Is leucine supplementation actually useful for building muscle? • Stronger by Science

You’ve probably heard that the amino acid leucine is the “switch” for muscle protein synthesis. For those of you who were around circa 2013 or so, leucine and branched-chain amino acids were pretty popular in the supplements-for-muscle-growth world, with supplement companies emphasizing the amount of leucine contained in their products. FWIW, this is still the case with some products. 

And to be totally fair, leucine being beneficial for muscle protein synthesis is not a false claim. Leucine is an essential amino acid that helps trigger mTORC1 signaling, which initiates protein synthesis. We even have some mechanistic evidence that lifting weights can increase muscle sensitivity to leucine for up to 48 hours after exercise.

However, the real question is not whether leucine can trigger muscle protein synthesis, but rather whether supplementing with leucine, when already consuming a diet relatively high in protein and lifting weights, actually leads to better gains in strength and muscle growth. 

A new systematic review in young, active adults suggests the answer is usually no. Across randomized trials involving healthy, trained participants following similar programs, adding leucine did not improve muscle growth, strength, or recovery compared to a placebo. 

The same appears to be true even when looking at meta-analyses on the topic in older adults, including those with sarcopenia. Leucine supplementation did not show any clear benefits for lean mass, hand grip strength, or leg press strength, in either older adults who resistance trained or those who didn’t. There appeared to be some benefit of leucine supplementation when it also included vitamin D for handgrip strength, but terms and conditions apply.

Similar to younger adults, resistance training paired with an adequate protein intake appears to be sufficient to increase strength and muscle mass. It’s worth highlighting that when mentioning “adequate” protein intake, we’re not necessarily talking about anything extreme. For example, some of the studies on older adults had participants consume roughly 1.2g of protein per kilogram of body weight, which is likely enough to tick a lot of muscle growth boxes.

Additionally, when looking specifically at the effect of BCAA or EAA supplementation, we see that the former is likely worse at spiking muscle protein synthesis than a complete source of protein, and the latter might be an “OK” option to consider if your protein intake is very low.

Overall, the good news is that it’s very likely that you don’t need to spend any money on leucine, BCAA, or EAA supplements, assuming your protein intake is not extremely low for very long periods of time (and you don’t need to suffer through actually taking a leucine supplement consistently. If you’ve ever tried it, you know the taste is absolutely vile). At the end of the day, even the odd low-protein day here and there is very unlikely to have a meaningful effect on your gains, especially if you consistently engage in resistance training.