Leucine

Leucine is one of the three branched-chain amino acids and the one most associated in research with triggering muscle protein synthesis. Complete animal proteins and soy are naturally leucine-rich, which is part of why they score well on protein-quality scales. That is a description of amino-acid chemistry, not a promise: we do not claim a leucine number on a label produces any specific result for you. Where a brand advertises added leucine, we note the dose from the panel and leave the physiology framed as general information.