A new study published in The Journal of Nutrition suggests that protein quality provides a small but significant impact on muscle strength in combination with prolonged resistance exercise training in both young and old adults.

Dietary protein is important to muscle mass, strength, and function. However, there is much debate regarding the source and quality of dietary proteins in supporting muscle protein synthesis, lean body mass, and strength when combined with resistance exercise. Numerous studies have shown that resistance exercise training combined with sufficient dietary protein leads to greater gains in muscle development in both young and older adults compared to resistance training alone. However, a blunted response observed in older adults supports recommendations for higher daily protein intakes for muscle maintenance. To determine the effect of different protein sources of varying quality on acute muscle protein synthesis and changes in lean body mass and strength, when combined with resistance exercise, Leigh Breen (University of Birmingham) and colleagues performed a meta-analysis.

The study, which was conducted in accordance with procedures for systematic reviews and meta-analyses, included a total of 27 studies in young (18-35 years) and older adults (> 60 years).  Parameters included the efficacy of the quality/source of dietary protein on indices of skeletal muscle anabolism, which included post-meal muscle protein synthesis (alone or after a single bout of resistance exercise) and muscle adaptation to prolonged (<6- weeks) resistance exercise training in healthy younger and older adults.  The authors hypothesized that when matched for dose, higher-quality protein sources would be associated with greater post-meal muscle protein synthesis, both alone and after a single bout of resistance exercise. In addition, enhanced lean body mass and strength in response to prolonged resistance exercise training would be greater in older individuals. 

The results showed that a higher quality of protein had a significant positive effect on post-meal muscle protein synthesis both at rest and following resistance exercise. A higher protein quality was associated with greater strength gains with prolonged resistance exercise training.  However, there was no observed association between lean body mass and protein quality. A corresponding editorial by Stefan Pasiakos (US Army Research Institute of Environmental Medicine) and Emily Howard (Oak Ridge Institute for Science and Education) stress the need for future studies to examine protein quality in the context of typical dietary eating patterns to guide recommendations for optimizing protein intake.


Morgan PT, O Harris D, Marshall RN, Quinlan JI, Edwards SJ, Allen SL, Breen L. Protein Source and Quality for Skeletal Muscle Anabolism in Young and Older Adults: A Systematic Review and Meta-Analysis. The Journal of Nutrition, Volume 151, Issue 7, July 2021, Pages 1901–1920, https://doi.org/10.1093/jn/nxab055.

Pasiakos SM, Howard EE. High-Quality Supplemental Protein Enhances Acute Muscle Protein Synthesis and Long-Term Strength Adaptations to Resistance Training in Young and Old Adults. The Journal of Nutrition, Volume 151, Issue 7, July 2021, Pages 1677–1679, https://doi.org/10.1093/jn/nxab099.

Images via canva.com.