Do older adults have a smaller muscle-building response to protein than younger adults?

Older adults can still mount a meaningful muscle-building response to dietary protein, but the average acute response is modestly smaller than in younger adults—a pattern termed anabolic resistance.

Clinical evidence

• Stable-isotope meta-analysis found lower post-meal myofibrillar muscle protein synthesis (MPS) in older versus younger adults (standardized mean difference −0.35, 95% CI −0.63 to −0.07), with substantial variation among studies.
• A systematic-review estimate suggested protein-stimulated MPS is approximately 28% lower in older adults on average.
• This is not an absent response: meal-based protein reliably increases acute MPS at older as well as younger ages. The difference is most appropriately interpreted as an average response to comparable meals, not as an inevitable response to every protein-containing meal.

Dose, exercise, and mechanisms

• Protein dose and amino-acid composition materially affect the age difference. Essential amino acids—especially leucine—and sufficiently high protein doses can narrow or eliminate the apparent deficit.
• After resistance exercise, young men reached a near-maximal acute MPS response with about 20 g whey, whereas older men responded more to 40 g than to 20 g. At rest, however, 40 g did not further increase MPS over 20 g in older men.
• Proposed biological contributors include less effective amino-acid delivery and uptake, reduced muscle capillary perfusion, and weaker anabolic signaling, including mTORC1-related pathways. These mechanisms remain incompletely established in humans.
• Inactivity appears to exacerbate anabolic resistance: step reduction and bed rest in older adults are associated with lower post-meal MPS, impaired anabolic signaling, and altered amino-acid transporter expression.

Bottom line

• For a 74-year-old woman, the claim is broadly supported: protein meals generally produce a somewhat smaller acute MPS response than in younger adults, but responsiveness is retained and may be substantially improved by adequate protein quality/dose, leucine-rich amino acids, resistance exercise, and avoiding prolonged inactivity.