BCAAs are anticatabolic

Strength athletes have been using BCAAs during their workouts for decades. BCAAs are believed to inhibit the breakdown of muscle tissue, and this is not just a figment of the imagination of supplements makers. Sports scientists at the Astrand Laboratory in Sweden published the results of a study that confirms this in the American Journal of Physiology – Endocrinology and Metabolism.

As their name suggests, BCAAs, or branched-chain amino acids, are amino acids with a branched side chain. The side chain makes the job of the enzymes in muscle cells, converting amino acids into energy during intensive exertion, easier. That’s why your muscle cells are happy to convert BCAAs into energy during an intensive training session, and that’s why athletes are fond of BCAA supplements. The more BCAAs you have in your muscles, the slower your muscle cells break down muscle fibre. The anabolic stimulus from your training remains the same, but you experience less muscle breakdown, so you build up more muscle mass.

Actually, this isn’t the whole story, as BCAAs have other effects too. Leucine is an anabolic stimulant for muscle cells, leucine and isoleucine stimulate fat burning in muscle cells, and isoleucine boosts the muscle cells’ glucose uptake. [J Nutr. 2005 Sep;135(9):2103-8.] But the emphasis in this new Swedish study is on the anticatabolic effect of BCAAs.

The researchers did an experiment with seven healthy test subjects, who didn’t normally do weight training. The researchers got them to train their legs by doing leg-presses. After an extensive warming up, they did 4 sets of 10 reps at 89 percent of their 1RM, followed by 4 sets of 15 reps at 65 percent of their 1RM.

The test subjects exercised one leg, and rested the other one.

On one occasion the subjects drank a sports drink that contained no active ingredients; on the other occasion they were given a drink containing BCAAs. If you want to know the exact composition: the BCAAs consisted of 45 percent leucine, 30 percent valine and 25 percent isoleucine. They used Ajinomoto products from Japan.

The subjects drank just before, during and just after their workout 150 ml of the sports drink, and then another 150 ml 15 and 45 minutes after training. In total the subjects consumed 900 ml sports drink. Per kg bodyweight they consumed 85 mg BCAAs. If you weigh 80 kg that amounts to 6.8 g BCAAs, which is not an extreme dose.

The supplementation boosted the BCAA concentration in the muscles and blood and activated the classic anabolic signal molecules in the muscle cells, mTOR and p70S6k. Nothing new. What was new was that the BCAAs reduced the concentration of the catabolic protein MAFbx, and inhibited the increase in the catabolic MuRF-1 as a result of training.

MAFbx and MuRF-1 are ubiquitins. They attach themselves to muscle proteins and then attract a molecular shredder – the proteasome – to the muscle proteins that are to be broken down.



“These observations, together with the BCAA-induced enlargement in p70S6k phosphorylation and attenuation of MAFbx expression and MuRF-1 total protein provide additional support for the view that BCAA has an anabolic effect on human skeletal muscle, an effect which appears to be similar in resting and exercising human muscle”, the Swedes conclude.

The researchers were not funded by the supplements industry, but by the Swedish National Centre for Research in Sports, the Swedish School of Sport and Health Sciences and the Karolinska Institutet.

Intake of branched-chain amino acids influences the levels of MAFbx mRNA and MuRF-1 total protein in resting and exercising human muscle.


Resistance exercise and amino acids are two major factors that influence muscle protein turnover. Here, we examined the effects of resistance exercise and branched-chain amino acids (BCAA), individually and in combination, on the expression of anabolic and catabolic genes in human skeletal muscle. Seven subjects performed two sessions of unilateral leg press exercise with randomized supplementation with BCAA or flavored water. Biopsies were collected from the vastus lateralis muscle of both the resting and exercising legs before and repeatedly after exercise to determine levels of mRNA, protein phosphorylation, and amino acid concentrations. Intake of BCAA reduced (P < 0.05) MAFbx mRNA by 30 and 50% in the resting and exercising legs, respectively. The level of MuRF-1 mRNA was elevated (P < 0.05) in the exercising leg two- and threefold under the placebo and BCAA conditions, respectively, whereas MuRF-1 total protein increased by 20% (P < 0.05) only in the placebo condition. Phosphorylation of p70(S6k) increased to a larger extent (?2-fold; P < 0.05) in the early recovery period with BCAA supplementation, whereas the expression of genes regulating mTOR activity was not influenced by BCAA. Muscle levels of phenylalanine and tyrosine were reduced (13-17%) throughout recovery (P < 0.05) in the placebo condition and to a greater extent (32-43%; P < 0.05) following BCAA supplementation in both resting and exercising muscle. In conclusion, BCAA ingestion reduced MAFbx mRNA and prevented the exercise-induced increase in MuRF-1 total protein in both resting and exercising leg. Further-more, resistance exercise differently influenced MAFbx and MuRF-1 mRNA expression, suggesting both common and divergent regulation of these two ubiquitin ligases. PMID: 22127230 [PubMed - indexed for MEDLINE] Source: http://www.ncbi.nlm.nih.gov/pubmed/22127230