You have probably heard that in order to lose weight, you need to expend more calories each day than you take in. However, you might wonder what exactly caloric expenditure means, or how your body goes about expending calories. There are several different ways in which you use calories each day.
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Though most people simply think of calories as things they don't want too many of, calories are just a measure of energy -- as pounds are a measure of weight. A calorie is, specifically, the amount of energy it takes to heat up 1 mL of water by 1 degree Celsius. The "Calories" listed on a food nutrition label are actually kcal, or kilocalories; the capital "C" indicates the difference between a food Calorie and a regular calorie.
Almost everything your cells do -- building new proteins and other functional and structural molecules, transmitting information and producing movement -- requires energy. For this reason, you consume nutrients and burn them to extract the calories of energy they contain. You then use this energy -- you expend these calories -- to engage in cellular processes. Caloric expenditure is literally the amount of energy your cells use up in a given period of time.
Types of Expenditure
There are many general categories of caloric expenditure. For instance, you need a certain number of calories each day -- it varies with age, gender, sex and body composition -- to maintain basic function. This is your resting metabolic rate. You also need calories to move around and do the things you do, exercise and otherwise. This is your physical activity energy expenditure. Finally, you use energy to burn the nutrients in the food you eat -- this is the thermic effect of food.
Your caloric expenditure each day depends upon many things: your age, gender, activity level, body type and genetic factors. Generally speaking, younger adults burn more calories each day than older adults, and men burn more than women. The larger you are, the more calories you'll expend, and active people burn far more calories than less active. Most average women burn about 1,800 to 2,200 calories a day, and most average men burn about 300 to 500 calories more.