Animal proteins stimulate muscle protein synthesis more effectively than most plant proteins in older adults due to higher leucine content and greater digestibility, but strategic combinations of plant proteins can produce comparable anabolic responses when total essential amino acid requirements are met.

When older adults consume animal proteins, the high amount of leucine in these proteins triggers a molecular signal in muscle cells that turns on protein building and turns off protein breakdown. This signal activates a key control center called mTORC1, which starts the production of new muscle proteins. At the same time, leucine reduces the activity of systems that destroy muscle proteins, so more muscle is kept than lost. Plant proteins can do the same if they provide enough total leucine and other essential amino acids together in one meal.