Your caloric intake should largely parallel the amount of calories you burn throughout the course of the day. On running days, you'll need more calories. On off days, you don't need as many calories. Of course, how many calories you need to consume depends on several variables: the duration and intensity of your running workouts, the amount of calories you burn naturally throughout the course of the day, and whether you want to lose, gain or maintain your weight.
Caloric Demands of Running
Running burns approximately 100 to 120 calories per mile of distance covered. You'll burn slightly more if you're larger or running faster, and fewer if you're smaller or running slower. This makes calculating the total number of calories burned over the course of a run simple: just multiple the number of miles you ran by 100 to 120 and you'll arrive at the total caloric deficit from your run. Remember to add back on any calories you consumed during the run.
Resting Metabolic Rate
Aside from running, your body burns a certain number of calories every day. This baseline number is called your resting metabolic rate, or RMR. Your age, height, weight and gender all affect your RMR. While there are numerous online resources for estimating your RMR, the most accurate way of determining your RMR is to go to a laboratory or sports clinic and have your body composition analyzed.
Using RMR to Estimate Total Calories Burned
During the course of normal activities throughout the day, you'll burn calories well in excess of your RMR, which represents how many calories your body burns if you do absolutely nothing other than breathe during the day. To figure out how many calories your body actually burns throughout the day, multiply your RMR by a certain number, depending on your level of activity. For example:
-- Light activity: multiply by 1.4
-- Moderate activity: multiply by 1.6
-- Heavy activity: multiply by 1.9
On resting days, use the "light activity" multiplier. On running days, use a larger multiplier depending on the duration and intensity of your run.
Planning Your Daily Calorie Intake
When figuring out how many calories to consume, use the total distance run and your RMR to calculate your baseline calorie expenditure. Add or subtract calories as needed depending on your body composition goals and you'll arrive at a calorie target for the day.
References
- University of Cincinnati: Know Your Number (RMR) to Lose Weight
- "American Journal of Clinical Nutrition"; The Effects of Aerobic Fitness on Resting Metabolic Rate; CE Broeder et al.; April 1992
- "American Journal of Clinical Nutrition"; A New Predictive Equation for Resting Energy Expenditure in Healthy Individuals, MD Mifflin et al.; February 1990
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