How Many Calories Does A Person Need?

Look at any nutrition label and you will find dietary recommendations for a 2,000 or 2,500 calorie diet. While these numbers are good estimates of the amount of calories your body needs, depending on your age, weight, activity level and gender, that number may vary. Generally, your body needs 1,500 to 3,500 calories per day.

Function

• Calories are a measurement of the amount of energy that your body needs and burns. Food calories exist in proteins, carbohydrates and fats. One gram of protein or carboyhydrate is equal to four calories. One gram of fat equals nine calories. According to the USDA's food pyramid, about 50 to 60 percent of the calories in a healthy diet should come from carbohydrates, 10 to 30 percent from protein and 20 to 35 percent from fat. The amount of calories your body needs is determined by three factors: your basal metabolic rate (BMR), the thermic effect of food and your activity level.

BMR

• Your BMR is the amount of calories your body needs at rest. Your BMR accounts for such basic functions as pumping blood and breathing. Your BMR typically accounts for about 70 percent of your caloric intake. To estimate your BMR, use the Harris Benedict Formula. For Men: BMR = 66 + (13.7 X wt in kg) + (5 X ht in cm) - (6.8 X age in years). For women: BMR = 655 + (9.6 X wt in kg) + (1.8 X ht in cm) - (4.7 X age in years)

Thermic Effect of Food

• Your body also needs calories to burn the food that you consume. This is known as the thermic effect of food and accounts for the amount of calories your body needs to burn the food you consume. Biting, chewing, swallowing and digesting require about 10 percent of your total caloric intake. For the 150-pound woman, the thermic effect would account for burning about 150 calories.

Activity Level

• Even the most sedentary person will burn calories. Talking on the phone, driving, sitting, cooking and doing other household chores require energy. Depending on your activity level, the amount of calories burned each day may be anywhere from 20 to 50 percent of your BMR. Use the Harris Benedict formula to determine the amount of calories burned due to your activity level.

  Sedentary: BMR x 1.2
  Lightly Active: BMR x 1.375
  Moderately Active: BMR x 1.55
  Very Active: BMR x 1.725
  Extra Active: BMR x 1.9

Weight Loss

• There are 3,500 calories in a pound. If your goal is to lose weight, you can either reduce your caloric intake or increase your caloric expenditure through exercise. Never reduce your caloric intake to below your BMR. Instead, consider reducing your daily calories by 200 and increasing your activity level to burn an additional 300 calories. At that rate, you will have burned one pound in one week.