The effects of whey protein supplementation on athletic performance and body composition in adolescent soccer players: a randomized controlled trial.

Although protein supplementation is a common sports nutrition strategy, there is little research on its effects in adolescent athletes. Our objective was to assess the effects of whey protein supplementation on athletic performance and body composition in adolescent soccer players over a 10-week competitive soccer season. Adolescent athletes (n = 22; 59% female, age: 15.6 ± 0.2 [mean ± SEM] years; BMI percentile: 55.9 ± 6.2%) were randomized to consume either whey protein (PRO; n = 10; 20 g protein) or an isocaloric placebo (CON; n = 12) twice daily. Outcome measures included: estimated V̇O2max (1.5 mile run), sprint time (30 yard dash), muscle strength and endurance (quadricep isometric leg extension; maximum voluntary contraction and repetitions to fatigue, respectively), and body composition (fat mass and fat-free mass). Assessments were conducted at baseline and postintervention. V̇O2max improved in both groups (p < 0.001), with greater (p = 0.04) increases in the PRO versus CON group. Sprint time improved in both groups (p = 0.03), with no significant differences between groups. Muscle strength was similar across the study for both groups. Muscular endurance declined in the PRO group compared to CON (p = 0.01). Fat-free mass increased in both groups (p = 0.02), whereas fat mass was unchanged. Our results indicate that whey protein supplementation during the competitive season in adolescent athletes improved V̇O2max compared to control. However, whey protein did not lead to improvements in sprint performance, musculoskeletal fitness, and body composition compared to control. clinicaltrials.gov (NCT05589129).