Do Branched-Chain Amino Acids (BCAA) Supplements Boost Muscle Mass?

Branched-Chain Amino Acid supplements are a multi-million dollar business, marketed for the widely-believed claim that these BCAAs can boost muscle mass by stimulating muscle protein synthesis, a belief based on rat studies going back 40 years. There haven’t been any human studies measuring protein synthesis after oral Branched-Chain Amino Acid administration, but there have been two studies using BCAA intravenous infusions. (Oral and IV amino acids have been shown to have comparable effects when it comes to muscle protein synthesis.) Both studies found that BCAAs actually caused a reduction in muscle protein synthesis. A review in the Journal of the International Society of Sports Nutrition entitled, “Branched-chain amino acids and muscle protein synthesis in humans: Myth or reality?” concluded that it was a myth: “We conclude that dietary BCAA supplements alone do not promote muscle anabolism [growth]…. In fact, available evidence indicates that BCAAs actually decrease muscle protein synthesis.”

Branched-Chain Amino Acids may, however, enhance protein synthesis when combined with a protein meal. Does this translate into muscle mass, strength, or function? In the context of adequate daily protein intake, there appears to be no benefit of adding Branched-Chain Amino Acids. For example, if you randomize older women to one of three groups, resistance exercise with BCAAs, resistance exercise with placebo, or no exercise, the women in the resistance exercise with Branch-chain group experienced a significant improvement in muscle mass and strength compared to the control group, but no better than the resistance exercise with placebo group.

There was a placebo-controlled trial of exercise therapy with or without BCAAs in elderly women after hip replacement that found a few benefits but didn’t seem to have an effect on any of the other variables, including hip strength on either side or functional independence. After accounting for this multiple testing, the effects they did find did not reach statistical significance. So, we are still left with the bottom line of a review in a journal of exercise metabolism: “In conclusion, the proposed benefits of Branched-Chain Amino Acids used in the marketing of supplements appear to be at odds with the overall state of the current literature, which does not support the efficacy of supplementation on muscle strength or muscle size.”