The Impact of Whey and Soy Protein Supplementation on Resistance Training in Young Adults: A Systematic Review and Meta-Analysis

Protein supplementation, particularly whey and soy protein, are widely used by individuals engaged in resistance exercise training (RET) to enhance lean body mass (LBM) and muscle strength. However, their effectiveness remain unclear due to conflicting study results. This systematic review and meta-analysis evaluated the effect of whey and soy protein supplementation on amino acid bioavailability, LBM, and strength performance in healthy young adults engaged in RET. Database searches were conducted in Cochrane, EBSCO Host, PubMed, and Scopus from inception to October 19, 2024 using a pre-defined search strategy. Initial screening resulted in a total of 1,813 studies that met the eligibility criteria. The inclusion criteria required participants to be trained or untrained young adults aged 18-30 years engaged in RET and taking either whey or soy protein in the form of concentrate or isolate with the primary outcome of LBM and secondary outcomes of bench press, squat, or plasma essential amino acid (EAA). The studies were assessed for risk of bias using the Cochrane RoB 2 tool, and a meta-analysis was conducted using a random-effects model. A total of 12 studies with 261 participants were included after full-text screening with the main reason for exclusion being wrong population. The analysis found no significant effect of either whey or soy protein supplementation on LBM. However, protein supplement increased peak plasma total EAA with whey protein significantly improved bench press (mean difference [MD] 8.87; 95% CI: 5.95-11.79) and squat performance (MD 9.60; 95% CI: 5.61-13.60), with low to no heterogeneity. These findings suggest whey protein supplementation can enhance strength without significantly altering LBM in young adults. However, further large-scale, high-quality randomized controlled trials are needed to establish definitive conclusions on the effects of protein supplementation RET. The review was registered August 30, 2024 in PROSPERO (CRD42024598070).