosis. Growing and maintaining healthy bones requires good nutrition, adequate intake of minerals and vitamins that are involved in maintaining bone health, and weight-bearing exercise.

Primary Prevention

Actions taken to avoid developing a disease before it starts are considered primary prevention30. Primary prevention of osteoporosis begins early on in life. About one half of mineralized bone is built during puberty and the requirements for calcium intake are higher at this time than at other times in life. Unfortunately, calcium intake in boys and girls during adolescence is usually below the recommended intake of 1,300 milligrams per day. To combat inadequate nutrition and physical inactivity in adolescents, the US Department of Health and Human Services launched the Best Bones Forever!™ campaign in 2009.US Department of Health and Human Services. Best Bones Forever! Last updated September 2009. http://www.bestbonesforever.gov/index.cfm This campaign is focused on promoting bone health, especially in girls, and reducing the incidence of osteoporosis in women.

30. Actions taken to avoid developing a disease before it starts.

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Interactive 9.2

Visit the Best Bones Forever!™ website.

http://www.bestbonesforever.gov/index.cfm

An article in the October 2008 issue of Food and Nutrition Research concluded that there is extensive evidence that when girls and boys exercise they increase their peak bone mass and build a stronger skeleton. The greatest benefits to bone health were observed when exercise was combined with good nutrition.Karlsson, M. K., A. Nordqvist, and C. Karlsson. “Physical Activity Increases Bone Mass during Growth.” Food and Nutrition Research 52 (Published online October 1, 2008). doi: 10.3402/ fnr.v52i0.1871 Because there is such a strong correlation between peak bone mass and a decreased risk for developing osteoporosis, a main thrust of organizations that promote bone health, such as the National Osteoporosis Foundation, is to provide information on how to increase skeletal health early on in life, particularly during the time period of peak bone growth, which is puberty.

Primary prevention extends throughout life, and people with one or more risk factors for osteoporosis should have their BMD measured. The National Osteoporosis Foundation recommends the following groups of people get BMD screening:

• Women who are sixty-five or older • Men who are seventy or older • Women and men who break a bone after age fifty • Women going through menopause with other risk factors • Men fifty to sixty-nine years of age with risk factorsNational

Osteoporosis Foundation. “National Osteoporosis Foundation on Bone Mineral Density Testing.” http://www.nof.org/node/501

Primary Prevention Tactics Nutrition: Eat Right for Your Bones

Eating a balanced diet throughout life is helpful in preventing the onset of osteoporosis and deleterious fractures in old age. There is ample scientific evidence to suggest that low intakes of calcium and vitamin D in adulthood are linked to an increased risk for developing osteoporosis. Therefore, it is essential to make sure

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your diet contains adequate levels of these nutrients. The roles of calcium and vitamin D in maintaining bone health are discussed in detail in Section 9.3 “Micronutrients Essential for Bone Health: Calcium and Vitamin D” of this chapter.

Physical Activity: Use It or Lose It

Mechanical stress is one of the activation signals for bone remodeling and can increase bone strength. Exercises that apply forces to the bone increase BMD. The most helpful are weight-bearing exercises such as strength training with weights, and aerobic weight-bearing activities, such as walking, running, and stair climbing. Certain aerobic exercises such as biking and swimming do not build bones, although they are very good for cardiovascular fitness. The importance of weight-bearing exercise to bone health is seen most clearly in astronauts. Investigators who analyzed the BMD of astronauts found that typically it decreases by 1.8 percent every month in space. That means during a six-month stay at a space station an astronaut may lose greater than 10 percent of their bone mass. The lack of gravity, which tugs on the bones of people on Earth every day, is what causes bone mass loss in astronauts. NASA imposes a rigorous workout to prevent and to restore the loss of bone mass in astronauts. While in space, astronauts exercise two-and-a-half hours each day on a treadmill, and use a resistance-exercise device where they pull rubberband-like cords attached to pulleys. Then, when they return to Earth astronauts undergo weeks of rehabilitation to rebuild both bone and muscle tissue.

Fall Prevention

Reducing the number of falls a person has decreases the likelihood of sustaining a fracture. Fairly simple modifications to a person’s environment, such as installing nightlights, railings on stairs, bars to hold onto in showers, and removing cords and throw rugs in walking paths can significantly reduce the likelihood of falling. Importantly, people at risk should have their vision and balance checked frequently.

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Secondary Prevention

A person who has undergone a DEXA scan and been diagnosed with osteopenia or osteoporosis has multiple strategies available to reduce the chances of breaking a bone. These types of treatment strategies are referred to as secondary prevention31. The OSG reports that the primary goals in the prevention and treatment of osteoporosis are to maintain bone health by preventing its loss and by actually building new bone.Office of the Surgeon General. “Bone Health and Osteoporosis: A Report of the Surgeon General.” October, 2004 http://www.surgeongeneral.gov/library/bonehealth/chapter_9.html To accomplish these goals, the OSG recommends a pyramid approach. The base of the pyramid focuses on balancing nutrition, increasing physical activity, and preventing falls (primary prevention tactics). The second step in the pyramid is to determine if any underlying disorders or diseases are causing osteoporosis and to treat them. The third step is pharmacotherapy and involves administering medications. The second and third steps in the pyramid are secondary prevention tactics.

Secondary Prevention Tactics

We have noted that certain medications and diseases either cause or aggravate osteoporosis. Treating diseases such as hyperparathyroidism or discontinuing the use of or lowering the dose of medications such as prednisone, substantially reduces the risk of further deterioration of bone tissue and fracture. (In Section 9.3 “Micronutrients Essential for Bone Health: Calcium and Vitamin D” of this chapter, you learned the mechanics of how the parathyroid hormone regulates calcium homeostasis.) When parathyroid hormone is present at continuously high levels in the blood, it causes a marked elevation in calcium levels. It raises blood calcium levels by increasing osteoclast activity, thereby increasing bone breakdown and bone loss. Hyperparathyroidism is treated by the surgical removal of the parathyroid gland tumor. Chronic kidney disease and vitamin D deficiency can also cause an increase in parathyroid hormone levels. When the increase in parathyroid hormone is the result of disorders in other organs, the condition is referred to as secondary hyperparathyroidism.

Treating diseases such as chronic kidney disease and Crohn’s disease, which are associated with decreased activation of vitamin D, increased calcium excretion, or malabsorption, is important in people who have not developed osteoporosis yet in order to arrest further losses in BMD. If these types of conditions exist simultaneously with osteoporosis, it is recommended that both disorders be treated to prevent further bone deterioration.

31. Strategies focused on halting or reversing a disease after it has developed.

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KEY TAKEAWAYS

• Osteoporosis is a childhood disease with old-age consequences. Primary prevention of osteoporosis begins early in life with proper diet and exercise.

• The strategies of secondary prevention that focus on treating osteoporosis aim to arrest further bone loss and reduce fracture risk.

• Osteoporosis prevention and treatment involves a three-tiered approach that incorporates lifestyle modifications, the assessment and treatment of underlying causes of the disease, and pharmacotherapy.

DISCUSSION STARTERS

1. Do you or any of your classmates have children? What could a parent of a teenager do to help their child achieve a high peak bone mass?

2. Discuss the tactics you might employ at your age to maximize your bone health and minimize your risk for developing osteoporosis.

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9.8 Deficiency, Supplementation, and Choices

LEARNING OBJECTIVES

1. List the groups most at risk for calcium inadequacy and explain why they are at risk.

2. Understand the benefits and risks of calcium supplementation.

Despite the wealth of evidence supporting the many health benefits of calcium (particularly bone health), the average American diet falls short of achieving the recommended dietary intakes of calcium. In fact, in females older than nine years of age, the average daily intake of calcium is only about 70 percent of the recommended intake. Here we will take a closer look at particular groups of people who may require extra calcium intake.

• Adolescent teens. A calcium-deficient diet is common in teenage girls as their dairy consumption often considerably drops during adolescence.

• Amenorrheic women and the “female athlete triad.” Amenorrhea refers to the absence of a menstrual cycle. Women who fail to menstruate suffer from reduced estrogen levels, which can disrupt and have a negative impact on the calcium balance in their bodies. The “female athlete triad” is a combination of three conditions characterized by amenorrhea, disrupted eating patterns, and osteoporosis. Exercise-induced amenorrhea and anorexia nervosa-related amenorrhea can decrease bone mass.Drinkwater, B., B. Bruemner, and C. Chesnut. “Menstrual History As a Determinant of Current Bone Density in Young Athletes.” JAMA 263, no. 4 (1990): 545–8. http://www.ncbi.nlm.nih.gov/pubmed/ 2294327?dopt=Abstract,Marcus, R. et al. “Menstrual Function and Bone Mass in Elite Women Distance Runners: Endocrine and Metabolic Features.” Ann Intern Med 102, no. 2 (1985):158–63. http://www.ncbi.nlm.nih.gov/pubmed/3966752?dopt=Abstract In female athletes, as well as active women in the military, low BMD, menstrual irregularities, and individual dietary habits together with a

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history of previous stress issues are related to an increased susceptibility to future stress fractures.Nattiv, A. “Stress Fractures and Bone Health in Track and Field Athletes.” J Sci Med Sport 3, no. 3 (2000): 268–79. http://www.ncbi.nlm.nih.gov/pubmed/ 11101266?dopt=Abstract.,Johnson, A.O., et al. “Correlation of Lactose Maldigestion, Lactose Intolerance, and Milk Intolerance.” Am J Clin Nutr 57, no. 3 (1993): 399–401. http://www.ncbi.nlm.nih.gov/pubmed/ 8438774?dopt=Abstract.

• The elderly. As people age, calcium bioavailability is reduced, the kidneys lose their capacity to convert vitamin D to its most active form, the kidneys are no longer efficient in retaining calcium, the skin is less effective at synthesizing vitamin D, there are changes in overall dietary patterns, and older people tend to get less exposure to sunlight. Thus the risk for calcium inadequacy is great.International Osteoporosis Foundation. “Calcium and Vitamin D in the Elderly.” © 2012. http://www.iofbonehealth.org/patients-public/about- osteoporosis/prevention /nutrition/calcium-and-vitamin-d-in-the- elderly.html.

• Postmenopausal women. Estrogen enhances calcium absorption. The decline in this hormone during and after menopause puts postmenopausal women especially at risk for calcium deficiency. Decreases in estrogen production are responsible for an increase in bone resorption and a decrease in calcium absorption. During the first years of menopause, annual decreases in bone mass range from 3–5 percent. After age sixty-five, decreases are typically less than 1 percent.Daniels, C. E. “Estrogen Therapy for Osteoporosis Prevention in Postmenopausal Women.” National Institute of Health: Pharmacy Update (March/April 2001).

• Lactose-intolerant people. Groups of people, such as those who are lactose intolerant, or who adhere to diets that avoid dairy products, may not have an adequate calcium intake.

• Vegans. Vegans typically absorb reduced amounts of calcium because their diets favor plant-based foods that contain oxalates and phytates.Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. (Washington, DC: National Academy Press, 2010). In addition, because vegans avoid dairy products, their overall consumption of calcium-rich foods may be less.

If you are lactose intolerant, have a milk allergy, are a vegan, or you simply do not like dairy products, remember that there are many plant-based foods that have a good amount of calcium (see Note 9.28 “Tools for Change” in Section 9.3 “Micronutrients Essential for Bone Health: Calcium and Vitamin D” and Table 9.2 “Nondairy Dietary Sources of Calcium”) and there are also some low-lactose and lactose-free dairy products on the market.

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Calcium Supplements: Which One to Buy?

Many people choose to fulfill their daily calcium requirements by taking calcium supplements. Calcium supplements are sold primarily as calcium carbonate, calcium citrate, calcium lactate, and calcium phosphate, with elemental calcium contents of about 200 milligrams per pill. It is important to note that calcium carbonate requires an acidic environment in the stomach to be used effectively. Although this is not a problem for most people, it may be for those on medication to reduce stomach-acid production or for the elderly who may have a reduced ability to secrete acid in the stomach. For these people, calcium citrate may be a better choice. Otherwise, calcium carbonate is the cheapest. The body is capable of absorbing approximately 30 percent of the calcium from these forms.

Beware of Lead

There is public health concern about the lead content of some brands of calcium supplements, as supplements derived from natural sources such as oyster shell, bone meal, and dolomite (a type of rock containing calcium magnesium carbonate) are known to contain high amounts of lead. In one study conducted on twenty-two brands of calcium supplements, it was proven that eight of the brands exceeded the acceptable limit for lead content. This was found to be the case in supplements derived from oyster shell and refined calcium carbonate. The same study also found that brands claiming to be lead-free did, in fact, show very low lead levels. Because lead levels in supplements are not disclosed on labels, it is important to know that products not derived from oyster shell or other natural substances are generally low in lead content. In addition, it was also found that one brand did not disintegrate as is necessary for absorption, and one brand contained only 77 percent of the stated calcium content.Ross, E. A., N. J. Szabo, and I. R. Tebbett. “Lead Content of Calcium Supplements.” JAMA 2000 Sep 20; 284 (2000): 1425–33.

Diet, Supplements, and Chelated Supplements

In general, calcium supplements perform to a lesser degree than dietary sources of calcium in providing many of the health benefits linked to higher calcium intake. This is partly attributed to the fact that dietary sources of calcium supply additional nutrients with health-promoting activities. It is reported that chelated forms of calcium supplements are easier to absorb as the chelation process protects the calcium from oxalates and phytates that may bind with the calcium in the

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intestines. However, these are more expensive supplements and only increase calcium absorption up to 10 percent. In people with low dietary intakes of calcium, calcium supplements have a negligible benefit on bone health in the absence of a vitamin D supplement. However, when calcium supplements are taken along with vitamin D, there are many benefits to bone health: peak bone mass is increased in early adulthood, BMD is maintained throughout adulthood, the risk of developing osteoporosis is reduced, and the incidence of fractures is decreased in those who already had osteoporosis. Calcium and vitamin D pills do not have to be taken at the same time for effectiveness. But remember that vitamin D has to be activated and in the bloodstream to promote calcium absorption. Thus, it is important to maintain an adequate intake of vitamin D.

The Calcium Debate

A recent study published in the British Medical Journal reported that people who take calcium supplements at doses equal to or greater than 500 milligrams per day in the absence of a vitamin D supplement had a 30 percent greater risk for having a heart attack.Bolland, M. J. et al. “Effect of Calcium Supplements on Risk of Myocardial Infarction and Cardiovascular Events: Meta-Analysis.” Br Med J 341, no. c3691 (July 29, 2010). Does this mean that calcium supplements are bad for you? If you look more closely at the study, you will find that 5.8 percent of people (143 people) who took calcium supplements had a heart attack, but so did 5.5 percent of the people (111) people who took the placebo. While this is one study, several other large studies have not shown that calcium supplementation increases the risk for cardiovascular disease. While the debate over this continues in the realm of science, we should focus on the things we do know:

1. There is overwhelming evidence that diets sufficient in calcium prevent osteoporosis and cardiovascular disease.

2. People with risk factors for osteoporosis are advised to take calcium supplements if they are unable to get enough calcium in their diet. The National Osteoporosis Foundation advises that adults age fifty and above consume 1,200 milligrams of calcium per day. This includes calcium both from dietary sources and supplements.

3. Consuming more calcium than is recommended is not better for your health and can prove to be detrimental. Consuming too much calcium at any one time, be it from diet or supplements, impairs not only the absorption of calcium itself, but also the absorption of other essential minerals, such as iron and zinc. Since the GI tract can only handle about 500 milligrams of calcium at one time, it is recommended to have split doses of calcium supplements rather than taking a few all at once to get the RDA of calcium.

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Other Choices that Affect Bone Health Too Much Soda

There are many proponents of low-phosphate diets for bone health. Scientific studies do provide evidence that diets consisting of a high intake of processed foods and cola beverages compromise bone health as well as increase the prevalence of obesity. Overall however, the data is inconsistent to show whether it is the phosphate content that is the culprit. The mechanism by which diets high in phosphate could cause a decrease in bone health is the following: a high dietary intake of phosphate leads to an increase in blood phosphate levels. High levels of phosphate in the blood stimulate the release of parathyroid hormone (PTH), which in turn stimulates bone resorption and calcium is lost from the bone. When calcium intake is adequate, it shuts off PTH release, but when calcium intake is inadequate and phosphate intake is high, bone health suffers. How much it suffers is under a considerable amount of debate in the scientific literature. It is a good idea to eat foods that are good sources for both calcium and phosphorus.

Tools for Change

While the scientific community debates the effects of phosphate, we do know that carbonated cola beverages have negative effects on bone health. A study published in the Archives of Pediatrics and Adolescent Medicine reports that teenage girls who were physically active and drank carbonated cola beverages were five times more likely to break a bone than physically active girls who did not drink carbonated beverages.Wyshak, G. “Teenaged Girls, Carbonated Beverage Consumption, and Bone Fractures.” Arch Pediatr Adolesc Med 154 (2000): 610–13. http://archpedi.ama-assn.org/cgi/content/full/154/6/ 610?ijkey=d457e7f399850f63fdb8ee9ff3c3a61afcf3e352 The Beverage Guidance Panel, headed by Dr. Barry Popkin from the University of North Carolina, Chapel Hill, recommends drinking not more than one 8-ounce carbonated soft drink per day. A bone-healthy diet is one that does not replace milk and high calcium snacks with carbonated soft drinks and processed foods.

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A Lactose-Free Diet

Evidence has been uncovered recently indicating that lactose-free diets result in decreased calcium absorption because dietary lactose has been shown to actually enhance calcium absorption. Thus, lactose intolerance (and lactose-free diets) may predispose one to inadequate bone mineralization, an issue now correlated to many other disorders involving pediatric patients. Researchers are still working to clarify the effects of lactose-free diets in youth on long-term bone mineral content and the risks of osteoporosis and bone fractures with aging. Calcium homeostasis is also affected by protein intake, vitamin D status,Holick, MF. Ann Epidemiol. 2009 Feb;19(2):73–8. Epub 2008 Mar 10.NIH Public Access: “Vitamin D Status: Measurements, Interpretations, and Clinical Application.” http://www.ncbi.nlm.nih.gov/pubmed/18329892. salt intake, and genetic and other factors, making long-term studies critical in determining the risks of each or all of these to bone health. Recent studies also indicate that in the future, genetic testing may be appropriate for spotting people who may be at a higher risk of lactase deficiency and subsequent decreased BMD. This may enable early intervention through dietary modification or supplementation.Heyman, M. B., MD, MPH. “Lactose Intolerance in Infants, Children, and Adolescents.” Pediatrics 118, no. 3 (September 1, 2006): 1279–86. doi: 10.1542/peds.2006-1721.

Bone Health: A Firm Foundation

In your effort to maintain proper bone health, and prevent and treat osteoporosis, you will need to eat a balanced diet of foods that contain not only calcium and vitamin D, but also the other important bone-building nutrients. You will also need to employ physical exercise habits to encourage bone activity, such as remodeling. By consuming foods rich in bone-building materials on a daily basis, you can reduce your need for supplementation. However, if you cannot get the required amounts of calcium you need through diet alone, there are inexpensive, safe, and effective calcium supplements to choose from. As with anything you choose to consume or with any activity that you choose to undertake, supplementation, diet, and exercise should be uniquely tailored to your circumstances.

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KEY TAKEAWAYS

• The groups of people who are most at risk for calcium inadequacy are adolescent teens, amenorrheic women, the female triad athlete, the elderly, lactose-intolerant people, those with milk allergies, and vegans.

• When taking calcium supplements, be sure to monitor vitamin D intake to ensure that the proper benefits are achieved. Split doses are more effective since the gastrointestinal tract can only absorb up to 500 milligrams at one time.

• There is need for caution when choosing different brands of calcium supplements. Oyster shell and other naturally derived brands tend to contain unusually high concentrations of lead. Other brands do not contain the stated amount of calcium as advertised.

• The best sources of calcium come from the diet. If you are considered at risk for inadequate calcium intake, then proper supplementation along with a good diet can produce positive results on bone health.

DISCUSSION STARTERS

1. Discuss the argument for and against calcium supplementation. Defend your personal view with scientific facts.

2. Visit the websites below and come up with your own opinion on whether carbonated cola beverages increase the risk of developing osteoporosis. Discuss with your classmates what evidence is lacking. What do you and your classmates think about the position of The Coca-Cola Company Beverage Institute? Do they make a good argument? Can you counter it with better scientific evidence?

http://www.medpagetoday.com/Endocrinology/Osteoporosis/ 4247

http://www.jacn.org/content/20/4/271.full

http://www.beverageinstitute.org/en_US/pages/expert- beverages-and-bone-health-harmful-helpful-or-no-effect.html

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9.9 End-of-Chapter Exercises

IT ’S YOUR TURN

1. Calculate your daily calcium intake by visiting the website of the International Osteoporosis Foundation, http://www.livestrong.com/ article/258803-how-to-calculate-calcium-intake/. Compare it to the RDA and UL for your age and sex.

2. Determine your risk factors for osteoporosis and plug them in the interactive tool at http://www.webmd.com/hw-popup/risk-of- osteoporosis to estimate your risk for osteoporosis.

3. Plan a dinner meal that contains at least one-third of the RDAs of calcium and vitamin D. To help you determine the calcium and vitamin D contents in foods, visit the USDA National Nutrient Database at http://www.nal.usda.gov/fnic/foodcomp/search/.

APPLY IT

1. Make a list of foods that increase calcium absorption and a list of foods that decrease calcium absorption. Based on your calculated calcium intake levels, determine which foods you should add or subtract from your diet. Now design a daily menu plan that incorporates the changes.

2. Go to the store and look at three calcium supplements. Record the brand names, type of calcium used in each brand, and amounts. Based on your daily calcium intake defend whether or not you need a calcium supplement. If you do decide you need a supplement, which brand would be your best choice?

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EXPAND YOUR KNOWLEDGE

1. Draw a cartoon that contains the cells and the four steps involved in the bone remodeling process. Make a timeline on your cartoon that links the processes of bone remodeling with the length of time it takes a broken bone to heal.

2. Summarize in a written discussion why it is critical to achieve a high peak bone mass early in young adulthood to reduce the risk of developing osteoporosis later in life. Provide a graph of the bone-life cycle in men and women.

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Chapter 10

Nutrients Important for Metabolism and Blood Function

Big Idea

Micronutrients come from many sources and some may surprise you; get them in the right amounts to support metabolism and blood health.

In a small town in the Appalachian Mountains, Joseph Lodge founded Lodge Iron Cookware in 1896. Today it is still a family-run business that provides Americans with pioneer-style iron cookware. Iron cookware was, and still is, prized for its heat retention, even heating, and durability. In fact, many pans sold one hundred years ago are still in use today. Unbeknownst to the American pioneers, the cookware also leaches iron, an essential mineral, into foods as they are cooked in cast-iron hardware.

Iron has several vital functions in the body. Primarily it is the oxygen carrier of the protein hemoglobin, which is found in red blood cells. Oxygen is essential for cellular metabolism. A reduction in the oxygen-carrying capacity of red blood cells hampers the synthesis of energy and consequently cell function. Additionally, iron is required for energy production and enzymatic synthesis of RNA and DNA. Therefore cells that are rapidly dividing are acutely sensitive to an iron deficiency. Since red blood cells are under a constant state of

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renewal in the body, low iron levels impede their synthesis, eventually causing anemia. A person with anemia experiences fatigue, shortness of breath, dizziness, muscle weakness, and pale skin. In infants and children iron-deficiency anemia can impair growth, motor control, mental functioning, behavior, and performance in school. Iron deficiency is the number-one nutritional deficiency in the world, and even in America it affects 10 percent of women of childbearing age and many infants, children, and adolescents.

Dietary sources of iron include red meats, poultry, leafy green vegetables, prunes, raisins, egg yolks, lentils, oysters, clams, artichokes, and enriched cereal grains. While there are many food sources of iron, only a small fraction of dietary iron is absorbed. One method of increasing dietary intake of iron is cooking foods in an iron skillet. Acidic foods high in moisture content, such as tomatoes, absorb more iron during cooking than nonacidic foods. For example, cooking spaghetti sauce in iron cookware can increase the iron content ten-fold. How much iron leaches into food is also dependent on cooking times; the longer food is in the pan the more iron is absorbed into the food. Stirring food more often increases contact time and thus more iron is absorbed from the cookware. The utility of iron cookware in increasing dietary intake of iron has prompted some international public health organizations to distribute iron cookware to high-risk populations in developing countries as a strategy to reduce the prevalence of iron-deficiency anemia worldwide.

You Decide

What are the different ways to build iron storehouses in your body without taking a pill?

In this chapter, we will discuss the importance of blood and its vital role in support of metabolism and pull together what we have learned about macronutrient metabolism. You will also learn the important roles micronutrients have in metabolism and how they support blood function and renewal. We will also consider food sources of these valuable nutrients. Read the facts, then decide the best way to supplement your diet with iron friendly eating and cooking.

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10.1 Blood’s Function in the Body and in Metabolism Support

LEARNING OBJECTIVE

1. List each component of blood and its major role.

You know you cannot live without blood, and that your heart pumps your blood over a vast network of veins and arteries within your body, carrying oxygen to your cells. However, beyond these basic facts, what do you know about your blood?

Blood is a connective tissue of the circulatory system, transporting absorbed nutrients to cells and waste products from cells. It supports cellular metabolism by transporting synthesized macromolecules and waste products. Additionally, it transports molecules, such as hormones, allowing for communication between organs. The volume of blood coursing throughout an adult human body is about 5 liters (1.3 gallons) and accounts for approximately 8 percent of human bodyweight.

What Makes Up Blood and How Do These Substances Support Blood Function?

Blood is about 78 percent water and 22 percent solids by volume. The liquid part of blood is called plasma and it is mostly water (95 percent), but also contains proteins, ions, glucose, lipids, vitamins, minerals, waste products, gases, enzymes, and hormones. You learned in Chapter 6 “Proteins” and Chapter 7 “Nutrients Important to Fluid and Electrolyte Balance” that the protein albumin is found in high concentrations in the blood. Albumin helps maintain fluid balance between blood and tissues, as well as helping to maintain a constant blood pH. In Chapter 7 “Nutrients Important to Fluid and Electrolyte Balance” we learned that the water component of blood is essential for its actions as a transport vehicle, and that the electrolytes carried in blood maintain fluid balance and a constant pH. Furthermore the high water content of blood helps maintain body temperature, and the constant flow of blood distributes heat throughout the body. Blood is exceptionally good at temperature control, so much so that the many small blood vessels in your nose are capable of warming frigid air to body temperature before it reaches the lungs.

The cellular components of blood include red blood cells, white blood cells, and platelets. Red blood cells1 are the most numerous of the components. Each drop of blood contains millions of them. Red blood cells are red because they each contain approximately 270 million hemoglobin proteins, which contain the mineral iron,

1. The most numerous cells in blood, which transport oxygen to all cells in the body.

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which when bound to oxygen turns red. The most vital duty of red blood cells is to transport oxygen from the lungs to all cells in the body so that they can make energy via aerobic metabolism. The white blood cells2 that circulate in blood are part of the immune system and they survey the entire body looking for foreign invaders to destroy. They make up about 1 percent of blood volume. Platelets3 are fragments of cells that are always circulating in the blood in case of an emergency. When blood vessels are injured platelets rush to the site of injury to plug the wound. Blood is under a constant state of renewal and is synthesized from stem cells residing in bone marrow. Red blood cells live for about 120 days, white blood cells live anywhere from eighteen hours to one year, or even longer, and platelets have a lifespan of about ten days.

Nutrients In

Once absorbed from the small intestine, all nutrients require transport to cells in need of their support. Additionally, molecules manufactured in other cells sometimes require delivery to other organ systems. Blood is the conduit and blood vessels are the highway that support nutrient and molecule transport to all cells. Water-soluble molecules, such as some vitamins, minerals, sugars, and many proteins, move independently in blood. Fat-soluble vitamins, triglycerides, cholesterol, and other lipids are packaged into lipoproteins that allow for transport in the watery milieu of blood. Many proteins, drugs, and hormones are dependent on transport carriers, primarily albumin. In addition to transporting all of these molecules, blood must transfer the oxygen breathed in by the lungs to all cells in the body. As discussed, the iron-containing hemoglobin molecule in red blood cells accomplishes this.

2. Cells of the immune system that survey the entire body looking for foreign invaders to destroy.

3. Fragments of cells that, when stimulated by blood vessel injury, rush to plug up the wound.

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Wastes Out

In the metabolism of macronutrients to energy, cells produce the waste products carbon dioxide and water. As blood travels through smaller and smaller vessels, the rate of blood flow is dramatically reduced allowing for efficient exchange of nutrients and oxygen for cellular waste products. The kidneys remove any excess water in the blood, and blood delivers the carbon dioxide to the lungs where it is exhaled. Also, the liver produces the waste product urea from the breakdown of amino acids, and detoxifies many harmful substances, all of which require transport in the blood to the kidneys for excretion.

All for One, One for All

We are not going to talk about the three musketeers, but we will talk about the way our bodies function and work harmoniously to sustain life. The eleven organ systems in the body completely depend on each other for continued survival as a complex organism. Blood allows for transport of nutrients, wastes, water, and heat, and is also a conduit of communication between organ systems. Blood’s importance to the rest of the body is aptly presented in its role in glucose delivery, especially to the brain. The brain metabolizes, on average, 6 grams of glucose per hour. In order to avert confusion, coma, and death, glucose must be readily available to the brain at all times. To accomplish this task, cells in the pancreas sense glucose levels in the blood. If glucose levels are low, the hormone glucagon is released into the blood and is transported to the liver where it communicates the signal to ramp-up glycogen breakdown and glucose synthesis. The liver does just that, and glucose is released into the blood, which transports it to the brain. Concurrently, blood transports oxygen to support the metabolism of glucose to energy in the brain. Healthy blood conducts its duties rapidly, avoiding hypoglycemic coma and death. This is just one

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Blood tests are helpful tools in diagnosing disease and provide much information on overall health. Blood Extracted From Arms by Amanda Mills, USCDCP, is in the public domain.

example of the body’s survival mechanisms exemplifying life’s mantra, “All for one, one for all.”

What Makes Blood Healthy?

Maintaining healthy blood, including its continuous renewal, is essential to support its vast array of vital functions. Blood is healthy when it contains the appropriate amount of water and cellular components, and proper concentrations of dissolved substances, such as albumin and electrolytes. As with all other tissues, blood needs macro- and micronutrients to optimally function. In the bone marrow, where blood cells are made, amino acids are required to build the massive amount of hemoglobin packed within every red blood cell, along with all other enzymes and cellular organelles contained in each blood cell. Red blood cells, similar to the brain, use only glucose as fuel, and it must be in constant supply to support red-blood-cell metabolism. As with all other cells, the cells in the blood are surrounded by a plasma membrane, which is composed of mainly lipids. Blood health is also acutely sensitive to deficiencies in some vitamins and minerals more than others, a topic that will be explored in this chapter.

What Can Blood Tests Tell You About Your Health?

Since blood is the conduit of metabolic products and wastes, measuring the components of blood, and particular substances in blood, can reveal not only the health of blood, but also the health of other organ systems. In standard blood tests performed during an annual physical, the typical blood tests conducted can tell your physician about the functioning of a particular organ or about disease risk.

A biomarker4 is defined as a measurable molecule or trait that is connected with a specific disease or health condition. The concentrations of biomarkers in blood are indicative of disease risk. Some biomarkers are cholesterol, triglycerides, glucose, and prostate-specific antigen. The results of a blood test give the concentrations of substances in a person’s blood and display the normal ranges for a certain population group. Many factors, such as physical activity level, diet, alcohol intake, and medicine intake can influence a person’s blood-test levels and cause them to fall outside the normal range, so results of blood tests outside the “normal” range are not always indicative of health problems. The assessment of

4. A measurable molecule or trait that is connected with a specific disease or health condition.

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multiple blood parameters aid in the diagnosis of disease risk and are indicative of overall health status.

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Interactive 10.1

Visit the websites of the National Heart, Lung, and Blood Institute and Lab Tests Online to find out more on what to expect on blood tests and how to interpret results.

http://www.nhlbi.nih.gov/health/dci/Diseases/bdt/bdt_whatdo.html

http://labtestsonline.org/

KEY TAKEAWAYS

• Blood is a connective tissue of the circulatory system, and the fluid in the body that transports absorbed nutrients to cells and waste products from cells.

• The fluid part of blood, plasma, makes up the largest amount of blood volume and contains proteins, ions, glucose, lipids, vitamins, minerals, waste products, gases, enzymes, and hormones. The cellular components of blood include red blood cells, white blood cells, and platelets. Blood is under a constant state of renewal and is synthesized from stem cells residing in bone marrow.

• As blood travels through smaller and smaller vessels the rate of blood flow is dramatically reduced, allowing for efficient exchange of nutrients and oxygen for cellular waste products.

• Blood is healthy when it contains the appropriate amount of water and cellular components, and proper concentrations of dissolved substances, such as albumin and electrolytes.

• The assessment of multiple blood parameters aid in the diagnosis of disease risk and are indicative of overall health status.

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DISCUSSION STARTERS

1. Why does the heart pump blood at a faster rate during exercise?

2. Come up with an estimate on how often it is safe to donate blood. Get the facts on donating blood by visiting the website of the Red Cross.

http://www.redcrossblood.org/donating-blood/eligibility- requirements

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10.2 Metabolism Overview

LEARNING OBJECTIVES

1. Summarize how energy from the energy-yielding nutrients is obtained and used, and how and where it is stored in the body for later use.

2. Explain the role of energy in the process of building tissues and organs.

Throughout the various chapters in this text we have explored the metabolism of carbohydrates, lipids, and proteins. In this next section we will compile this information for a clear picture of the importance of metabolism in human nutrition.

Metabolism5 is defined as the sum of all chemical reactions required to support cellular function and hence the life of an organism. Metabolism is either categorized as catabolism6, referring to all metabolic processes involved in molecule breakdown, or anabolism7, which includes all metabolic processes involved in building bigger molecules. Generally, catabolic processes release energy and anabolic processes consume energy. The overall goals of metabolism are energy transfer and matter transport. Energy is transformed from food macronutrients into cellular energy, which is used to perform cellular work. Metabolism transforms the matter of macronutrients into substances a cell can use to grow and reproduce and also into waste products. In Chapter 6 “Proteins”, you learned that enzymes are proteins and that their job is to catalyze chemical reactions. (Recall that the word catalyze means to speed-up a chemical reaction and reduce the energy required to complete the chemical reaction, without the catalyst being used up in the reaction.) Without enzymes, chemical reactions would not happen at a fast enough rate and would use up too much energy for life to exist. A metabolic pathway is a series of enzymatic reactions that transforms the starting material (known as a substrate) into intermediates, which are the substrates for the next enzymatic reactions in the pathway, until, finally, an endproduct is synthesized by the last enzymatic reaction in the pathway. Some metabolic pathways are complex and involve many enzymatic reactions, and others involve only a few chemical reactions.

To ensure cellular efficiency, the metabolic pathways involved in catabolism and anabolism are regulated in concert by energy status, hormones, and substrate and end-product levels. The concerted regulation of metabolic pathways prevents cells from inefficiently building a molecule when it is already available. Just as it would be inefficient to build a wall at the same time as it is being broken down, it is not

5. The sum of all chemical reactions required to support cellular function and hence the life of an organism.

6. All metabolic processes involved in molecule breakdown and the release of energy.

7. All metabolic processes involved in building bigger molecules, which consume energy.

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metabolically efficient for a cell to synthesize fatty acids and break them down at the same time.

Catabolism of food molecules begins when food enters the mouth, as the enzyme salivary amylase initiates the breakdown of carbohydrates. The entire process of digestion converts the large polymers in food to monomers that can be absorbed. Carbohydrates are broken down to monosaccharides, lipids are broken down to fatty acids, and proteins are broken down to amino acids. These monomers are absorbed into the bloodstream either directly, as is the case with monosaccharides and amino acids, or repackaged in intestinal cells for transport by an indirect route through lymphatic vessels, as is the case with fatty acids and other fat-soluble molecules. Once absorbed, blood transports the nutrients to cells. Cells requiring energy or building blocks take up the nutrients from the blood and process them in either catabolic or anabolic pathways. The organ systems of the body require fuel and building blocks to perform the many fucntions of the body, such as digesting, absorbing, breathing, pumping blood, transporting nutrients in and wastes out, maintaining body temperature, and making new cells.

Energy metabolism8 refers more specifically to the metabolic pathways that release or store energy. Some of these are catabolic pathways, like glycolysis (the8. The metabolic pathways thatrelease or store energy.

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splitting of glucose), β-oxidation (fatty-acid breakdown), and amino acid catabolism. Others are anabolic pathways, and include those involved in storing excess energy (such as glycogenisis), and synthesizing triglycerides (lipogenesis). Table 10.2 “Metabolic Pathways” summarizes some of the catabolic and anabolic pathways, and their functions in energy metabolism.

Table 10.2 Metabolic Pathways

Catabolic Pathways Function

Anabolic Pathways Function

Glycolysis Glucose breakdown Gluconeogenesis Synthesize glucose

Glycogenolysis Glycogen breakdown Glycogenesis Synthesize glycogen

β-oxidation Fatty-acid breakdown Lipogenesis Synthesizetriglycerides

Proteolysis Protein breakdown to aminoacids Amino-acid synthesis

Synthesize amino acids

Catabolism: The Breakdown

All cells are in tune to their energy balance. When energy levels are high cells build molecules, and when energy levels are low catabolic pathways are initiated to make energy. Glucose is the preferred energy source by most tissues, but fatty acids and amino acids can also be catabolized to the cellular energy molecule, ATP. The catabolism of nutrients to energy can be separated into three stages, each containing individual metabolic pathways. The three stages of nutrient breakdown allow for cells to reassess their energy requirements, as endproducts of each pathway can either be further processed to energy or diverted to anabolic pathways. Additionally, intermediates of metabolic pathways can sometimes be diverted to anabolic pathways once cellular energy requirements have been met. The three stages of nutrient breakdown are the following:

• Stage 1. Glycolysis for glucose, β-oxidation for fatty acids, or amino- acid catabolism

• Stage 2. Citric Acid Cycle (or Kreb cycle) • Stage 3. Electron Transport Chain and ATP synthesis

The breakdown of glucose begins with glycolysis, which is a ten-step metabolic pathway yielding two ATP per glucose molecule; glycolysis takes place in the cytosol and does not require oxygen. In addition to ATP, the end-products of glycolysis include two three-carbon molecules, called pyruvate. Pyruvate can either

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be shuttled to the citric acid cycle to make more ATP or follow an anabolic pathway. If a cell is in negative-energy balance, pyruvate is transported to the mitochondria where it first gets one of its carbons chopped off, yielding acetyl-CoA. Acetyl-CoA, a two-carbon molecule common to glucose, lipid, and protein metabolism enters the second stage of energy metabolism, the citric acid cycle. The breakdown of fatty acids begins with the catabolic pathway, known as β-oxidation, which takes place in the mitochondria. In this catabolic pathway, four enzymatic steps sequentially remove two-carbon molecules from long chains of fatty acids, yielding acetyl-CoA molecules. In the case of amino acids, once the nitrogen is removed from the amino acid the remaining carbon skeleton can be enzymatically converted into acetyl-CoA or some other intermediate of the citric acid cycle.

In the citric acid cycle acetyl-CoA is joined to a four-carbon molecule. In this multistep pathway, two carbons are lost as two molecules of carbon dioxide. The energy obtained from the breaking of chemical bonds in the citric acid cycle is transformed into two more ATP molecules (or equivalents thereof) and high energy electrons that are carried by the molecules, nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FADH2). NADH and FADH2 carry the electrons to the inner membrane in the mitochondria where the third stage of energy synthesis takes place, in what is called the electron transport chain. In this metabolic pathway a sequential transfer of electrons between multiple proteins occurs and ATP is synthesized. The entire process of nutrient catabolism is chemically similar to burning, as carbon molecules are burnt producing carbon dioxide, water, and heat. However, the many chemical reactions in nutrient catabolism slow the breakdown of carbon molecules so that much of the energy can be captured and not transformed into heat and light. Complete nutrient catabolism is between 30 and 40 percent efficient, and some of the energy is therefore released as heat. Heat is a vital product of nutrient catabolism and is involved in maintaining body temperature. If cells were too efficient at transforming nutrient energy into ATP, humans would not last to the next meal, as they would die of hypothermia.

Anabolism: The Building

The energy released by catabolic pathways powers anabolic pathways in the building of macromolecules such as the proteins RNA and DNA, and even entire new cells and tissues. Anabolic pathways are required to build new tissue, such as muscle, after prolonged exercise or the remodeling of bone tissue, a process involving both catabolic and anabolic pathways. Anabolic pathways also build energy-storage molecules, such as glycogen and triglycerides. Intermediates in the catabolic pathways of energy metabolism are sometimes diverted from ATP production and used as building blocks instead. This happens when a cell is in positive-energy balance. For example, the citric-acid-cycle intermediate, α- ketoglutarate can be anabolically processed to the amino acids glutamate or

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glutamine if they are required. Recall from Chapter 6 “Proteins” that the human body is capable of synthesizing eleven of the twenty amino acids that make up proteins. The metabolic pathways of amino acid synthesis are all inhibited by the specific amino acid that is the end-product of a given pathway. Thus, if a cell has enough glutamine it turns off its synthesis.

Anabolic pathways are regulated by their end-products, but even more so by the energy state of the cell. When there is ample energy, bigger molecules, such as protein, RNA and DNA, will be built as needed. Alternatively when energy is insufficient, proteins and other molecules will be destroyed and catabolized to release energy. A dramatic example of this is seen in children with Marasmus. These children have severely compromised bodily functions, often culminating in death by infection. Children with Marasmus are starving for calories and protein, which are required to make energy and build macromolecules. The negative-energy balance in children who have Marasmus results in the breakdown of muscle tissue and tissues of other organs in the body’s attempt to survive. The large decrease in muscle tissue makes children with Marasmus look emaciated or “muscle-wasted.”

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In a much less severe example, a person is also in negative-energy balance between meals. During this time, blood-glucose levels start to drop. In order to restore blood-glucose levels to their normal range, the anabolic pathway, called gluconeogenesis, is stimulated. Gluconeogenesis is the process of building glucose molecules from certain amino acids and it occurs primarily in the liver. The liver exports the synthesized glucose into the blood for other tissues to use.

Energy Storage

In contrast, in the “fed” state (when energy levels are high), extra energy from nutrients will be stored. Glucose can be stored only in muscle and liver tissues. In these tissues it is stored as glycogen, a highly branched macromolecule consisting of thousands of glucose monomers held together by chemical bonds. The glucose monomers are joined together by an anabolic pathway called glycogenesis. For each molecule of glucose stored, one molecule of ATP is used. Therefore, it costs energy to store energy. Glycogen levels do not take long to reach their physiological limit and when this happens excess glucose will be converted to fat. A cell in positive- energy balance detects a high concentration of ATP as well as acetyl-CoA produced by catabolic pathways. In response, catabolism is shut off and the synthesis of triglycerides, which occurs by an anabolic pathway called lipogenesis, is turned on. The newly made triglycerides are transported to fat-storing cells called adipocytes. Fat is a better alternative to glycogen for energy storage as it is more compact (per unit of energy) and, unlike glycogen, the body does not store water along with fat. Water weighs a significant amount and increased glycogen stores, which are accompanied by water, would dramatically increase body weight. When the body is in positive-energy balance, excess carbohydrates, lipids, and protein are all metabolized to fat.

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KEY TAKEAWAYS

• The overall goals of metabolism are energy transfer and matter transport. Metabolism is defined as the sum of all chemical reactions required to support cellular function and is either categorized as catabolism (referring to all metabolic processes involved in molecule breakdown) or anabolism (which includes all metabolic processes involved in building bigger molecules). Generally, catabolic processes release energy and anabolic processes consume energy.

• A metabolic pathway is a series of enzymatic steps that transforms a substrate (the starting material) into intermediates, which are substrates for the proceeding enzymatic reactions until finally an end- product is synthesized by the last enzymatic reaction in the pathway.

• The organ systems of the body require fuel and building blocks to digest, absorb, breathe, pump blood, transport nutrients in and wastes out, maintain body temperature, and make new cells amongst a multitude of other functions.

• When energy levels are high, cells build molecules, and when energy levels are low, catabolic pathways are stimulated to release energy.

• The energy released by catabolic pathways powers anabolic pathways in the building of bigger macromolecules.

• In the “fed” state (when energy levels are high), extra nutrient fuel will be stored as glycogen or triglycerides.

DISCUSSION STARTERS

1. Discuss the practicality of storing energy in early human civilizations and the consequences of these metabolic processes in today’s world. Refer back to the story of the Pima Indians in Chapter 1 “Nutrition and You” and the concept of the “thrifty gene.”

2. Can an overweight person blame their excess weight on having a slower metabolism?

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10.3 Vitamins Important for Metabolism and for Blood Function and Renewal

LEARNING OBJECTIVES

1. Summarize the role of the B vitamins in metabolism. 2. Explain how Vitamin K supports a life-saving function of blood.

While the macronutrients (carbohydrates, lipids, and proteins) and alcohol can be catabolized to release energy, vitamins and minerals play a different kind of role in energy metabolism; they are required as functional parts of enzymes involved in energy release and storage. Vitamins and minerals that make up part of enzymes are referred to as coenzymes9 and cofactors10, respectively. Coenzymes and cofactors are required by enzymes to catalyze a specific reaction. They assist in converting a substrate to an end-product. Coenzymes and cofactors are essential in catabolic pathways and play a role in many anabolic pathways too.

In addition to being essential for metabolism, many vitamins and minerals are required for blood renewal and function. At insufficient levels in the diet these vitamins and minerals impair the health of blood and consequently the delivery of nutrients in and wastes out, amongst its many other functions. In this section we will focus on the vitamins that take part in metabolism and blood function and renewal.

9. Vitamins that make up part of enzymes required for converting a substrate to an end-product.

10. Minerals that make up part of enzymes required for converting a substrate to an end-product.

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Vitamins: Functions in Catabolic Pathways, Anabolic Pathways, and Blood Thiamine (B1)

Thiamine is especially important in glucose metabolism. It acts as a cofactor for enzymes that break down glucose for energy production. Additionally, thiamine plays a role in the synthesis of ribose from glucose and is therefore required for RNA, DNA, and ATP synthesis. The brain and heart are most affected by a deficiency in thiamine. Thiamine deficiency, also known as beriberi, can cause symptoms of fatigue, confusion, movement impairment, pain in the lower extremities, swelling, and heart failure. It is prevalent in societies whose main dietary staple is white rice. During the processing of white rice, the bran is removed, along with what were called in the early nineteenth century, “accessory factors,” that are vital for metabolism. Dutch physician Dr. Christiaan Eijkman cured chickens of beriberi by feeding them unpolished rice bran in 1897. By 1912, Sir Frederick Gowland Hopkins determined from his experiments with animals that the “accessory factors,” eventually renamed vitamins, are needed in the diet to support growth, since animals fed a diet of pure carbohydrates, proteins, fats, and minerals failed to grow.Encyclopedia Brittanica Blog. “Frederick Gowland Hopkins

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and his “Accessory Food Factors.” Accessed October 1, 2011. http://www.britannica.com/blogs/2011/06/frederick-gowland-hopkins-accessory- food-factors/. Eijkman and Hopkins were awarded the Nobel Prize in Physiology (or Medicine) in 1929 for their discoveries in the emerging science of nutrition.

Riboflavin (B2)

Riboflavin is an essential component of flavoproteins, which are coenzymes involved in many metabolic pathways of carbohydrate, lipid, and protein metabolism. Flavoproteins aid in the transfer of electrons in the electron transport chain. Furthermore, the functions of other B-vitamin coenzymes, such as vitamin B6 and folate, are dependent on the actions of flavoproteins. The “flavin” portion of riboflavin gives a bright yellow color to riboflavin, an attribute that help lead to its discovery as a vitamin. Riboflavin deficiency, sometimes referred to as ariboflavinosis, is often accompanied by other dietary deficiencies (most notably protein) and can be common in people that suffer from alcoholism. Its signs and symptoms include dry, scaly skin, mouth inflammation and sores, sore throat, itchy eyes, and light sensitivity.

Niacin (B3)

Niacin is a component of the coenzymes NADH and NADPH, which are involved in the catabolism and/or anabolism of carbohydrates, lipids, and proteins. NADH is the predominant electron carrier and transfers electrons to the electron-transport chain to make ATP. NADPH is also required for the anabolic pathways of fatty-acid and cholesterol synthesis. In contrast to other vitamins, niacin can be synthesized by humans from the amino acid tryptophan in an anabolic process requiring enzymes dependent on riboflavin, vitamin B6, and iron. Niacin is made from tryptophan only after tryptophan has met all of its other needs in the body. The contribution of tryptophan-derived niacin to niacin needs in the body varies widely and a few scientific studies have demonstrated that diets high in tryptophan have very little effect on niacin deficiency. Niacin deficiency is commonly known as pellagra and is characterized by diarrhea, dermatitis, dementia, and sometimes death.

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Pantothenic Acid (B5)

Pantothenic acid forms coenzyme A, which is the main carrier of carbon molecules in a cell. Acetyl-CoA is the carbon carrier of glucose, fatty acids, and amino acids into the citric acid cycle. Coenzyme A is also involved in the synthesis of lipids, cholesterol, and acetylcholine (a neurotransmitter). Vitamin B5 deficiency is exceptionally rare. Signs and symptoms include fatigue, irritability, numbness, muscle pain, and cramps. You may have seen pantothenic acid on many ingredients lists for skin and hair care products; however there is no good scientific evidence that pantothenic acid improves human skin or hair.

Pyroxidine (B6)

Pyroxidine is the coenzyme involved in nitrogen transfer between amino acids and therefore plays a role in amino-acid synthesis and catabolism. Also, it functions to release glucose from glycogen in the catabolic pathway of glycogenolysis and is required by enzymes for the synthesis of multiple neurotransmitters and

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hemoglobin. A deficiency in vitamin B6 can cause signs and symptoms of muscle weakness, dermatitis, mouth sores, fatigue, and confusion.

Vitamin B6 is a required coenzyme for the synthesis of hemoglobin. A deficiency in vitamin B6 can cause anemia, but it is of a different type than that caused by insufficient folate, cobalamin, or iron; although the symptoms are similar. The size of red blood cells is normal or somewhat smaller but the hemoglobin content is lower. This means each red blood cell has less capacity for carrying oxygen, resulting in muscle weakness, fatigue, and shortness of breath.

Biotin

Biotin is required as a coenzyme in the citric acid cycle and in lipid metabolism. It is also required as an enzyme in the synthesis of glucose and some nonessential amino acids. A specific enzyme, biotinidase, is required to release biotin from protein so that it can be absorbed in the gut. There is some bacterial synthesis of biotin that occurs in the colon; however this is not a significant source of biotin. Biotin deficiency is rare, but can be caused by eating large amounts of egg whites over an extended period of time. This is because a protein in egg whites tightly binds to biotin making it unavailable for absorption. A rare genetic disease-causing malfunction of the biotinidase enzyme also results in biotin deficiency. Symptoms of biotin deficiency are similar to those of other B vitamins, but may also include hair loss when severe.

Folate

Folate is a required coenzyme for the synthesis of the amino acid methionine, and for making RNA and DNA. Therefore, rapidly dividing cells are most affected by folate deficiency. Red blood cells, white blood cells, and platelets are continuously being synthesized in the bone marrow from dividing stem cells. A consequence of folate deficiency is macrocytic, also called megaloblastic, anemia. Macrocytic and megaloblastic mean “big cell,” and anemia refers to fewer red blood cells or red blood cells containing less hemoglobin. Macrocytic anemia is characterized by larger and fewer red blood cells. It is caused by red blood cells being unable to produce DNA and RNA fast enough—cells grow but do not divide, making them large in size.

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Folate is especially essential for the growth and specialization of cells of the central nervous system. Children whose mothers were folate-deficient during pregnancy have a higher risk of neural-tube birth defects. Folate deficiency is causally linked to the development of spina bifida, a neural-tube defect that occurs when the spine does not completely enclose the spinal cord. Spina bifida can lead to many physical and mental disabilities. Observational studies show that the prevalence of neural- tube defects was decreased after the fortification of enriched cereal grain products with folate in 1996 in the United States (and 1998 in Canada) compared to before grain products were fortified with folate. Additionally, results of clinical trials have demonstrated that neural-tube defects are significantly decreased in the offspring of mothers who began taking folate supplements one month prior to becoming pregnant and throughout the pregnancy. In response to the scientific evidence, the Food and Nutrition Board of the Institute of Medicine (IOM) raised the RDA for folate to 600 micrograms per day for pregnant women. Some were concerned that higher folate intakes may cause colon cancer, however scientific studies refute this hypothesis.

Cobalamin (B12)

Cobalamin contains cobalt, making it the only vitamin that contains a metal ion. Cobalamin is an essential part of coenzymes. It is necessary for fat and protein catabolism, for folate coenzyme function, and for hemoglobin synthesis. An enzyme requiring cobalamin is needed by a folate-dependent enzyme to synthesize DNA. Thus, a deficiency in cobalamin has similar consequences to health as folate

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deficiency. In children and adults cobalamin deficiency causes macrocytic anemia, and in babies born to cobalamin-deficient mothers there is an increased risk for neural-tube defects. In order for the human body to absorb cobalamin, the stomach, pancreas, and small intestine must be functioning properly. Cells in the stomach secrete a protein called intrinsic factor that is necessary for cobalamin absorption, which occurs in the small intestine. Impairment of secretion of this protein either caused by an autoimmune disease or by chronic inflammation of the stomach (such as that occurring in some people with H.pylori infection), can lead to the disease pernicious anemia, a type of macrocytic anemia. Vitamin B12 malabsorption is most common in the elderly, who may have impaired functioning of digestive organs, a normal consequence of aging. Pernicious anemia is treated by large oral doses of vitamin B12 or by putting the vitamin under the tongue, where it is absorbed into the blood stream without passing through the intestine. In patients that do not respond to oral or sublingual treatment vitamin B12 is given by injection.

A summary of the prominent functions of the B vitamins in metabolism and blood function, and their deficiency syndromes is given in Table 10.3 “B-Vitamin Functions in Metabolism and Blood, and Deficiency Syndromes”.

Table 10.3 B-Vitamin Functions in Metabolism and Blood, and Deficiency Syndromes

B Vitamin Function Deficiency: Signs and Symptoms

B1 (thiamine)

Coenzyme: assists in glucose metabolism, RNA, DNA, and ATP synthesis

Beriberi: fatigue, confusion, movement impairment, swelling, heart failure

B2 (riboflavin)

Coenzyme: assists in glucose, fat and carbohydrate metabolism, electron carrier, other B vitamins are dependent on

Ariboflavinosis: dry scaly skin, mouth inflammation and sores, sore throat, itchy eyes, light sensitivity

B3 (niacin) Coenzyme: assists in glucose, fat, and protein metabolism, electron carrier

Pellagra: diarrhea, dermatitis, dementia, death

B5 (pantothenic acid)

Coenzyme: assists in glucose, fat, and protein metabolism, cholesterol and neurotransmitter synthesis

Muscle numbness and pain, fatigue, irritability

B6 (pyroxidine)

Coenzyme; assists in amino-acid synthesis, glycogneolysis, neurotransmitter and hemoglobin synthesis

Muscle weakness, dermatitis, mouth sores, fatigue, confusion

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B Vitamin Function Deficiency: Signs and Symptoms

Biotin Coenzyme; assists in glucose, fat, and protein metabolism, amino-acid synthesis

Muscle weakness, dermatitis, fatigue, hair loss

Folate Coenzyme; amino acid synthesis, RNA,DNA, and red blood cell synthesis Diarrhea, mouth sores, confusion, anemia, neural-tube defects

B12 (cobalamin)

Coenzyme; fat and protein catabolism, folate function, red-blood-cell synthesis

Muscle weakness, sore tongue, anemia, nerve damage, neural- tube defects

Do B-Vitamin Supplements Provide an Energy Boost?

Although some marketers claim taking a vitamin that contains one-thousand times the daily value of certain B vitamins boosts energy and performance, this is a myth that is not backed by science. The “feeling” of more energy from energy-boosting supplements stems from the high amount of added sugars, caffeine, and other herbal stimulants that accompany the high doses of B vitamins. As discussed, B vitamins are needed to support energy metabolism and growth, but taking in more than required does not supply you with more energy. A great analogy of this phenomenon is the gas in your car. Does it drive faster with a half-tank of gas or a full one? It does not matter; the car drives just as fast as long as it has gas. Similarly, depletion of B vitamins will cause problems in energy metabolism, but having more than is required to run metabolism does not speed it up. Buyers of B-vitamin supplements beware; B vitamins are not stored in the body and all excess will be flushed down the toilet along with the extra money spent.

B vitamins are naturally present in numerous foods, and many other foods are enriched with them. In the United States, B-vitamin deficiencies are rare; however in the nineteenth century some vitamin-B deficiencies plagued many people in North America. Remember the video in Chapter 1 “Nutrition and You” on niacin deficiency? Niacin deficiency, also known as pellagra, was prominent in poorer Americans whose main dietary staple was refined cornmeal. Its symptoms were severe and included diarrhea, dermatitis, dementia, and even death. Some of the health consequences of pellagra are the result of niacin being in insufficient supply to support the body’s metabolic functions.

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Dietary Reference Intakes and Sources of B Vitamins

B vitamins are water-soluble and are not stored in significant amounts in the body. Therefore, they must be continuously obtained from the diet. Fortunately, B vitamins are generally well-absorbed in the gut. It should be noted that B vitamins are lost from foods during storage, processing, and cooking. To maximize B vitamin uptake, fruits and vegetables should not be stored for long periods of time, should be eaten more as whole foods, and vegetables should be steamed rather than boiled. Also, alcohol disrupts intestinal absorption of B vitamins. The US Department of Agriculture has reports of the nutrient contents in foods, including all B vitamins, available at their website. (See Note 10.25 “Interactive 10.2”.)

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Interactive 10.2

The USDA has an interactive database of nutrient contents in food. To view reports of single nutrients simply click on the one you are interested in and view the report.

http://www.ars.usda.gov/Services/docs.htm?docid=20958

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Vitamin K: Functions in Metabolism and Blood

There is emerging evidence that vitamin K may play a role in energy metabolism, but currently the exact functions of vitamin K-dependent enzymes in energy metabolism remain elusive. Recall from Chapter 9 “Nutrients Important for Bone Health”, vitamin K is required for optimal bone metabolism. Vitamin K is also critical for blood function. It is a coenzyme for enzymes involved in blood clotting. Blood-clotting proteins are continuously circulating in the blood. Upon injury to a blood vessel, platelets stick to the wound forming a plug. The clotting factors circulating close by respond in a series of protein-protein interactions resulting in the formation of the fibrous protein, fibrin, which reinforces the platelet plug (see Note 10.26 “Video 10.4” for an animation of the blood-clotting cascade of events).

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A deficiency in vitamin K causes bleeding disorders. It is relatively rare, but people who have liver or pancreatic disease, celiac disease, or malabsorption conditions are at higher risk for vitamin K deficiency. Signs and symptoms include nosebleeds, easy bruising, broken blood vessels, bleeding gums, and heavy menstrual bleeding in women. The function of the anticoagulant drug warfarin is impaired by excess vitamin K intake from supplements. Calcium additionally plays a role in activation of blood-clotting proteins as discussed in the previous chapter.

Dietary Reference Intakes and Sources of Vitamin K

The RDA for vitamin K for adult males is 120 mcg/day and for adult females is 90 mcg/day. As discussed in Chapter 9 “Nutrients Important for Bone Health”, vitamin K is present in many foods and most highly concentrated in green leafy vegetables. See Table 10.7 “Dietary Sources of Vitamin K” for a list of dietary sources of vitamin K.

Table 10.7 Dietary Sources of Vitamin K

Food Micrograms per Serving Percent Daily Value

Broccoli (½ c.) 160.0 133

Asparagus (4 spears) 34.0 28

Cabbage (½ c.) 56.0 47

Spinach (½ c.) 27.0 23

Green peas (½ c.) 16.0 13

Cheese (1 oz.) 10.0 8

Ham (3 oz.) 13.0 11

Ground beef (3 oz.) 6.0 5

Bread 1.1 <1

Orange 1.3 1

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KEY TAKEAWAYS

• Vitamins and minerals play a different kind of role in energy metabolism; they are required as functional parts of enzymes involved in energy release and storage.

• The water-soluble B vitamins are involved as coenzymes in the breakdown of nutrients and in the building of macromolecules, such as protein, RNA, and DNA.

• B-vitamin deficiencies are relatively rare especially in developed countries; although the health consequences can be severe as with folate deficiency during pregnancy and the increased risk of neural-tube defects in offspring.

• The B vitamins, pyroxidine (B6), folate, and cobalamin (B12) are needed for blood-cell renewal and/or function.

• Vitamin K is necessary for blood clotting.

DISCUSSION STARTERS

1. Discuss how the actions of B vitamins are interdependent; meaning the level of one affects the function of another.

2. Have a classroom debate on whether it is prudent for the federal government to regulate claims on micronutrient supplements, such as those containing B vitamins.

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10.4 Minerals Important for Metabolism and for Blood Function and Renewal

LEARNING OBJECTIVES

1. List the primary function of each of the minerals involved in metabolism.

2. Summarize the roles of minerals important in blood function and renewal.

Minerals: Functions in Catabolic Pathways, Anabolic Pathways, and Blood Renewal and Function Magnesium

Magnesium is the eleventh most abundant element in the human body and is known to participate as a cofactor in hundreds of metabolic reactions. ATP exists as a complex with magnesium and therefore this mineral is involved in all reactions that synthesize or require ATP including carbohydrate, lipid, protein, RNA, and DNA synthesis. Many Americans do not get the recommended intake of magnesium from their diets. Some observational studies suggest mild magnesium deficiency is linked to increased risk for cardiovascular disease. Signs and symptoms of severe magnesium deficiency may include tremor, muscle spasms, loss of appetite, and nausea.

Iron

Red blood cells contain the oxygen-carrier protein hemoglobin. It is composed of four globular peptides, each containing a heme complex. In the center of each heme, lies iron. Iron is a key component of hundreds of metabolic enzymes. Many of the proteins of the electron-transport chain contain iron–sulfur clusters involved in the transfer of high-energy electrons and ultimately ATP synthesis. Iron is also involved in numerous metabolic reactions that take place mainly in the liver and detoxify harmful substances. Moreover, iron is required for DNA synthesis. The great majority of iron used in the body is that recycled from the continuous breakdown of red blood cells.

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The iron in hemoglobin binds to oxygen in the capillaries of the lungs and transports it to cells where the oxygen is released. If iron level is low hemoglobin is not synthesized in sufficient amounts and the oxygen-carrying capacity of red blood cells is reduced, resulting in anemia. When iron levels are low in the diet the small intestine more efficiently absorbs iron in an attempt to compensate for the low dietary intake, but this process cannot make up for the excessive loss of iron that occurs with chronic blood loss or low intake. When blood cells are decommissioned for use, the body recycles the iron back to the bone marrow where red blood cells are made. The body stores some iron in the bone marrow, liver, spleen, and skeletal muscle. A relatively small amount of iron is excreted when cells lining the small intestine and skin cells die and in blood loss, such as during menstrual bleeding. The lost iron must be replaced from dietary sources.

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The bioavailability of iron is highly dependent on dietary sources. In animal-based foods about 60 percent of iron is bound to hemoglobin, and heme iron is more bioavailable than nonheme iron. The other 40 percent of iron in animal-based foods is nonheme, which is the only iron source in plant-based foods. Some plants contain chemicals (such as phytate, oxalates, tannins, and polyphenols) that inhibit iron absorption. Although, eating fruits and vegetables rich in vitamin C at the same time as iron-containing foods markedly increases iron absorption. A review in the American Journal of Clinical Nutrition reports that in developed countries iron bioavailability from mixed diets ranges between 14 and 18 percent, and that from vegetarian diets ranges between 5 and 12 percent.Centers for Disease Control and Prevention. “Iron and Iron Deficiency.” Accessed October 2, 2011. http://www.cdc.gov/nutrition/everyone/basics/vitamins/iron.html. Vegans are at higher risk for iron deficiency, but careful meal planning does prevent its development. Iron deficiency is the most common of all micronutrient deficiencies and will be explored in depth in Section 10.5 “Iron-Deficiency Anemia”.

Zinc

Zinc is a cofactor for over two hundred enzymes in the human body and plays a direct role in RNA, DNA, and protein synthesis. Zinc also is a cofactor for enzymes involved in energy metabolism. As the result of its prominent roles in anabolic and energy metabolism, a zinc deficiency in infants and children blunts growth. The reliance of growth on adequate dietary zinc was discovered in the early 1960s in the Middle East where adolescent nutritional dwarfism was linked to diets containing high amounts of phytate. Cereal grains and some vegetables contain chemicals, one being phytate, which blocks the absorption of zinc and other minerals in the gut. It is estimated that half of the world’s population has a zinc-deficient diet.Prasad, Ananda. “Zinc deficiency.” BMJ 2003 February 22; 326(7386): 409–410. doi: 10.1136/ bmj.326.7386.409. Accessed October 2, 2011. http://www.ncbi.nlm.nih.gov/pmc/ articles/PMC1125304/?tool=pmcentrez. This is largely a consequence of the lack of red meat and seafood in the diet and reliance on cereal grains as the main dietary staple. In adults, severe zinc deficiency can cause hair loss, diarrhea, skin sores, loss of appetite, and weight loss. Zinc is a required cofactor for an enzyme that synthesizes the heme portion of hemoglobin and severely deficient zinc diets can result in anemia.

Iodine

Recall from Chapter 1 “Nutrition and You” the information about the discovery of iodine and its use as a means of preventing goiter, a gross enlargement of the thyroid gland in the neck. Iodine is essential for the synthesis of thyroid hormone,

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which regulates basal metabolism11, growth, and development. Low iodine levels and consequently hypothyroidism has many signs and symptoms including fatigue, sensitivity to cold, constipation, weight gain, depression, and dry, itchy skin and paleness. The development of goiter may often be the most visible sign of chronic iodine deficiency, but the consequences of low levels of thyroid hormone can be severe during infancy, childhood, and adolescence as it affects all stages of growth and development. Thyroid hormone plays a major role in brain development and growth and fetuses and infants with severe iodine deficiency develop a condition known as cretinism, in which physical and neurological impairment can be severe. The World Health Organization (WHO) estimates iodine deficiency affects over two billion people worldwide and it is the number-one cause of preventable brain damage worldwide.World Health Organization. “Iodine Status Worldwide.” Accessed October 2, 2011. http://whqlibdoc.who.int/publications/2004/ 9241592001.pdf.

Selenium

Selenium is a cofactor of enzymes that release active thyroid hormone in cells and therefore low levels can cause similar signs and symptoms as iodine deficiency. The other important function of selenium is as an antioxidant, which was discussed in detail in Chapter 8 “Nutrients Important As Antioxidants”.

Copper

Copper, like iron, assists in electron transfer in the electron-transport chain. Furthermore, copper is a cofactor of enzymes essential for iron absorption and transport. The other important function of copper is as an antioxidant, which was also discussed in Chapter 8 “Nutrients Important As Antioxidants”. Symptoms of mild to moderate copper deficiency are rare. More severe copper deficiency can cause anemia from the lack of iron mobilization in the body for red blood cell synthesis. Other signs and symptoms include growth retardation in children and neurological problems, because copper is a cofactor for an enzyme that synthesizes myelin, which surrounds many nerves.

Manganese

Manganese is a cofactor for enzymes involved in glucose production (gluconeogenesis) and amino-acid catabolism in the liver. Manganese deficiency is uncommon.

11. Metabolic pathways necessary to support and maintain the basic functions of the body (e.g. breathing, heartbeat, liver, and kidney function) while at rest.

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Chromium

The functioning of chromium in the body is less understood than that of most other minerals. It enhances the actions of insulin so plays a role in carbohydrate, fat, and protein metabolism. Currently, the results of scientific studies evaluating the usefulness of chromium supplementation in preventing and treating Type 2 diabetes are largely inconclusive. More research is needed to better determine if chromium is helpful in treating certain chronic diseases and, if so, at what doses.

A summary of the prominent functions of minerals in metabolism and their related deficiency syndromes is given in Table 10.8 “Mineral Functions in Metabolism and Blood and Deficiency Syndrome”.

Table 10.8 Mineral Functions in Metabolism and Blood and Deficiency Syndrome

Mineral Function Deficiency: Signs and Symptoms

Macro

Magnesium ATP synthesis and utilization, carbohydrate, lipid, protein, RNA, and DNA synthesis

Tremor, muscle spasms, loss of appetite, nausea

Trace

Iron Assists in energy production, DNA synthesis required for red blood cell function

Anemia: fatigue, paleness, faster heart rate

Zinc Assists in energy production, protein, RNA and DNA synthesis; required for hemoglobin synthesis

Growth retardation in children, hair loss, diarrhea, skin sores, loss of appetite, weight loss

Iodine Making thyroid hormone, metabolism, growth and development

Goiter, cretinism, other signs and symptoms include fatigue, depression, weight gain, itchy skin, low heart-rate

Selenium Essential for thyroid hormoneactivity fatigue

Copper Assists in energy production, ironmetabolism Anemia: fatigue, paleness, faster heart rate

Manganese Glucose synthesis, amino-acidcatabolism

Impaired growth, skeletal abnormalities, abnormal glucose metabolism

Chromium Assists insulin in carbohydrate,lipid and protein metabolism abnormal glucose metabolism

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Dietary Reference Intakes for Minerals and Dietary Sources

The mineral content of foods is greatly affected by the soil from which it grew, and thus geographic location is the primary determinant of the mineral content of foods. For instance, iodine comes mostly from seawater so the greater the distance from the sea the lesser the iodine content in the soil.

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Bioavailability

Minerals are not as efficiently absorbed as most vitamins and so the bioavailability of minerals can be very low. Plant-based foods often contain factors, such as oxalate and phytate, that bind to minerals and inhibit their absorption. In general,