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Etymology: French calorie, from Latin calor (heat).
The calorie is a unit heat, a form of energy. In most fields, its use is archaic, and the SI unit of energy, the joule, has become accepted. However, the kilocalorie or Calorie (with a capital c) remains in common use as a unit of food energy. It was first defined by Professor Nicolas Clément in 1824 as a kilogram-calorie, and this definition entered French and English dictionaries between 1841 and 1867.
The word has two conflicting definitions, one used (now rarely) in physics, and one used quite commonly in nutrition and physiology.
- In physics, (also called gram calorie, small calorie) the amount of heat required to raise the temperature of a gram of water from 14.5 °C to 15.5 °C at standard atmospheric pressure - approximately 4.184 joules. (/The Random House Dictionary of the English Language/, Library of Congress Catalog Card Number 67-12237, s.v.) It is rarely used, having been replaced by the SI unit.
- In physiology, (also called kilocalorie, kilogram calorie, or large-c Calorie) the energy needed to increase the temperature of a kg of water by 1 °C, exactly 1000 small calories, or about 4.184 kJ. (/The Random House Dictionary of the English Language/, Library of Congress Catalog Card Number 67-12237, s.v.) It is used to express the fuel value of food or the heat emitted by an organism.
The factors used to convert measurements in calories to their equivalents in joules are numerically equivalent to expressions of the specific heat capacity of water in SI units. See "Versions" below for an explanation of the units.
- 1 calIT = 4.1868 J (1 J = 0.23885 calIT) (International Steam Table calorie, 1956)
- 1 calth = 4.184 J (1 J = 0.23901 calth) (Thermochemical calorie)
- 1 cal15 = 4.18580 J (1 J = 0.23890 cal15) (15°C calorie)
Versions
The energy needed to increase the temperature of a gram of water by 1 degree Celsius depends on the starting temperature and is difficult to measure precisely. Accordingly, there have been several definitions of the calorie:
- 15 °C calorie (cal15): the amount of energy required to warm 1 g of air-free water from 14.5 °C to 15.5 °C at a constant pressure of 101.325 kPa (1 atm). Experimental values of this calorie ranged from 4.1852 J to 4.1858 J. The CIPM in 1950 published a mean experimental value of 4.1855 J, noting an uncertainty of 0.0005 J.
- 20 °C calorie: the amount of energy required to warm 1 g of air-free water from 19.5 °C to 20.5 °C at a constant pressure of 101.325 kPa (1 atm). This is about 4.182 J.
- 4 °C calorie: the amount of energy required to warm 1 g of air-free water from 3.5 °C to 4.5 °C at a constant pressure of 101.325 kPa (1 atm).
- Mean calorie: 1/100 of the amount of energy required to warm 1 g of air-free water from 0 °C to 100 °C at a constant pressure of 101.325 kPa (1 atm). This is about 4.190 J
- International Steam Table Calorie (1929): (1/860) W h = (180/43) J exactly. This is approximately 4.1860 J.
- International Steam Table Calorie (1956) (calIT): 1.163 mW h = 4.1868 J exactly. This definition was adopted by the Fifth International Conference on Properties of Steam (London, July 1956).
- Thermochemical calorie (calth): 4.184 J exactly.
- IUNS calorie: 4.182 J exactly. This is a definition implied by the Committee on Nomenclature of the International Union of Nutritional Sciences.[citation needed]
The two perhaps most popular definitions used in older literature are the "15 °C calorie" and the "thermochemical calorie". Since the many different definitions are a source of confusion and error, all calories are now deprecated in favour of the SI unit for heat and energy: the joule (J).
Nutrition
Because human adipose (fat) tissue contains about 87% lipids, one kilogram of it stores the caloric energy of roughly 870 grams of pure fat, or 7800 kcal. In principle one has to create a 7800 kcal deficit or surplus between energy intake and use to lose or gain 1 kg of body fat, respectively, or 3500 kcal per pound. [1] However, if one eats 7800 kcal more than the body needs, one won't necessarily gain 1 kg of fat, since muscle and other tissues may be built. In the same way, if one eats 7800 kcal less than their maintenance level, they may not lose 1 kg of fat, since muscle and sugars may be metabolized to generate energy.
External links
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