It therefore became of great interest to researchers to determine what the people of this country were actually eating. In 1909 the U.S. Department of Agriculture (USDA) began to identify changes in the foods available to the civilian public by determining the disappearance of foods into the wholesale and retail markets. This is still done annually by subtracting data on exports, year-end inventories, nonfood uses, and military procurement from data on total production, imports, and beginning-of-the-year inventories. Overestimates result from this method, however, because losses that occur during processing, marketing, and home use are not taken into account. Thus, the resultant information is sometimes called availability or use of foods or nutrients (Stamler, 1979).

The USDA estimates national per capita use of foods or food groups by dividing the total available food by the total U.S. population. These data provide information on overall trends in available foods, but they do not indicate how use varies among population subgroups or individuals.

Since 1935 the USDA's Human Nutrition Information Service (HNIS) has conducted a series of Nationwide Food Consumption Surveys (NFCS). The first four (1935, 1942, 1948 [urban only], and 1955) surveyed household food use over a 7-day period. No record was made of waste or difference in use among household members. Surveys conducted in 1965–1966, 1977–1978, and 1987–1988 included information on the kinds and amounts of foods eaten by individuals in the household in addition to household food use. For the reasons given later in this chapter, the 1977–1978 survey served as the major source of consumption data used by the committee in the present study.

The USDA has conducted a planned series of surveys since 1985 solely concerned with individual food intake (USDA, 1985, 1986a,b, 1987a,b,c, 1988). The results of the most recent surveys have not yet been published. In these surveys, called Continuing Surveys of Food intakes of Individuals (CSFII), data are collected on three separates samples: women 19 to 50 years old and their children 1 to 5 years old (the core group); a sample of low-income women and their children; and in 1985 only, men 19 to 50 years old. In the 1989, 1990, and 1991 surveys, data were collected on all individuals.

The National Center for Health Statistics (NCHS), a division of the Department of Health and Human Services, has conducted the National Health and Nutrition Examination Surveys (NHANES) since 1971. The purpose of these surveys is to monitor the overall nutritional status of the population of the United States through comprehensive health and medical histories, dietary interviews, physical examinations, and laboratory measurements. The committee opted not to use the results from these surveys, however, because the number of observations within the age and demographic categories of interest were inadequate for the purposes of the present study.

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