Protein builds muscle. The 'anabolic window' doesn't seem to.

Meta-analysis of randomised trials. 525 people. included trials lasted 6 to 21 weeks of resistance training (minimum 6 weeks required).

Many trials, added up. In each one, chance decided who did what.

Who: 23 RCTs of people doing resistance training; mostly untrained young men, plus some women, older adults and only 4 studies in trained lifters. 525 subjects in the muscle-growth analysis, 478 in the strength analysis

• Timing, at first glancesmall
• With total protein accounted fornone
• Timed groups ate more protein1.66 vs 1.33

More to know, from our read of the paper:

• 'Timing' was defined as protein within 1 hour before and/or after training vs no protein within 2 hours; the paper did not test a 30-minute window specifically
• Control groups' meal timing varied a lot (from ~2 hours to many hours after training), so the authors say it is difficult to determine whether a clear anabolic window exists beyond which adaptations suffer
• Most included studies used subjects inexperienced with resistance training; only 4 studies in trained subjects, so power to detect a timing effect in trained lifters was low
• Only 3 included studies matched total protein intake between groups; authors say the small number limits firm conclusions
• Causality cannot be drawn: authors acknowledge protein timing might have produced the effect and the higher protein intake could be coincidental

A meta-analysis of 23 randomized trials (525 people, 6–21 weeks of lifting). Protein within an hour of training looked like it helped muscle growth a little. But the timed groups were also eating more protein a day (1.66 vs 1.33 g/kg). Once total protein was accounted for, timing made no significant difference, and it never helped strength. Mostly beginners were studied, and the paper doesn't rule out a longer window, so timing isn't proven useless, just not proven to matter.

We read the abstract and the full text of this paper and checked every number on this page against it (16 facts, checked on 2026-09-27). The study design is named above. Cohort and other observational studies are described as linked, not proven. Found an error? Email theis@onestudyaday.com.