leucine

Leucine is an essential amino acid—you must get it from food—and it helps trigger muscle protein synthesis. Whey, meat, eggs, and some other high-quality proteins are relatively rich sources; collagen is relatively low in leucine, so whey is the stronger choice if the goal is muscle growth, repair, or strength. 1 2

For plant-based meals, the discussion suggests using an isolated protein or adding leucine; a roughly one-gram capsule with a meal was offered as one possible way to raise leucine intake. 3