If 1.6g/kg builds muscle and 2.2g/kg builds slightly more, does 3g/kg or 4g/kg build even more than that? The research says no, consistently — and understanding why is more useful than just memorizing the number.
What the dose-response research actually shows
Multiple meta-analyses, including a frequently cited 2018 review by Morton et al. pooling data across dozens of resistance training studies, plot protein intake against measured muscle and strength gains and find a clear plateau: benefits climb steadily from low intake up through roughly 1.6g/kg, continue with diminishing but still real returns up to around 2.2g/kg, and essentially flatten beyond that — additional protein past this point doesn't correlate with additional muscle gain in the pooled data, even in heavily trained, calorie-surplus populations.
Why the body doesn't just "use more" indefinitely
Muscle protein synthesis is triggered and regulated by a signaling cascade (see our leucine threshold guide), not a simple more-input-equals-more-output relationship. Once that signaling pathway is fully activated by an adequate protein dose, additional amino acids beyond what the pathway can use for that window don't create a proportionally larger building response — they're used for other body functions, or their carbon skeletons are used for energy, but they're not converted into extra muscle tissue just because they're available.
Is excess protein actively harmful, though?
For a healthy person with normal kidney function, no strong evidence points to intake up to 3-4g/kg as actively harmful in the research (see our kidney health guide) — it's simply not more effective, not dangerous. The practical cost is usually opportunity cost: calories and money spent on protein beyond the useful range could go toward carbohydrates supporting training performance, fats supporting hormone production, or fiber-rich foods supporting the gut and satiety benefits discussed in our fiber tradeoff guide.
Practical takeaway
1.6-2.2g/kg captures essentially all of the muscle-building benefit the research can currently demonstrate. Pushing meaningfully past that ceiling isn't dangerous for most healthy people, but it's also not doing the extra work the "more is always better" framing of protein-maxxing content implies.