Branched-chain amino acids, known by the abbreviation BCAA (Branched-Chain Amino Acids), are among the best-selling food supplements in the world. Among athletes there is a strong belief that BCAA protect muscle mass, delay fatigue and speed up recovery. But what does science say about these claims?
What are BCAA and why do they matter?
The BCAA leucine, isoleucine and valine are three of the nine essential amino acids found in protein sources of food. They are specific in that they make up roughly 20 % of all the amino acids in muscle protein and are the only amino acids that can be oxidised (burned) directly in the muscles, rather than only in the liver.
The main promises vs. the scientific reality
Supplement manufacturers list a long set of benefits for BCAA. Let us look at the most common ones in the light of the available scientific analyses:
The idea that BCAA serve as a source of energy spread on the basis of a study by Goldberg and Chang (1978). BCAA can indeed be oxidised during physical activity, but later studies (Wagenmakers et al., 1989; Knapik et al., 1991) showed that their contribution to total energy expenditure is very small. What is more, taking in carbohydrates during exercise limits the use of BCAA as a source of energy even further.
The claim that BCAA limit the breakdown of muscle protein comes from early laboratory studies which showed increased synthesis and reduced degradation of proteins. Later studies in healthy people (Frexes-Steed et al., 1992; Nair et al., 1992) disproved this claim.
The central fatigue hypothesis assumes that BCAA compete with the amino acid tryptophan for entry into the brain. Less tryptophan means less serotonin, which should delay the feeling of exhaustion. Although BCAA do indeed change the ratio of these substances in the blood, studies (Blomstrand et al., 1995, 1997; Madsen et al., 1997).
It is true that the leucine contained in BCAA stimulates the signals for muscle growth. However, to build new muscle tissue the body needs all 9 essential amino acids, not just the three contained in BCAA. Koopman et al. (2005) showed that even adding extra leucine to a protein drink with the complete spectrum of amino acids brought no further benefit.
On a reduction diet, BCAA may have a small positive effect on protecting muscle mass (Jackman et al., 2017) – but only thanks to leucine, because neither isoleucine nor valine has an effect on stimulating muscle growth (Wilkinson et al., 2013).
Here the scientific evidence is somewhat more favourable. Some studies suggest that BCAA may slightly reduce perceived muscle soreness after demanding eccentric training – but without any effect on muscle function.
Conclusion for athletes
Despite their enormous popularity, the evidence for the sporting effects of BCAA – whether in terms of performance or muscle growth – is unconvincing. If you take in enough good-quality protein from your normal diet or from protein supplements, supplementing with BCAA alone will probably not bring you any additional benefit. Their use in intra-workout, recovery or pre-workout drinks is inefficient and ineffective.
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