While other amino acids are metabolized primarily in the liver, the branched-chain amino acids (BCAAs) are unique in that the major portion of their metabolism occurs in muscle. Under low-calorie conditions, especially when there’s not enough protein in the diet, cortisol is released in a stress-related response. In muscle, cortisol promotes the breakdown of amino acids—the branched-chain aminos.
Based on that finding, some have suggested that taking supplemental BCAAs provides anticatabolic effects in hard-training athletes. In that scenario, the supplemental BCAAs are sacrificed instead of the existing BCAAs in muscle, thereby sparing the muscle. Besides interacting with cortisol, BCAAs also promote testosterone release to some extent, especially if taken prior to intense exercise. Testosterone is an anabolic hormone, directly opposing the catabolic activities of cortisol.
A study presented at the 2005 meeting of the American College of Sports Medicine highlighted another beneficial effect of BCAA supplements that has particular relevance for those on low-carbohydrate diets.1 A major problem with low-carb diets is the depletion of readily available energy substrates, such as glycogen, which is the primary fuel that powers anaerobic exercise, such as weight training. The primary source of glycogen in the diet is carbohydrate.
Glycogen promotes the production of substances important in the synthesis of ATP, the immediate source of energy for muscular contraction. One such substance is oxaloacetate. Without it the cycle that normally produces ATP just doesn’t function well, leading to a drop in energy and training intensity.
But an intermediate substance called succinyl coenzyme-A (SCA) enhances oxaloacetate availability. That’s where BCAAs enter the picture, since they directly increase SCA. The new study hypothesized that the energy-promoting effect of BCAAs was so potent that it could even overcome the effects of carbohydrate depletion.
The study featured seven men who depleted their existing glycogen stores through exercise and lack of food. Then one group took 300 milligrams per kilogram (2.2 pounds) of BCAAs, while the other group got a placebo. After that the men rode exercise bikes to exhaustion. Those in the BCAA group showed higher blood glucose levels than the placebo group. The BCAA group also appeared to more readily burn fat during exercise. The increased fat availability, coupled with the higher glucose levels, overcame the normal negative effects of glycogen depletion during exercise.
1 Adolpho, T., et al. (2005). Influence of branched-chain amino acid supplementation on free fatty acid oxidation during endurance exercise after muscle glycogen depletion. Med Sci Sports Exer. 37:S349.
©,2013 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited.
