Nutrition 331 Nutrition for Health

Study Guide

Unit 1: Overview of Nutrition and Assessment of Nutritional Status

Introduction

The human body is constantly undergoing changes that are governed by genetics and highly dependent on the availability of nutrients. In this unit, we will take an overview of nutrition by defining the terms nutrition and nutrient, and by identifying the major classes of nutrients. We will 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. We will also discuss different techniques for assessing nutritional status.

Objectives

After completing this unit, you should be able to

1. define nutrition.
2. discuss the nature of nutrients.
3. describe four methods of assessing nutritional status.
4. describe four methods of diet information collection for nutritional analysis of individuals or groups of people.
5. explain the uses and limitations of food composition databases.

Section 1: Nutrition as an Applied Science

Since nutrition draws on and applies principles from many disciplines, it is often referred to as an applied science. The disciplines on which nutrition researchers draw 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 molecular and cellular levels and thereby help explain nutritional phenomena in the body. Genetics helps nutritionists understand why certain people are more susceptible than others to nutrition-related diseases, such as heart disease and type 2 diabetes. Anthropology, psychology, sociology, and religion explain people’s choices of foods. Microbiology, agriculture, geography, and business determine the kinds and quantities of food available to us.

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 is related to such diseases as cancer, obesity, hypertension, colon disease, and type 2 diabetes. These diseases are common causes of premature death and make significant contributions to health care costs. About 28 percent of Canadians die of cancer and another 19 percent from heart disease. That means these two diseases account for close to half of all deaths in Canada. Government (federal, provincial/territorial, and local) and health organizations (e.g., Heart and Stroke Foundation, Canadian Diabetes Association) are developing strategies to promote prevention or delay the onset of such health problems. Nutrition policies or recommendations are strategies (among others) to help Canadians reduce their risks.

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

Another area in which nutrition figures prominently is food development. When manufacturers formulate a new food, nutrition science may be used.

Section 2: The Nutrients

The human body is composed almost entirely of nutrients derived from food. The nutrients that must be provided directly by foods are termed essential nutrients; other nutrients can be synthesized by the body from various components of food. The processes by which nutrients are handled in the body are the subject of the multidisciplinary science of nutrition.

The six major classes of nutrients are carbohydrates, lipids (fats), protein, vitamins, minerals, and water. Water, which is often neglected in the study of nutrients, constitutes about 60 percent of body weight.

As they are required in relatively large amounts (grams or litres), carbohydrates, lipids, proteins, and water are called macronutrients. The eText refers to carbohydrates, lipids, and proteins as energy-yielding nutrients (p. 6). Vitamins and most minerals are required in smaller amounts (milligrams or micrograms), so they are called micronutrients.

Section 3: Assessment of Nutritional Status

Canadians are generally well nourished. However, deficiencies and marginal nutrient intakes still occur, as revealed by nutrition surveys. Obesity and other diseases of dietary excess, such as heart disease, are common. To help determine how well nourished a person or a population group is, nutritionists have developed a standardized system for assessing nutritional status. Comprehensive and generally recognized, it is based on a combination of four assessment techniques, each of which offers a different type of information: history, anthropometric measures, physical examination, and laboratory tests. These four techniques complement each other in the diagnosis and confirmation of nutritional deficiency or excess, and they allow for detection of any nutritional disorder.

Assessment Techniques

History

A nutritional history includes an assessment of the person’s diet. Methods for making such an assessment are described later in this unit. In addition, many other aspects of the person’s history are recorded, including medical history, particularly of diet-related conditions. (Examples include alcoholism, anorexia, cancer, drug addiction, hypertension, liver disease, pregnancy, and diabetes.) Socioeconomic history is also important because it provides information about personal, financial, and environmental influences on food intake. For example, a poor education tends to lead to a less nutritious diet, as does living alone.

Anthropometric Measures

A second technique that may reveal nutrition problems is the taking of anthropometric measures, the physical characteristics of the body, such as height and weight. These measures alert the assessor to serious problems such as growth failure in children, wasting or swelling of body tissues in adults, and obesity—conditions that reflect nutrient deficiencies or excesses. Anthropometric measures are discussed further in Unit 8.

Physical Examination

A third nutritional assessment tool is a physical examination that looks for clues to poor nutritional health status. Various parts of the body can be inspected, particularly the hair, eyes, skin, tongue, and fingernails; posture may also be assessed. A physical examination can provide evidence of deficiencies, imbalances, and toxicity status.

Laboratory Tests

A fourth way to detect a developing deficiency, imbalance, or toxic state is to take samples of body fluids, such as blood or urine, and analyze them in a laboratory. In the early stages of malnutrition, body changes may not be obvious, but biochemical (laboratory) tests may reveal problems. A large number of different biochemical tests are available, and it takes much expertise to interpret their results. The most well known of such tests is blood hemoglobin, which indicates whether iron levels are in the normal range. Some of these tests will be mentioned in later units.

Biochemical abnormalities occur long before clinical (or physical) symptoms appear. However, biochemical abnormalities shown by laboratory tests do not indicate whether the cause is inadequate dietary intake (primary deficiency) or something other than diet (secondary deficiency). Factors causing secondary deficiency can include inefficient absorption and excessive excretion (loss of the nutrient). The only way of confirming whether a nutritional deficiency is dietary in origin is to do a dietary assessment.

Collecting Diet Information

Dietary assessment of nutrient intake is a subcategory of nutritional history. There are four methods of collecting diet information: diet history, food diaries, 24‑hour food recall, and food frequency analysis.

Diet History

This type of assessment is most commonly used by health professionals, such as dietitians, to assess an individual’s eating habits or usual food intake. A diet history can reveal socioeconomic and cultural influences, food intolerances, food likes and dislikes, seasonal variation in intakes, appetite and taste changes, physical disabilities (chewing, swallowing, mobility), shopping and cooking practices, and storage options such as refrigerators and cupboards. A diet history is usually conducted along with one of the three other diet assessment methods to determine nutrient intake for the total diet or to assess specific nutrients.

This type of history serves health professionals well for planning healthy eating strategies with a patient or client to encourage long-term changes. This method is rarely used in research studies because it is time consuming, and, consequently, too expensive.

Food Diary

With this assessment, an individual keeps a diary with detailed information about the foods eaten: type, amount, and method of preparation. Other details may be recorded such as the time of day of meals and snacks. Sometimes the food is weighed before eating to increase the accuracy of the food diary.

As part of Assignment 1, you will be asked to keep a food diary for one day.

24-Hour Food Recall

This method is commonly used in research studies to determine typical food and nutrient intake. It is not a practical tool for assessing an individual’s diet to determine potential nutritional deficiencies.

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 estimate serving sizes more accurately.

Food Frequency

This method of assessing diets and nutrient intakes is widely used in epidemiological studies (discussed in Unit 2). Such studies track the diet consumption of a large group of people—hundreds, if not thousands, of participants.

The information tracked includes how often a particular food or type of food is consumed during a specified period of time—day, week, month, or year. A typical question for a food frequency questionnaire is, “How often do you consume broccoli?”

Section 4: Food Composition Databases

Food composition databases—in print or on nutrient analysis software—list the average nutrient composition of foods. The nutrient content of a given food is influenced by

• the variety or strain of the food.
• the geographic location and season of production.
• the mineral content of the soil and the fertilizer used.
• the stage of maturity at harvest.
• the method of processing.
• the method and length of time of storage.
• the method of cooking.

Food composition databases have two main uses:

• They are a resource to determine the amounts of nutrients a person or a group of people are consuming. A group may consist of people in a research study. A food composition database could also be used to assess the nutritional value of a menu for a seniors’ lodge or daycare.
• They are used to identify foods that tend to be high or low in specific nutrients.

Limitations of Food Composition Tables

All food composition tables have some limitations, most of which are listed below.

• Several nutrients are not included in food composition tables (e.g., fatty acids and trace minerals such as iodine).
• Not all foods have been tested for all nutrients, so many have missing values. For example, in the software program Diet and Wellness Plus, many fast foods are missing the B vitamins and many minerals.
• 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 of nutrients a food contains.
• Mixed dishes, such as soups, stews, and casseroles, may vary widely in nutrient composition.
• As the legislation on enrichment and fortification differs between countries, certain Canadian food products have a nutrient composition slightly different from that of similar American products, for example. Nutrient values in the computerized diet analysis program are based on American data, so minor variations may exist in Canadian foods—especially for vitamins A and D, and also for iron in breakfast cereals. Nevertheless, for the general purpose of understanding diet evaluation, such variations are not critical.

Review Questions

See eText Chapter 1, Self-Check:

• questions 1, 2, 3, and 8