Be wary of Internet hype about branched chain amino acids, which for the most part is aimed at athletes and body builders looking to enhance performance and endurance. Marketers of these products note that BCAAs stimulate protein building in muscle and may help reduce muscle breakdown, but they don't tell you that they are readily available. Because our bodies can't make the three essential branched chain amino acids - leucine, isoleucine, and valine - we have to get them from food. Fortunately, that's pretty easy. All meats contain BCAAs. Red meat provides the most, but you can also get adequate amounts in pork, poultry, eggs and fish, as well as milk, yogurt and cheeses. Vegetable proteins that provide them include quinoa, legumes, nuts and seeds.
I discussed your question with Tieraona Low Dog, M.D., director of the Fellowship at the Arizona Center for Integrative Medicine and an expert on dietary supplements. She says that most people who are getting adequate protein in their diets do not need a BCAA supplement. She also notes that some evidence shows that a protein-carbohydrate snack before and after a hard workout will allow free amino acids to help rebuild damaged muscle tissue. She views whey protein as a good source of BCAAs; it is the protein supplement she generally recommends. She suggests soy protein for the lactose intolerant.
Dr. Low Dog also tells me that BCAAs are being studied for possible use in the treatment of mania and neurodegenerative disorders, and reports that the U.S. military looked at increasing the BCAA content of food rations for troops in high-intensity combat field operations but decided against it because there wasn't clear evidence of benefit.
BCAAs are promoted for many non-athletic uses, including treatment of ALS (amyotrophic lateral sclerosis), but follow up reports indicate this use leads to lung failure and higher death rates among patients. BCAAs are also used to prevent fatigue, improve concentration, restore appetite in cancer patients, and reduce muscle wasting in people confined to bed. There is little evidence that they are effective for these conditions.
It is probably safe to take BCAAs for up to six months, but be aware of possible side effects, including fatigue and loss of coordination (which could be dangerous when driving). It is best not to take BCAAs at all if you're pregnant or breast-feeding, if you consume alcohol in excess, have diabetes or a disorder called branched-chain keto-aciduria; the supplements can cause seizures in those with this condition.
If your interest in BCAAs is related to improving your athletic performance, you may be interested in what the U.S. Olympic Committee's Sport Performance Division has to say on the subject: "It is not necessary to supplement BCAAs. Choosing protein-rich foods of high biological value spread throughout the day will supply your body with ample amounts of branched chain amino acids."
Andrew Weil, M.D.