Actually calories have nothing to do with food! They are really measurements of heat energy your body needs.
The food you take into your body can be considered a “fuel,” much like car runs on fuel. The breaking down of the food in the body tissues is a form burning that fuel and giving off heat to produce energy. In order to measure how much fuel we are taking in and how much the body needs, we use a measurement, calories.
A person who takes in a proper amount of fuel, or a normal number of calories, will be at his proper weight. But a person who takes in more fuel, or calories, than his body needs to burn each day finds that his body transforms this extra fuel into fat and stores it away simply as fat.
Each person needs different amounts of energy. Children need more than adults because they are growing rapidly. Larger people need more energy than smaller people because they have more body cells to feed. Men need more energy than women because they have more muscle tissue.
People in cold climates need more energy than people in warmer climates because their bodies use up their supply of energy more quickly to keep the body at normal temperature. And a person who does hard, physical work needs more energy than one who sits or rests all day.