Protein recommendations are a case study in how a correct number becomes wrong advice when its purpose is forgotten. The RDA — 0.8 g/kg — was derived to prevent deficiency in average adults. It was never asked whether it optimizes muscle retention, recovery, or aging. Those questions have different answers.
What the evidence layers show
| Population | Evidence-based range | Why |
|---|---|---|
| Sedentary adults | 0.8–1.2 g/kg | RDA floor; slight margin is free insurance |
| Strength training | 1.6–2.2 g/kg | Synthesis maxes ~1.6; extra covers hard blocks and mistakes |
| Cutting (deficit) | 1.8–2.4 g/kg (higher for lean) | Muscle preservation is hardest exactly when calories are lowest |
| Endurance | 1.4–1.8 g/kg | Amino oxidation rises with mileage |
| 65+ | 1.5–2.0 g/kg | Anabolic resistance — older muscle needs bigger doses |
The key trials: a 2018 meta-regression (Morton et al.) found protein intake benefits to strength and lean mass plateau around 1.6 g/kg overall, with the confidence interval extending to ~2.2 — and later work shows the plateau shifts higher in deficit and with age.
Distribution — the forgotten half
Muscle-protein synthesis responds to doses, not just totals: roughly 0.4–0.55 g/kg per meal (30–45 g for most trainees) triggers near-maximal synthesis, and the response partially refractory within a few hours. Practically: 3–5 protein feedings, roughly even, beat one 150 g dinner followed by nothing. Total still dominates — but distribution is the cheapest remaining gain.
The kidney question, settled (mostly)
Decades of data in healthy adults — including bodybuilders at 3+ g/kg for a year and 1,500+ participant cohort studies — find no harmful effect of high protein on kidney function, bone density, or hydration. The exceptions are exactly where clinicians have always said: existing chronic kidney disease, where protein is prescribed and restricted. If your kidneys are healthy, the evidence says eat the protein; if they are not, this article is not your doctor.
Practical summary
- Set the total by goal with our protein calculator: 1.6–2.2 g/kg active, up to 2.4 cutting.
- Split it 3–5 ways, 30–45 g per meal.
- Lean sources first (they carry fewer calories per gram of protein); powders are logistics, not magic.
- Re-check the total when your weight, goal, or age band changes.