Food supply nutrients and dietary guidance, 1970-99

Food Review, Sept-Dec, 2001 by Shirley Gerrior, Lisa Bente

The variety and the types of food in the U.S. food supply since 1970 paralleled consumer preferences which evolved over the years due to influences such as increased ethnic diversity, more elderly consumers, and effective Federal Government nutrition policy and dietary guidance. Consumer demand for more healthful foods challenged the food industry to evolve as well. By 1999, the available food supply contained two-fifths more grain products, about one-third more fruit, about one-tenth more vegetables, and one-fourth more legumes, nuts, and soy products per capita than in 1970. The availability of lean red meat and low-fat and skim milks also increased between 1970 and 1999 (fig. 1). Such foods enhanced the health benefits of the food supply. However, despite the high interest in nutrition by Americans in the late 1980s and 1990s, and the increased supply of healthful foods, the availability of caloric sweeteners and fats and oils in the food supply also increased by one-third more per capita from 1970 to 1999 to record high amounts. A large proportion of the increase came from sugars and fats added to foods, such as soft drinks, cakes, cookies and pies, fruit ades, salad dressings, and rich dairy desserts.

USDA Estimates Food Supply and Nutrients

USDA's Economic Research Service (ERS) annually calculates the amount of food available for consumption on a per capita basis in the United States. Food supply data measure national consumption of several hundred basic commodities. For most commodity categories, the available food supply is measured as the sum of annual production, beginning inventories, and imports minus exports, farm and nonfood uses, and end-of-the year inventories. Per capita consumption is calculated by dividing the available food supply by the total U.S. population as of July 1 each year.

Using the ERS per capita consumption data and nutrient composition information from USDA's Agricultural Research Service, USDA's Center for Nutrition Policy and Promotion calculates the nutrient content of the food supply. Per capita consumption for each commodity is multiplied by the amount of food energy and each of 27 nutrients and dietary components in the edible portion of the food. Results for each nutrient from all foods are totaled and converted to amount per capita per day (table 1). Nutrients added to certain commodities commercially through fortification and enrichment are also included in the nutrient content of the food supply. Since food supply data represent the disappearance of food into the marketing system, per capita consumption and nutrient estimates typically overstate the amount of food and nutrients people actually ingest.

Food Supply Nutrients and Dietary Guidance, 1970-99

The 2000 edition of the Dietary Guidelines for Americans, the most recent Federal nutrition recommendations, places greater emphasis and gives more explicit recommendations for particular nutrients and foods than previous editions. The guidelines differentiate between total fat, saturated fat, and cholesterol and recommend a diet that is low in saturated fat and cholesterol and is moderate in total fat. Other dietary recommendations include daily varieties of fruits and vegetables and grains, particularly whole grains, and foods and beverages that limit intake in sugars.

The Dietary Guidelines for Americans also recommends that consumers use the Food Guide Pyramid to guide food choices. Using the pyramid helps ensure that an adequate amount and mix of nutrients are consumed each day, as no single food can supply all the nutrients needed for good health. For example, good sources of calcium are milk, cheeses, dark-green leafy vegetables, and foods with added calcium, such as soy-based beverages and fruit juices. Good sources of iron include lean meats, spinach, and enriched grains.

Since 1941, the Recommended Dietary Allowances (RDA) have been recognized as the most authoritative source of information on nutrient levels for healthy people. The 10th edition of the RDAs in 1989 increased public awareness of the impact of nutrition on chronic disease. In light of new research findings and the public's heightened interest in nutrition and health, a new series of nutrient reference values, the Dietary Reference Intakes (DRI), was developed.

The DRIs replace and expand on the RDAs and thus extend the scope and application of previous guidance. The DRIs provide information on the function of each nutrient, the factors that determine each nutrient's requirements (for example, physical activity), and the relationship of each nutrient to risk of disease. Recommended values are provided for each age group--from birth through childhood, sexual maturity, midlife, and old age--as well as for pregnancy and lactation. Whereas the RDAs provided one nutrient value, the DRIs provide four values: the RDA value as well as three new types of reference values: the Estimated Average Requirement, the Adequate Intake, and the Tolerable Upper Intake Level (see box).