There has been considerable work defining protein needs to maintain lean body mass and muscle function in a variety of age groups and among those with differing health status. A newer question posed by scientists working in this area is the timing of protein intake relative to exercise bouts and the optimal distributions of intake throughout the day. However, there remains a great deal of debate because of the differing responses obtained by the studies. In an attempt to better understand the effect of timing of protein supplementation on body composition and muscle function, Wirth and colleagues conducted a systematic review and meta-analysis of the existing literature. They published the results of this study in the June 2020 issue of The Journal of Nutrition.

Data for this work were identified through searches of multiple databases. The authors identified randomized controlled trials for inclusion in their analyses. Variables of interest for the meta-analysis included lean body mass, handgrip strength, and leg press strength, which were pooled by age group and timing of protein intake. A total of 65 studies were included, providing observations of 2907 participants.

Lean body mass was improved in adults and older adults with protein supplementation, but it did not improve handgrip strength in older adults or leg press strength in adults or older adults. Exercise training appeared to not affect the outcomes, and the timing of protein intake did not influence the responses in lean body mass or strength for handgrip or leg press. The authors concluded that there is a positive impact of protein supplementation on the lean body mass of adults and older adults that occurs independently of the timing of consumption. They also state the need for further work to determine if there is any benefit on muscle strength as the outcomes were not definitive.

References Wirth J, Hillesheim E, Brennan L. The role of protein intake and its timing on body composition and muscle function in healthy adults: A systematic review and meta-analysis of randomized controlled trials. The Journal of Nutrition, Volume 150, Issue 6, June 2020, Pages 1443–1460, https://doi.org/10.1093/jn/nxaa049.

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Nancy Turner, PhD

Nancy Turner is a Professor of Nutrition at Michigan State University.  Her research focus is on the role of diet on colon cancer and inflammatory bowel disease.  She is the author of many papers on this topic, as well as the co-editor of a book, and co-author of a textbook.