Does Protein Ingestion Timing Affect Exercise-Induced Adaptations? A Systematic Review with Meta-Analysis

What the research tells us

Direct comparisons of protein before versus after training found no clear difference in lean mass (SMD −0.08, 95% CI −0.398 to 0.244) or chest-press strength (0.07, −0.248 to 0.395). A leg-press signal favoured before-training intake, but was based on only two studies.

Scope & interpretation

Authors rated certainty low for lean mass and chest press, and very low for leg press and muscle thickness. The leg-press estimate was SMD 0.70 (0.005–1.388), p=.048; the chest-versus-leg subgroup difference was not significant (p=.07). Dietary control varied, and one study reported differing protein intake. A null result does not establish equivalence.

• Full text in PubMed Central ↗

Study at a glance

POPULATION & SAMPLE

Six reports representing five randomized studies, including trained younger adults and untrained older adults; one study included people with type 2 diabetes.

EXPOSURE / INTERVENTION / SUBJECT

Random assignment to protein before versus after repeated resistance-training sessions, generally near the session; one comparison used intake at least two hours afterward.

OUTCOMES

Lean mass, strength, fat mass and muscle thickness.

TIME FRAME

Included training interventions lasted 6–16 weeks; database search through 15 January 2024.

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