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Researchers, led by Stuart Phillips, Kinesiology, have found dietary protein supplements can significantly improve muscle strength and size when taken by healthy adults who lift weights. The study, published online in the British Journal of Sports Medicine and reported in The New York Times, also found that the effects of protein supplements are not as big as some supplement companies say.

Researchers combed through thousands of studies searching for specific criteria, including randomized controlled trials, human participants and study durations of at least six weeks. In all, they analyzed 49 high-quality individual studies with 1863 participants.

The benefits of protein supplements increase with resistance training experience but become less effective in older adults, pointing to a need for greater supplementation to reach optimal results as we age. And there is a limit to the amount of protein that is beneficial, plateauing at roughly 1.6 grams of dietary protein per kilogram of bodyweight per day.

“There have been mixed messages sent to clinicians, dieticians, and ultimately practitioners about the efficacy of protein supplementation,” says Robert Morton, lead author on the study and a PhD student in the Exercise Metabolism Research Group at McMaster. “This meta-analysis puts that debate to rest.”