This prospective, single-blind, randomized controlled trial investigates the comparative effects of plant-based protein (soy and rice blend) versus animal-based protein (whey) supplementation on body composition parameters in elite male youth soccer players. Twenty-five players (ages 16-18.7 years) from Udinese Calcio's Primavera (U-19) category are randomized into three groups: Plant Protein Group (n=8), Animal Protein Group (n=9), and Placebo Group (n=8). The intervention consists of post-training protein supplementation (17g protein/dose) administered within 15-30 minutes after each training session over a 4-week microcycle during the competitive season. Body composition is assessed using a multi-compartmental model including anthropometry (ISAK protocol), bioelectrical impedance analysis (BIA), and dual-energy X-ray absorptiometry (DEXA).
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.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
DOUBLE
Enrollment
25
Composition per dose: 330ml soy beverage (10.8g protein) + 22g plant protein powder (6.6g protein) = 17.4g total protein. Administered post-training (15-30 min after), prepared 8 hours before, stored at 4°C, supervised consumption verified by nutrition staff.
Composition per dose: 200ml rice beverage (0.2g protein) + 22g neutral whey protein (12.0g protein) + 11g vanilla whey protein (5.1g protein) = 17.3g total protein. Administered post-training (15-30 min after), prepared 8 hours before, stored at 4°C, supervised consumption verified by nutrition staff.
Composition per dose: 200ml rice beverage (0.2g protein) + vanilla flavoring = 0.2g total protein. Administered post-training (15-30 min after), prepared 8 hours before, stored at 4°C, supervised consumption verified by nutrition staff. Identical appearance to active supplements to maintain blinding.
Udinese Calcio
Udine, Udine, Italy
Change in Fat-Free Mass (Lean Body Mass)
Change in fat-free mass (kg) from baseline to week 4, assessed using a multi-compartmental model combining bioelectrical impedance analysis (BIA), anthropometry according to ISAK protocol, and dual-energy X-ray absorptiometry (DEXA). Fat-free mass represents total body mass minus fat mass.
Time frame: Baseline (Week 0) and Final Assessment (Week 4)
Change in Body Fat Percentage
Change in body fat percentage from baseline to week 4, calculated using the Faulkner formula from skinfold measurements and validated by DEXA assessment. The Faulkner formula is: % FAT = (TR+SE+SI+AB) × 0.153 + 5.783, where TR=triceps, SE=subscapular, SI=suprailiac, AB=abdominal skinfolds in millimeters.
Time frame: Baseline (Week 0) and Final Assessment (Week 4)
Change in Total Body Mass
Change in total body weight (kg) from baseline to week 4.
Time frame: Baseline (Week 0) and Final Assessment (Week 4)
Change in Total Lean Mass by DEXA
Change in whole-body lean mass (kg) from baseline to week 4, assessed by dual-energy X-ray absorptiometry (DEXA) as a single composite measurement of total lean tissue.
Time frame: Baseline (Week 0) and Final Assessment (Week 4)
Change in Sum of Skinfolds
Change in sum of 8 skinfolds from baseline to week 4, measured according to ISAK protocol. The 8 individual skinfold measurements (triceps, subscapular, biceps, iliac crest, supraspinal, abdominal, front thigh, and medial calf in millimeters) will be summed to create a single aggregate value representing total subcutaneous adiposity. Results will be reported as mean change in total sum of skinfolds ± standard deviation.
Time frame: Baseline (Week 0) and Final Assessment (Week 4)
Change in Limb Circumferences
Changes in circumference measurements from baseline to week 4, measured according to ISAK protocol. The 3 circumference measurements (relaxed arm, mid-thigh, and medial calf in centimeters) will be analyzed separately and reported as individual values for each site. Results will show mean change ± standard deviation for each circumference measurement independently.
Time frame: Baseline (Week 0) and Final Assessment (Week 4)
Supplementation Adherence Rate
Percentage of prescribed supplement doses consumed throughout the 4-week intervention period, calculated as (number of doses consumed / number of doses prescribed) × 100. Adherence is verified by direct observation and documentation by nutrition staff at each administration.
Time frame: Throughout 4-week intervention period
Adverse Events
Number and type of adverse events (gastrointestinal distress, allergic reactions, or any other adverse effects) related to supplement consumption.
Time frame: Throughout 4-week intervention period and 1 week post-intervention
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