The amount of energy needed to increase the temperature of a gram of water by 1C is called a calorie. It is also used to measure the amount of energy that your metabolism expends during workouts and during rest. The calories in food provide the energy that your body needs. An average diet contains between 2,000 to 2,500 calories. Athletes who workout at intense levels and multiple times per day need more calories for energy. In addition to a good workout it is important to consider the number of calories you consume, and to make sure those calories come from foods that provide necessary nutrients.