Final answer:
Before the 1990s, a balanced diet included four food groups: milk, meat, vegetable and fruit, and bread and cereal. No single food provided all nutrients, so variety was key. This guidance evolved into newer systems like the Food Guide Pyramid and MyPlate.
Step-by-step explanation:
Before the 1990s, the United States Department of Agriculture (USDA) recommended that a balanced diet include servings from four separate food groups: the milk group; the meat group; the vegetable and fruit groups; and the bread and cereal group. To meet various nutritional needs, the specific servings suggested were: two servings from the meat group, which included meat, fish, poultry, eggs, peas, beans, or nuts; four servings of green or yellow vegetables, tomatoes, or citrus fruits from the vegetable and fruit groups; and four servings of whole grains or fortified cereal products from the bread and cereal group. It was understood that no single food could provide all the necessary nutrients, so variety within each food group was essential for a healthy diet.
As nutritional science advanced, the USDA's food guidance also evolved into systems like the Food Guide Pyramid and most recently, MyPlate, which categorize foods into five groups: vegetables, fruits, grains, proteins, and dairy. MyPlate is a visual guide that suggests the relative proportions of different types of foods to include in each meal for a balanced diet.