As a nutritionist, I've found that many runners tend to overestimate how much they need, causing them to overeat during the day and gain unwanted weight during the season. And eating too much during training can trigger a multitude of stomach issues (e.g., nausea, diarrhea, vomiting, side stitches, sloshing) and ultimately hinder your performance.
Below is a step-by-step guide to help you determine your total calorie needs during training runs, and your target calorie replacement needs based on your race pace. Happy running trails!
Determining Your Total Calorie Needs
Step 1: Determine running calorie expenditure per mile
0.63 x body weight (pounds)
Step 2: Determine goal race pace or how many miles per hour you'll cover
Example: An eight-minute miler will cover 7.5 miles/hour
Step 3: Calculate hourly expenditure based on goal race pace
Example: An eight-minute miler would multiply 7.5 by the figure from step 1.
Step 4: Determine hourly calorie replacement needs
0.3 x the figure from step 3 (Note: Research shows runners can physically absorb about 30 percent of what they expend.)
Sample Case Study
John is a 200-pound marathoner preparing for the Rock 'n' Roll Arizona Marathon with a goal of breaking the three-hour mark. He's had issues with premature muscle fatigue and cramping during previous marathons, which has led him to seek nutritional advice for race-day fueling. We used the guidelines specified above to help calculate and devise the perfect nutrition plan for his needs.
Step 1: John's calorie burn each mile:
0.63 x 200 lbs = 126 calories/mile
Step 2: John's goal marathon pace:
John's goal marathon pace to break three hours is 6:50 per mile, which means he'll be running 8.78 miles per hour.
Step 3: John's hourly expenditure based on his goal marathon pace:
8.78 miles per hour x 126 calories per mile = 1,106 calories burned per hour
Step 4: Goal calorie replacement after 60-90 minutes of racing:
0.3 x 1,106 calories = 331 calories/hour
Step 5: John's calorie replacement:
The first 90 minutes of the marathon, John plans to use the course-provided water at aid stations to maintain hydration. After 90 minutes, John's goal is to consume approxiamtely 330 calories per hour until he finishes, which means he'll need approximately 500 calories.
John will carry three heaping servings of his InfinIT in a large gel flask topped off with water. He'll take shots of the concentrate every 10 minutes along with course-provided water so that he'll consume two servings between 1:30 and 2:30 and the final serving between 2:30 and the finish line.
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