The number of calories that the body needs to burn to work properly is different for every person. The nutritional labels on the food cartons or containers state that the "percent daily values" are based on a 2,000 calorie diet -- 2,000 calories being the amount an average person needs to eat in a day. Your body may need more or less depending on your height, weight, sex, age and activity level.

There are three main factors involved in calculating how many calories your body needs per day:

• your level of physical activity;
• the amount of energy your body needs to process food itself; and
• your basal metabolic rate (BMR). This is the amount of energy your body needs to function at rest keeping all your systems operating - the heart beating, lungs breathing, kidneys working, etc. It accounts for about 60 to 70 percent of the calories you burn in a day. In general, men have a higher rate than women.