Amino Acids Overview
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
Amino acids have been used in connection with the following conditions (refer to the individual health concern for complete information):
|Science Ratings||Health Concerns|
Bronchitis (N-acetyl cysteine)
Chronic obstructive pulmonary disease (N-acetyl cysteine)
Cold sores (lysine)
Congestive heart failure (propionyl-L-carnitine, taurine)
Alzheimer’s disease (acetyl-L-carnitine)
Athletic performance (creatine)
Benign prostatic hyperplasia (alanine, glutamic acid, glycine)
Chronic fatigue syndrome (carnitine)
Congestive heart failure (arginine)
Depression (5-HTP, DLPA, L-phenylalanine, tyrosine)
High triglycerides (carnitine)
HIV support (N-acetyl cysteine)
Infertility (male) (arginine, carnitine)
Intermittent claudication (carnitine)
Liver support (taurine)
Migraine headaches (5-HTP)
Weight loss and obesity (5-HTP)
Alcohol withdrawal (DLPA, glutamine, tyrosine)
Athletic performance (arginine/ornithine, carnitine)
High blood pressure (arginine, taurine)
HIV support (glutamine, methionine)
Liver support (methionine)
Peptic ulcer (glutamine)
Rheumatoid arthritis (DPA)
and relatively consistent scientific data showing a substantial health benefit.
Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.
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.
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 function.3
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 protein intake.
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 2):S169–75 [review].
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 1992;50:14–8.
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.
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The information presented in Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires September 2008.