Comparison of basal whole-body protein kinetics and muscle protein synthesis between young and older adults.
Level 4 - case-series / case-control
Cross-sectional comparison between young and older adult cohorts
PubMed 33278070 · doi:10.14814/phy2.14633
What was done
Basal whole-body protein kinetics (synthesis, breakdown, and net balance) and muscle fractional synthetic rate (FSR) were measured using stable isotope tracers (L-[ring-2H5]phenylalanine and L-[ring-2H2]tyrosine) in 91 young (18–38 years, 52% female) and 66 older (51–81 years, 53% female) healthy adults.
What was found
There were no group-by-sex interaction effects (p > .05). Older adults had higher whole-body protein synthesis (mean difference old vs. young ± SE: 28.54 ± 8.15 mg/kg LBM/hr; p = .001) and breakdown (15.44 ± 7.33 mg/kg LBM/hr; p = .038), resulting in a less negative net balance (young: -31.22 ± 7.42 vs. old: -18.11 ± 21.60 mg/kg LBM/hr; p < .001). Basal muscle FSR was not significantly different between age groups (difference: 0.007 ± 0.003 %/hr; p = .052). Across all ages, females had higher whole-body protein synthesis (difference: 19.10 ± 7.00 mg/kg LBM/hr) and breakdown (difference: 19.22 ± 6.31 mg/kg LBM/hr; both p < .01) compared to males.
Why it matters
These findings suggest that basal age-related muscle loss is not driven by reduced basal muscle protein synthesis or a more negative basal whole-body protein balance, highlighting higher basal turnover and amino acid recycling in older adults.
Limits
The study is cross-sectional, preventing causal or longitudinal tracking of sarcopenia progression. Measurements were restricted to the postabsorptive (basal) state, leaving postprandial responses unmeasured, and participants were exclusively healthy adults, which may not generalize to frail older populations.
Cited by
- supports Human muscle protein turnover (breakdown and synthesis) occurs at a rate of 1 to 2% per day, independent of age.