The Role of Protein Intake and its Timing on Body Composition and Muscle Function in Healthy Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized controlled trials
PubMed 32232404 · doi:10.1093/jn/nxaa049
What was done
This systematic review and meta-analysis searched PubMed, Web of Science, CINAHL, and Embase through March 2019 for randomized controlled trials evaluating the effect of protein supplementation and protein intake timing on body composition (lean body mass [LBM]) and muscle function (handgrip strength, leg press strength, and muscle synthesis) in healthy adults. Analyses were stratified by age (18–55 vs. >55 y) and intake timing. Quality of evidence was evaluated using GRADE.
What was found
Across 65 included studies with 2,907 participants (1,514 men, 1,380 women, 13 unknown sex), protein supplementation significantly increased LBM in adults aged 18–55 y (mean difference [MD] 0.62 kg; 95% CI: 0.36, 0.88; 26 studies pooled for LBM) and older adults (MD 0.46 kg; 95% CI: 0.23, 0.70). Protein supplementation did not significantly improve handgrip strength in older adults (MD 0.26 kg; 95% CI: -0.51, 1.04; 8 studies) or leg press strength in adults (MD 5.80 kg; 95% CI: -0.33, 11.93; 24 studies total for leg press) or older adults (MD 1.97 kg; 95% CI: -2.78, 6.72). Subgroup analyses showed no effect of specific protein intake timing on LBM or strength. Removing studies without exercise training had no impact on outcomes, and data regarding muscle synthesis were scarce and inconclusive.
Why it matters
Protein supplementation produces modest increases in lean body mass in both younger and older adults irrespective of intake timing, casting doubt on the necessity of specific protein timing strategies for muscle mass.
Limits
Data on muscle protein synthesis were scarce and inconclusive. Functional strength outcomes (handgrip and leg press) did not show statistically significant improvements, and only a fraction of included studies provided data for each specific meta-analysis outcome.
Cited by
- supports Multiple consecutive meta-analyses show that specific protein timing and intake protocols do not significantly affect muscle strength gains.