Nutrition 330 Introductory Nutrition

Study Guide: Unit 1

An Overview of Nutrition

The human body is constantly undergoing changes that are governed by genetics and that are highly dependent on the availability of nutrients. In this unit, we define the terms nutrition and nutrient, and identify the major classes of nutrients. We also examine some of the factors that influence our food intake. Eating too little or too much can create an imbalance of nutrients and result in nutritional problems; therefore, we discuss different techniques for assessing nutritional status. Finally, we identify the criteria for determining the reliability of nutrition information and its sources.

This unit consists of three sections:

1.1—The Nutrients
1.2—Assessing Nutritional Status
1.3—Appraising Nutritional Information

Objectives

After completing this unit, you should be able to

1. define the term nutrition.
2. define nutrient and identify the major classes of nutrients.
3. define and differentiate among, calorie, kilocalorie (Calorie), and kilojoule, and give the kilocalorie values (per gram) for carbohydrate, lipid, protein, and alcohol.
4. explain some of the factors that govern the way we eat.
5. identify the four components of a complete nutritional assessment and describe the type of information supplied by each component.
6. identify the four methods of collecting diet information: 24‑hour food recall, food diary or diet record, food frequency, and diet history.
7. list the factors that can influence the nutrient values in the food composition table and discuss the limitations of food composition tables.
8. describe the criteria for evaluating the reliability of experimental studies or published research.
9. identify some reliable sources of nutritional information.

1.1 The Nutrients

Introduction

The human body is composed almost entirely of nutrients derived from food. Nutrients that must be provided from foods are termed essential; those that can be synthesized by the body from various components of food are non‑essential. The study of the processes by which nutrients are handled in the body constitutes the multi‑disciplinary science of nutrition.

Objectives

After completing this section, you should be able to

• define the term nutrition.
• define nutrient and identify the major classes of nutrients.
• define and differentiate among, calorie, kilocalorie (Calorie), and kilojoule; and give the kilocalorie values (per gram) for carbohydrate, lipid, protein, and alcohol.
• explain some of the factors that govern the way we eat.

Key Terms

After completing section 1.1, you should be able to define and use the following terms in context:

Reading Assignment

• Chapter 1: Introduction, page 3

An Overview of Nutrition

Since nutrition draws on and puts into practice principles from many disciplines, it is often called an applied science. The disciplines that contribute to nutrition include biochemistry, physiology, anatomy, genetics, anthropology, psychology, sociology, religion, microbiology, agriculture, geography, and business. Biochemistry, physiology, and anatomy help nutritionists understand how nutrients are processed in the body at the molecular and cellular levels and thereby help explain nutritional phenomena in the body. Genetics helps nutritionists understand why certain people are more susceptible to nutritional diseases such as heart disease and diabetes. Anthropology, psychology, sociology, and religion explain people’s choices of foods. Finally, microbiology, agriculture, geography, and business all determine the availability and supply of food.

Nutrition is of tremendous importance in helping to explain the causes of disease. Since the 1960s, medical researchers have made major advances in discovering how diet relates to such diseases as cancer, obesity, hypertension, colon disease, and diabetes. This understanding has major implications for public health policy; for example, governments and medical organizations issue diet recommendations for the general public based on these findings.

Nutrition is also very much involved in therapy. In many diseases, including those mentioned above, diet is important as a component of actual treatment or as a part of patient care.

Nutrition also figures prominently in the development of new food products. Nutrition science plays a role when manufacturers formulate a new food.

Reading Assignment

• Chapter 1: The Nutrients, pages 6–12

The Nutrients

The six major classes of nutrients are carbohydrates, lipids (fats), protein, vitamins, minerals, and water.

Of these, carbohydrates, lipids, and proteins are the energy‑yielding nutrients (see Table 1‑2, p. 8). Alcohol also releases energy, but it is not considered a nutrient because it is not required for the growth, maintenance, or repair of body tissues. Vitamins and minerals do not provide energy, but facilitate the release of energy from carbohydrates, lipids, proteins, and alcohol. They also play a role in many body processes.

Water—often neglected in the study of nutrients—constitutes about 60% of an adult’s body weight. It is an essential nutrient that provides the environment in which nearly all of the body’s activities are conducted.

As they are required in relatively large amounts (grams or litres), carbohydrates, lipids, proteins, and water are called macronutrients. Vitamins and most minerals, however, are required in smaller amounts (milligrams or micrograms) and are called micronutrients.

On page 8, the textbook authors differentiate clearly between calorie and kilocalorie as units used for measuring heat energy in foods.

Kilojoule is the international unit of energy under le système international d’unites (SI). Canada has adopted the SI system; thus, metric units, such as litres, centimetres, and kilograms, have replaced the imperial system of quarts, feet, pounds, etc. Kilocalorie (abbreviated kcal) is still commonly used. However, some publications include energy values in both kilocalories and kilojoules. Be sure that you know the difference in values:

1 kilocalorie (kcal) = 4.2 kilojoules (kJ)

Reading Assignment

• Chapter 1: Food Choices, pages 3–5

Food Choices

After you read through the section in the textbook, examine the lifestyle factors that govern the way you eat.

Your text refers to a growing trend in the food industry: manufacturing and marketing foods with “extras.” These foods are called functional foods, defined as foods with health benefits that extend beyond their nutritional contributions. The examples in the text are just a few of the many choices that are now available. Other examples include yogourts with probiotic cultures, bread with prebiotic fibre, dry pasta with added fibre, omega‑3 eggs, and omega‑3 milk. Blueberries, pomegranates, and tomatoes are promoted for their high concentration of antioxidants, and almonds and walnuts for their heart‑healthy fats. Examine the foods in your kitchen. Do you choose such foods? Are they more expensive than regular foods? If so, is it worth paying more for these foods?

Study Questions

Start the Study Questions to test your knowledge of what you just learned. The Study Questions will open in a new window or browser tab.

1.2 Assessing Nutritional Status

Introduction

Canadians are generally well nourished, but nutrition surveys reveal that deficiencies and marginal nutrient intakes still occur, and obesity is common. A standardized system of assessing nutritional status has been developed to determine how well nourished a person or a population group is. Comprehensive and generally recognized, the system is based on a combination of four assessment techniques. Each technique offers different types of information, and the techniques complement each other in diagnosing and confirming nutritional deficiency or excess, as well as in detecting the stages of development of deficiency or excess.

Objectives

After completing this section, you should be able to

• identify the four components of a complete nutritional assessment and describe the type of information supplied by each component.
• identify the four methods of collecting diet information: 24‑hour food recall, food diary or diet record, food frequency, and diet history.
• list the factors that can influence the nutrient values in the food composition table and discuss the limitations of food composition tables.

Key Terms

After completing section 1.2, you should be able to define and use the following terms in context:

Reading Assignment

• Chapter 1: “Nutrition Assessment,” pages 22–25

Nutrition Assessment

Figure 1.7 (p. 24) describes the stages in the development of a nutrient deficiency, using iron as an example (pp. 24–25). You should remember that a subclinical deficiency shows up as a biochemical abnormality and occurs long before clinical (or physical) symptoms appear. However, laboratory tests do not indicate whether the cause of a subclinical deficiency is inadequate dietary intake (primary deficiency) or something other than diet (secondary deficiency), such as inefficient absorption or excessive excretion or loss of the nutrient. The only way of confirming whether a nutritional deficiency is dietary in origin is to do a dietary assessment by estimating nutrient intakes.

We will refer to some specific details of nutrition assessment (e.g., drug‑nutrient interactions and biochemical tests) as we discuss the different nutrients in later units.

Reading Assignment

• “Diet History,” pages E‑2 to E‑4 of Appendix E

Diet History

Dietary assessment of nutrient intake is a part of the historical information gathered in a complete nutritional assessment. The four methods of collecting diet information are discussed next.

1. 24‑hour food recall

In this commonly used method of obtaining food intake data, a trained interviewer asks the subject to recall everything eaten or drunk during the past 24 hours (or the previous day). Usually, food models and measurement aids are used to help the subject to estimate portion sizes more accurately. This method has been used in many epidemiological studies where it is necessary to measure dietary intake.

2. Food-frequency questionnaire

This method is used to rank how often a particular food or type of food is consumed during a specified period of time—day, week, month, or year. It provides qualitative information on whether dietary intake of a certain food or food group is high or low. To be useful for assessing quantitative nutrient intake, subjects must indicate the usual portion sizes that they consume. The use of food models and measuring aids can help people to estimate their portion sizes. In the last 20 years, the food frequency method has been widely used in epidemiological studies of dietary intake over an extended period.

This method and the 24‑hour food recall are both prone to significant error due to inaccuracy in people’s ability to accurately remember what they have been eating.

3. Food record or food diary

This method requires that the subject keep a diary of food intake, indicating the type of food, amount, and method of preparation. The investigator may also want to know the time of day meals are eaten, with whom, where, and how the subject is feeling. Sometimes, food people weigh food before eating it to increase accuracy in the estimation of portion sizes. However, the inconvenience of having to weigh food can cause a person to eat less. Studies have shown that a three‑ or five‑day record is as accurate as a seven‑day record.

4. Diet history

This method is aimed at eliciting both qualitative and quantitative information on long‑standing food habits (or usual food intake). A diet history questionnaire can reveal socioeconomic and cultural influences, food intolerances, food likes and dislikes, seasonal variation in intakes, appetite and taste changes, physical disabilities (chewing, swallowing, motor skills, mobility), shopping and cooking practices, and the presence or absence of facilities for refrigeration and storage. A diet history is usually incorporated with other methods—the 24‑hour food recall, food diary, or food frequency—to determine the quantitative nutrient intake of the total diet or of selected foods. Of the four methods, diet history is by far the most comprehensive.

No single method of obtaining diet information is suitable for all purposes; each has strengths and weaknesses that require trade‑offs. If a combination of methods is used, the researcher can balance the shortcomings of one with the strengths of another.

Diet information, and any other component in a complete nutritional assessment, may accumulate many sources of error during data collection, processing, and analysis. A team of skilled professionals is necessary to provide accurate and meaningful interpretation of the data offered by each assessment technique.

Ensure that you understand the difference between the assessment of nutritional status and the collection of diet information. Assessing a person’s diet (and therefore their nutrient intake) is only one component of determining their nutritional status.

Food Composition

Once diet information is collected, it is analyzed using data in food composition tables. These tables list the average nutrient composition of foods. The nutrient content of foods is influenced by the factors listed below:

• the geographic location and season of production
• the mineral content of the soil
• the stage of maturity at harvest
• the diet of the animal or the type of fertilizer used in the growing of the plant
• the method of processing
• the length and method of storage
• the method of cooking the food
• the methods of analysis
• the difference in water content of the samples analyzed.

Some of the limitations of food composition tables are listed below:

• Many trace minerals such as iodine and chromium are not included.
• For some nutrients, data are incomplete.
• With so many influencing factors, nutrient data are, at best, an approximation of the actual composition of foods. Some variation of nutrient values is unavoidable in different food composition tables.
• The calculated amount of a nutrient in a given food should not be assumed to be completely absorbed by the body; certain factors can enhance or inhibit the absorption of nutrients. The values listed represent only the amount a food contains.
• Mixed dishes, such as soups, stews, and casseroles, may vary widely in nutrient composition, depending on the type and amount of ingredients used.
• As legislation on enrichment and fortification differs between the two countries, certain Canadian food products have a nutrient composition that differs slightly from that of US products. Nutrient values in the Diet and Wellness Plus program are based on US data, so minor variations may exist in Canadian foods, especially vitamins A and D, and folic acid and iron in enriched and fortified breakfast cereals. Nevertheless, for the general purpose of understanding a diet evaluation, such variations are not critical.

Study Questions

Start the Study Questions to test your knowledge of what you just learned. The Study Questions will open in a new window or browser tab.

1.3 Appraising Nutrition Information

Introduction

Nutrition is a large field in which it takes years of education and training to become an “expert.” Unfortunately, a master’s degree or a doctorate in nutrition science does not guarantee credibility. Some “mail‑order universities” sell degrees (or at least, certificates) stating that the holder has a degree. To obtain such degrees, a candidate does not need to read any book or pass any examination, and yet can call himself or herself a “nutritionist.”

The titles Registered Dietitian, Professional Dietitian, and Dietitian are all protected by law through provincial legislation. To become a practising dietitian in Canada requires earning an undergraduate degree in nutrition from an accredited university, completion of a dietetic internship or equivalent, and passing a provincial examination. Only after completing these steps is a person eligible to use the legally protected title of that province. In Canada, this title can be represented by any of the following abbreviations: RD, RDN, PDt, RDt, or DtP. While some registered dietitians call themselves nutritionists, the title Registered Nutritionist is protected only in British Columbia, Quebec, Nova Scotia, and (as Registered Dietitian‑Nutritionist) New Brunswick. In the other six provinces, “nutritionist” is an unprotected title that can be used by anyone. See Table H1‑1 on page 32.

Other sources of reliable nutrition information include physicians who have made a special study of nutrition (most physicians have not) and nutrition scientists.

Objectives

After completing this section, you should be able to

• describe the criteria for evaluating the reliability of experimental studies or published research.
• identify some reliable sources of nutritional information.

Reading Assignment

• Chapter 1: “The Science of Nutrition,” pages 12–18

  This reading is very informative. However, there are two notable errors. First, what is labelled as “cross‑sectional studies” in Figure 1‑4 is a population comparison. Second, the third paragraph under “Correlations and Causes” (page 16) inaccurately states that it is essential to find evidence of the mechanism in order to “prove that A causes B.”  In reality, there are many examples where the weight of evidence from epidemiological and human intervention studies that indicate that A causes B is so strong and consistent that experts in the area are confident in stating that the evidence “proves that A causes B,” even though the mechanism of how A causes B is not known.

• Chapter 1: Highlight 1: “Nutrition Information and Misinformation—On the Net and in the News,” pages 29–34

Nutrition Information and Misinformation

Unfortunately, much of the nutrition information directed at the public is unreliable. Nutrition information is often oversimplified, and studies are often not scientifically controlled. Claims are often based on hunches, unrepeated individual experiences (anecdotes), or testimonial evidence, and are exaggerated with such gimmicks as “something for nothing” or “money‑back guarantee.” Often, expensive special foods or dietary supplements are promoted, which may be superfluous or even harmful to well‑balanced nutrition.

Figure H1‑2 on page 34 illustrates problems often seen on the labels of supplements. These problems are widespread in both Canada and the United States. For example, supplements are commonly promoted with claims that they will boost the immune system, detoxify the body, or induce weight loss. Such supplements are sold through advertisements that regularly appear in newspapers or through multi‑level marketing (like Avon). The claims made for such supplements are seldom based on solid research and have a low level of credibility (Temple et al., 2009; Temple, 2010). People should not purchase such supplements unless they obtain solid evidence that the supplement is both safe and effective. The staff in health-food stores cannot be trusted to supply such information. A pharmacy is a much better place to consider buying a supplement as pharmacists are well trained and are governed by a code of ethics that deters them from giving false information.

When you are trying to choose a reliable book on nutrition, follow the steps outlined below:

1. Check the author’s educational background and present affiliation.
2. Search for any special‑interest reason for the publication; for example, is the author promoting the sale of special supplements or products?
3. Look for any scientific evidence for the claims; reliable journalists usually document their statements with research evidence.
4. Check on the date of publication to ensure that the information is current.

Many medical journals include nutritional studies. Unfortunately, most professional journals are too technical for those with a minimal background on the subject.

When in doubt, one can consult a public health nutritionist or dietitian in a hospital. Reliable websites are listed in your textbook on page 34. The Health Canada, Mayo Clinic, and Medline Plus websites are also additional sources of valuable information on nutrition.

Study Questions

Start the Study Questions to test your knowledge of what you just learned. The Study Questions will open in a new window or browser tab.

References