Although more than 80 amino acids exist in nature, only 20 of these combine to create the various proteins in the human body. Nine of these are called "essential amino acids," meaning that they must be attained from food. The essential amino acids are isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Histidine is considered semi-essential because we only need to get it from a dietary source as infants. Our bodies produce the other 11, called "nonessential amino acids": arginine, alanine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, proline, serine and tyrosine.
"Amino acids are linked together to form a compound called polypeptides. Long chains of polypeptides result in the formation of proteins," explains Samer Koutoubi, M.D., Ph.D., professor in the nutrition and exercise department at Bastyr University in Washington. When we eat protein, it is broken down into individual amino acids and then reassembled into proteins in the body. To clarify how individual amino acids are put together, Nelda Mercer, a licensed dietician and spokeswoman for the American Dietetic Association, likens them to the building blocks of language. "Different combinations of amino acids create different kinds of protein," she says. "It's just like how you can make many different words using the 26 letters of the alphabet."
The proteins that amino acids combine to create play an essential role in the human body. Among its many functions, protein is used to build and repair cells, create hormones and enzymes, regulate fluids, produce antibodies and provide energy. "Every single protein has a purpose and function to make us healthy," Mercer says.
Although amino acids are present in nearly everything we eat, the richest individual sources of amino acids are animal-derived foods such as meat, eggs and dairy products. "When food protein contains all of the essential amino acids in the right balance to meet the human needs, we call it a complete protein," explains Koutoubi.
Soy is an example of a nonanimal food that is also a complete protein. But vegans who don't like soy can still easily get all the protein they need. While it was once believed that plant-based foods had to be combined in one meal to replicate a complete protein, recent research shows that simply eating a variety of foods will ensure the proper amount of protein, even without meat or dairy. "You don't have to be as meticulous as we once thought you had to be," says Mercer, "as long as you have a pool of amino acids throughout the day."
According to Mercer, if you eat a healthy and varied diet, you should be able to get all the amino acids you need. "In the United States, it's going to be very rare in our culture that we're not getting enough protein in our diet. If you're getting enough calories, you're getting enough protein" says Mercer, who does not recommend taking amino acids supplements.
According to Mercer, most people require a half-gram of protein per body pound per day, although there are competing ideas about protein intake. Serious athletes may require more, since they expend so much energy. Although we need protein to survive, ingesting too much protein can lead to weight gain, dehydration, osteoporosis and kidney problems.
Some health professionals, however, say that some common medical conditions warrant amino acid supplementation. David Zeiger, D.O., medical director of Healthworks Integrative Health Clinic in Chicago, says that he often prescribes amino acid supplements to his patients for conditions ranging from angina and diabetes to depression and growth problems. Zeiger says that even normal, healthy adults can benefit from a supplement of glutathione—a combination of cysteine, glycine and glutamic acid—which helps the liver to detoxify the body. "Every human being needs additional amino acids in his diet because today we are constantly exposed to toxins in our food and water," he says. Current research is also exploring the potential benefits of glutathione in patients suffering from cancer, heart disease and immunodepression.
Zeiger strongly cautions, however, against self-medication. "It is always a good idea to consult a doctor who knows about nutrition medicine," he says. "If you take the wrong amount, you can lose the benefit. Or you can really hurt yourself." Amino acids should be taken in combination with one another and in the proper ratio. Imbalanced amino acid supplementation can be potentially dangerous, says Zeiger, citing the example of lysine and arginine. When taken together in the wrong ratio, he says, the two amino acids can cause herpes breakouts.
The debate over amino acid supplements has gotten a lot of attention in recent years because so many athletes have been seeking amino acids out to enhance their performance. According to Zeiger, there is evidence that taking several grams of amino acids a day can indeed stimulate the endocrine system to produce more growth hormone, which in turn may help to build muscle. But Zeiger says that improper self-medication of amino acids in the athletic community is common and may cause conditions such as dehydration, gigantism, infertility and hyperactivity. There has been some anecdotal evidence that taking large amounts of amino acids or amino acid derivatives such as creatine might cause stomach cramps and diarrhea. And many dieticians, including Mercer, say there is simply not enough research showing that amino acids can enhance athletic performance to justify the potentially dangerous imbalances in the body that this kind of supplementation can cause.
Amino acid as natural remedy
According to Samer Koutoubi, M.D., Ph.D., associate professor at Bastyr University, amino acids can be used to treat numerous conditions. He recommends retailers remind consumers to work with a qualified health practitioner if they wish to investigate these uses.
- Alanine, glycine and glutamic acid: Benign prostatic hypertrophy
- Arginine: Wound healing, infertility, heart attack and stroke prevention, hypertension and chronic fatigue, especially muscular fatigue with myalgia
- Carnitine: Heart disease, myopathy, hyperlipidemias and alcoholism
- Cysteine, N-acetylcysteine (NAC) or glutathione: Intolerance to xenobiotics, detoxification impairments, free radical-associated disorders, pulmonary conditions and AIDS
- Glutamine: Gastrointestinal tract repair, total parenteral nutrition, wasting disorders, immune support, chemotherapy side effects, surgery, burns and alcoholism
- Glycine: Detoxification impairments and wound healing
- Histidine: Rheumatoid arthritis
- Leucine, isoleucine and valine: Alcoholism, surgery, starvation, infection, muscle building and total parenteral nutrition
- Lysine: Herpes simplex (HSV-1, HSV-2)
- Phenylalanine, tyrosine: Depression and Parkinson's disease
- S-Adenosylmethionine (SAM): Depression, osteoarthritis, fibromyalgia and liver disorders
- Taurine: Intolerance to chlorine, hypochlorite (bleach), phenols, nitrites, amines or Aldehydes, fat malabsorption in cystic fibrosis, seizures, eye disorders, gallbladder disease, heart disease and alcoholism
- Tryptophan: Insomnia, depression, restless leg syndrome, alcoholism, weight control and Parkinson's disease
Other uses for aminos
Amino acids also have several non-health uses. The controversial food additive, monosodium glutamate, for example, contains glutamic acid; the nonsugar sweetener, aspartame (Equal) is produced from aspartic acids and phenylalaline; and collagen, the wrinkle-defying skin care ingredient, is made up of several different amino acids—and is also produced naturally in the body.
Natural Foods Merchandiser volume XXVI/number 3/p. 94, 96