Does Protein Ingestion Timing Affect Exercise-Induced Adaptations? A Systematic Review with Meta-Analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized controlled trials
PubMed 40647175 · doi:10.3390/nu17132070
What was done
A systematic review and meta-analysis of randomized controlled trials was conducted across PubMed, Web of Science, and Scopus up to January 15, 2024 (PROSPERO: CRD42023464503). Eligible studies were randomized trials directly comparing protein supplementation before versus after exercise sessions for a minimum duration of 4 weeks. Risk of bias was assessed using a critical appraisal checklist for RCTs. Random-effects meta-analyses evaluated outcomes of repeated maximum (RM) strength (chest press and leg press) and lean body mass.
What was found
Of 3,311 identified records, 6 reports representing 5 studies met inclusion criteria: - Chest press RM: No timing effect (SMD: 0.07; 95% CI: -0.248 to 0.395; I² = 0%, p = 0.653). - Leg press RM: Ingesting protein before training showed greater strength gains than after training (SMD: 0.70; 95% CI: 0.005 to 1.388; I² = 31%, p = 0.048), but the subgroup difference between chest press and leg press was not statistically significant (p = 0.07). - Lean body mass: No timing effect (SMD: -0.08; 95% CI: -0.398 to 0.244; I² = 0%, p = 0.641).
Why it matters
By isolating studies that directly compared pre-exercise to post-exercise protein ingestion head-to-head, this analysis confirms that protein timing relative to workouts does not meaningfully alter lean body mass adaptations.
Limits
The total evidence base is small, comprising only 5 studies (6 reports). The abstract does not provide the total participant count, participant training status, sex, age, or daily total protein intakes, and the leg press effect estimate has wide confidence intervals.
Cited by
- supports Multiple consecutive meta-analyses show that specific protein timing and intake protocols do not significantly affect muscle strength gains.