The vast majority of Americans eat more than enough protein and also more than enough of each essential amino acid for normal purposes. Anyone not consuming an adequate number of calories, dieters, and some strict vegetarian body builders may not consume adequate amino acids. In these cases, the body will break down the protein in muscle tissue and use those amino acids to meet the needs of more important organs or simply not build more muscle mass despite increasing exercise. 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.
Some athletes have higher amino acids requirements.
2 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 nutritionally oriented doctors for specific purposes, such as lysine for herpes or phenylalanine for pain. Most diets provide more protein than the body needs, causing excess nitrogen to be excreted as urea in urine. The excess nitrogen has been linked in some studies with reduced kidney function in old age. Moreover, several studies have found that when people have impaired kidney function, restricting dietary intake of protein improves their health status.