Published in the Journal of the International Society of Sports Nutrition, researcher Robert R. Wolfe of the University of Arkansas for Medical Sciences looked at existing studies specifically on BCAA consumption and muscle building.
He found that ingestion of BCAAs leucine, valine, and isoleucine had a limited effect on building muscle. “The few studies in human subjects have reported decreases, rather than increases, in muscle protein synthesis after intake of BCAAS,” he wrote
This is mainly due to the way essential amino acids are transported into muscle cells—supplementing all three branched-chain amino acids makes them ‘compete’ to use an, limiting the transport rate of amino acid into cells.
BCAA reduced rate of muscle protein synthesis
Wolfe based his conclusion partly on two human trials conducted in the 1990s, where study participants were given BCAA intravenously.
“While the infusion of BCAAs is not the conventional manner in which a dietary supplement would be consumed, intravenously infused and orally ingested amino acids have been shown to elicit comparable effects on muscle protein synthesis,” Wolfe wrote.
The researchers in this previous study found that infusion not only failed to increase the rate of muscle protein synthesis in both trials, but actually reduced the rate of muscle protein synthesis and the rate of muscle protein turnover.
More for endurance, not bodybuilding
According to Dr Susan Kleiner, a sports nutrition formulation expert, the findings of this study are in line with the conclusion she has operated under in her practice. "I have not recommended BCAAs to my clients for supplementation because I consult in an evidence-based manner," she said.
"With the publication of this review, it may be appropriate to let clients know that BCAA supplementation may decrease their MPS and turnover, making them certainly not helpful, and possibly harmful, to their goals."
Though the science to back BCAA’s role in building muscle is still limited, it still has its place in sports nutrition, according to Jose Antonio, CEO of the International Society of Sports Nutrition and editor-in-chief of its journal.
“BCAAs still play a role in reducing muscle soreness,” he said. “There are instances where consuming whole protein just won't be convenient, for example. long training rides on a bike.”
He added that this study sheds light on how marketers should position BCAA supplements. “BCAAs should not be marketed as a muscle building supplement, but something to take intra-workout to reduce soreness.”
Source: Journal of the International Society of Sports Nutrition
Published online, https://doi.org/10.1186/s12970-017-0184-9
Branched-chain amino acids and muscle protein synthesis in humans: myth or reality?
Author: Robert R. Wolfe