Protein Distribution and Leucine Supplementation Effects on Body Composition and Performance in Tactical Athletes

This study is an 8-week, three-arm, parallel-group randomized controlled trial conducted in healthy male tactical trainees (18-35 years) enrolled in a Ministry of Defense training program. Participants will undergo a high-volume concurrent training regimen exceeding 30 hours per week, including resistance training, load carriage, aerobic conditioning, and combat-based drills.

Participants (n=69) will be randomized in a 1:1:1 ratio to one of three iso-caloric dietary interventions providing 1.6 g/kg/day of protein:

• EVEN: Protein evenly distributed across three daily meals (08:00, 13:00, 18:00).
• FAST: Skewed protein distribution with a 16-hour protein-free window (21:00-13:00), omitting protein at breakfast and concentrating intake at lunch and dinner.
• FAST-RESCUE: Identical to FAST, with addition of 5 g free-form leucine consumed at breakfast.

Energy intake will be individualized based on measured resting metabolic rate and estimated physical activity level. Dietary adherence will be monitored daily using a mobile application and weekly dietitian supervision.

Primary Outcome:

• Change in lean body mass measured by bioelectrical impedance analysis from baseline to Week 8.

Secondary Outcomes:

• Maximal strength (isometric mid-thigh pull, maximal voluntary contraction, handgrip strength)
• Anaerobic performance (Wingate test, countermovement jump)
• Serum biomarkers (creatine kinase, urea, testosterone, inflammatory markers)
• Urinary titin N-terminal fragment to creatinine ratio (UTF/Cr) as a marker of myofibrillar damage

Assessments will be performed at baseline, Week 5, and Week 8. Data will be analyzed according to the intention-to-treat principle using linear mixed models to evaluate Group × Time interactions.

Inclusion criteria

• Male participants aged 18-35 years
• Enrolled in an active Ministry of Defense tactical training program
• Physically active and medically cleared to participate in intensive training
• Willing and able to comply with the dietary intervention and training protocol
• Provide written informed consent prior to participation

Exclusion criteria

• Musculoskeletal or neuromuscular injury or impairment limiting participation in exercise training
• Cardiopulmonary disease (including recent myocardial infarction or unstable angina)
• History of cancer, diabetes, thyroid disease, hypertension, or chronic renal failure
• Cognitive impairment affecting ability to provide informed consent
• Use of medications that may affect metabolism, muscle physiology, or exercise performance
• Known allergy or intolerance to study dietary components or leucine supplementation
• Non-compliance with study protocol requirements