Branched-Chain Amino Acid Ingestion Stimulates Muscle Myofibrillar Protein Synthesis following Resistance Exercise in Humans.
Level 2 - randomized trial
Individual crossover intervention trial in humans
PubMed 28638350 · doi:10.3389/fphys.2017.00390
What was done
Ten young (20.1 ± 1.3 years), resistance-trained men completed two trials ingesting either 5.6 g of branched-chain amino acids (BCAAs) or a placebo drink immediately after resistance exercise. Myofibrillar muscle protein synthesis was measured during 4 hours of post-exercise recovery using a primed, constant infusion of L-[ring 13C6] phenylalanine and muscle biopsies taken pre- and 4 hours post-drink. Blood samples were collected before and after ingestion, and Western blotting was used to assess the phosphorylation status of mTORC1 signaling proteins in muscle biopsies collected pre, 1 hour, and 4 hours post-drink.
What was found
Plasma leucine (300 ± 96%), isoleucine (300 ± 88%), and valine (144 ± 59%) peaked 0.5 hours post-drink with BCAA ingestion. Phosphorylation status at 1 hour post-drink was significantly higher in BCAA versus placebo for S6K1 Thr389 (P = 0.017) and PRAS40 (P = 0.037). Myofibrillar muscle protein synthesis was 22% higher (P = 0.012) with BCAA (0.110 ± 0.009%/h) than placebo (0.090 ± 0.006%/h). Phenylalanine rate of appearance was approximately 6% lower in BCAA (18.00 ± 4.31 micromol/kgBM) than placebo (21.75 ± 4.89 micromol/kgBM; P = 0.028).
Why it matters
This study demonstrates that consuming BCAAs alone, without other essential amino acids or intact protein, is sufficient to activate mTORC1 signaling and stimulate post-exercise myofibrillar protein synthesis above resting placebo levels.
Limits
The sample size is very small (n = 10) and limited strictly to young, resistance-trained men. The trial did not include a positive control group ingesting intact protein or all essential amino acids to determine whether BCAAs alone produce a maximal anabolic response, and measurements ended at 4 hours post-ingestion.
Cited by
- context Branched-chain amino acid (BCAA) supplements provide minimal additional benefit for muscle protein synthesis beyond the specific action of leucine.