It may not seem fair -- but metabolism is about science, not justice. Even if you work just as hard as your taller, bigger-boned friend -- you'll burn fewer calories provided you're doing the same exercise at the same intensity level for the same amount of time. But remember -- calories burned is not a competition. Even if you don't burn as many as you'd like or think you deserve, you're still doing your body a world of good through exercise.
How You Burn Calories
About 60 to 75 percent of the calories you burn daily are due to simple functions such as breathing, pumping blood and producing hormones. Another 10 percent of the calories you burn are due to digestion. The final 15 to 30 percent of daily burn comes from the calories you burn during exercise and daily functions, such as washing dishes, showering and walking to your car. A larger person has to support a bigger engine, so her body has to work harder to do all of these tasks.
How many more calories a larger person burns compared to a smaller person depends on the activity. For example, a 125-pound person who runs 10-minute miles for 30 minutes burns approximately 300 calories, while a 185-pound person burns 444 calories. A rock climbing adventure burns about 240 calories per half-hour for the 125-pound person, while the 185-pound person sizzles 344 calories. Cycle for 30 minutes at a 16-mph pace and your 125-pound frame burns about 360 calories in a half hour, compared to the 533 of your 185-pound partner.
You may exercise the same amount of time at the same intensity as your larger friend, but you can't eat the way she does and expect similar weight results. For example, if you and your friend are eating the same number of calories on a calorie-restricted eating plan while exercising the same amount and intensity, she will likely lose more weight than you because she burns more calories all day long due to her larger frame. If she eats to maintain her weight and you match her calorie-for-calorie, you will likely gain weight because your smaller frame requires fewer calories for maintenance.
As you lose weight, you burn fewer calories during exercise as well as through daily activity and body functions. This can affect your rate of weight loss because the same exercise and calorie intake that yielded big results on the scale now creates a smaller calorie deficit. A pound of weight loss happens when you create a 3,500-calorie deficit -- no matter your size. To keep a consistent rate of weight loss, you'll have to either increase your exercise duration and intensity to burn more calories or decrease your calorie intake even further. At some point, weight loss will plateau because you simply can't exercise more or safely trim calories further.
Andrea Cespedes is a professionally trained chef who has focused studies in nutrition. With more than 20 years of experience in the fitness industry, she coaches cycling and running and teaches Pilates and yoga. She is an American Council on Exercise-certified personal trainer, RYT-200 and has degrees from Princeton and Columbia University.