Background: Weight loss via dietary intervention results not only in loss of fat mass, but also loss of lean mass, which could conceivably reduce muscle strength. We conducted a systematic review and meta-analysis to identify how diet-induced weight loss in overweight and obese adults impacts muscle strength, as assessed by one repetition maximum strength testing, isokinetic dynamometry, isometric dynamometry, and handgrip strength testing.
Methods: 27 publications involving 33 interventions met the selection criteria. Due to variability in methodology and muscle groups tested, only isokinetic dynamometry for knee extensor strength and handgrip strength data could be meta-analysed.
Results: One repetition maximum strength testing in 13 interventions reported no significant changes, with the exception of 1 intervention that observed a decrease in upper and an increase in lower body strength compared to baseline and in response to diet-induced weight loss. Meta-analysis of the 7 interventions that assessed knee extensor strength by isokinetic dynamometry found a significant decrease relative to baseline following diet-induced weight loss (-9.0 [95% confidence interval] [-13.8, -4.1] Nm, P<0.001). Qualitative assessment of the 7 remaining interventions assessing other muscles by isokinetic dynamometry revealed a significant decrease in muscle strength in 1 intervention and non-significant differences in 6 interventions. Isometric dynamometry revealed significant decreases in muscle strength in 2 interventions, non-significant changes in 4, and significant increases in 4 interventions. Meta-analysis of 10 interventions measuring handgrip strength showed a non-significant decrease (-1.7 [-3.6, 0.1] kg, P=0.07) relative to baseline following diet-induced weight loss.
Conclusion: Isokinetic dynamometry of knee extension showed a significant decrease in muscle strength with diet-induced weight loss, and handgrip data showed an overall trend for decreased muscle strength. Further research is warranted to ensure that different types of diet-induced weight loss do not reduce muscle strength in a way that adversely impacts on long-term quality of life.