Do protein powders build muscle?

What the powder changes

Whey, casein, soy and other powders differ in their ingredients and how they are digested. A powder may be convenient if you need more protein, but the grams on its label do not tell you whether it will improve your strength, muscle size or recovery.

See how to store powders, shakes and bars and how to compare them.1

What the evidence can show

A controlled study can compare a particular powder with another product while participants train. Results can depend on people’s usual diet, training, age and health, as well as the length of the study and what it measures. Results for one research product do not automatically apply to every bar or shake. See collagen compared with whey.2

How much difference did research find?

A 2018 review combined 49 trials involving 1,863 healthy adults who did resistance training for at least six weeks. In studies that measured fat-free mass, groups taking protein supplements gained about 0.30 kg more on average than comparison groups. Fat-free mass includes water and other tissues as well as muscle. This does not mean each person gained 0.30 kg of muscle. Training, diets and supplements varied across the studies. One review author disclosed support and speaking fees from the US National Dairy Council.

The review also combined tests of the maximum weight a person could lift once in different exercises. On average, supplement groups improved by 2.49 kg more than comparison groups. The 95% confidence interval ran from 0.64 to 4.33 kg more, reflecting uncertainty in the estimate. This group average is not a promise for one person or every exercise.

A different measure, maximum voluntary muscle contraction, did not show a statistically significant difference. That does not prove the groups were identical. Everyone in these comparisons did resistance training, so the results do not establish what a powder does without training.4

One trial, different outcomes

In one 12-week trial, 68 healthy young men doing resistance training were randomly assigned a soy–dairy protein blend (23), whey protein (22) or a carbohydrate comparison (23). The two protein products provided about 22 g of protein a day; this describes the study, not a recommended intake. Researchers reported small differences in lean mass and did not find a statistically significant treatment difference in strength. That does not prove the groups were identical. This was one group of people; its findings do not settle every question about protein products. DuPont Nutrition & Health and public grants helped fund the trial.5

When the answer becomes less certain

More powder can also mean more calories, sweeteners or repeated ingredients. If you have a medical condition or take medicines that affect how your body handles protein, ask a qualified clinician for advice. This guide does not set an intake target or recommend a brand.

For a different situation—eating enough when a medicine reduces appetite—see food and nausea with semaglutide or tirzepatide.3