CHAPTER 1 Nutrition: Linking Food and Health and
In Depth: Nutrition Research: Challenges and Controversies
Chapter Summary
Nutrition is the science of food and how food nourishes our body and affects our health. Because of its importance to wellness, nutrition has been included in the national health promotion and disease prevention plan known as Healthy People 2030. The six essential nutrients found in the foods we eat are carbohydrates, fats, proteins, vitamins, minerals, and water. Although only carbohydrates, fats, and proteins provide energy, all the nutrients have specific roles critical to human growth and function. The Dietary Reference Intakes (DRIs) are reference standards for nutrient intakes for healthy people in the United States and Canada and should be used for dietary planning. Malnutrition occurs when a person’s nutritional status is out of balance.
Research involves applying the scientific method. A scientific theory represents a conclusion drawn from repeated experimentation. Different types of studies provide different types of information. Good sources of reliable nutrition information include individuals who are registered dietitians, licensed dietitians, or those who hold an advanced degree in nutrition. In addition, government health agencies can offer reliable information related to nutrition, as well as other areas of health and wellness.
Learning Objectives
After studying this chapter, your students should be able to do the following:
1. Define the term nutrition and describe its evolution as a science.
2. Explain how nutrition supports health.
3. Identify the six classes of nutrients essential for health.
4. Distinguish among six groups of Dietary Reference Intakes for nutrients.
5. Describe the steps of the scientific method.
6. Discuss the design and primary goals of three basic types of nutrition research.
7. List several professionals, government agencies, and organizations that are trustworthy sources of nutrition information.
The chapter’s In Depth essay will additionally enable them to:
1. Describe how conflict of interest and bias can compromise nutrition-related studies.
2. Explain how to evaluate nutrition-related research reports and media claims.
Chapter Outline
I. What Is the Science of Nutrition and How Did It Evolve??
A. Nutrition is the science that studies all aspects of food and its influence on our body and health.
1. Nutrition is a relatively new scientific discipline.
2. Early nutrition research focused on making a link between dietary deficiencies and illness.
3. After WWII, nutrition research began to focus on the goals of supporting health and preventing and treating chronic diseases.
II. How Does Nutrition Support Health?
A. A nutritious diet provides chemicals for energy and essential functions.
1. Healthful nutrition and regular physical activity can increase feelings of wellbeing.
2. Consuming a nutritious diet contributes to health in a variety of ways, including by providing the energy and functional chemicals that help us to perform activities of daily living.
B. A nutritious diet reduces the risk for disease.
1. Nutrition appears to play a role from a direct cause to a mild influence in the development of many diseases.
2. Poor nutrition is a direct cause of deficiency diseases.
a. Deficiency diseases have been substantially reduced; however, poverty remains a major contributor to nutritional deficiencies around the world
3. Poor nutrition is strongly associated with three chronic diseases heart disease, stroke, and diabetes among the top 10 causes of death in the U.S. and all linked to obesity.
III. What Are Nutrients?7
A. Nutrients are chemicals found in foods that are critical to human growth and function.
1. The six nutrient groups are carbohydrates, fats and oils (two types of lipids), proteins, vitamins, minerals, and water.
2. Organic nutrients contain carbon and hydrogen.
3. Inorganic nutrients do not contain carbon and hydrogen.
B. Three macronutrients provide energy.
1. Carbohydrates, fats, and proteins are the only nutrients that provide energy, and they are referred to as macronutrients.
2. Energy is measured in kilocalories (kcal).
a. Carbohydrates and protein provide 4 kcal per gram.
b. Alcohol provides 7 kcal per gram.
c. Fats provide 9 kcal per gram.
3. Carbohydrates are a primary fuel source.
a. Sources of carbohydrates include grains, vegetables, fruits, legumes, dairy products, seeds, and nuts.
4. Fats also provide energy.
a. Fats contain proportionally less oxygen and water than do carbohydrates, which results in a higher energy yield per gram.
b. Fats are an important energy source for our bodies at rest and during lowintensity exercise.
c. Foods that contain fats are essential for the absorption into our body of certain vitamins that are soluble only in fat.
i. Solid fats include butter, lard, and margarine.
ii. Liquid fats include vegetable oils.
d. Cholesterol is a form of lipid that our body can produce independently, and it can also be consumed in the diet.
5. Proteins support tissue growth, repair, and maintenance.
a. Proteins are different from carbohydrates and fats in that they contain nitrogen.
b. The building blocks of protein are amino acids.
c. Proteins can provide energy but are not a primary source.
d. Proteins play a major role in growth, structural repair, and maintenance by assisting in regulating metabolism, healing wounds, breakdown of foods, and fluid balance.
e. Sources of protein include meat and dairy products and, to a lesser extent, vegetables, whole grains, seeds, nuts, and legumes.
C. Micronutrients assist in the regulation of body functions.
1. Vitamins and minerals are referred to as micronutrients.
2. Vitamins are organic compounds that help regulate our bodies’ functions.
3. Although vitamins do not contain energy, they are essential to energy metabolism.
4. Vitamins are also critical in building and maintaining healthy body tissues.
5. Vitamins are classified as fat-soluble and water-soluble.
6. Minerals are inorganic substances because they do not contain carbon and hydrogen.
7. All minerals maintain their structure no matter what environment they are in.
8. Minerals assist in fluid regulation and energy production, are essential to the health of bones and blood, and help rid our body of harmful by-products of metabolism.
9. The two categories of minerals are major minerals and trace minerals.
D. Water supports all body functions.
1. Water is an inorganic macronutrient that is vital for our survival.
2. Sources of water include fluids and solid foods.
E. Foods also provide beneficial non-nutrient compounds.
1. Functional foods contain biologically active ingredients that provide health benefits beyond their nutrients.
2. Examples include probiotic foods such as yogurt and phytochemicals in plants.
IV. How Much of Each Nutrient Do Most People Need?
A. Use the Dietary Reference Intakes (DRIs) to check your nutrient intake.
1. The DRIs are for healthy people only.
2. The Estimated Average Requirement (EAR) guides the recommended dietary allowance.
a. It represents the average daily nutrient intake level estimated to meet the requirements of half the healthy individuals of a particular age and sex.
3. The Recommended Dietary Allowance (RDA) meets the needs of nearly all healthy people.
a. It is the average daily nutrient intake level that meets the nutrient requirements of 97–98% of healthy individuals of a particular age and sex.
4. The Adequate Intake (AI) is based on estimates of nutrient intakes.
a. It is a recommended average daily nutrient intake level assumed to be adequate and is used when RDA cannot be determined.
5. The Tolerable Upper Intake Level (UL) is the highest level that poses no health risk.
a. It is an intake level likely to pose no risk of adverse health effects to almost all individuals of a particular age and sex.
6. The Estimated Energy Requirement (EER) is the intake predicted to maintain a healthy weight.
7. The Acceptable Macronutrient Distribution Range (AMDR) is associated with reduced risk for chronic diseases.
a. For a given energy source, it specifies the range of intakes associated with reduced risk of chronic disease while providing adequate intake of essential nutrients.
8. You can help your body maintain a healthful weight, support physical activity, obtain adequate nutrition, and reduce risk for chronic disease by eating foods that meet the DRIs.
V. How Do Nutrition Scientists Evaluate Claims?
A. The scientific method enables researchers to test a hypothesis.
1. Observation of a phenomenon initiates the research process.
2. A hypothesis is a possible explanation for an observation.
3. An experiment is designed to test the hypothesis.
a. The researcher must determine the type of data to collect and how to collect data most accurately.
b. Key elements of a well-designed experiment are an adequate sample size; a control group; and a method of controlling for other factors that may influence results.
4. Data are collected and analyzed to determine whether they support or reject the hypothesis.
B. Repetition of research is required to develop theories.
1. Most hypotheses need to be refined after the initial results are obtained.
2. When replicated by others, the experiment must produce similar results and lead to similar conclusions, or the hypothesis becomes invalid.
3. You should never accept one report as absolute fact on any topic.
4. A theory may be developed following extensive research.
VI. Why Do Nutrition Scientists Use Different Types of Research?
A. Animal studies can inform human studies.
1. Drawbacks include ethical concerns and the fact that results may not apply directly to humans.
2. Animal studies have nevertheless advanced our understanding of many aspects of nutrition.
B. Epidemiological studies explore patterns within populations.
1. Prevalence refers to the actual percentage of the population that has a particular disease at a given period of time; incidence refers to the rate of new cases within a period of time.
2. Observational studies are used in assessing the nutritional habits, disease trends, and other health phenomena of large populations.
3. Case control studies involve comparing a group of individuals with a particular condition to a similar group without the condition.
C. Experimental trials examine cause and effect.
1. Experimental trials are tightly controlled experiments in which an intervention is given to determine its effect on a certain disease or health condition.
a. Randomized trials are studies in which researchers randomly assign participants to intervention groups and control groups.
b. Single-blind experiments are those in which participants are unaware of the treatment they are receiving, but researchers know who is getting the treatment and who is not.
c. Double-blind experiments are those in which neither the researchers nor the participants know who is receiving the treatment or intervention.
d. A placebo is an imitation treatment that has no real effect on participants. Studies that include them are often called placebo-controlled double-blind randomized control (or clinical) trials.
D. Systematic reviews synthesize the findings of multiple studies.
1. A systematic review is a synthesis of the findings of quality studies on a particular research topic.
2. A meta-analysis may be included and contains a synthesis of the data of the individual studies.
E. Different study types vary in quality of evidence.
1. Systematic reviews with meta-analyses, position papers, and guidelines are of highest Quality.
2. Expert opinions and anecdotal evidence are of lowest quality.
VII. Which Sources of Nutrition Advice Are Trustworthy?
A. Trustworthy experts are educated and credentialed.
1. A registered dietitian nutritionist (RDN) possesses at least a bachelor’s degree, completion of a supervised clinical experience, passing grade on a national examination, and maintenance of registration with the Academy of Nutrition and Dietetics.
2. A licensed dietitian must meet the credentialing requirements of a given state. Each state has its own laws regulating licensure or registration.
3. Many individuals are educated and experienced in nutrition and hold an advanced degree, master’s degree (MA or MS) or doctoral degree (PhD) in nutrition.
4. A physician, or medical doctor, is licensed to practice medicine but typically has limited experience and training in nutrition.
5. “Nutritionist” is a term that generally has no definition or laws regulating it.
B. Government agencies are usually trustworthy.
1. The National Institutes of Health (NIH) is the leading medical research agency in the world.
2. Many institutes within the NIH conduct research into nutrition-related health issues.
3. The Centers for Disease Control and Prevention (CDC) protects the health and safety of Americans.
4. The National Health and Nutrition Examination Survey (NHANES) tracks the food and nutrient consumption of Americans.
5. The Behavioral Risk Factor Surveillance System (BRFSS) tracks lifestyle behaviors that increase risk for chronic disease.
C. Professional organizations provide reliable nutrition information.
1. The Academy of Nutrition and Dietetics is the largest organization of food and nutrition professionals in the world.
2. The American Society for Nutrition (ASN) is a research society whose goal is to improve the quality of life through the science of nutrition.
3. American College of Sports Medicine (ACSM) is the leading sports medicine and exercise science organization in the world.
4. The Obesity Society (TOS) is the leading scientific society dedicated to the study of obesity.
VIII. Nutrition Debate: Dietary Reference Intakes: Can They Be Applied to Chronic Diseases?
A. Developing DRIs for associations between nutrients and chronic diseases presents challenges.
1. Insufficient evidence of high quality.
2. Use of observational studies that indicate correlations but not cause and effect.
3. Use of dietary questionnaires that can be inaccurate and time consuming for the participant.
B. Developing DRIs addressing chronic diseases is more complex than addressing toxicities and deficiencies.
1. Relationships between nutrients and chronic diseases are expressed as relative risks rather than absolute risk.
2. Relative risk for a given disease can be influenced by more than one nutrient, and a single nutrient can influence more than one chronic disease.
C. Despite challenges, including chronic disease endpoints in setting DRIs could help Reduce our current burden of chronic disease.
IX. In Depth, Nutrition Research: Challenges and Controversies
A. How can conflict of interest and bias compromise nutrition research?
1. Conflict of interest can lead to researcher bias.
a. Bias can be an inclination toward or against a particular person, situation, or outcome.
b. Researcher bias is an factor, such as investment in the product or gifts from the producer), that might influence the researcher to favor certain results.
c. Conflicts of interest must be clearly identified in all research studies to ensure that findings are accurate and trustworthy.
2. Other types of bias can also affect the validity of research findings.
a. Selection bias occurs when participants in the study are not randomly selected.
b. Dietary exposure assessment bias occurs when self-reported dietary intake tools are used in the study.
c. Recall bias results from differences in the ability of participants to accurately recall and report their dietary intake.
d. Reporting bias occurs when there are differences between reported and unreported results.
e. Publication bias refers to the tendency for scientific journals to publish studies reporting positive results.
3. There are many ways to improve nutrition research.
a. Journals could strengthen their enforcement of disclosure requirements.
b. The research community could help create conditions that allow the public health sector to work independently of the industry sponsor.
c. Researchers could develop more accurate markers of nutrient and food intake for self reporting studies.
d. Researchers could provide full access to datasets used in their studies.
e. A global system could be developed to register all RCTs and make results available to the public.
f. Journal editors could publish more studies with negative findings.
B. How can you evaluate nutrition-related research reports and media claims?
1. Recognize nutrition misinformation and disinformation.
a. Misinformation is inaccurate or incomplete information that can be misleading.
b. Disinformation is intentionally spreading false information.
2. Investigate the sources and content of media reports about nutrition studies.
a. Who is reporting the information?
b. Is the research reputable?
c. Where do the data fit in the hierarchy of evidence?
d. Are the claims too good to be true?
3. Evaluate the credibility of websites and social media.
a. Examine the names and credentials of the contributing people.
b. Check the date of the web page or social media post to confirm that it is recent.
c. Check the source of the web address or social media account (ex. .gov, .org, .edu).
d. Watch for dramatic claims of “cures” and “quick fixes”.
e. Is it consistent with other credible sources or does it contradict what is accepted as common knowledge?
Key Terms
bias
carbohydrates case control studies
Centers for Disease Control and Prevention (CD C)
chronic diseases
conflict of interest
correlation
dietary exposure assessment bias
Dietary Reference Intakes (DRIs)
disinformation epidemiological studies
fats
experimental trials
fat-soluble vitamins
food health hypothesis incidence inorganic macronutrients
major minerals
meta-analysis
metabolism
micronutrients
minerals misinformation
National Institutes of Health (NIH)
nutrients
nutrition
observational studies
In-Class Discussion Questions
organic placebo
prevalence proteins
publication bias
recall bias
registered dietitian nutritionist (RDN)
reporting bias
researcher bias
scientific method
selection bias
systematic review theory
trace minerals
vitamins
water-soluble vitamins
1. Give some examples describing how good nutrition can support wellness.
2. Discuss how each of the six classes of nutrients contributes to human growth and function.
3. Describe how the DRIs can be used for preventing nutrient deficiency and for reducing risk of chronic disease.
4. Discuss the difference between a hypothesis and a theory and how they relate to the scientific method.
5. Give examples of professionals and organizations that can be trusted for accurate nutrition information and explain criteria that can be used for evaluating them.
6. Discuss some links between diet and chronic disease risk.
In-Class Activities
1. Estimate portion sizes of premeasured foods that have been placed in the classroom. Examples of foods that can be used for this activity include salad or vegetables; sliced fruit; cereal; cooked meat; snack foods such as potato chips, popcorn, or nuts; butter or peanut butter; cheese; and pasta or rice. Ask students to make note of the most appropriate units for measuring these foods. For example, note differences between fluid ounces versus solid ounces and weight versus volume. This activity is helpful to prepare for recording food intake described in the MyDietAnalysis Activity that follows.
2. Invite one or more guest speakers who work in the area of nutrition to share their job experiences with the class.
3. List the steps of the scientific method in the wrong order. Ask the class to place them, one by one, in the correct order.
MyDietAnalysis Activity
1. Have your students choose three days during which their eating habits are typical. A good guideline is to include two weekdays and one weekend day. Have them record all foods and drinks they consume for each of the three days. Be sure they estimate the quantities of each item to the best of their abilities. Ask them to enter this information into their diet analysis software and to compare their intakes to the DRIs appropriate for their age and gender. It is not necessary to meet 100% of each DRI every day. A general guideline is meeting between 80% and 120% of the requirements over a one-week period. Have them answer the following questions:
a. For how many nutrients analyzed did you meet requirements?
b. How many nutrients were less than 80% of requirements?
c. How many nutrients were greater than 120% of requirements? Keep this assessment for use in future activities.
Web Resources
Main Chapter
www.eatright.org
The Academy of Nutrition and Dietetics
Obtain a list of registered dietitians in your community from the largest organization of food and nutrition professionals in the United States.
www.cdc.gov
Centers for Disease Control and Prevention
Visit this site for additional information about the leading federal agency in the United States that protects the health and safety of people.
www.cdc.gov/nchs/
National Center for Health Statistics
Visit this site to learn more about the National Health and Nutrition Examination Survey (NHANES) and other national health surveys.
www.nih.gov
National Institutes of Health
Find out more about the National Institutes of Health, an agency under the U.S. Department of Health and Human Services.
www.ncbi.nlm.nih.gov/pmc/
PubMed Central
Search PubMed at the U.S. National Library of Medicine for summaries of research studies on health topics of your choice.
nutrition.org
American Society for Nutrition
Learn more about the American Society for Nutrition and its goal to improve quality of life through the science of nutrition.
www.acsm.org
American College of Sports Medicine
Find information about the leading sports medicine and exercise science organization in the world.
www.obesity.org/
Obesity Society
Learn about this interdisciplinary society and its work to understand, prevent, and treat obesity to improve the lives of those affected through research, education, and advocacy.
www.nationalacademies.org/hmd/health-and-medicine-division
The National Academies of Sciences, Engineering and Medicine Health and Medicine Division
Learn about the Health and Medicine Division (formerly the Institute of Medicine) and its history of examining the nation’s nutritional well-being and providing sound information about food and nutrition. Select “Food and Nutrition” from the drop-down menu in the Explore by Topic bar to learn more.
In Depth: Nutrition Research: Challenges and Controversies www.cochranelibrary.com
The cochrane library
Visit the cochrane library for high-quality, independent research evidence on health topics that concern you.
WWW.NNLM.GOV/GUIDES/INTRO-HEALTH-LITERACY
The national library of medicine’s health literacy page Health literacy is the capacity to access and understand health-related information. This site identifies the skills needed for health literacy, the consequences of low health literacy, and much more.