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

Estimated V̇O2max improved in both groups over the 10-week season, with greater increases in the whey protein group compared to control.

• V̇O2max improved in both groups (p < 0.001)
• The PRO group showed greater increases than CON group (p = 0.04)
• V̇O2max was assessed via the 1.5 mile run test
• Study duration was 10 weeks during a competitive soccer season

Sprint time improved in both groups over the intervention period, with no significant difference between the whey protein and control groups.

• Sprint time improved in both groups (p = 0.03)
• No significant between-group differences were observed
• Sprint performance was assessed using the 30 yard dash
• Whey protein supplementation did not confer additional benefit over placebo for sprint performance

Muscle strength (maximum voluntary contraction) was similar across the study period for both groups.

• Quadricep isometric leg extension was used to assess muscle strength
• No significant differences within or between groups were reported for muscle strength
• Both PRO and CON groups showed similar muscle strength trajectories over the 10-week period

Muscular endurance declined in the whey protein group compared to the control group.

• Muscular endurance decline in PRO versus CON was statistically significant (p = 0.01)
• Muscular endurance was assessed via repetitions to fatigue on quadricep isometric leg extension
• This finding suggests whey protein supplementation did not preserve or improve muscular endurance during the competitive season

Fat-free mass increased in both groups over the 10-week intervention, while fat mass remained unchanged.

• Fat-free mass increased in both groups (p = 0.02)
• Fat mass was unchanged in both groups
• No significant between-group differences in body composition outcomes were observed
• Whey protein supplementation did not confer additional benefit over placebo for fat-free mass gains

The study enrolled adolescent soccer players who were randomized to consume either whey protein or an isocaloric placebo twice daily for 10 weeks.

• Total sample size was n = 22 adolescent athletes (59% female)
• Mean age was 15.6 ± 0.2 years (mean ± SEM); mean BMI percentile was 55.9 ± 6.2%
• PRO group (n = 10) consumed 20 g protein twice daily; CON group (n = 12) consumed an isocaloric placebo twice daily
• Assessments were conducted at baseline and post-intervention
• Trial was registered at clinicaltrials.gov (NCT05589129)