Synergistic Effect of Increased Total Protein Intake and Strength Training on Muscle Strength: A Dose-Response Meta-analysis of Randomized Controlled Trials
What this study found
Protein supplementation improved muscle strength primarily when combined with resistance training. Across all trials, the intergroup difference in muscle strength percentage change was MD 1.40% (95% CI 0.55 to 2.24); with resistance training the effect was MD 2.01% (95% CI 1.09 to 2.93), while without resistance training it was MD 0.13% (95% CI -1.53 to 1.79). The dose-response with resistance training was 0.72% (95% CI 0.40 to 1.04%) per 0.1 g/kg BW/d increase in total protein intake up to about 1.5 g/kg BW/d, beyond which no further gains were seen. Isotonic strength improved, but…
- Study & population
- Dose-response meta-analysis of randomized controlled trials in adults aged 19 to 87 years (mean age 55.6 years), with both women and men represented.
- Intervention
- Active interventions increased total protein intake, usually through protein-rich test foods or beverages added to usual meals; 4 trials altered the meal content itself.
- Key limitation
- This was a synthesis of heterogeneous trials with wide variation in protein dose, delivery method, and intervention duration, which ranged from 3 weeks to 2 years.
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Open PDFOriginal abstract
Background Protein supplementation augments muscle strength gain during resistance training. Although some studies focus on the dose-response relationship of total protein intake to muscle mass or strength, the detailed dose-response relationship between total protein intake and muscle strength increase is yet to be clarified, especially in the absence of resistance training. Objective We aimed to assess the detailed dose-response relationship between protein supplementation and muscle strength, with and without resistance training. Design Systematic review with meta-analysis. Data Sources PubMed and Ichushi-Web (last accessed on March 23, 2022). Eligibility Criteria Randomized controlled trials investigating the effects of protein intake on muscle strength. Synthesis Methods A random-effects model and a spline model. Results A total of 82 articles were obtained for meta-analyses, and data from 69 articles were used to create spline curves. Muscle strength increase was significantly augmented only with resistance training (MD 2.01%, 95% CI 1.09–2.93) and was not augmented if resistance training was absent (MD 0.13%, 95% CI − 1.53 to 1.79). In the dose-response analysis using a spline model, muscle strength increase with resistance training showed a dose-dependent positive association with total protein intake, which is 0.72% (95% CI 0.40–1.04%) increase in muscle strength per 0.1 g/kg body weight [BW]/d increase in total protein intake up to 1.5 g/kg BW/d, but no further gains were observed thereafter. Conclusion Concurrent use of resistance training is essential for protein supplementation to improve muscle strength. This study indicates that 1.5 g/kg BW/d may be the most appropriate amount of total protein intake for maintaining and augmenting muscle strength along with resistance training.