If you indulge in a high-calorie snack, can the calories be burned off calorie for calorie? In other words, if you eat a chocolate cake worth 350 calories, can you counteract it by burning the same 350 calories doing specific exercise?
- Jamie*

When it comes to balancing food eaten with activity, there's a simple equation: energy in = energy out (in other words, calories eaten = calories burned). So, yes, it is possible to burn off food calorie for calorie with exercise. But it's not very practical.

We all need a certain number of calories just to keep our bodies functioning — we're burning calories even while we sleep. In addition, we need calories to fuel our bodies for daily activities like walking, doing school work, and exercising. Everyone has different needs, but the bottom line is that if we eat more than our bodies use, we gain weight — unless we work off the extra calories.

How quickly a person burns off calories depends on things like age, size, and puberty stage. It also depends on how vigorous the physical activity is: Running at 5 mph burns more calories than walking at 2 mph.

So why isn't it realistic to think in terms of exercising away every additional calorie? Most of us don't have the time. It may take 2 minutes to eat a 350-calorie piece of cake, but someone who weighs 100 pounds (about 45 kg) would need to walk for more than 2 hours to burn it off. If you grab a burger, fries, and milkshake after school, and your body doesn't need those calories, you'd have to spend the rest of the day on the treadmill walking it off.

That's why the best approach to eating is to aim for balance: Eat healthy meals and snacks, be aware of portion sizes, and aim for at least 60 minutes a day of moderate to vigorous physical activity.

Reviewed by: Mary L. Gavin, MD
Date reviewed: October 2011

*Names have been changed to protect user privacy.