In order to eat fewer calories than you need, you have to determine how many calories you actually need. Adults can calculate their approximate energy needs using the following formula:

A. Body weight multiplied by 12 (for men) or 11 (for women) e.g., 150 lbs. x 12 = 1800

B. Activity One third body weight multiplied by the number of hours you don't sleep, typically 16 hours 150 lbs. x 1/3 = 50 x 16 = 800

C. Required Calories A + B 1800 + 800 = 2600

Thus, we determine that a 150-pound man requires approximately 2600 calories per day. The "Basal Metabolic Rate" is the number of calories a man of that weight would burn just to keep the heart beating, the lungs pumping, etc. You would just burn your basal metabolic rate worth of calories if you slept all day. Thus the "Activity" calculation is approximately the amount of calories a person would expend by spending his or her whole day sitting around. If you are engaging in activities other than sitting all day, you can increase your activity hours by the number of hours you are actually active.

Adult females can calculate their approximate energy needs using the same formula, except that the "Basal Metabolic Rate" is determined by multiplying body weight times 11 instead of 12. Children and teenagers require more calories by body weight, but the amount varies by age and by individual child. It is best to consult a physician before altering a childs diet, however activity and exercise increases wont hurt the average youth of today.