Reviews/Dietary Protein and Muscle/No extra gain above 1.6 g per kg
Training Adaptations · DPM-TRA-02 · v2
Across several independent trials, giving people more protein than a moderate amount did not add extra muscle or strength when they were doing resistance training [2][5][6][1][4], and plant-based high-protein diets built muscle just as well as meat-based ones [11]. The catch is that the best-designed trials only pushed intake up to about 1.6 grams per kilogram and stopped there [2][5], so they show benefits level off by 1.6 rather than proving nothing is gained above it. The one study that clearly went higher (1.8 versus 2.9 g/kg) looked at recovery and muscle soreness, not actual muscle growth [3]. One supplement trial even found a bit more muscle thickness with protein in the weakest participants [8], cutting against a blanket no-benefit statement. Because no included trial directly pits about 1.6 against a clearly higher intake measuring muscle mass, the panel supported the claim's general direction but did not treat the exact 1.6 threshold as settled.
Every included RCT that raised protein above moderate levels reported no added muscle or strength benefit with resistance training: moderate versus ~1.6 g/kg did not potentiate strength or lean mass [2], a high-protein arm in seniors produced only minor body-composition change and no performance gain [5], 1.4 versus 0.8 g/kg did not affect muscle volume or strength in older women [6], and supplement-versus-placebo designs showed training adaptations occurred regardless of the extra protein [1][4]. Vegan and omnivorous high-protein diets (~1.8–2.0 g/kg) produced comparable lean-mass and fibre gains [11]. The direction is consistent, but the strongest designs cap intake at ~1.6 g/kg [2][5], and the only clearly supra-1.6 comparison, 1.8 versus 2.9 g/kg, assessed creatine kinase, soreness and phase angle rather than muscle accretion [3]. The contested point: The evidence divides on whether a plateau reached by ~1.6 g/kg demonstrates that intake above 1.6 adds nothing, since the on-target trials stop at the boundary [2][5] and the only higher-dose contrast measures recovery, not muscle [3]. A further split comes from [8], where thickness increases were significantly greater in the protein group than placebo in the weakest subjects, a pro-protein signal the blanket claim does not accommodate.
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Threshold not interrogated: the strongest designs cap intake at the boundary — [2]'s HIGH arm is '∼1.6 g·kg-1·day-1' and [5] reaches ~1.6 — so they show a plateau by 1.6, not that intake ABOVE 1.6 adds nothing.
Outcome indirectness: [3] is the only clearly supra-1.6 comparison (1.8 vs 2.9 g/kg) but measures creatine kinase, soreness and phase angle, not muscle mass or hypertrophy, so it cannot carry a muscle-accretion claim.
Where it remains uncertain. The strongest designs cap intake at ~1.6 g/kg [2][5] and the single supra-1.6 trial (1.8 vs 2.9 g/kg) measured recovery not hypertrophy [3], while [8] found greater thickness with protein in the weakest subjects.
Aleatory
The supra-1.6 and short-term trials are small — [3] N=14, [4] N=18 — leaving a small genuine hypertrophy difference within the noise.
Epistemic
No included trial compares ~1.6 g/kg against a clearly higher intake on muscle mass; [2] and [5] cap at ~1.6 and [6] at 1.4, so the above-1.6 region is unmeasured for hypertrophy.
Inferential
The only clearly supra-1.6 contrast [3] (1.8 vs 2.9 g/kg) measures creatine kinase, soreness and phase angle, so muscle-accretion conclusions are inferred from recovery markers.
The load-bearing papers from a corpus of 12, each classified by what it does to the claim. Every DOI is taken from the corpus the claim was graded on.
No hypertrophy benefit of added protein once intake is adequate
“protein supplementation did not enhance resistance exercise-induced increases in myofiber hypertrophy, satellite cell content, or myonuclear addition in young healthy men”
Panel auditInternal validity: medium · scope of inference: Young healthy men; whether a protein supplement adds to training-induced hypertrophy when baseline intake is adequate.Key limitations: no total g/kg intake reported · supplement-vs-placebo not a high-vs-moderate total-intake contrast · young men only
Direct test of moderate (~1.0) vs higher (~1.6 g/kg); no added strength or LBM — supports plateau at or by 1.6
“higher protein intake above moderate amounts does not potentiate resistance training adaptations in previously untrained middle-aged adults”
Panel auditInternal validity: medium · scope of inference: Previously untrained middle-aged adults; whether ~1.6 g/kg beats ~1.0 g/kg for training adaptations.Key limitations: high arm at 1.6, not above it · muscle mass only an exploratory outcome · untrained middle-aged adults
Only comparison above 1.6 (1.8 vs 2.9 g/kg); no benefit, but on recovery markers rather than muscle mass
“a short term PROHIGH diet did not improve markers of muscle damage or soreness in comparison to a PROMOD approach following repeated days of intensive training”
Panel auditInternal validity: medium · scope of inference: Resistance-trained individuals; short-term recovery, not muscle accretion, across two above-threshold intakes.Key limitations: no muscle-mass outcome · only 10 days · n=14
3 of 12 papers shown. The full review lists all of them, with the panel’s arbitration →
Claims are graded at each quarterly release, and re-graded between releases only when a pivotal trial lands. Every change is a new version of the claim.
The convergent no-added-benefit evidence supports the claim's spirit, but no included primary trial directly compares ~1.6 against a clearly higher intake on a muscle-mass outcome, so confidence stays in the Uncertain band.
Release 2026-q4 re-graded every claim from its corpus under protocol v0.19. An earlier release's grade is shown for the record; it came from an earlier protocol and is not a movement.
Assumptions that carry weight but are not themselves established.
The panel records the gap that would most move the claim, and the study that would close it.
Direct ~1.6 versus clearly-higher intake on muscle mass. The exact above-1.6 region is interrogated only indirectly; the on-target designs [2][5] cap at the boundary. The panel rates this the highest-importance open gap for the claim, and names the study design that would close it: A longer RCT randomising trained participants to ~1.6 versus ~2.2+ g/kg total daily intake with resistance training, measuring muscle volume and fibre CSA.
Open question: Does total protein intake clearly above 1.6 g/kg/day add muscle mass beyond ~1.6 g/kg during resistance training? Why it is still open: No included trial compares ~1.6 against a clearly higher intake on a muscle-mass outcome; [2] and [5] cap at ~1.6 and [3] measures recovery.
Priors is a sceptical first reader, not peer review, and not medical advice.
Release 2026-q4 · graded 21 Oct 2026 · protocol v0.19