Limitations to current science

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.