ABSTRACT
Classical nutritionists use the term Calorie or kilocalorie (kcal) to represent the amount of heat required to raise the temperature of 1 kg of water 1°C.1 The international unit of energy is the joule. One Calorie or kcalorie is equal to 4.184 kilojoules or 4.2 kjoules (kJ). There are cogent reasons to express energy in terms of kjoules. Nutritionists have realized that the energy provided by food is used for more than heat production. It is also used for mechanical work (muscle movement) and for electrical signaling (vision; neuronal messages) and is stored as chemical energy. The joule is 107 ergs, where 1 erg is the amount of energy expended in accelerating a mass of 1 g by 1 cm/s. The international joule is dened as the energy liberated by one international ampere owing through a resistance of one international ohm in 1 s. Even though the use of joules or kilojoules is being urged by international scientists as a means to ease the confusion in discussions about energy, students will still nd the term Calorie or kcal in many texts and references. In some texts, the term calorie, spelled with a lower case c, is used. This heat is actually 1/1000th of the heat unit spelled with an upper case C. Physicists use the term calorie to represent the amount of heat required to raise the temperature of 1 g of water 1°C. Note that this denition uses 1 g, not 1 kg, as stated previously. Even though it is not correct, the term calorie is used in some nutrition literature when in fact Calorie or kcal is intended.
