The proposed benefits of BCAAs are some of the following; supports muscle growth, supports recovery, reduces feeling of fatigue.
But do they really work? Are they beneficial?
Well maybe not….A 2017 review paper (which reviews all the existing research on that topic up to date) published in the Journal of the International Society of Sports Nutrition shows that many of BCAA supplements proclaimed benefits may be bunk.
What it essentially comes down to is that BCAAs only contain 3 of the 9 essential amino acids. But all 9 essential amino acids are REQUIRED for muscle protein synthesis (MPS/muscle growth). Thus, when BCAAs are taken IN THE ABSENCE OF THE OTHER 6 ESSENTIAL AMINO ACIDS, then the body digs into existing muscle tissue to pull out the other needed essential amino acids so that it can build new muscle. But here’s the catch, the NET effect from breaking down existing muscle tissue to build new muscle tissue is actually an overall decrease in MPS. Still confused? Think “1 step forwards 2 steps back”. This is the equivalent here.
You’re breaking down existing muscle to build new muscle, but when you consider both of these events; it’s an overall decrease in muscle growth.
BCAAs and Fatigue
What about the proposed benefits of BCAAs for “reduction in fatigue?”
This comes from the idea that BCAAs limit the amount of serotonin in the brain during training/competition. Increase of serotonin in the brain during exercise promotes feelings of fatigue. It is thought that the amino acids in the BCAA supplement COMPETE with the precursor of serotonin (tryptophan) for getting across the blood brain barrier and into the brain. In other words, BCAAs block tryptophan and ultimately serotonin from getting into the brain and making you feel tired.
Seems plausible right? But this fatigue reducing effect is not consistently found in exercise training studies using BCAAs. This is the likely reason why:
BCAA also competitively inhibit tyrosine uptake into brain, and thus catecholamine synthesis and release. Since increasing brain catecholamines enhances physical performance, BCAA ingestion could lower catecholamines, reduce performance and thus negate any serotonin-linked benefit.
It’s important to emphasize that individual differences are also likely at play, considering some individuals are more susceptible than others to low serotonin. For instance, depression or migraines are associated with low serotonin.
ONE MORE THING. The idea that you should drink BCAAs all day long to “stave off muscle loss” or to “block hunger” as is often advertised is not a great idea based on what we have discussed – you could limit neurotransmitter production.
Wolfe R. R. (2017). Branched-chain amino acids and muscle protein synthesis in humans: myth or reality?. Journal of the International Society of Sports Nutrition, 14, 30. doi:10.1186/s12970-017-0184-9
Choi et al. (2013). Oral branched-chain amino acids supplements that reduce brain serotonin during exercise in rats also lower brain catecholamines. Journal of Amino Acids. doi: 10.1007/s00726-013-1566-1.