The Council on Food and Nutrition of the American Medical Association defines nutrition as the science of food, the nutrients and the substances therein, their action, interaction, and balance in relation to health and disease, and the process by which the body ingests, absorbs, transports, utilizes, and excretes food substances (Insel, Turner, & Ross, 2007).
People require energy and certain essential nutrients. Energy is provided by food that contains macronutrients, required in large amounts (protein, carbohydrate, fats). Essential nutrients are those the body cannot make on its own and must obtain from food. They include micronutrients such as vitamins and minerals, required in small amounts; as well as certain amino acids and fatty acids like omega three and six (Insel et al., 2007).
Nutrient needs vary according to the life stages. Specific guidelines and requirements for food and nutrients are described in the Dietary Guidelines for Americans most recently revised in 2005.
The Dietary Guidelines for Americans provide science-based advice to promote health and to reduce risk for major chronic diseases through diet and physical activity. Major causes of morbidity and mortality in the United States are related to poor diet and a sedentary lifestyle. Some specific diseases linked to poor diet and physical inactivity include cardiovascular disease, type 2 diabetes, hypertension, osteoporosis, and certain cancers. Furthermore, poor diet and physical inactivity, resulting in an energy imbalance (more calories consumed than expended), are the most important factors contributing to the increase in overweight and obesity in this country. Combined with physical activity, following a diet that does not provide excess calories according to the recommendations in this document should enhance the health of most individuals (U.S. Department of Health and Human Services, 2005).
A basic premise of the Dietary Guidelines is that nutrient needs should be met primarily through consuming foods. Foods provide an array of nutrients and other compounds that may have beneficial effects on health. In certain cases, fortified foods and dietary supplements may be useful sources of one or more nutrients that otherwise might be consumed in less than recommended amounts. However, dietary supplements, while recommended in some cases, cannot replace a healthful diet (U.S. Department of Health and Human Services, 2005).