Mostly Proven

Claim check · Protein

Does more protein always build more muscle?

More protein, more muscle? Only up to a point, and the point is blurry.

Mostly proven

With lifting, extra protein adds a small gain. The ceiling is an estimate, not a line.

The claim

More protein always means more muscle.

What the evidence says

A meta-analysis of 49 randomized trials (1,863 healthy adults, all doing resistance training for 6 weeks or more) found that extra protein added a small gain on top of lifting: +0.30 kg fat-free mass (95% CI 0.09–0.52) and +2.49 kg on a one-rep max (0.64–4.33). In a break-point analysis across 42 study groups, gains stopped rising above a total intake of about 1.6 g per kg per day (estimate 1.03–2.20), but that break point was not statistically significant (p = 0.079). The effect shrank with age. For people over 65, a consensus group suggests at least 1.0–1.2 g per kg.

The numbers

  • Morton 2018: 49 RCTs, 1,863 participants, resistance training of 6 weeks or more; extra protein: fat-free mass +0.30 kg (0.09–0.52), one-rep max +2.49 kg (0.64–4.33); effect smaller with increasing age.
  • No further fat-free-mass gain beyond about 1.62 g/kg/day in a break-point analysis of 42 study groups (723 participants): 95% CI 1.03–2.20; the break point was not statistically significant (p = 0.079).
  • PROT-AGE 2013 (consensus): people over 65 at least 1.0–1.2 g/kg/day, more if active; severe kidney disease is an exception.

Verdict: Mostly proven

With lifting, extra protein adds a small gain. The ceiling is an estimate, not a line.

Why only this far: Small effect, wide uncertainty around the plateau (1.03–2.20 g/kg), healthy adults only, older adults’ needs rest on consensus.

Evidence level A: Randomized trials or meta-analyses of randomized trials. How verdicts work.

What we don’t know

Where exactly the ceiling is. The effect is small, and the estimate is uncertain.

Sources

Checked 15 Oct 2026. Every link opens the original paper or its PubMed record.

  1. Morton et al., Br J Sports Med 2018Meta-analysis of 49 randomized controlled trials (protein supplementation with resistance training)DOI 10.1136/bjsports-2017-097608 · PubMed 28698222A 2020 correction (Br J Sports Med 2020;54(19):e7) concerns a conflict-of-interest statement. The numbers are unchanged.
  2. Bauer et al., J Am Med Dir Assoc 2013 (PROT-AGE)Position paper / expert consensusDOI 10.1016/j.jamda.2013.05.021 · PubMed 23867520

Disclosure: one author reports grants and honoraria from the US National Dairy Council, which also supported trials in the analysis; another reported advisory work for a sports-supplement maker (2020 correction).

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