How Many Calories Can My Body Metabolize?

The number of calories you metabolize depends on how much muscle mass and other lean tissues you have, as well as your age, gender, health and fitness level, and activity level, according to sports dietitian Ellen Coleman, author of "Ultimate Sports Nutrition."

Basal Metabolic Rate

Basal metabolic rate, or BMR, estimates how many calories you metabolize when you are at rest, according to exercise physiologist William McArdle. The more muscles you have, the more calories you burn when you exercise and rest. For example, if you have 90 lb. of muscle, you would burn about 1,230 calories a day without factoring in exercise. If you have 100 lbs. of muscle, you would burn about 1,345 calories a day.

Physical Activity

Estimate how many calories you need per day by adding the number of calories you burn during exercise with your BMR. According to McArdle, an average man burns 2 to 5 calories per minute during light exercise such as walking or cycling at 6 mph on a level surface. During heavy exercise, such as weight training or cross-country skiing, 7.5 to 10 calories per minute are burned. For example, if you did heavy weight training for 20 minutes, multiply 20 by 9, which equals 180 calories burned. Similarly, if you did 30 minutes of cycling --considered a "light" exercise -- at 6 mph, multiply 3 calories by 30, which equals 90 calories burned.

Environmental Factors

Athletes who play in the cold or heat will need and burn more calories than those who play in warmer weather, according to Coleman. Your body burns an additional 5 to 20 percent more calories in cold weather. Exercising in the heat imposes a small additional oxygen intake; exercising in the cold promotes shivering, which burns more calories. If you BMR is 1250 calories, you would burn an additional 62.5 to 250 calories per day by exercising in more extreme than moderate conditions.