Just how much calories do we lose while running? It depends. Weight and pace play a large role in determining this. Generally, the heavier you are (independent of speed), the more calories you’ll burn. Also, the faster or less efficient you run, the more calories you’ll also be burning. When running a race we have to keep in mind the calories we need to consume for the amount we are burning. Ideally you don’t want your caloric debt (the amount you burn being more than the amount you consume) to be too high. It is possible to have near zero caloric debt, but as anyone who has ever drank too much gatorade or eaten too many gels can attest to; can do damage to our stomachs and the stuff just ends up on the road as a Jackson Pollock creation.
A heavier person burns more calories because a larger body mass requires their body to do more work, which requires more energy. I’ll confuse you more with this example: Two identical cars are filled to the top with gas and travel the same route to some destination. One car is loaded with 5 passengers and the trunk is filled with suitcases. The other car only has the driver and an empty trunk. Which car do you think will use up less gasoline and travel farther? The car with less weight!
We also burn more calories the faster we run because faster body movements require more oxygen. In response, we consume more oxygen to keep us moving. It’s in the consumption and conversion of oxygen into usable energy where we burn more calories. Lack of running efficiency also leads to greater caloric loss. Poor aerobic capacity and poor running form will burn more calories because the aerobic and muscular inefficiencies require more energy. Wasted movement over the course of a marathon adds to caloric debt. Yes, flailing your arms from side-to-side rather than up and down burns more calories, which isn’t good for someone trying to run a faster time.
Some things to keep in mind to lessen caloric debt in a race: lose some weight, work on maintaining a good aerobic base, and fix those running flaws that cause wasted movements. Wasted movements may be the result of a limited range of motion and lack of muscular development. Lessening your caloric needs during a race helps with faster times because you don’t have to slow down or stop to refuel. NASCAR serves as a good example. The car that is running the most efficient (less wind resistant, shorter lines on turns, less braking, etc) and takes fewer pit stops usually wins the race. Control those things that can be controlled (like our diets and our running workouts) and more likely than not you’d have ran a good race. In short, low caloric debt doesn’t necessitate frequent consumption; we can get by with fewer calories during the course of a race. Then, after the race, game on with the brews and burgers! Recovery!
This is a very unscientific graph based on numbers inputted into http://www.healthstatus.com/calculate/cbc. Taken from http://www.sushi-suzuki.com/blog/2007/10/which-burns-more-calories-running-or.html