Evidence explainerWhey protein (and other protein powders)
How Much Protein Builds Muscle? Gains Leveled Off Near 1.6 g/kg a Day
Protein powder helps most when your diet falls short of a total that is easy to calculate. A 49-trial analysis found where the extra gains stopped.
Key takeaways
- Across 49 resistance-training trials (1,863 people), protein supplements added about 2.5 kg to one-rep-max strength and 0.3 kg to fat-free mass [2].
- Extra fat-free mass gains stopped beyond a total protein intake of about 1.62 g/kg/day [2].
- ODS cites 1.2 to 2.0 g/kg/day for athletes, versus an RDA of 0.8 g/kg/day for healthy adults [1].
- The benefit shrank with age and was larger in people who already lift [2].
- No UL is set for protein; diets of two to three times the RDA did not appear to harm kidney function or bone health [1].
The evidence, graded
Pulled from our monograph evidence tables. Grades follow our evidence-grading policy.
- Grade AImprovedStrength and fat-free mass gains during resistance trainingProtein supplements added about 2.5 kg to one-rep-max strength gains and 0.3 kg to fat-free mass gains. The effect on fat-free mass shrank with age and was larger in resistance-trained people.
- Grade BMixedStrength, physical performance and body composition in adults 60+Whey did not improve handgrip strength, walking tests, lean body mass or fat mass overall. With resistance training, it modestly improved lower-body strength (SMD 0.25).
The number the trials point to
A 2018 meta-analysis pooled 49 randomized trials with 1,863 healthy adults doing at least 6 weeks of resistance training [2]. Protein supplements added 2.49 kg to one-rep-max strength gains and 0.30 kg to fat-free mass gains versus control [2].
The key finding was a ceiling. Once total protein intake passed 1.62 g/kg/day, extra protein produced no further gains in fat-free mass [2]. That is total protein from food and supplements, not powder alone.
RDA vs athlete targets
The RDA is 0.8 g/kg/day for healthy adults and 0.85 g/kg/day for adolescents [1]. Newer data suggest athletes need 1.2 to 2.0 g/kg/day, and possibly more during short periods of intense training or calorie cutting [1].
Many people already get a lot. In NHANES 2007 to 2008, average daily protein intake was 100 g for men and 69 g for women [1]. Whether a powder adds anything depends on where your own total sits against those targets.
How much at a time
Most complete proteins are about 40% essential amino acids, so a meal or snack with 25 g of protein supplies about 10 g of them [1]. The AND, DoC and ACSM suggest 0.3 g/kg of high-quality protein (about 20 g for a 150 lb person) within 2 hours after exercise and then every 3 to 5 hours [1].
Timing matters less than many think; we cover that in the anabolic window.
Who gains most, and who gains least
In the 49-trial analysis, the effect on fat-free mass got smaller with age and was larger in people with resistance-training experience (0.75 kg) [2].
In adults 60 and older, a 2024 meta-analysis of 30 trials (2,105 people) found whey did not improve grip strength, walking tests or lean mass overall, though it modestly improved lower-body strength when combined with resistance training [3]. Training is what made the difference there.
Is more protein risky?
The Food and Nutrition Board has not set a UL for protein, but advises caution with high intakes from foods plus supplements because data on adverse effects are limited [1]. High-protein diets of two to three times the RDA do not appear to compromise kidney function or bone health in healthy people [1].
A systematic review of 11 documents linked chronic, excessive whey use to kidney and liver effects, especially with a sedentary lifestyle [4]. Anyone with kidney disease should set a protein target with their clinician. Whey and casein come from milk, so check labels if you avoid dairy [1].
Quick answers
Is 1.6 g/kg the maximum you should eat?
It is where extra muscle gains leveled off in one large meta-analysis, not a safety limit [2]. ODS cites up to 2.0 g/kg/day for athletes, and no UL is set [1].
Does whey work better than plant protein?
In a meta-analysis of 9 trials, soy and animal proteins, including whey, gave similar gains in strength and lean mass [5]. Rice protein lacks isoleucine and soy lacks methionine, so many plant products blend sources [1].
Do I need protein powder at all?
Not if food covers your target; ODS lists meats, poultry, seafood, eggs, dairy, beans and nuts as protein sources and describes supplements as an option if needed [1].
Keep reading
Full monographs
Related articles
- The Anabolic Window: A Meta-Analysis Found Total Protein Mattered More Than Timing
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References
- [1]Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2024.
- [2]A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med, 2018.
- [3]Effectiveness of whey protein supplementation on muscle strength and physical performance of older adults: A systematic review and meta-analysis of randomized clinical trials. Clin Nutr, 2024.
- [4]Whey protein supplementation and its potentially adverse effects on health: a systematic review. Appl Physiol Nutr Metab, 2021.
- [5]No Difference Between the Effects of Supplementing With Soy Protein Versus Animal Protein on Gains in Muscle Mass and Strength in Response to Resistance Exercise. Int J Sport Nutr Exerc Metab, 2018.