Protein is broken down during digestion into amino acids, which the body uses for processes including tissue maintenance and muscle protein synthesis. Essential amino acids must come from the diet, so the quality of a protein depends not only on how much protein it contains, but also on its essential amino-acid composition and digestibility. 

“Different plant proteins can complement each other’s amino-acid profiles.” No single plant protein needs to do everything. Cereal and legume proteins have different amino-acid patterns, which is why combining sources can improve the overall nutritional profile. Pea and soy proteins, for example, can complement other plant proteins when used in appropriate mixtures. 

“Leucine acts as an important signal for the machinery involved in muscle protein synthesis.” Leucine is one of the essential amino acids and plays an important signalling role in the regulation of muscle protein synthesis. However, leucine doesn’t work in isolation—the body also requires adequate total protein and the other essential amino acids to support the process.