amino acids are the building blocks of protein. twenty amino acids are needed to build the various proteins used in the growth, repair, and maintenance of body tissues. eleven of these amino acids can be made by the body itself, while the other nine (called essential amino acids) must come from the diet. the essential amino acids are isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. another amino acid, histidine, is considered semi-essential because the body does not always require dietary sources of it. the nonessential amino acids are arginine, alanine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, proline, serine, and tyrosine. other amino acids, such as carnitine, are used by the body in ways other than protein-building and are often used therapeutically.

foods of animal origin, such as meat and poultry, fish, eggs, and dairy products, are the richest dietary sources of the essential amino acids. plant sources of protein are often deficient in one or more essential amino acids. however, these deficiencies can be overcome by consuming a wide variety of plant foods. for example, grains are low in lysine, whereas beans provide an excess of lysine. it was previously believed that, in order for vegetarians to obtain adequate amounts of protein, all of the essential amino acids had to be “balanced” at each meal. for example, a grain and a bean had to be consumed at the same meal. however, more recent research has indicated that, while consuming a proper mix of amino acids is important, it is not necessary to consume them all at the same meal.1

the vast majority of americans eat more than enough protein and also more than enough of each essential amino acid for normal purposes. dieters, some strict vegetarian body builders, and anyone consuming an inadequate number of calories may not be consuming adequate amounts of 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 will simply not build more muscle mass despite increasing exercise.

nutrition experts recommend that protein, as a source of amino acids, should 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.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 doctors for specific purposes, such as lysine for herpes or phenylalanine for pain.

the branched-chain amino acids (bcaas) are leucine, isoleucine, and valine. bcaas are considered essential amino acids because human beings cannot survive unless these amino acids are present in the diet.

dairy products and red meat contain the greatest amounts of bcaas, although they are present in all protein-containing foods. whey protein and egg protein supplements are other sources of bcaas. bcaa supplements provide the amino acids leucine, isoleucine, and valine.

only a person deficient in protein would become deficient in bcaas, because most foods that are sources of protein supply bcaas. few people in western societies are protein deficient

most diets provide an adequate amount of bcaas for most people, which is about 25–65 mg per 2.2 pounds of body weight.1 2 athletes involved in intense training often take 5 grams of leucine, 4 grams of valine, and 2 grams of isoleucine per day to prevent muscle loss and increase muscle gain, though most research does not support this use of bcaas.

side effects have not been reported with the use of bcaas. until more research is conducted, people with als should avoid taking supplemental bcaas. in one study, supplementation with a large amount of bcaas (60 grams) caused alterations in the blood levels of tryptophan, phenylalanine, and tyrosine.3 the changes in the blood levels of these amino acids could, in theory, cause depression in susceptible individuals. until more is known, individuals with a history of depression should consult a doctor before supplementing with bcaas. people with kidney or liver disease should not consume high amounts of amino acids without consulting their doctor