The number of calories your body burns each day is called your total energy expenditure. The following three factors make up your total energy expenditure:

• Basic needs. Even when your body is at rest, it requires energy for the basics, such as fuel for organs, breathing, circulating blood, adjusting hormone levels, plus growing and repairing cells. Calories expended to cover these basic functions are your basal metabolic rate (BMR). Typically, a person's BMR is the largest portion of energy use, representing two-thirds to three-quarters of the calories used each day. Energy needs for these basic functions stay fairly consistent and aren't easily changed.

• Food processing. Digesting, absorbing, transporting and storing the food you consume also takes calories. This accounts for about 10 percent of the calories used each day. For the most part, your body's energy requirement to process food stays relatively steady and isn't easily changed.

• Physical activity. Physical activity — such as playing tennis, walking to the store, chasing after the dog and any other movement — accounts for the remainder of calories used. You control the number of calories burned depending on the frequency, duration and intensity of your activities.