A "calorie" is a unit of heat that measures how much energy we put into the body and how much energy we burned or used. A person's calorie-intake can affect his weight. If he consumes too much calories needed by his body, then it will be stored as a body fat (provided that he doesn't do anything to burn the excess calories). To prevent such occurrence, it is important not to consume too much calories. This will also prevent health problems. It is also best to exercise to burn some of the calories.