Dietary Assessment

Definition

A dietary assessment is an estimation of food and nutrients eaten over a particular time period. A number of dietary assessment tools are used by dietitians, nutritionists, and physicians to aid in dietary counseling. These include:

• food records or diaries (including weighed food intakes)
• dietary recalls
• food frequency questionnaires (FFQs)
• dietary histories
• observed intakes
• chemical analyses of duplicate collections of foods consumed
• biological assessments (e.g., doubly labeled water, plasma carotene, etc.)

Purpose

A dietary assessment is often conducted to determine the macronutrient (energy or caloric, protein, carbohydrate, and fat) content and the micronutrient (vitamin and mineral) content of the diet to assist in guiding dietary counseling. Validation of dietary assessment instruments is important in order to accurately evaluate the diet for certain risk factors associated with chronic diseases such as diabetes. A dietary assessment is often used as a tool to help the patient lose weight or to prevent or treat conditions or diseases that are influenced by food intake and nutritional status (e.g., cardiovascular disease, obesity, diabetes, hyperlipidemia).

Consumption of too little or too much of certain vitamins and minerals may lead to a nutrient deficiency or a nutrient toxicity respectively. A guide to the amount or vitamins, minerals, and marconutrients an average person needs to consume to remain healthy has been developed. In the United States, this guide is called the Dietary Reference Intakes (DRI). The DRIs have replaced Recommended Dietary Allowances (RDAs), an earlier measure of these nutrients. DRIs encompass both the RDAs and the upper recommended intake limits for each nutrient. The RDA designates a level of vitamin and minerals that is adequate for approximately 97-98% of healthy people in the population. The dietitian may use a dietary assessment to compare an individual's intake to the general population's requirements for nutrients to ensure the diet has the proper balance of calories, protein, carbohydrate, fat, vitamins, and minerals.

Precautions

Dietary assessments are estimations based on food intake at a particular time and can only estimate dietary adequacy or inadequacy since intake varies from day to day. For example, fruit and vegetables may be lacking on a day that was surveyed for the dietary assessment, while overall the diet may be adequate in fruit and vegetable intake. Thus, care must be taken regarding generalizations about deficiencies or adequacy of nutrient intake. Intake of calories, fats, carbohydrates, and protein varies less from day to day and may be estimated more accurately than vitamin and mineral intakes.

Description

Some of the most common tools that assist in providing dietary guidance include food records, 24-hour dietary recalls, food frequency questionnaires, diet histories, and certain biochemical indices. These tools are explained in greater detail below. Furthermore, a scientific assessment of nutritional status may be made by using a combination of the information collected from clinical evaluations, biochemical tests, and dietary information. The clinical evaluation includes measurements of various anthropometric parameters such as height, weight, and percent body fat as determined by skin folds or hydrostatic weighing. In addition, a clinical evaluation may include observation for signs of nutrient deficiencies in the mouth, skin, eyes, and nails. The information collected from a clinical evaluation can be compared with that obtained from the dietary assessment and biochemical tests to provide a comprehensive picture of the patient's current nutritional status and relative risk factors for diet-related illnesses.

Food records

This method of dietary assessment instructs individuals to record the time of consumption of all foods and beverages consumed for a specified duration, typically one to seven days. This is done in order to quantify intake. Three- or seven-day food records are the most commonly used. Recorded amounts for food records can be estimated or weighed. The weighed food record is preferred for assessing individual requirements because of its ability to determine intake quantitatively. Disadvantages of the method are that it is laborious and it may be a considerable burden to correctly measure and record intake. Portion sizes can be obtained through the use of household measures, cups, spoons, and scales.

24-hour recall

The 24-hour recall is a method for quantifying dietary intake for a group average and is not suited for individual dietary characterization, although it is often used for this purpose. A person's previous 24-hour food intake is assessed by an interviewer to provide detailed descriptions of portion sizes, condiments used, cooking method, and brand names of food items consumed within a 24-hour period. Quantities are often estimated in household measures or by using pictures or models of portion sizes to assist in more accurately quantifying intake. Advantages of the 24-hour recall are that it is inexpensive, quick, and places little burden on the patient. Single 24-hour recalls do not provide sufficient information about nutrient intake and do not account for day to day variations in intake. However, 24-hour recalls can be repeated on several occasions with the same individual in order to increase accuracy and precision of the assessment.

Food frequency questionnaire

The FFQ is generally designed to provide qualitative data regarding food consumption patterns rather than solely evaluating nutrient composition and intake. The aim is to assess the frequency at which certain foods are eaten on a daily, weekly, monthly or yearly basis. Advantages of the FFQ are that it is quick, inexpensive, and can be administered by patients themselves. One disadvantage is that it cannot provide adequate quantitative data to use for individuals, although semi-quantitative FFQs provide some measure of information about the quantity of food consumed. In addition, the FFQ does not often address culture-specific foods since it usually contains lists of standard North-American foods. Accuracy and validation in specific cultures necessitates the use of another dietary assessment tool.

Diet history

The diet history attempts to measure an individual's food intake over a longer time period than provided by other methods of dietary assessment. It consists of three parts: a 24-hour recall, a food frequency questionnaire, and a 3-day food record, although the components are often modified. Portion sizes are estimated using a variety of methods including household measures, food models or pictures, household utensils, or actual food. An advantage of the diet history is that it provides qualitative and quantitative data of food intake. It also considers seasonal and day to day variations. One disadvantage is that the method is labor-intensive.

Other methods

Diagnostic laboratory tests may also be used to further identify a patient's nutritional status. Serum albumin, hemoglobin, or hematocrit are used to measure plasma protein. Lymphocytes counts and various skin tests are used to measure immune system integrity, and various urine tests, such as a calculation of urinary nitrogen, are used as an indication of protein metabolism. Other indices include urinary potassium, serum concentrations of carotenoids, and stable isotopes that measure water turnover, which is an indicator of energy expenditure. These indices are often more reliable and representative of true intake than methods that rely solely on the subject's ability to record or recall intake.

The use of a portable electronic tape recording scales, photographs, voice-taped, and videotaped recordings also have been used as dietary assessment tools.

Other sources that can be used for dietary reference and guidance for food choices are The Dietary Guidelines for Americans, published by the United States Department of Agriculture (USDA) and the United States Department of Health and Human Services (HHS). These agencies provide science-based guidance to help promote health and reduce risk for major chronic diseases through diet and physical activity.

Preparation

Systematic problems exist in tracking the quantification of food intake using dietary assessment tools that depend on self-reported measures (when patients subjectively report their own food intake). This is because these methods rely on the patient's ability to recall or record their food intake accurately. Therefore, selection of the appropriate method for dietary assessment is important to meet the goals of dietary counseling.

Complications

Measurement of dietary intake typically relies on self-reported data. Most dietary collection tools using self-reported intake have not included a test for accuracy or bias to validate the data collected. These validations are logistically difficult to conduct for individuals eating at home.

There are also subgroups of the population that may be more likely to provide inaccurate intake data, creating error. In general, obese people are more apt to underestimate their food consumption because they may go on a diet or deliberately omit foods during the food-recording period. Individuals may also alter their food intake temporarily in order to conform to socially acceptable levels and types of food consumption if they are aware that their food intake is being monitored. For example, during a 24-hour recall, obese people may be unwilling to admit to a dietitian that they over indulged the previous day; therefore, they may underreport their food intake.

Another source of error may be due to inaccurate weighing and measuring of foods. Errors involved in the estimation of food portions can reach 90% but are more typically 20-50% when scales are not used to weigh foods.

Results

Dietary assessments may indicate a nutritional problem or inadequacy, but it is up to the individual to implement the necessary dietary modifications. If an individual fails to follow the recommended dietary guidance following dietary assessment, he or she will not receive any benefit from the assessment.

Health care team roles

In general, only registered dietitians(RD's)have sufficient training and knowledge to accurately assess the clinical evaluation and nutritional adequacy of a patient's diet. The term "nutritionist" is not regulated by law. Therefore anyone can call him or herself a nutritionist. A physician may also have a nutrition background or specialization and thus be able to conduct a dietary assessment or provide nutrition advice. However, individuals should be aware that many physicians do not have any specialized nutritional backgrounds or diet-related knowledge.

KEY TERMS

Dietary assessment— An estimation of food and nutrients eaten over a particular time period. Some of the most common dietary assessment methods are food records, dietary recalls, food frequency questionnaires, and diet histories.

Dietitian— A dietitian is a health professional who has a bachelor's degree, specializing in foods and nutrition, and in addition undergoes a period of practical training in a hospital or community setting. Many dietitians further their knowledge by pursuing master's or doctoral degrees. The title "dietitian" is protected by law so that only qualified practitioners who have met education qualifications can use that title.

Macronutrient— A nutrient such as protein, carbohydrate, or fat.

Micronutrient— An substance such as a vitamin or mineral that in small amounts is essential to the growth and health of humans and animals.

Nutritionist— Some dietitians call themselves "nutritionists," but in general, the term "nutritionist" is not protected by law; therefore anyone may choose call themselves a nutritionist.

Resources

BOOKS

Bronner, Felix, ed. Nutritional and Clinical Management of Chronic Conditions and Diseases. Boca Raton, FL: CRC Press, 2005.

Institute of Medicine, ed. Dietary Reference Intakes for Energy, Carbs, Fiber, Fat, Fatty Acids, Cholesterol, Protein, And Amino Acids. Washington: National Academies Press, 2005.

Lutz, Carroll A., and Karen Rutherford Przytulski. Nutrition And Diet Therapy, 4th ed. Philadelphia: F. A. Davis Company, 2006.

Temple, Norman J., Ph.D., et al. Nutritional Health: Strategies For Disease Prevention, 2nd ed. Totowa, NJ: Humana Press, 2005.

PERIODICALS

Cheng, C., Graziani, C., Diamond, J.J. " Validation Of The Dietary Risk Assessment Food Frequency Questionnaire Against The Keys Score For Saturated Fat And Cholesterol." Journal of Nutrition Education and Behavior. 37 no. 3 (2005): 152-153.

Kennedy, E., Meyers, L. "Dietary Reference Intakes: Development And Uses For Assessment Of Micronutrient Status Of Women—A Global Perspective." American Journal of Clinical Nutrition. 81 no. 5 (2005): 1194S-1197S.

Probst, Y.C., and L.C. Tapsell "Overview Of Computerized Dietary Assessment Programs For Research And Practice In Nutrition Education." Journal of Nutrition Education and Behavior 37 no. 1 (2005): 20-6.

ORGANIZATIONS

American Dietetic Association. 120 South Riverside Plaza, Suite 2000, Chicago, IL 60606-6995. (800) 877-1600. http://www.eatright.org.

American Heart Association National Center. 7272 Greenville Avenue, Dallas, Texas 75231. (800) AHA-USA1. http://www.americanheart.org.

Food and Nutrition Information Center, Agricultural Research Service, USDA. National Agricultural Library, Room 105, 10301 Baltimore Avenue, Beltsville, MD 20705-2351. (301) 504-5719. Fax: (301) 504-6409. http://www.nal.usda.gov/fnic.

International Food Information Council. 1100 Connecticut Avenue, NW, Suite 430, Washington, DC 20036. (202) 296-6540. Fax (202) 296-6547, http://www.ific.org.

USDA Food and Nutrition Service. 3101 Park Center Drive, Alexandria, VA 22302. http://www.fns.usda.gov/fns.

U.S. Department of Health and Human Services. 200 Independence Avenue, S.W., Washington, D.C. 20201. (202) 619-0257 or (877) 696-6775. http://www.hhs.gov.

U.S. Department of Health and Human Services, Centers for Disease Control and Prevention (CDC). 1600 Clifton Rd, Atlanta, GA 30333. (800) CDC-INFO. http://www.cdc.gov.

OTHER

U. S. Department of Agriculture (USDA), Agricultural Research Service. 5601 Sunnyside Avenue, Beltsville, Maryland 20705. "USDA Nutrient Database for Standard Reference, Release 18." Nutrient Data Laboratory Homepage, 2005. www.ars.usda.gov/ba/bhnrc/ndl.

Esha Research. Total Dietary Assessment Software Revised CD-Rom (CD-ROM) New York: John Wiley & Sons, 2006.