Some animal evidence suggests that low protein intake promotes longevity. However, Dr. Phillips proposes these models may be missing a major element. For example, lab animals are raised and live in a somewhat sterile environment where they are fed on schedule. Generally, they lack ordinary exposure to diseases and accidents that can promote sudden stretches of disuse and consequent atrophy of muscles.

Without adequate muscle reserve built when young and preserved when old, we more quickly reach a "disability threshold." In this clip, Dr. Stuart Phillips discusses how building muscle reserves under adequate nutrition delays the disability threshold and contributes to more successful aging.