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.
Where are they found?
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
Amino acids have been used
in connection with the following conditions (refer to the individual
health concern for complete information):
Bronchitis (N-acetyl cysteine)
pulmonary disease (N-acetyl cysteine)
Cold sores (lysine)
failure (propionyl-L-carnitine, taurine)
hyperplasia (alanine, glutamic acid, glycine)
DLPA, L-phenylalanine, tyrosine)
HIV support (N-acetyl cysteine)
Liver support (taurine)
Weight loss and
(DLPA, glutamine, tyrosine)
High blood pressure
HIV support (glutamine, methionine)
Liver support (methionine)
Peptic ulcer (glutamine)
Who is likely to be deficient?
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
How much is usually taken?
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.
Are there any side effects or interactions?
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. Most, but not all studies have found that when people have impaired
kidney function, restricting dietary intake of protein slows the rate of decline of kidney
Excessive protein intake also can increase excretion of calcium, and some evidence has linked high-protein
diets with osteoporosis,4
particularly regarding animal protein.5 On the other hand, some protein is needed
for bone formation. A double-blind study showed that elderly people whose diets provided
slightly less than the recommended amount of protein suffered less bone loss if they consumed
an additional 20 grams of protein per day.6 A doctor can help people assess their
For the drug interactions safety check, refer to the individual amino acids.
1. Young VR, Pellett PL. Plant proteins in relation to human protein and
amino acid nutrition. Am J Clin Nutr 1994;59(suppl):1203S–12S.
2. Lemon P. Is increased dietary protein necessary or beneficial for
individuals with a physically active lifestyle? Nutr Rev 1996;54(4 Pt
3. Sitprija V, Suvanpha R. Low protein diet and chronic renal failure in
Buddhist monks. BMJ 1983;287:469–71.
4. Heaney R. Protein intake and the calcium economy. J Am Diet
Assoc 1993;93:1259–60 [review].
5. Abelow BJ, Holford TR, Insogna KL. Cross-cultural association between
dietary animal protein and hip fracture: a hypothesis. Calcif Tiss Int
6. Schürch MA, Rizzoli R, Slosman D, et al. Protein supplements
increase serum insulin-like growth factor-I levels and attenuate proximal femur bone loss in
patients with recent hip fracture. Ann Intern Med 1998;128:801–9.