Effect of Plant vs Animal Protein Supplementation on Body Composition in Youth Soccer Players (PLANT-ANIMAL-P)

BACKGROUND AND RATIONALE Protein supplementation is widely used in elite sports to support muscle protein synthesis and recovery. While animal-based proteins (particularly whey) have traditionally been considered superior due to their complete amino acid profile, plant-based proteins have gained attention for ethical, environmental, and health reasons. However, limited evidence exists comparing their efficacy in elite youth athletes during competitive periods with high training loads. This study addresses this gap by comparing isocaloric, iso-nitrogenous plant-based and animal-based protein supplements on body composition in elite male youth soccer players during a 4-week competitive phase.

STUDY DESIGN Prospective, single-blind, randomized controlled trial with three parallel arms (1:1:1 allocation). Participants are unaware of group assignment and cannot identify supplement content due to identical packaging and delivery methods.

POPULATION Male youth soccer players (ages 16-18.7 years) from Udinese Calcio's Primavera (U-19) category during the 2025-2026 season, maintaining regular training schedules (minimum 4 sessions/week) combining technical-tactical field training and strength conditioning.

INTERVENTION

Participants are randomized to three groups:

• Plant Protein Group (n=8): 330ml soy beverage + 22g plant protein powder = 17.4g total protein
• Animal Protein Group (n=9): 200ml rice beverage + 33g whey protein (22g neutral + 11g vanilla) = 17.3g total protein
• Placebo Group (n=8): 200ml rice beverage + vanilla flavoring = 0.2g total protein

Supplements are administered post-training (15-30 minutes) under direct nutrition staff supervision. Consumption is verified before participants leave the recovery area.

SUPPLEMENT PREPARATION Prepared 8 hours before consumption (09:00h) in individual labeled containers. Liquids measured with precision graduated containers, protein powder added via funnel (11g scoop). Containers manually shaken, refrigerated at 4°C, and re-shaken before consumption (17:00h).

BLINDING Single-blind design: participants unaware of three distinct groups; all containers and delivery identical. Nutrition staff aware of assignments (necessary for preparation and safety).

TRAINING CONTEXT Intervention occurs during competitive season with official matches every Saturday. Training microcycle features undulating workload with high-volume sessions (field + gym) on Tuesdays and Wednesdays. Following baseline assessment, players receive general nutritional guidelines but no strict dietary control (maintains ecological validity).

BODY COMPOSITION ASSESSMENT Multi-compartmental model maximizes precision. Participants maintain 8-hour fast and perform last urination 30 minutes before 07:00h assessment.

Assessment sequence:

1. Bioelectrical Impedance Analysis (BIA 101 BIVA PRO): Verifies stable hydration via Bioelectrical Impedance Vector Analysis (BIVA)

2. Anthropometry (ISAK protocol): International Society for Advancement of Kinanthropometry standardized restricted profile. Same certified evaluator performs all measurements on right body side:

   • 8 skinfolds: triceps, subscapular, biceps, iliac crest, supraspinal, abdominal, front thigh, medial calf
   • 3 circumferences: relaxed arm, mid-thigh, calf
   • Body fat via Faulkner formula: %FAT = [(triceps+subscapular+suprailiac+abdominal) × 0.153 + 5.783]
3. Dual-Energy X-ray Absorptiometry (DEXA): Gold standard providing detailed fat mass, lean mass, bone mineral density, and regional distribution analysis

Assessment timeline: Baseline (Week 0) and Final (Week 4) with identical protocols.

STATISTICAL ANALYSIS Primary analysis: One-way ANOVA (or Kruskal-Wallis if non-normal) comparing mean fat-free mass changes between groups. Post-hoc tests (Bonferroni/Tukey HSD) for pairwise comparisons if significant. Secondary analyses use similar approaches. Intention-to-treat includes all randomized participants; per-protocol includes participants with ≥80% adherence. Baseline values, training load, and dietary intake may be covariates in ANCOVA models. Significance: α=0.05 (two-tailed).

SAMPLE SIZE N=25 (8-9 per group) based on feasibility given specialized population. This pilot study may detect moderate-large effects (Cohen's d≥0.6-0.8) using sensitive multi-compartmental methods.

SAFETY MONITORING Participants instructed to report adverse effects immediately. Regular check-ins during training, standardized adverse event documentation, classification by severity and relationship to intervention. Medical staff available during all sessions.

STUDY OBJECTIVES Primary: Compare effects of plant-based vs animal-based vs placebo protein supplementation on lean body mass changes in elite male youth soccer players over 4 weeks during competitive season.

Secondary: Compare effects on body fat percentage, total body mass, regional body composition, individual skinfold measurements, circumferences, adherence rates, and adverse events.