Calories Needed And Calorie Expenditure Per Day

Knowing your daily calorie requirements is important because it can help you plan exercise and nutrition to lose, gain or maintain your weight. Too many calories can cause excess weight gain and fat storage, while extremely low calorie diets, fewer than 1,200 calories for women and fewer than 1,500 calories for men, can cause nutritional deficiencies, slowed metabolism and binge eating, which leads to weight gain.

Basic Calorie Needs

Every person needs a certain amount of energy to perform daily functions like breathing and sleeping. This calorie requirement is known as your basal metabolic rate, or BMR, and can be measured by a registered dietitian with diagnostic tools or estimated by an equation that takes into account your age, sex, height and current weight. As an example, a 30-year-old woman who is 5 feet 7 inches tall and weighs 150 pounds has a BMR of 1,481 calories per day. A 30-year-old male who is 5 feet 10 inches tall and weighs 180 pounds has a BMR of 1,872 calories per day. Variables that affect BMR include genetics and the ratio of fat to lean tissue in each person’s body.

Extra Calorie Expenditure

Total energy expenditure is a combination of BMR and calories burned through physical activity. One way to measure caloric expenditure from activity is to multiply your BMR by an activity factor calculated by the Harris-Benedict formula, one of the most established, though not perfect, equations for calculating total calorie burn. Sedentary people should multiply their BMR by 1.2. Lightly active people should multiply BMR by 1.375. Moderately active people should multiply their BMR by 1.55, and very active people should multiply their BMR by 1.725. A more specific way to measure extra calorie expenditure is to track your physical activity and calorie burn with a heart rate monitor and add that to your BMR.

Formulas and Resources

To estimate your daily calorie needs, first find your BMR. The established BMR formula for women is 655 plus 4.35 multiplied by weight in pounds + 4.7 multiplied by height in inches. Take this number and subtract 4.7 multiplied by age in years to get an estimate of BMR. For men, BMR is 66 + 6.23 multiplied by weight in pounds plus 12.7 multiplied by height in inches. Take this number and subtract 6.8 multiplied by age in years for an estimate of BMR. Multiply BMR by your activity factor to get total daily expenditure. Energy expenditure formulas are built into online calculators such as the Interactive DRI from the United States Department of Agriculture, which you can use. Calculating energy expenditure using established formulas can give you a starting estimate of how many calories you need every day, but no equation is perfect, so use formulas as a starting point for health planning and work with your physician or dietitian on personal needs.

Calories and Health Goals

Knowing how many calories you need per day can help you plan a diet and physical activity program to meet your specific goals. It takes a 3,500-calorie deficit or surplus to lose or gain 1 pound, respectively. Someone who wants to lose 1 to 2 pounds per week, a rate deemed safe by the National Heart Lung and Blood Institute, would need to reduce daily calories by 500 to 1,000 per day. Someone who needs to gain weight would have to increase calories by 500 more than they expend every day to gain 1 pound per week.