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What the hell are BCAAs?

Branched-Chain Amino Acids (BCAAs) are three essential amino acids that contribute towards muscle growth. Because they’re present in high levels, notably in animal protein, supplementation is often unnecessary for people with sufficient dietary protein intake.

Branched Chain Amino Acids (BCAAs) refers to the three amino acids: leucine, isoleucine, and valine.

How do they work?

Supplementing with BCAAs prevents a serum decline in BCAAs – this decline occurs during exercise. A serum decline would normally cause a tryptophan influx into the brain, followed by serotonin production, which causes fatigue. Preventing this serum decline reduces the level of fatigue experienced through this mechanism during exercise.

On top of this, isoleucine is used for increasing glucose uptake into cells – it appears to improve glucose consumption and uptake, whilst leucine is used to improve muscle protein synthesis.

Leucine is one of the three branched chain amino acids and is often referred to as the 'main' amino acid due to the most sought after benefit of BCAAs (muscle building) being mostly due to leucine. Leucine is an activator of the protein mTOR, which then induces muscle protein synthesis via S6K; the other two BCAAs (valine and isoleucine) may also activate mTOR, but are much weaker than leucine in doing so (and because of this, 5g of leucine will be more effective than 5g mixed BCAAs).

In isolation, there’s currently no notably significant benefit of valine supplementation that can’t be replicated by either leucine or isoleucine supplementation.

When are they useful?

For people with low dietary protein intake, BCAA supplementation can promote muscle protein synthesis and increase muscle growth over time. Where protein intake is adequate, BCAA supplementation may not be necessary.

The overriding metabolic goal of using BCAAs is to maximize the anabolic state. It’s widely spoken that BCAAs induce an anabolic state by stimulating muscle protein synthesis. However, an abundant availability of all essential amino acids (EAAs) is needed for significant stimulation of muscle protein synthesis (MPS). MPS will be limited by the lack of availability of any of the EAAs, whereas a shortage of non-essential amino acids (NEAAs) can be compensated for by increased de novo production of the deficient NEAAs.

BCAAs are important to ingest on a daily basis, but many protein sources, such as meat and eggs, already provide BCAAs as well as EAAs. Supplementation is unnecessary for people with a sufficiently high protein intake (1-1.5g per kg of bodyweight a day or more).

What are the dosages?

The standard dosage for isoleucine is 48-72mg per kilogram of bodyweight, assuming a non-obese person. The standard leucine dosage is between 2-10g. A combination dose is 20g of combined BCAAs, with a balanced ratio of leucine and isoleucine.


BCAA supplementation isn’t necessary if enough BCAAs are provided through diet - dietary BCAA supplements alone don’t promote muscle anabolism.


Blomstrand, E., 2006. A role for branched-chain amino acids in reducing central fatigue. The Journal of nutrition, 136(2), pp.544S-547S.

Volpi, E., Kobayashi, H., Sheffield-Moore, M., Mittendorfer, B. and Wolfe, R.R., 2003. Essential amino acids are primarily responsible for the amino acid stimulation of muscle protein anabolism in healthy elderly adults. The American journal of clinical nutrition, 78(2), pp.250-258.

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(1), pp.1-7.

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