Branched-chain amino acids (BCAA)

1. Enhanced endurance capacity/reduced fatigue.
2. Improved recovery following muscle damage (reduced soreness/damage).
3. Increased muscle mass via activating muscle protein synthesis.

BCAAs are essential amino acids metabolised primarily within the skeletal muscle and they play an important role in both cellular energy homeostasis² and in the regulation of muscle protein synthesis.³ Theoretically, by supporting energy metabolism and by stimulating muscle protein synthesis it is suggested that BCAA/ leucine may support muscle growth. Furthermore, there is some evidence that BCAA/leucine supplementation may assist in the recovery from muscle damaging exercise via similar mechanisms to those described above.

Finally, BCAA supplementation may provide substrate to working muscle under glycogen depleted conditions and due to BCAA competition for transport into the brain with tryptophan, BCAA supplementation may limit tryptophan entry into the brain. Theoretically this would reduce serotonin production in the brain and limit the onset of fatigue.⁴

The evidence for BCAA/leucine supplementation supporting endurance performance is equivocal.⁴ A recent study⁵ suggests that 20 g of BCAA ingested 1hr prior to a ramp test on a treadmill can delay fatigue. However, like much of  the BCAA literature around endurance performance/fatigue there are significant flaws in the research. In the case of ⁵ the placebo is not matched for calories. A thorough analysis of the most recent research on BCAA and endurance performance is needed to determine their efficacy for promoting performance. There is a great deal of heterogeneity in the literature around supplementation protocols and dosing strategies and so firm recommendations on this are difficult. There is an argument however, that because BCAAs become significant substrates during prolonged exercise that supplementing may prevent muscle damage/breakdown, but there is little evidence to support this notion. For instance, 20 g of BCAA supplemented before and during a 100 km race (3 g 1hr before followed by 17 g throughout a 100 km race) did not affect performance or markers of muscle damage.⁶

There is building evidence for BCAA supplementation to augment the response to damaging exercise. A meta-analysis of the literature from 2007-2013 suggests that BCAA supplementation may significantly reduce the severity of delayed onset muscle soreness following damaging exercise when compared to placebo treatments.⁷ Additionally, a systematic literature review carried out on research published up to August 2017 suggests that there may be a modest benefit of BCAA supplementation for markers of muscle damage.⁸ In an analysis of the dosing strategies in this systematic review⁸ it is suggested that a daily intake greater than 200 mg*kg*day-1 (~16 g) for at least 7 days prior to the damaging exercise may alleviate some of the impacts of muscle damage on muscle performance (force decrement, plasma CK). However, it should be noted that the placebo in all the included trials is devoid of any protein. So, it remains to be seen if BCAA supplementation would be better/worse than intact protein for this outcome measure. Furthermore, the systematic review suggests efficacy of BCAA supplementation only if the damage is low-moderate.

Because BCAA/leucine are critical for signalling to increase muscle protein synthesis³, it has long been thought that BCAA/leucine supplementation may enhance muscle protein synthesis and therefore growth in response to nutrition/exercise. However, the case for supplementing BCAA/leucine in isolation seems to be weak at best. For instance, when 5.6 g (equivalent content in 20 g of Whey) of BCAA were supplemented following a session of resistance exercise the resulting increase in muscle protein synthesis was only 22%.⁸ With intact protein we would expect this stimulatory response on muscle protein synthesis to be at least double that. So, whilst BCAAs, when taken in isolation following resistance exercise, can stimulate muscle protein synthesis they probably should not be recommended over whole foods containing sufficient high-quality protein. However, there may be a case for utilising BCAA/leucine to “top up” the anabolic potential of sub-optimal meals. The leucine content of a meal seems to be the key driver of the anabolic response (muscle protein synthesis) to that meal. Approximately 2.5 g of leucine per meal (equivalent to ~20 g of whey protein) seems to be sufficient to maximise muscle protein synthesis.³ Furthermore, when a suboptimal dose of whey protein (6.25 g whey, 0.75 g of leucine) in a mixed macronutrient beverage is “topped up” with leucine to contain 3 g of leucine, it produces a similar muscle protein synthesis response in the recovery from resistance exercise  as 25 g of whey protein (3g of leucine).⁹ These data suggest that leucine could be used to enhance the anabolic potential of certain meals that may not, on their own, maximise muscle protein synthesis. This could take the form of supplementing sub-optimal meals (plant-based meals, meals with less than 20-30 g of high-quality protein) with up to 3 g of additional leucine. However, we do not know if this strategy would support muscle growth in the long term.

Endurance performance: The evidence on the role of BCAA/leucine in supporting endurance performance or preventing damage from long duration activity is very heterogeneous and equivocal. From the literature so far, a clear dosing strategy cannot reliably be suggested especially considering that the placebo is often not optimal for assessing outcomes. There is probably room in the literature for a systematic review/meta-analysis to address this aspect of BCAA/Leucine supplementation.

Muscle damage recovery: The evidence for BCAA supplementation in reducing the severity of symptoms following muscle damage protocols (drop jumps, repeated eccentric contractions) is building. But the benefits appear to be marginal and given that the placebo is often simply a calorically matched product devoid of protein it would be hard to argue for the supplementation protocol to be implemented in place of a sound diet with sufficient high quality protein. Furthermore, the supplementation protocols that seem to be effective (when compared against placebos containing no protein) are likely impractical given the large daily doses required (16-20 g).

Muscle anabolism: Where intact and high-quality protein can be consumed in sufficient quantities to maximise muscle anabolism there appears to be little-no need to supplement with BCAA/Leucine. However, where a meal is going to be sub-optimal for maximising muscle anabolism (plant based protein or less than 20-30 g of high quality protein) then there may be a benefit to supplementing that meal with leucine up to a total of 2.5-3 g of leucine. It should be noted that the “benefit” in this instance is purely for muscle protein synthesis and there is not yet firm evidence of this kind of dosing strategy augmenting other outcomes such as muscle growth, strength, or recovery in athletic populations.

While there is some evidence supporting the claims that BCAA/leucine supplementation favourably influences skeletal muscle protein metabolism, efficacy is significantly less than acute ingestion of high biological value proteins. As such, these more efficacious interventions should be prioritised over BCAA/leucine. The fortification of lower biological value proteins with additional BCAA/leucine to optimise muscle anabolism is recognised and discussed in a separate fact sheet on isolated protein supplements.

1. Huang J., Nkrumah P.N., Appiah-Sefah G., Tang S. (2013). Authentication of pure L-Leucine products manufactured in China by discriminating between plant and animal sources using nitrogen stable isotope technique. Journal of Food Science, 78, 490 – P494.
2. Kainulainen H., Hulmi J., Kujala U. (2013). Potential role of branched-chain amino acid catabolism in regulating fat oxidation. Exercise and Sport Science Reviews, 41(4), 194-200.
3. Gorissen S., and Phillips S. (2019). Branched-Chain Amino Acids (Leucine, Isoleucine, and Valine) and Skeletal Muscle. Nutrition and Skeletal Muscle, 16, 263-279.
4. Williams M. (2005). Dietary Supplements and Sports Performance: Amino Acids. Journal of the International Society of Sports Nutrition, 2(2), 63-67.
5. AbuMoh’d M., Matalgah L., and Al-Abdulla Z. (2020). Effects of Oral Branched-Chain Aino Acids (BCAAs) Intake on Muscular and Central Fatigue During an Incremental Exercise. Journal of Human Kinetics, 31(72), 69-78.
6. Knechtle B., Mrazek C., Wirth A., Knechtle P., Rust C., Senn O., Rosemann T., Imoberdorf R., Ballmer P. (2012). Brahcned-Chain Amino Acid Supplementation during a 100km Ultra-Marathon – A Randomized Controlled Trial. J Nutr Sci Vitaminol, 58, 36-44.
7. Fedawa M., Spencer S., Williams T., Becker Z and Fuqua C. (2019). Effect of Branced-Chain Amino Acid Supplementation on Muscle Soreness Following Exercise: A Meta-Analysis. International Journal for Vitamin and Nutrition Research, 89, 348-356.
8. Jackman S., Witard., Philp A., Wallis G., Baar K., Tipton K. (2017). Branched-Chain Amino Acid Ingestion Stimulates Muscle Myofibrillar Protein Synthesis Following Resistance Exercise in Humans. Frontiers in Physiology.
9. Churchward-Venne T., Breen L., Di Donato D., Hector A., Mitchell C., Moore D., Stellingwerff T., Breuille D., Offord E., Baker S., Phillips S. (2014). Leucine supplementation of a low-protein mixed macronutrient beverage enhances myofibrillar protein synthesis in young men: a double-blind randomized trial. American Journal of Clinical Nutrition, 99(2), 276-86.