A calorie is a unit of energy. You gain calories from food and beverages and burn them off through activity. It takes more energy to run a bigger engine, so larger people tend to take in and use up more calories than smaller people. When doing the same activities, such as walking, an overweight person will usually burn more calories than a smaller person.
How You Burn
Your body burns calories to maintain its existence. Breathing, pumping blood and producing hormones requires energy. These activities make up your basal metabolic rate, which accounts for 60 percent to 75 percent of the total calories you burn daily. Your size, gender and age affect your basal metabolic rate. Another 10 percent of the calories you burn daily happens when you digest food. The remaining 15 percent to 30 percent of calories burned come from movement, from focused exercise such as brisk walks to getting up out of a chair. When you are overweight or highly muscular, it takes more energy to get your body moving, and you burn more calories.
An overweight person burns more calories doing almost any activity, from walking to washing the dishes. It is harder for the body to move the extra weight, so it uses extra energy. You may also be more inefficient at exercise when you are overweight, leading to a higher calorie burn. For example, a 125-pound person walking for 30 minutes at a pace of 3.5 mph burns approximately 120 calories. A 185-pound person doing the same activity burns 58 calories more, or 178 calories in a half hour.
Because you can burn more calories quickly when you are overweight, you may experience more significant weight loss when starting an exercise program than a friend who only has a few pounds to lose. Weight loss happens when you create a calorie deficit, meaning you eat fewer calories than you burn off. Because you burn more calories than your skinny friend, you can create a bigger deficit and see results. You have to watch your food intake, however. If you eat back all the calories you burn off during a walk, you will not lose weight.
If you are overweight and out of shape, you may lack stamina. If you are only able to sustain a walk of 10 to 15 minutes, you will burn fewer calories during that exercise session than a smaller person who can last an hour. Work your way up to at least 50 minutes per day, five times weekly for significant weight loss.