If we look at the calories meaning, it is the amount of energy that is required to raise the temperature of one gram of water by 1 degree Celsius and at a temperature of one atmosphere. The amount of energy that is needed to raise the temperature of the water is also referred to as the specific heat of the water. So, the Calorie can also be defined as a way to measure energy by means of heat. After 1942 calories were mostly viewed in the term of joules, which is the unit of energy in the SI system. When we buy products, we often see the calories mentioned on the food package. They are not actual calories but refer to kilocalories. Calories are also used in physics or chemistry calculations. But these are not used when human nutrition and metabolism are discussed.