A pound of fat and a pound of muscle weigh the same, but they have different energy requirements. Muscle burns more calories than fat. People who are heavily muscular typically have a high basal metabolic rate, or BMR, which means they burn a significant number of calories, even when resting.
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Your Body Needs Energy
Your body burns calories when you move, but it also needs energy to maintain itself. For example, your lungs use energy when you breathe, and your heart uses energy to beat. You even burn calories at the cellular level as cells grow and repair themselves. The different body processes require various amounts of energy, so your particular body composition affects the number of calories you burn while performing everyday activities.
Muscles and Burning Calories
Research shows that 1 pound of muscle burns seven to 10 calories per day, while 1 pound of fat burns only 2 to 3 calories, according to the American Council on Exercise. It notes that the difference isn't huge, so gaining 3 to 5 pounds of muscle mass -- the typical results of a strength-training program that spans several months -- only has a net caloric effect of burning 15 to 30 more calories a day.
Men Vs. Women
Men generally require more energy to maintain their weight than women. Part of the reason is that men are more muscular than woman. Having relatively more muscle creates a greater need for energy, which leads to an increased need for calories in the diet. However, not all women or men have the same physical characteristics, so you should consider any daily-calorie recommendations to be rough estimates.
Your Body's Composition
A doctor can perform measurements to analyze your body's composition and then use the results to recommend how many calories you need to eat every day. Body-composition tests include skinfold measurements and water-displacement tests, which doctors use to determine how much of your body weight is due to body fat. Maintaining a high percentage of muscle and a low percentage of body fat is typically the healthiest way to live.