The Short Answer: ~1.6 g/kg a Day
If you lift to build muscle, a large meta-analysis suggests your daily protein target is lower than the gym-floor myths claim. The review, published in the British Journal of Sports Medicine, pooled 49 randomized controlled trials and 1,863 healthy adults. Its break-point analysis put the plateau at about 1.62 g of protein per kg of body weight per day. Beyond that, extra protein did not further increase resistance-training-induced gains in fat-free mass (FFM).
The upper end of the 95% confidence interval reached roughly 2.2 g/kg/day. That gives you a practical range: 1.6 g/kg is the point where benefits level off on average, and 2.2 g/kg is a reasonable ceiling if you want a margin of safety.
What That Looks Like on a Plate
The math is simple:
- 70 kg (154 lb): about 112 g/day at 1.6 g/kg, up to about 154 g at 2.2 g/kg
- 80 kg (176 lb): about 128 g/day, up to about 176 g
- 90 kg (198 lb): about 144 g/day, up to about 198 g
These figures are total daily protein from food and supplements combined. They are not an amount to add on top of what you already eat. Many people eating a decent diet already get most of the way there.
What the Trials Showed
The researchers included only randomized controlled trials with at least six weeks of resistance exercise training that also used protein supplementation. Compared with training alone, protein supplementation produced these average improvements:
- Strength (1RM): +2.49 kg
- Fat-free mass: +0.30 kg
- Muscle fiber cross-sectional area: +310 µm²
- Mid-femur cross-sectional area: +7.2 mm²
All of these were statistically significant. The gains are real but modest. Protein supplementation is an enhancer, not a replacement for progressive overload, adequate calories and consistent training.
Who Benefits Most?
Two moderators stood out in the analysis.
Trained lifters. Protein supplementation was more effective in resistance-trained individuals, who gained an extra 0.75 kg of FFM compared with less-trained people. One plausible explanation is that experienced lifters have less room for rapid "newbie gains," so nutrition details matter more. That is an interpretation, not something the data prove.
Younger adults, more than older ones. The effect of supplementation on FFM shrank with age, by about 0.01 kg per year of age. Older adults are not off the hook, though. Aging is associated with blunted muscle responses to protein, and the study does not say older lifters should eat less. It says that in these trials, supplementation added less on top of training as age increased. Older lifters should still aim for adequate total intake and not treat the plateau as a ceiling to stay under.
Whey, Shakes and Real Food
Most supplementation trials rely on convenient, protein-dense products such as whey powders and ready-to-drink shakes. A shake is a practical way to close a gap: a typical scoop delivers around 20 to 25 g of protein with little prep. The review's finding is about total protein intake, not a magic product. If you reach about 1.6 g/kg from chicken, eggs, dairy, legumes and tofu, the plateau logic still applies.
A simple approach:
- Calculate your target (body weight in kg × 1.6).
- Spread it over three to five meals or snacks.
- Use a shake only to fill the gap between what you eat and your target.
- Stop chasing extra grams once you are in the 1.6 to 2.2 g/kg zone.
Caveats Worth Knowing
The 1.6 g/kg figure is an average break point, not a hard biological limit. The confidence interval spans a wide range, so individual needs vary. The analysis also measured fat-free mass, a proxy for muscle that includes water, organs and other non-fat tissue.
The authors disclosed a potential conflict of interest: senior author Stuart Phillips has received funding and honoraria from the US National Dairy Council, which supported some of the trials reviewed. That does not invalidate the findings, but it is context for readers weighing them.
The review also covered only healthy adults. It does not address people with kidney disease or other medical conditions, who should consult a clinician about protein targets.
The Bottom Line
For most people lifting to gain muscle, around 1.6 g/kg/day is the point of diminishing returns, and 2.2 g/kg is a sensible upper bound. Eating well beyond that is unlikely to speed up muscle growth. Put the effort into training quality, sleep, total calories and consistency, and use protein shakes where they make hitting your number easier.
