The U.S. Department of Agriculture says a normal caloric burn is about 2,000 calories per day, but author and nutrition professor Marion Nestle reports it’s more like 3,050 calories a day for the average man and 2,400 for the average woman. The differences in these estimates make clear that knowing how many calories the normal body burns per day varies and can’t easily be calculated. Equations to estimate your calorie burn exist, but they’re just that – estimates. The normal daily calorie burn varies from person to person according to size, body composition, gender, age and physical activity.
A calorie is simply a measurement of energy – the amount of heat required to raise the temperature of a milliliter of water by 1 degree. Your body uses this energy to function.
You hear fitness instructors promise to help you burn calories, or fitness gadget infomercials say their product will melt calories away. While exercise does make up some of your natural daily calorie burn, simply existing – breathing, pumping blood and digesting food – also uses calories. The caloric amount used to simply survive is known as your basal metabolic rate, or BMR. Activities of daily life, from washing dishes to showering, also burn some calories and add to your BMR, as does any physical activity you do – whether that’s running a marathon or building a house.