Branched chain amino acids

Branched Chain Amino Acids (BCAA) are the 3 amino acids leucine, Isoleucine and valine to which you were introduced during module 2. These are referred to as BCAA because their variable side chain has at least 1 methyl group, which you will recall consists of a central carbon attached to 3 hydrogens. This side chain prevents their processing in the liver, and grants them some interesting functional properties.

Branch chain amino acids make up around 33% of the stored amino acids in the body with the majority of them occurring in skeletal muscle. The key BCAA is leucine, as it is the consumption of leucine which activates the process of muscle protein synthesis. Consumption of proteins containing high levels of leucine create a higher protein synthetic response than a protein with a lower leucine content, and when that leucine content is artificially matched the response is the same. In the search for increased muscle mass, be that for the purposes of bodybuilding, athletic performance or health, this is a very important concept.

Logically it follows that leucine should be used, but this would not result in the ideal situation. All three amino acids are classed as essential, and all are found in high levels in muscle tissue. They serve functions in muscle cells (isoleucine improves glucose metabolism in muscle cells, valine’s role is as yet undefined) but their cellular catabolism (breaking down for subsequent use) shares the same two initial steps. Branch Chain Amino Acid Transferases, either cytosolic (expressed in the cytosol – the watery interior of the cell) or mitochondrial, referred to as BCATm and BCATc function to process the three BCAAs and, an overconsumption of leucine can therefore impair the absorption of sufficient isoleucine and valine. The typical ratio of L:IL:V is 2:1:1 in most foods with a complete amino acid profile and so this ratio is typically adopted for supplementary BCAA, too.

Consumption of BCAAs before training can improve performance during that training session compared to placebo, and post-workout BCAA supplementation can improve recovery compared to placebo. However, these two statements do not necessarily tell the whole story.

BCAA are constituents of whole proteins, and therefore the consumption of a whole protein would have the same effect, provided the same BCAA dosage was consumed (note that, as mentioned, around 3g of leucine will maximally stimulate muscle protein synthesis and so more than this is not necessarily better, regardless of the source). A whole protein would also provide the other essential and non-essential amino acids used to maintain overall positive protein balance and therefore arguably provide more benefit. Ultimately, in those looking to maximise the muscle protein synthetic response from a training session, following the protein distribution guidelines in module 2 – consume protein 3-5 times per day, ensuring you eat something within 2 hours before and after training, rendering BCAA supplementation obsolete.

BCAA have been theorised to reduce soreness, improve recovery and reduce muscle loss during a fat loss phase but, again, this is not supported in any literature.

An argument could be made that supplementation of leucine may be efficacious however. If you regularly consume meals which do not meet the ideal intake level of this amino acid, research indicates that a similar muscle protein synthetic response to whey can be induced by leucine enriched wheat protein (a protein that typically does not stimulate MPS highly). Vegans who consume meals with only one protein source therefore might consider this an option if maximal muscle gain is the goal.