BLUF (Bottom Line Up Front)
A systematic review of 30 studies examining the effects of combat ration (CR) use over 3 to 40 days found that military personnel consistently lost body weight (BW), fat mass (FM), and fat-free mass (FFM) while consuming operational rations such as Meals Ready to Eat (MRE’s). These losses were most severe in prolonged, high-intensity training environments, such as selection/indoctrination courses, reconnaissance missions, cold-weather warfare training, and extended infantry operations. The primary cause was a significant energy deficit, as soldiers burned far more calories than they consumed. While short-term deficits had minimal effects on performance, prolonged underfeeding led to declines in endurance, strength, and cognitive function.
Key Discussion Points
Purpose of the Study
This study systematically reviewed 30 military nutrition studies that assessed the effects of exclusive combat ration consumption (e.g., MREs, LRPs, Arctic rations) during field training or deployment. The primary objectives were to determine:
- The extent of body weight and composition changes during sustained CR consumption.
- The influence of mission duration, intensity, and operational demands on weight loss.
- The performance consequences of prolonged energy deficits.
- Potential strategies to improve energy balance and prevent excessive weight loss.
The research included personnel from multiple military branches across a range of training courses and operational scenarios, including:
- Selection & Schools
- U.S. Army Ranger School
- Marine Infantry Officer Course (IOC)
- Australian Special Forces Selection
- Finnish Special Operations Forces Selection
- Reconnaissance & Long-Range Patrolling
- U.S. Army Long-Range Reconnaissance Missions
- Australian Defence Force Reconnaissance Elements
- Cold-Weather & Mountain Warfare
- U.S. Marine Corps Mountain Warfare Training
- Arctic Survival Training (Norwegian Army, Finnish Military)
- Extended Infantry Training
- U.S. Army and Marine Infantry Field Exercises
- NATO Infantry Training Courses
Effects of Combat Rations on Body Weight and Composition
Weight Loss by Training Type
- Short missions (3–7 days): Minimal weight loss (~0.1–3%), primarily from water weight fluctuations, with negligible performance effects.
- Extended missions (8–30+ days): More significant reductions in body weight (4–10%), with potential impacts on endurance and strength.
- Extreme weight loss cases: The most severe recorded loss was 8.3% in 12 days during the U.S. Army Ranger School Jungle Phase, due to severe caloric restriction and environmental stress.
| Training Environment | Duration | Weight Loss (%) |
|---|---|---|
| Short Infantry Field Exercises | 3–7 days | 0.1–3% |
| Long-Range Reconnaissance | 14+ days | 4–6% |
| U.S. Army Ranger School (Jungle) | 12 days | 8.3% |
| Arctic/Mountain Warfare | 20+ days | 5–7% |
| Schools & Selections | 30+ days | 10–17.5% |
Energy Deficits: The Primary Cause of Weight Loss
The main cause of weight loss across all studies was an energy deficit, where total daily energy expenditure (TDEE) exceeded total daily energy intake (TDEI).
Key Energy Findings
- Highest TDEE recorded: 29.8 MJ/day (~7,125 kcal/day) during mountain warfare training, a rate comparable to elite endurance athletes like Tour de France cyclists.
- Average TDEI on CR-only diets: ~50% of TDEE, meaning soldiers routinely under-consumed available calories.
- Worst energy deficit observed: ~9.3–10 MJ/day (~2,200–2,400 kcal/day) in high-intensity courses such as the U.S. Marine Infantry Officer Course (IOC).
Most Severe Energy Deficits Occurred In:
- Schools and Selections
- Candidates faced intense physical exertion, sleep deprivation, and caloric restriction.
- Energy intake was sometimes as low as 1,500–2,000 kcal/day, far below expenditure needs.
- Reconnaissance Missions
- Limited food access during long-range patrols.
- Soldiers prioritized operational security over proper nutrition.
- Cold-Weather Warfare Training
- Metabolic demands skyrocketed due to thermoregulation.
- Ration calories were insufficient, leading to increased energy deficits.
Fat Mass vs. Lean Mass Loss: What Gets Burned First?
- Fat Mass (FM) Loss: The primary contributor to weight loss in the early stages of calorie restriction.
- Lean Mass (FFM) Loss: More significant after prolonged energy deficits and in already lean soldiers.
High-Risk Groups for Lean Mass Loss
- Soldiers with <10% body fat at the start of training.
- Extended calorie-restricted training environments (14+ days).
- Up to 3.6% lean mass loss was recorded in Finnish SOF soldiers.
Practical Takeaways:
- Soldiers with higher body fat could sustain weight loss without immediate performance declines.
- Lean soldiers were at greater risk of muscle loss, reducing strength and endurance.
Performance Implications of Extended Weight Loss
| % Body Weight Lost | Impact on Performance |
|---|---|
| 0–3% (Short Missions) | Negligible impact; mainly water weight fluctuations. |
| 4–6% (Long Recon Missions) | Reduced endurance due to glycogen depletion. |
| 7–10% (Extended Training) | Decreased strength, slower recovery, reduced cognitive function. |
| >10% (Extreme Cases – Schools & Selections) | Severe declines in strength, power, and mental clarity. |
Weight loss exceeding 10% led to measurable declines in reaction time, decision-making, and muscular endurance.
Strategies to Prevent Excessive Weight Loss
1. Mandatory Supplementation
- High-calorie, protein-rich supplements reduced lean mass loss.
- Voluntary intake was ineffective—soldiers often skipped extra food due to time constraints or stress.
2. Structured Meal Breaks in Field Training
- Units that enforced regular eating schedules had lower energy deficits.
- Long-range patrols with irregular meals experienced greater weight loss.
3. Higher Protein Intake
- 1.5–2.0 g/kg/day of protein helped preserve lean mass.
- Lower protein intake correlated with higher FFM loss
4. Recovery Protocols for Soldiers Losing >5% BW
- Individuals losing >5% BW in a short period should undergo recovery-focused feeding.
- For >10% BW loss, soldiers should transition off CR-only diets to fresh food-based recovery meals.
Conclusion
This review provides the most comprehensive analysis of how combat rations impact military weight loss and performance. The primary issue is chronic caloric shortfall, leading to predictable declines in endurance, strength, and cognitive function over time.
To optimize soldier readiness, military dietitians must prioritize energy-dense rations, structured meal plans, and increased protein intake to reduce unnecessary weight loss and performance declines.
Bibliography
Body weight and body composition changes during military training and deployment involving the use of combat rations: A systematic literature review.