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What Factors Affect Your Calorie Needs?

Your dietary calorie needs depend on your age, sex, metabolism, activity level, and body size. To get an idea of the total calories you should include in your daily diet, multiply your current weight by 15 if you’re moderately active or by 13 if you’re not.

The following list looks at factors that affect your calorie needs.

  • Your age: Calorie needs peak at about age 25 and then decline by about 2 percent every 10 years. So if you’re 25 years old and need 2,200 calories to maintain your weight, you’ll need only 2,156 by the time you’re 35; 2,113 at age 45; 2,071 at age 55; and so on.

    The aging body replaces muscle with fat, which burns fewer calories than muscle does. Staying active and doing muscle-strengthening exercises keeps muscle mass in tact. Recent work with seniors proves that you can build muscle at any age.

  • Your sex: An adult man has less body fat and about 10 to 20 percent more muscle than a woman of the same size and age. Because muscle burns more calories than fat does, a man’s calorie needs are generally about 5 to 10 percent higher than a woman’s. The exception for women is during pregnancy and breast-feeding.

  • Your metabolism: A living body needs a minimum number of calories to maintain vital functions, such as breathing and keeping its heart beating. This minimum number is called Basal Metabolic Rate (BMR).

    A quick way to approximate your BMR is to multiply your current weight by 10 if you’re a woman or by 11 if you’re a man. A 150-pound woman needs about 1,500 calories a day; a 175-pound man needs about 1,925 calories. Additional calories are needed for digestion and activity.

  • Your genetic blueprint: The metabolic rate that you inherit from your family in part determines the number of calories that your body needs to function, and you can’t change this. Inherited metabolic diseases, specifically those that affect your thyroid, can cause you to burn calories very quickly or very slowly. A malfunctioning thyroid gland can sabotage your best weight-loss efforts. Your physician can perform tests to determine your thyroid function.

  • Your body shape and the shape you’re in: Your body shape and size affect the number of calories you need because muscle burns more calories than body fat does. So if you’re solid and have a greater proportion of muscle to fat, your metabolism is higher. Likewise, if you have more body fat and less muscle, your metabolism is lower, and you have a greater tendency to store fat than someone who is tall and thin.

  • Your activity level: When you’re active, you burn calories. And if you burn (or expend) more calories than you eat, you lose weight. The kind of exercise you choose, and how long and how intensely you do it, determines exactly how many calories you burn. Some types of activity even help your body burn calories after you stop exercising — an added bonus!

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