Journal Title (Medline/Pubmed accepted abbreviation): J. Int. Soc. Sports Nutr
Summary of background and research design:
- Many, but not all, studies show that increased amounts of dietary protein can help increase muscle mass and muscle strength.
- The “protein spread theory” and the “protein change theory” are two current theories that attempt to explain differences between studies that show positive effects and studies that do not show positive effects of dietary protein on muscle mass and strength.
- Protein spread theory- there must be a large enough percent difference (“spread”) in protein intake (g protein/kg body weight/day) between the high protein group and the low protein group during dietary intervention to see differences between groups.
- Protein change theory- there must be a large enough percent difference in protein intake between the diets before intervention and the diets during intervention (“change”) to observe a difference in muscle mass and strength.
Hypothesis: The difference in dietary intakes between protein and control groups (protein spread theory) and before and after intervention (protein change theory) is key in showing efficacy of protein supplements on performance enhancement.
Protocol: An extensive search was undertaken to identify all published studies that investigate the effect of increased dietary protein on muscle size and strength in an exercise setting.
Summary of research findings:
- Seventeen studies were identified that met their criteria. Ten showed that protein provided gains in muscle mass and strength; seven did not.
- Among the studies that showed a beneficial effect of protein, the average protein intake (in g/kg body weight/day) was 66.1% greater in the higher protein group vs. the lower protein group. The average difference between groups in the studies that did not show beneficial effects was 10.2%.
- Twelve studies reported dietary intake at baseline. Of the studies that showed benefits, the average increase in dietary protein intake between baseline and at intervention was59.5% vs.6.5% in the studies that showed no effect. In fact, all studies that had participants increase dietary protein intakes at least 19.5% showed muscular benefits during the study.
Key practice applications
: These data support both the protein spread theory and the protein change theory. For individuals, these data suggest that an approximate 20% increase in dietary protein- an approximate increase of about 1.31 g protein/kg body weight/day to equal a total of about 2.09 g/kg/day total is an appropriate supplement to one’s current diet in order to obtain gains in muscle strength and muscle mass, along with appropriate resistance or physical training.
There are many other factors that contribute to the amount of gains that can be made from protein supplements such as the type of protein (e.g. whey, soy, egg), the status of the participant (e.g. untrained, trains recreationally, elite athlete), current diet of the participant, age, and genetics. Therefore, this theory is likely incomplete as written. It can be improved as more evidence becomes available, but may never be true for all individuals.
Limitations: All of the differences between conditions are reported relatively without exact values of protein (in g/kg/day) taken into account. Therefore, recommendations are only estimated.
Key search terms for this article (5-7 terms): protein, protein change theory, protein spread theory, whey, muscle growth, strength, muscle mass