You’re logging 70-mile weeks, completing back-to-back long runs, and wondering why you’re constantly exhausted, getting sick, or paradoxically gaining weight despite massive training volume. The problem often isn’t your training plan—it’s miscalculating your calorie needs for ultra marathon training. Getting this wrong sabotages performance, recovery, and race-day readiness.
Why Ultra Training Calorie Needs Differ Dramatically
Ultra marathon training isn’t like typical marathon prep. The volume, intensity distribution, and recovery demands create unique caloric requirements that generic calculators completely miss.
A runner logging 70 miles weekly at moderate pace burns 1,200-1,500 MORE calories per day than their sedentary baseline. Add strength training, elevation gain, and recovery needs, and calorie requirements can reach 3,500-4,500 daily—far beyond what most runners actually consume.
The Undereating Epidemic in Ultra Running
Research shows 40-60% of ultra runners chronically undereat during heavy training blocks. This manifests as:
- Persistent fatigue despite adequate sleep
- Declining performance on easy runs
- Frequent illness or upper respiratory infections
- Irregular menstrual cycles (females)
- Poor workout recovery
- Irritability and mood swings
- Stalled or declining race times
Calculating Your Base Metabolic Rate (BMR)
Start with your BMR—calories burned at complete rest. Use the Mifflin-St Jeor equation, which research shows is most accurate for athletes:
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
Example: 35-year-old male, 70kg (154 lbs), 175cm (5’9″) BMR = (10 × 70) + (6.25 × 175) – (5 × 35) + 5 = 1,669 calories
This is your baseline—what you’d burn lying in bed all day. Everything else adds to this number.
Activity Multipliers for Ultra Marathon Training
Generic “active lifestyle” multipliers (1.5-1.7x BMR) severely underestimate ultra training demands. Use sport-specific calculations instead.
Weekly Mileage Adjustments
Base Training (30-50 miles/week): BMR × 1.6 = Total Daily Energy Expenditure (TDEE)
Build Phase (50-70 miles/week): BMR × 1.8 = TDEE
Peak Training (70-100+ miles/week): BMR × 2.0-2.2 = TDEE
Example continued: 70kg runner, BMR 1,669, logging 65 miles weekly 1,669 × 1.8 = 3,004 calories per day
Adding Intensity and Terrain
Flat, easy terrain: Use base multipliers above
Moderate hills (500-1,000ft gain per 10 miles): Add 10% to calculated TDEE
Mountain training (1,000+ ft gain per 10 miles): Add 20-25% to calculated TDEE
High-intensity workouts (tempo, intervals): Add 150-300 calories per hard workout day
The Calorie Burn Reality: Running Isn’t Magic
Many runners overestimate calorie burn, leading to overeating and unwanted weight gain. Realistic burn rates:
Easy pace (conversational effort):
- 100 calories per mile for 150 lb (68kg) runner
- 120 calories per mile for 180 lb (82kg) runner
Moderate pace (comfortably hard):
- 110 calories per mile for 150 lb runner
- 135 calories per mile for 180 lb runner
Note: Running faster burns slightly more per mile, but differences are smaller than most assume. A 10-minute mile and 8-minute mile differ by only 10-15% calorie burn—not the 50% many believe.
The Weekly Calorie Swing
Your calorie needs for ultra marathon training fluctuate dramatically day-to-day. A typical training week might look like:
Monday (Rest): 2,200 calories Tuesday (12 miles moderate): 3,400 calories Wednesday (6 miles easy): 2,800 calories Thursday (Workout: 10 miles with tempo): 3,500 calories Friday (Rest): 2,200 calories Saturday (Long run: 20 miles): 4,200 calories Sunday (Recovery: 8 miles easy): 3,000 calories
Weekly average: 3,043 calories per day Range: 2,200-4,200 calories per day
Eating the same 3,000 calories daily works, but many runners feel better matching intake to training demand.
Adjusting for Body Composition Goals
Most ultra runners should maintain weight during heavy training. However, some need to adjust:
Maintaining Weight (Most Runners)
Eat calculated TDEE. Monitor weekly weigh-ins—stable weight indicates accurate calculations.
Warning signs you’re eating too little:
- Weight loss exceeding 0.5 lb per week
- Performance decline
- Constant hunger
Warning signs you’re eating too much:
- Weight gain exceeding 0.5 lb per week
- Increased body fat percentage
- Feeling sluggish
Losing Body Fat (Carefully)
Only attempt during base phase—NEVER during peak training. Create modest 250-300 calorie daily deficit (0.5 lb per week loss maximum).
Critical rules:
- Never cut below BMR
- Prioritize protein (1.6-2.2g per kg body weight)
- Accept slightly compromised training quality
- Stop if performance crashes
Fueling for Performance (Not Weight Loss)
Many runners sabotage training by restricting calories for aesthetic goals. Research consistently shows that underfueling during peak training:
- Reduces training adaptation by 20-30%
- Increases injury risk by 40%+
- Compromises immune function
- Results in poor race-day performance
Macronutrient Distribution for Ultra Training
Once total calories are determined, distribution matters for calorie needs ultra marathon training optimization:
Carbohydrates: 55-65% of total calories
- 5-7g per kg body weight on moderate days
- 7-10g per kg on high-volume days
- Fuels glycogen stores and workout quality
Protein: 20-25% of total calories
- 1.6-2.2g per kg body weight
- Supports muscle repair and immune function
- Higher end for high-mileage weeks
Fats: 20-25% of total calories
- 0.8-1.2g per kg body weight
- Essential for hormone production and vitamin absorption
- Don’t fear dietary fat
Example: 70kg runner, 3,000 calories daily
- Carbs: 1,800 cal (450g) = 6.4g per kg
- Protein: 600 cal (150g) = 2.1g per kg
- Fat: 600 cal (67g) = 0.95g per kg
Practical Tracking and Adjustment
Theory means nothing without implementation. Use these strategies to ensure adequate fueling:
Week 1-2: Establish Baseline
Track everything you eat using apps like MyFitnessPal or Cronometer. Weigh food initially for accuracy. Record:
- Total daily calories
- Weight (same time daily)
- Energy levels (1-10 scale)
- Workout performance notes
Week 3-4: Analyze and Adjust
Review data:
- Weight trend (losing/gaining/stable)
- Energy and performance patterns
- Hunger levels throughout day
Adjust intake by 200-300 calories if weight changing >0.5 lb weekly.
Month 2+: Intuitive with Check-Ins
After 4-6 weeks of tracking, most runners develop intuition for appropriate intake. Spot-check with 3-day food logs monthly to prevent drift.
Common Calorie Calculation Mistakes
Mistake #1: Using generic fitness tracker estimates Solution: Manually calculate using formulas above—trackers overestimate by 20-30%
Mistake #2: Ignoring day-to-day variation Solution: Eat more on high-volume days, less on rest days
Mistake #3: Cutting calories during peak training Solution: Maintain or increase intake during highest volume weeks
Mistake #4: Not accounting for increased metabolism Solution: Re-calculate every 4-6 weeks as fitness improves
Mistake #5: Forgetting about recovery nutrition Solution: Post-workout fueling counts toward daily total—don’t skip it
Key Takeaways
- Ultra marathon training increases daily calorie needs by 1,200-1,500+ calories above sedentary baseline, requiring 3,000-4,500 total daily calories for most runners
- Calculate personalized needs using BMR (Mifflin-St Jeor equation) multiplied by sport-specific activity factors (1.6-2.2x depending on weekly mileage)
- Running burns approximately 100-135 calories per mile depending on body weight, with smaller differences between paces than most runners assume
- Chronic undereating affects 40-60% of ultra runners, causing persistent fatigue, declining performance, frequent illness, and poor recovery
- Match daily intake to training demand with 500-2,000 calorie swings between rest days and long-run days for optimal energy and recovery
Fuel Your Training, Not Your Frustration
Calculating your calorie needs for ultra marathon training isn’t about obsessive tracking forever—it’s about establishing a baseline understanding of your body’s actual requirements. Spend 4-6 weeks measuring carefully, then trust the patterns you’ve learned.
Your next breakthrough might not come from adding another long run or interval session. It might come from finally eating enough to support the training you’re already doing. Start tracking today, adjust based on results, and watch your energy, recovery, and performance transform when you stop fighting your body and start fueling it properly.
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