“Whey protein builds muscle.”
Whey protein does help build muscle, but only as a small add-on to strength training.
If you strength train and find it hard to get enough protein from food, whey is a convenient way to add some, and it adds a little extra muscle on average. It will not build muscle without training, and protein from food works too.
Train first. If your protein intake is below about 0.7 grams per pound of body weight a day, a scoop of whey is one easy way to close the gap.
Safety note: Whey comes from milk, so it is not suitable for people with a milk allergy.
Training trials show whey adds a small amount of extra muscle and strength on top of resistance training, and protein supplements help most when total protein intake is low. It is mostly true, with moderate confidence, because training does most of the work, the added effect is modest, and the trials vary a lot.
Whey protein does help build muscle, but only as a small add-on to strength training. In a 2026 review of 78 trials, whey beat a placebo by a small margin for both lean mass and strength, and in a 49-trial review, protein supplements added about two-thirds of a pound of lean mass on average. In the trials, training did most of the work, and extra protein stopped adding lean mass once total intake passed about 0.7 grams per pound of body weight a day.
Whey is digested quickly and raises blood leucine more than casein or soy. In a small lab study of 18 young men, whey raised muscle building after exercise about 31 percent more than soy and about 122 percent more than casein, but short-term muscle building measured in a lab is not the same as more muscle over months.
- Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, Aragon AA, Devries MC, Banfield L, Krieger JW, Phillips SM. 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. British Journal of Sports Medicine. 2018;52(6):376-384. DOI: 10.1136/bjsports-2017-097608. PMID: 28698222. PMCID: PMC5867436. Correction: Br J Sports Med. 2020;54(19):e7, DOI: 10.1136/bjsports-2017-097608corr1, PMID: 32943392
- Drummond MDM, Silva RAD, Junior NC, Melo MS, Ferreira MHL. Which Protein-Based Dietary Supplements Most Effectively Enhance Fat-Free Mass and Strength Gains in Healthy Adults Undergoing Resistance Training? A Network Meta-Analysis. Translational Sports Medicine. 2026;2026:5557511. DOI: 10.1155/tsm2/5557511. PMID: 41635649. PMCID: PMC12862422
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