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

A Prospective, Single-Blind, Randomized Controlled Trial Comparing Plant-Based and Animal-Based Protein Supplementation Effects on Body Composition and Lean Mass in Elite Male Youth Soccer Players: A 4-Week Intervention Study

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).

Study Overview

• Status: Completed
• Conditions: Athletic Performance Enhancement; Body Composition Optimization; Nutritional Supplementation in Athletes
• Intervention / Treatment: Dietary supplement: Plant-Based Protein Supplement; Dietary supplement: Animal-Based Protein Supplement (Whey); Dietary supplement: Placebo

Detailed Description

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
• Enrollment (Actual): 25
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Italy
  • Udine
    • Udine, Udine, Italy, 33100
      • Udinese Calcio

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child; Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Active contract with Udinese Calcio's Primavera (U-19) category during the 2025-2026 season
• Regular participation in the team's technical-tactical and strength training program (minimum 4 sessions per week)
• Signed informed consent (parental consent for participants under 18 years)
• Commitment to adhere to measurement protocol requiring 8-hour fast and assessment at 07:00h
• Commitment to adhere to post-training supplementation protocol with administration at 17:00h
• Confirmed presence and availability for both baseline assessment (Week 0) and final assessment (Week 4)

Exclusion Criteria:

• Open injury records or currently in functional readaptation phase at study initiation
• Consumption of ergogenic or nutritional supplementation independently and external to the club-supervised protocol during the 4 weeks prior to study or during the study period
• Previous diagnosis or current symptomatology compatible with eating disorders
• Known allergies or intolerances to soy, rice, dairy-based proteins, or vanilla flavoring
• Current use of medications that may affect body composition or protein metabolism (anabolic steroids, growth hormone, corticosteroids, thyroid hormones)
• Diagnosed chronic diseases that may affect protein metabolism or body composition (diabetes mellitus, chronic kidney disease, liver disease, malabsorption syndromes)

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Double

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Plant Protein Group; Participants receive plant-based protein supplementation (17.4g protein per dose) consisting of 330ml soy beverage and 22g plant-based protein powder, administered within 15-30 minutes post-training under direct supervision for 4 weeks during competitive season.	Dietary supplement: Plant-Based Protein Supplement; 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.; Other Names: Soy protein; Plant protein blend; Vegetable protein
Active Comparator: Animal Protein Group; Participants receive animal-based protein supplementation (17.3g protein per dose) consisting of 200ml rice beverage and 33g whey protein powder blend, administered within 15-30 minutes post-training under direct supervision for 4 weeks during competitive season.	Dietary supplement: Animal-Based Protein Supplement (Whey); 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.; Other Names: Whey protein; Dairy protein; Milk protein
Placebo Comparator: Placebo Group; Participants receive placebo supplementation (0.2g protein per dose) consisting of 200ml rice beverage and vanilla flavoring, administered within 15-30 minutes post-training under direct supervision for 4 weeks during competitive season. Appearance and delivery identical to active interventions.	Dietary supplement: Placebo; 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.; Other Names: Placebo comparator; Control

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
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.	Baseline (Week 0) and Final Assessment (Week 4)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
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.	Baseline (Week 0) and Final Assessment (Week 4)
Change in Total Body Mass	Change in total body weight (kg) from baseline to week 4.	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.	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.	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.	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.	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.	Throughout 4-week intervention period and 1 week post-intervention

Collaborators and Investigators

• Sponsor: Antonio Molina Lopez
• Collaborators: Universidad Europea de Madrid; Universidad Pablo de Olavide
• Investigators: Principal Investigator: Antonio Blas Molina Lopez, Phd, CTS-595 Research Group, Centre for Research into Physical and Sporting Performance. Universidad Pablo de Olavide

Study record dates

Study Major Dates

• Study Start (Actual): January 17, 2026
• Primary Completion (Actual): February 18, 2026
• Study Completion (Actual): March 30, 2026

Study Registration Dates

• First Submitted: March 8, 2026
• First Submitted That Met QC Criteria: May 2, 2026
• First Posted (Actual): May 6, 2026

Study Record Updates

• Last Update Posted (Actual): May 6, 2026
• Last Update Submitted That Met QC Criteria: May 2, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: Body composition; Soy protein; Athletic performance; Protein supplementation; Lean mass; Sports nutrition; Soccer players; Fat-free mass; Youth athletes; Elite athletes; Plant-based protein; Animal-based protein; Post-exercise nutrition
• Additional Relevant MeSH Terms: Amino Acids, Peptides, and Proteins; Proteins; Food; Diet, Food, and Nutrition; Physiological Phenomena; Food and Beverages; Beverages; Dairy Products; Milk; Dietary Proteins; Plant Proteins; Animal Proteins, Dietary; Soy Foods; Vegetable Products; Vegetables; Whey; Whey Proteins; Soybean Proteins; Plant Proteins, Dietary; Milk Proteins
• Other Study ID Numbers: UC-PLANTANIMAL-PROT-2026

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Sharing Time Frame: Individual participant data will be available immediately following publication of the primary manuscript and will remain available for at least 5 years. Supporting documents (study protocol and statistical analysis plan) will be available indefinitely.
• IPD Sharing Access Criteria: De-identified individual participant data will be shared with researchers who provide a methodologically sound proposal for academic purposes. Requests should be directed to the corresponding author at antoniomolina@centrosnutrifarma.es. Requestors will need to sign a data access agreement and specify the intended use of the data. Data will be provided in anonymized CSV format via secure file transfer within 30 days of approval.
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; SAP

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No