Older adults require approximately 40 grams of high-quality protein or 20 grams of essential amino acids per meal to elicit a muscle protein synthesis response comparable to that seen in younger adults, due to age-related anabolic resistance that blunts the response to lower doses.

Older muscles need more protein because their cells don't respond as strongly to amino acids, and less of the protein's amino acids reach the muscles. The key signal that tells muscles to build new protein becomes harder to trigger, and the liver and gut absorb more of the amino acids before they can get to the muscles. To overcome this, older adults must eat more protein to push enough amino acids through to activate the muscle-building signal.