A dietary assessment is an estimation of food and nutrients eaten over a particular time point. There are a number of dietary assessment tools used by dietitians, nutritionists, and doctors that aid in dietary counseling. These include:
- food records or diaries (including weighed intakes)
- dietary recalls• food frequency questionnaires (FFQs)
- dietary histories
- observed intakes
- chemical analyses of duplicate collections of foods consumed
- biological assessments (e.g. doubly-labelled water, plasma carotene, etc.)
A dietary assessment is often conducted to determine the macronutrient (energy or caloric, protein, and fat) content and the micronutrient (vitamin and mineral) content of the diet to assist in providing dietary counseling. The validation of dietary assessment instruments is important to evaluate the diet in terms of a chronic disease risk factor. It 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 (i.e. cardiovascular disease, cancer, obesity, diabetes, hyperlipidemia).
A guide to the amount an average person needs each day to remain healthy has been determined for each vitamin and mineral as well as macronutrients. In the United States, this guide is called the recommended daily allowance (RDA). Consumption of too little or too much of certain vitamins and minerals may lead to a nutrient deficiency or a nutrient toxicity respectively. The RDA suggests a level of vitamin and minerals that is adequate for approximately 98% of healthy people in the population. The dietitian may use the dietary assessment to compare it to population requirements for nutrients (such as the RDA) to ensure the diet has proper intakes of energy, protein, fat, vitamins, and minerals. The RDA is under revision and will become the Dietary Reference Intakes, and will be applicable to Canadians and Americans.
Dietary assessments are estimations based on an intake of a particular time point and cannot generalize that the diet is adequate or inadequate since intake varies 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 energy, carbohydrates, and protein varies less from day to day and may be estimated more closely than vitamin and mineral intakes.
Some of the most common tools that assist in providing dietary advice include food records, 24 hour dietary recalls, food frequency questionnaires, diet histories, and several other methods including 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 (determined by skinfolds or hydrostatic weighing). In addition, a clinical evaluation may also include observations 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.
This method instructs subjects to record at the time of consumption all foods and beverages consumed for a specified duration, typically one to seven days, in order to quantify intake. Three or seven day food records are the most common. Food records can be estimated or weighed, the latter providing a more precise measure of intake. Portion sizes can be obtained through the use of household measures, cups, spoons, and scales. All days of the week should be proportionally included to avoid day of the week effects on nutrient and compositional intake. The weighed food record is the preferred method 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.
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 probed by an interviewer to provide detailed descriptions of portion sizes, condiments used, cooking method, and brand names. Quantities are often estimated in household measures or using food models for assistance to more accurately quantify intake. Recalls can be repeated on several occasions in the same person in order to increase accuracy and precision. Advantages of the 24-hour recall is that it is inexpensive, quick, and places little burden on the patient. Single 24-hour recalls do not provide sufficient information on nutrient intakes and cannot account for day to day variation in intake, however, repeated 24 hour recalls can be used to more precisely estimate intake.
Food frequency questionnaire
A food frequency questionnaire (FFQ) is generally designed to provide qualitative data regarding food consumption patterns rather than nutrient composition and intake. The aim is to assess the frequency at which certain foods are consumed, for example, daily, weekly, monthly or yearly. Advantages of the FFQ are that it is quick, inexpensive, and can be administered by patients themselves. Disadvantages are that it cannot provide adequate quantitative data to use for individuals, although semi-quantitative FFQs provide some measure of quantity. As well, it does not address culture-specific foods since it primarily contains lists of somewhat standard North-American type foods. Accuracy and validation in specific cultures necessitates the use of another dietary assessment tool.
The diet history attempts to measure usual intake in the past over a longer time period than other methods of dietary assessment. It consists of three parts, although it is often modified, including a 24 hour recall, a food frequency questionnaire, and a 3 day food record. Portion sizes are estimated by a variety of methods including household measures, food models, household utensils, photographs, 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. Disadvantages are that the method is labor-intensive.
The use of a portable electronic set of tape recording scales (PETRA), photographs, voice-taped, and videotaped recordings have been used as dietary assessment tools.
Biochemical 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 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 which rely on the subject's ability to record or recall intake.
Other sources that can be used for dietary reference and guidance for food choices are "The Dietary Guidelines for Americans" which is published by the U.S. Department of Agriculture and Health and Human Services. The "Food Guide Pyramid" was created by the U.S. Department of Agriculture to help Americans choose foods from each food grouping. It focuses on fat intake, which is too high in most Americans.
There are also a number of internet websites where food records or recalls can be self-administered by patients for dietary assessment. Some of these websites are listed in the resources sections below.
Systematic problems exist in the quantification of food intake using dietary assessment tools that depend on self-reported measures (i.e. when the patient subjectively reports their own food intake). This is due to the fact that these methods rely on the patient's ability to recall or record food intake accurately. Therefore, selection of the appropriate method for dietary assessment is important to meet the goals of dietary counseling.
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 difficult to conduct because in an individual who is eating at home, there are few methods to use as a reference to validate the dietary intake data.
There are subgroups of the population that are 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 alter their food intake temporarily as they are cognizant that their food intake is being monitored, possibly to conform to socially acceptable foods and food habits. For example, during a 24 hour recall, an obese person may not want to admit to a dietitian that they overate the previous day, therefore, they may under-report their food intake.
Another source of error comes from weighing and measuring foods. Errors involved in the estimation of food portions can reach 90% but are typically 20-50% when scales are not used to weigh foods.
Dietary assessment—An estimation of food and nutrients eaten over a particular time point. Some of the most common dietary assessment methods are food records, dietary recalls, food frequency questionnaire, and diet histories.
Dietitian—A dietitian is a health professional who has a bachelor's degree, specializing in foods and nutrition, and 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.
Nutritionist—Some dietitians call themselves "nutritionists," but in general, the term "nutritionist" is not protected by law, therefore anyone can call themselves a nutritionist.
A dietary assessment may indicate where a nutritional problem or inadequacy may lie, but it is up to an individual to implement the necessary dietary modifications. If a patient does not follow the recommended dietary guidance following dietary assessment, then they will not receive any benefit from dietary assessment. Typically, modest effects are seen in weight loss or reduction in serum lipids often due to failure to fully comply with the dietary recommendations provided.
Health care team roles
In general, only registered dietitians (R.D.s) have sufficient training and knowledge to accurately assess the clinical evaluation and nutritional adequacy of a patient's diet. Although there are many websites and software programs that provide guidance for self-use for conducting a basic dietary assessment, these should be used with caution. The term "nutritionist" is not regulated by law; therefore anyone can call themselves a nutritionist. A doctor may also have a nutrition background or specialization
Institute of Medicine, ed. Dietary Reference Intakes: Applications in Dietary Assessment. Washington: National Academy Press, 2001.
Institute of Medicine, ed. Dietary Reference Intakes: Risk Assessment (Compass Series). Washington: National Academy Press, 1999.
Larson-Duyff, Roberta. The American Dietetic Association's Complete Food & Nutrition Guide. New York: John Wiley & Sons, 1998.
Netzer, Corinne T. The Complete Book of Food Counts. New York: Dell Publishing Co., 2000.
American Dietetic Association. 216 W. Jackson Blvd. Chicago, IL 60606-6995. (312) 899-0040. <http://www.eatright.org/>.
Food and Nutrition Information Center Agricultural Research Service, USDA. National Agricultural Library, Room 304, 10301 Baltimore Avenue, Beltsville, MD 20705-2351. (301) 504-5719. Fax: (301) 504-6409. <http://www.nal.usda.gov/fnic/>. <firstname.lastname@example.org>.
U.S. Department of Agriculture, Agricultural Research Service. "USDA Nutrient Database for Standard Reference, Release 13." Nutrient Data Laboratory Homepage 1999. <http://www.nal.usda.gov/fnic/foodcomp>.
Food and Nutrition Professionals Network <http://nutrition.cos.com/>.
Crystal Heather Kaczkowski, MSc.