A unit of energy. One calorie is the amount of energy needed to raise the temperature of 1 gram of water by 1°C. However, the term calorie is also used in medicine and dietetics to mean kilocalorie, a larger unit equal to 1,000 calories. Normally, when calorie intake matches the amount of energy expended, body weight remains constant. If intake exceeds expenditure, weight is usually gained; if expenditure exceeds intake, weight is usually lost. In general, fats contain the most calories. Energy can also be measured in joules: 1 calorie equals 4.2 joules. (See also calorimetry; diet and disease.)
A unit of energy. Two units are called by this name. The small calorie, or gram calorie, is the amount of heat required to raise one gram of water one degree centigrade in temperature.
The large Calorie or kilocalorie, which is used in the study of dietetics and physiological processes, is the amount of heat required to raise one kilogram of water one degree centigrade in temperature. The number of Calories required to carry on the processes necessary for life and body warmth – such as the beating of the heart, the movements of the chest in breathing, and the chemical activities of the secreting glands – is, for an adult person of ordinary weight, somewhere in the neighbourhood of 1,600. For ordinary sedentary occupations an individual requires about 2,500 Calories; for light muscular work slightly over 3,000 Calories; and for hard continuous labour around 4,000 Calories daily.
Under the International System of Units (SI UNITS – see APPENDIX 6: MEASUREMENTS IN MEDICINE) the kilocalorie has been replaced by the joule, the abbreviation for which is J (1 kilocalorie=4,186·8 J). The term Calorie, however, is so well established that it has been retained in this edition. Conversion from Calories (or kilocalories) to joules is made by multiplying by 4·2 .
n. a unit commonly defined as the approximate amount of energy required to raise the temperature of 1 gram of water by 1°C at atmospheric pressure. The energy value of foods should be expressed in kilocalories (one kilocalorie (kcal) is equal to 1000 calories). The SI unit is the *joule: 1 calorie = 4.1855 joules. The average adult requires 1994 kcal (women) or 2250 kcal (men) per day.
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