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

  • 2026-01-01
  • Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme 51
    • Grace A Zimmerman
    • Naomi Mmp de Hart
    • Isaac Z Ou
    • Victoria R Miranda
    • Eric D Bastian
    • Micah J Drummond
    • Christopher M Depner
    • Tanya M Halliday

Study Design

Type
Randomized Controlled Trial (RCT)
Population
adolescent soccer players (n = 22; 59% female, age: 15.6 ± 0.2 years; BMI percentile: 55.9 ± 6.2%)
Methods
randomized to consume either whey protein (PRO; n = 10; 20 g protein) or an isocaloric placebo (CON; n = 12) twice daily
Duration
10-week competitive soccer season
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).

Research Insights

  • Whey Protein→Improved Estimated VO2max

    V̇O2max improved in both groups (p < 0.001), with greater (p = 0.04) increases in the PRO versus CON group.

    Effect
    Beneficial
    Effect size
    Small
    Dose
    20 g protein twice daily
  • Whey Protein→Reduced Muscular Endurance

    Muscular endurance declined in the PRO group compared to CON (p = 0.01).

    Effect
    Harmful
    Effect size
    Small
    Dose
    20 g protein twice daily
  • Whey Protein→Unchanged Fat Mass

    Fat-free mass increased in both groups (p = 0.02), whereas fat mass was unchanged.

    Effect
    Neutral
    Effect size
    Small
    Dose
    20 g protein twice daily
  • Whey Protein→Unchanged Muscle Strength

    Muscle strength was similar across the study for both groups.

    Effect
    Neutral
    Effect size
    Small
    Dose
    20 g protein twice daily
  • Whey Protein→Unchanged Sprint Time

    Sprint time improved in both groups (p = 0.03), with no significant differences between groups.

    Effect
    Neutral
    Effect size
    Small
    Dose
    20 g protein twice daily
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