Eat a balanced diet. The key to good nutrition is a varied diet that includes every kind of nutrient. To aid in planning a balanced diet, nutritionists have devised systems that group foods according to nutrient content. The Food Guide Pyramid pictured in this article is one such system, developed by the United States Department of Agriculture (USDA). The pyramid shape calls attention to the recommended amounts to eat from each of the major food groups. The groups at the broad base of the pyramid-that is, grains, fruits, and vegetables-should form the largest part of a healthful diet. Fewer daily servings should be chosen from the meat and dairy groups near the top. Fats, oils, and sweets, at the narrow tip of the pyramid, should be eaten sparingly.

In the United States, the Food and Nutrition Board of the National Academy of Sciences issues Recommended Dietary Allowances (RDA's). RDA's are estimated amounts of various nutrients needed daily to avoid deficiency and maintain good nutrition in healthy people. The board issues a standard called adequate intake (AI) in cases where the board's experts feel there is insufficient evidence to establish an RDA. RDA's and AI's for particular nutrients may vary, depending on a person's sex or age. This article includes a table of certain RDA's.

RDA's and AI's are part of a larger category of standards called dietary reference intakes (DRI's). DRI's also include guidelines called tolerable upper intake levels (UL's). UL's define the maximum daily intake that is unlikely to harm health. DRI's are being developed in a joint effort by the U.S. Food and Nutrition Board and Health Canada. The World Health Organization is creating a set of similar standards.

The Nutrition Labeling and Education Act of 1990 requires that all packaged and processed food sold in the United States carry labels with nutritional information. The labels help people compare their daily dietary needs with the nutritional content of the foods they eat. Nutrition labels list the amounts of fats, carbohydrates, cholesterol, and certain other nutrients in one serving of the labeled food. The nutrients listed are those considered most important to health, as determined by the U.S. Food and Drug Administration (FDA). The label also provides a Daily Value percentage for each nutrient to show how it fits into a healthful diet. The percentages are based on guidelines called Daily Reference Values (DRV's), which the FDA established as the amounts of these nutrients that a healthy person should consume each day.