On average, a runner burns approximately 100 calories for every mile. By that logic, a marathoner would then burn slightly more than 2,600 calories during a race, right? Not so fast—that's simply an average number of calories burned. The total calories you might burn during a marathon depends on your gender, weight and age.
Variations in Calories Burned
The number of calories you burn while running a marathon depends on a number of factors. Male runners, for example, typically require more energy for physical exertion than their female counterparts. Age is also a major factor, as older runners typically have a slower resting metabolic rate. Lastly, body weight plays a role in calorie burning. For example, you'll burn more calories if you're 210 pounds than if you weigh 125 pounds.
One thing that doesn't matter—your speed. While a faster runner will burn more calories than a slower runner in the same amount of time, they will both still average 100 calories a mile.
Use a Calculator
Handy online exercise calculators can give you an estimate of how many calories you'll burn during your marathon. Don't take it as gospel, though, as other factors are in play. According to a calculator from the Cleveland Clinic, a 130-pound runner will burn a little more than 2,220 calories during her 26.2 run, while a 165-pound runner will break 2,820 calories. On the higher end, a 210-pound runner will burn nearly 3,600 calories.
Replenishing Those Calories
While you'll burn plenty of calories during a marathon, you also want to eat many of them back in order to have fuel to complete the run. If your muscles are depleted of glycogen, you'll hit the metaphorical "wall" that so many runners mention. In short, you're out of fuel. Therefore, aim for about 60 grams of carbs for every hour you spend running. A gel has between 21 and 27 grams, while a banana has between 24 and 30 grams.