Food groupings are classified by dividing foods into fundamental categories. The group designations align foods according to their composition and nutritional properties based on the science of nutrition. The United States Department of Agriculture classifies food groups. The basic five food groups are grains, fruits, vegetables, milk and meat, according to the USDA.
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Carbohydrate foods contain sugars and starches to provide energy in the form of glucose. The body prefers glucose for the brain, central nervous system and red blood cells to function. The Institute of Medicine’s Dietary Reference Intakes for Macronutrients list the food groups consisting of grains, vegetables and fruits as sources of carbohydrates. Grains include foods such as whole wheat, rolled oats, barley, rye and brown rice. Corn, pasta, potatoes and breads constitute vegetables that contain carbohydrate in the form of starch. Fruit sources of carbohydrate food include apples, grapefruit, grapes, peaches and oranges. The Institute of Medicine advises about 55 percent of the daily diet should contain carbohydrates. Plain sugar, candy bars and carbonated sodas constitute another source of carbohydrates under discretionary calories, but the publication “Health” counsels against using these sources due to the lack of other nutrients in the foods.
Proteins supply energy, but the primary role of protein in the diet is for healing injured tissue and for growth and development in the body. “Alive: The Canadian Journal of Health and Nutrition" describes the other essential function of protein in maintaining the immune system and hormonal balance. Examples of proteins fall under the meat, milk and vegetable food group. The meat food group contains both animal protein such as poultry, meat, eggs and fish, and plant proteins such as nuts, seeds, beans and legumes. The milk food group contains the protein foods milk, cheese and yogurt. The vegetable foods with protein content includes such items as peas, tofu, soybeans and lentils. The Institute of Medicine recommends that 20 percent of the diet contain protein.
Three forms of fat -- saturated, monounsaturated and polyunsaturated -- produce fatty acids such as omega-3 fatty acid and omega-6 fatty acid that are required by over half the cells in the body, according to "Consumer Medical Journal." Omega-3 fatty acids are needed for neurological growth and development. Omega-6 fatty acids form the structural membranes in cells and are required for normal skin function. Olive, avocado, canola and peanut oils contain monounsaturated fat; fish, walnut, safflower and corn oils contain polyunsaturated fats. The Institute of Medicine only advises the intake of foods with monounsaturated and polyunsaturated fats. The modern diet should contain 30 percent fat for the total caloric intake.
Vitamins and Minerals
The USDA’s Dietary Guidelines for Americans 2010 explains the sources of the micronutrients in the food groups. Some sources of micronutrients, such as vitamin E, exist in all but the milk food groups. A source of vitamin E is a grain with fortified cereals, a fruit in avocados, a vegetable in carrot juice and a meat group with sardines. The other vitamin and minerals range across the food groups. The complete classifications of all the vitamin and minerals can be found in the USDA’s Dietary Guidelines for Americans 2010.