The Calorie is the measuring unit of heat. It corresponds to the amount of heat necessary to bring one litre of water from 14.5° to 15.5° C, under normal atmospheric pressure. The “calorie”, used in nutrition, is in fact one kilocalorie. In the International System, the unit used to measure energy is the Joule (1 kilocalorie = 4,18 kilojoules). Lipids yield 9 Kcal/g. Carbohydrates and proteins yield 4 Kcal/g.