Proteins contribute four calories per gram. They are large complex molecules composed of amino acids. Proteins are needed for the structure, processes, proper functioning, repair, and regulation of the organs and tissues of the human body—including the brain and nervous system.
Current Dietary Guidelines for Americans recommend that the average person should aim to get from ten to thirty-five percent of their daily calories from protein (depending on their activities). Some ingest more protein than their brain and body need, while others, often the very elderly, may not eat quite enough. The Physicians Committee for Responsible Medicine (PCRM), which includes eminent physicians Doctors Dean Ornish and John McDougall, recommends getting most of your macronutrition from plant-based vegetables, fruits, whole grains, nuts, and beans (with small amounts of animal products for those not wishing to eat vegetarian or vegan).