the character of the food supply. Foods were no longer strictly seasonal in nature, because they could be shipped from different climates. This trend accelerated with the advent of refrigerated railcars and trucks. Innovations in food processing were also important. In 1869, processed foods consisted chiefly of milled flour and cornmeal, refined sugar, cured meats, and processed dairy products. Today, in addition to these foods, the consumer finds canned, frozen, fermented, and dehydrated foods, as well as foods fabricated in the laboratory to resemble traditional foods. These include drinks resembling fruit juices, but containing no fruit juice, and analogs of meat or fish made from soybeans or wheat gluten. Innovations such as sugared breakfast cereals and a variety of snack items were unheard of before World War II. Hampe and Wittenberg (1964) estimate that 60% of the items on supermarket shelves in 1960 came into existence during the 15 years after the end of World War II. Home refrigerators and freezers also increased the homemaker's ability to select and store a variety of foods. Today's large supermarkets carry as many as 15,000 different items from which consumers must choose, complicating the task of nutrition educators.
The next section focuses on changes in the food supply during the twentieth century and describes national surveys to determine the U.S. population's intake of foods, nutrients, and, to a limited extent, pesticides and industrial chemicals. This is followed by a discussion of the limitations of the studies and a section on consumption trends.
Changes in foods available to the public from 1909 to the present have been ascertained from USDA data based on the disappearance of foods into wholesale and retail markets. Annually, foods available to the civilian population are estimated by subtracting data on exports, year-end inventories, nonfood use, and military procurement from data on total production, imports, and beginning-of-the-year inventories. These quantities are larger than those actually consumed, because they fail to take into account losses that occur during processing, marketing, and home use. Since they do not represent actual consumption, they are referred to here as availability or use of foods or nutrients.
The USDA estimates per-capita use of foods or food groups by dividing total available food by the population of the 50 states and the District of Columbia. The nutritive value of the food supply is calculated from per-capita use by using nutritive values found in food composition tables. Although these data provide no information on how foods are distributed among individuals or population groups, or on changes in patterns of waste and other losses, they nevertheless reflect changes in overall patterns of foods available over time. Furthermore, these data are similar to data produced in many other countries, and they have been useful in epidemiologic research across countries, such as studies of dietary lipids and atherosclerotic diseases (Stamler, 1979).
NFCS focuses on the food use of households and the dietary intakes and patterns of individuals. These surveys have been conducted approximately every 10 years since 1935 by USDA's Human Nutrition Information Service (HNIS), but the first four surveys (in 1935, 1942, 1948, and 1955) obtained information only on household food use over a 7-day period. These data reflect food use in an economic sense only and do not take into account food waste or how food is distributed among household members. Beginning in 1965, data have been collected on intakes by individuals. Surveys were conducted in 1965-1966 and in 1977-1978; separate surveys were conducted in 1977-1978 in Puerto Rico, Alaska, and Hawaii, and among low-income and elderly populations. The most recent NFCS, 1985 and 1986, were the Continuing Surveys of Food Intakes of Individuals (CSFII), designed to be conducted annually. The household screening procedures for CSFII were designed to provide three separate samples: (1) women 19 to 50 years of age and their children 1 to 5 years of agethe core group; (2) a similar age sample of low-income women and children; and (3) men 19 to 50 years of age. Data have been published on both the 1985 and 1986 surveys (USDA, 1985, 1986a,b, 1987a,b,c, 1988).
In the Ten-State Nutrition Survey conducted during 1968-1970, DHHS studied low-income