Protein ingestion to stimulate myofibrillar protein synthesis requires greater relative protein intakes in healthy older versus younger men.
Level 3 - non-randomized controlled study
Retrospective pooled dose-response analysis of controlled metabolic tracer experiments
PubMed 25056502 · doi:10.1093/gerona/glu103
What was done
Researchers retrospectively analyzed pooled data from metabolic tracer experiments measuring myofibrillar protein synthesis (MPS) via primed constant infusion of L-[ring-13C6]phenylalanine. They evaluated healthy older (~71 years) and younger (~22 years) men following a single bolus ingestion of 0 to 40 g of high-quality dietary protein. Ingested protein doses were normalized to total body mass and lean body mass (LBM), with dose-response relationships analyzed via biphase linear regression and breakpoint modeling.
What was found
Basal MPS did not differ between older (0.027 ± 0.04%/h; mean ± 95% CI) and younger men (0.028 ± 0.03%/h; p = .53). The initial slope of the MPS response to increasing protein doses was significantly lower in older men (p < .05). Breakpoint analysis showed MPS plateaued at 0.40 ± 0.19 g/kg body mass in older men versus 0.24 ± 0.06 g/kg in younger men (p = .055). Normalized to lean body mass, the plateau occurred at 0.60 ± 0.29 g/kg LBM in older men versus 0.25 ± 0.13 g/kg LBM in younger men (p < .01).
Why it matters
This establishes relative per-meal protein thresholds for older adults, showing that age-related anabolic resistance requires older men to consume roughly 67% more protein per unit of body mass (and over double per unit of lean mass) than young men to maximally stimulate muscle protein synthesis.
Limits
The total participant count (n) is not reported in the abstract. The study is a retrospective secondary analysis of acute, single-meal laboratory tracer studies. It included only healthy men, so findings cannot be directly generalized to women, frail elderly populations, or long-term chronic muscle mass maintenance.
Cited by
- supports Older adults require at least 25 to 40 grams of protein per meal to reach the threshold that stimulates muscle protein synthesis.