Feel like stuffing your face after a grueling day at the office? Try exercising instead. A new study suggests that exercise keeps you from chowing down on more than your body needs after a tough mental task.

Previous research has shown that people eat more after such tasks, like tests or grant deadlines, say University of Alabama scientists in a release. (This phenomenon might explain the "freshman 15," notes the New York Times.) The problem is that mental activity uses energy, and our brain, wanting that energy replenished, tells us we're hungry.

Hence, the food binge. The researchers, however, found that people who were asked to perform tests ate less pizza afterward if they exercised for 15 minutes in the interim.

Why? Scientists aren't entirely sure, but they suspect it has to do with a spike in lactate levels in the blood triggered by the exercise. The theory is that the brain uses the lactate as fuel and gets sated that way, limiting the urge to overeat.

"Lactate may have replenished the brain's energy needs," says researcher Gary Hunter, adding that more research is needed to figure out the interplay of both lactate and blood sugar in eating behavior.

All told, the group that exercised added 200 fewer calories than those who simply rested, a figure that accounts for the calories expended during exercise, according to the study published in the journal Medical & Science in Science & Exercise.

(Here's the trouble with eating when tired.)

This article originally appeared on Newser: Tired Brain Makes Us Overeat, but There's a Fix