Nutrition experts recommend that protein, as a source of amino acids, account for 10–12% of the calories in a balanced diet. However, requirements for protein are affected by age, weight, state of health, and other factors. On average, a normal adult requires approximately 0.36 grams of protein per pound of body weight. Using this formula, a 140-pound person would need 50 grams (or less than 2 ounces) of protein per day. An appropriate range of protein intake for healthy adults may be as low as 45–65 grams daily. Some athletes have higher amino acid requirements. Most American adults eat about 100 grams of protein per day, or about twice what their bodies need and at least as much as any athlete requires.
Supplements of individual amino acids are recommended by doctors for specific purposes, such as lysine for herpes or phenylalanine for pain.