Measurement of Dietary Intake

The assimilation of exogenous nutrients is a fundamental biological process necessary both to support metabolic functions and to permit physical growth. The study of man's quest to produce or otherwise acquire food has occupied social and biological scientists alike. The quantitative and qualitative description of the food and nutrient intakes of individuals, however, has most commonly been undertaken by nutritionists. This paper reviews the purposes, methods, and interpretation of dietary studies, with emphasis on the measurement and determinants of the dietary intake of children, particularly those in less developed countries. Before addressing the specifics of dietary studies, it is important to distinguish between the measurement of dietary intake and the assessment of nutritional status. Although it is commonly asserted that dietary studies are undertaken to evaluate the nutritional status of an individual or a population, nutritional status is more appropriately measured by clinical, physiological, or functional parameters. In short, dietary intake is only one of several factors (others being infections, physiological stage of life, and genetic endowment) that may influence the nutritional status of an individual. If an individual's consumption of a certain essential nutrient is habitually lower than the recommended dietary allowance, he may be at risk of nutritional deficiency or he may simply have a lower physiological requirement for that nutrient than the statistically determined recommended allowance. Since the recommended allowance of a nutrient (with the exception of total energy) is usually defined as the level of intake sufficient to satisfy the requirements of 97 percent of the members of the physiological subgroup (defined, for example, by age and sex), it is obvious that many individuals may consume less than these allowances without showing any evidence of nutritional deficiency (Hegsted, 1975). Nutritional status, then, is the physical expression of the relationship between