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

February 26, 2026 updated by: Gepner Yftach, Tel Aviv University

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.

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Detailed Description

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.

Study Type

Interventional

Enrollment (Estimated)

69

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact Backup

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult

Accepts Healthy Volunteers

Yes

Description

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

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Prevention
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Other: EVEN (Even Protein Distribution)
Participants consume an iso-caloric diet providing 1.6 g/kg/day protein, distributed evenly across three daily meals at approximately 08:00, 13:00, and 18:00, with each meal providing ~one-third of daily protein. Participants follow an overnight protein fasting window of approximately 21:00-08:00.
Behavioral: Even Protein Distribution
Iso-caloric diet providing 1.6 g/kg/day protein evenly distributed across three daily meals for 8 weeks.
Experimental: FAST (Protein-Fasting Morning; Protein at Lunch + Dinner)
Participants consume an iso-caloric diet providing 1.6 g/kg/day protein using a skewed distribution that creates a 16-hour protein-free window (21:00-13:00) by omitting protein at breakfast (breakfast contains carbohydrate and fat only). Daily protein intake is concentrated at lunch and dinner to achieve the total 1.6 g/kg/day target.
Behavioral: Skewed Protein Distribution (16-hour Protein-Fasting Window)
Iso-caloric diet providing 1.6 g/kg/day protein with protein omitted at breakfast and concentrated at lunch and dinner, creating a 16-hour daily protein-free window for 8 weeks.
Experimental: FAST-RESCUE (FAST + Leucine at Breakfast)
Identical dietary pattern to FAST: iso-caloric diet with 1.6 g/kg/day protein, protein-free breakfast, and protein concentrated at lunch and dinner, creating a 16-hour protein-free window (21:00-13:00).
Dietary supplement: L-leucine supplementation
Participants ingest 5 g free-form L-leucine at breakfast (~08:00) daily for 8 weeks. Leucine is provided as unflavored, pharmaceutical-grade instantized powder, reconstituted in water and consumed at the protein-free breakfast meal.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Change in Lean Body Mass (LBM)
Time Frame: Baseline (Week 1) to Week 8
Lean body mass (kg) assessed by multi-frequency bioelectrical impedance analysis (BIA) using the SECA mBCA 515.
Baseline (Week 1) to Week 8

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Change in Fat Mass Percentage
Time Frame: Baseline (Week 1), Week 5, and Week 8
Fat mass percentage (%) assessed by multi-frequency bioelectrical impedance analysis (SECA mBCA 515).
Baseline (Week 1), Week 5, and Week 8
Change in Fat-Free Mass (FFM)
Time Frame: Baseline (Week 1), Week 5, and Week 8
Fat-free mass (kg) assessed by multi-frequency bioelectrical impedance analysis (SECA mBCA 515).
Baseline (Week 1), Week 5, and Week 8
Change in Skeletal Muscle Mass (SMM)
Time Frame: Baseline (Week 1), Week 5, and Week 8
Skeletal muscle mass (kg) assessed by multi-frequency bioelectrical impedance analysis (SECA mBCA 515).
Baseline (Week 1), Week 5, and Week 8
Change in Maximal Strength - Isometric Mid-Thigh Pull (IMTP)
Time Frame: Baseline (Week 1), Week 5, and Week 8
Maximal force during IMTP measured using a force plate system (k-Delta). Best of two trials recorded.
Baseline (Week 1), Week 5, and Week 8
Change in Maximal Voluntary Isometric Contraction (MVC)
Time Frame: Baseline (Week 1), Week 5, and Week 8
Knee extension MVC force measured using a strain gauge system. Best of trials recorded per protocol procedures.
Baseline (Week 1), Week 5, and Week 8
Change in Handgrip Strength
Time Frame: Baseline (Week 1), Week 5, and Week 8
Handgrip strength measured with a handgrip dynamometer; best value recorded.
Baseline (Week 1), Week 5, and Week 8
Change in Countermovement Jump (CMJ) Performance
Time Frame: Baseline (Week 1), Week 5, and Week 8
Jump height measured via force plate system; best of two trials recorded.
Baseline (Week 1), Week 5, and Week 8
Change in Peak Power Output (Wingate Test)
Time Frame: Baseline (Week 1), Week 5, and Week 8
Peak power output (W) during a 30-second Wingate Anaerobic Test performed on a cycle ergometer.
Baseline (Week 1), Week 5, and Week 8
Change in Mean Power Output (Wingate Test)
Time Frame: Baseline (Week 1), Week 5, and Week 8
Mean power output (W) during a 30-second Wingate Anaerobic Test performed on a cycle ergometer.
Baseline (Week 1), Week 5, and Week 8
Change in Urinary Titin N-terminal Fragment to Creatinine Ratio (UTF/Cr)
Time Frame: Baseline (Week 1) and Week 5
Urinary titin N-terminal fragment (UTF) normalized to creatinine as a biomarker of myofibrillar damage, assessed from morning urine samples using ELISA methods described in the protocol.
Baseline (Week 1) and Week 5
Change in Serum Creatine Kinase (CK)
Time Frame: Baseline (Week 1), Week 5, and Week 8
Serum CK concentration measured from blood samples as a marker of muscle damage.
Baseline (Week 1), Week 5, and Week 8
Change in Serum Urea (Blood Urea Nitrogen, BUN)
Time Frame: Baseline (Week 1), Week 5, and Week 8
Serum urea concentration (mg/dL or mmol/L) measured from venous blood samples.
Baseline (Week 1), Week 5, and Week 8
Change in Total Testosterone
Time Frame: Baseline (Week 1), Week 5, and Week 8
Serum total testosterone measured from blood samples.
Baseline (Week 1), Week 5, and Week 8
Change in C-Reactive Protein (CRP)
Time Frame: Baseline (Week 1), Week 5, and Week 8
Serum C-reactive protein concentration (mg/L) measured from venous blood samples.
Baseline (Week 1), Week 5, and Week 8
Change in Tumor Necrosis Factor-alpha (TNF-α)
Time Frame: Baseline (Week 1), Week 5, and Week 8
Serum TNF-α concentration (pg/mL) measured from venous blood samples.
Baseline (Week 1), Week 5, and Week 8
Change in Interleukin-6 (IL-6)
Time Frame: Baseline (Week 1), Week 5, and Week 8
Serum IL-6 concentration (pg/mL) measured from venous blood samples.
Baseline (Week 1), Week 5, and Week 8
Change in Resting Metabolic Rate (RMR)
Time Frame: Baseline (Week 1) and Week 8
Resting metabolic rate (kcal/day) assessed by indirect calorimetry using a metabolic cart under standardized fasting conditions.
Baseline (Week 1) and Week 8

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Tel Aviv University

Investigators

  • Principal Investigator: Yftach Gepner, PhD, Tel Aviv University

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

March 1, 2026

Primary Completion (Estimated)

December 1, 2028

Study Completion (Estimated)

December 1, 2028

Study Registration Dates

First Submitted

February 22, 2026

First Submitted That Met QC Criteria

February 22, 2026

First Posted (Actual)

February 27, 2026

Study Record Updates

Last Update Posted (Actual)

March 2, 2026

Last Update Submitted That Met QC Criteria

February 26, 2026

Last Verified

February 1, 2026

More Information

Terms related to this study

Keywords

Other Study ID Numbers

  • 0011980-1

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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