A systematic review and meta-analysis: Effects of protein hydrolysate supplementation on fat-free mass and strength in resistance-trained individuals.

The quality of the existing evidence on the effects of protein hydrolysate supplementation on fat-free mass (FFM) and upper and lower body strength under resistance exercise intervention has not been evaluated. We conducted a structured literature search in PubMed, Web of Science, Cochrane Library, and Scopus database. A random effect model was used with continuous data of FFM and upper and lower body strength for healthy participants over 18 years old who received resistance training for 4 weeks and took protein hydrolysate or equivalent control supplements. Sensitivity and subgroup analyses were also conducted. Data from 330 participants in eight studies showed that supplemental protein hydrolysate had a positive effect on the FFM (n = 13, SMD = 0.36, 95% confidence interval (CI): 0.16-0.56,  = 0.000) and lower (n = 7, SMD = 0.43, 95% CI: 0.16-0.69,  = 0.001) and upper (n = 5, SMD = 0.17, 95% CI: -0.06-0.41,  = 0.145) body strength of resistance-trained individuals compared with placebo, showing an increase in physical fitness and muscle strength. However, the current evidence is insufficient to establish ingestion recommendations.