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

The Effect of Protein Distribution and Leucine Supplementation on Body Composition, Physical Performance, and Myofibrillar Damage in Tactical Athletes: a Randomized Controlled Trial During 8 Weeks of Intensive Training

This randomized controlled trial will examine the effects of within-day protein distribution and leucine supplementation on body composition, physical performance, and biomarkers of muscle damage in tactical athletes during an 8-week intensive training program. Sixty-nine healthy male participants (18-35 years) enrolled in a Ministry of Defense training course will be randomly assigned to one of three iso-caloric dietary groups providing 1.6 g/kg/day of protein: (1) evenly distributed protein across three meals (EVEN), (2) a 16-hour daily protein fasting pattern with protein concentrated at lunch and dinner (FAST), or (3) the same fasting pattern with 5 g leucine supplementation at breakfast (FAST-RESCUE).

Primary outcomes include changes in lean body mass. Secondary outcomes include strength, anaerobic performance, and biochemical markers of muscle damage, including urinary titin N-terminal fragment (UTF). Assessments will be conducted at baseline, Week 5, and Week 8.

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:

1. EVEN: Protein evenly distributed across three daily meals (08:00, 13:00, 18:00).
2. 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.
3. 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