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<small>Etymology: French ''calorie'', from Latin ''calor'' (heat), from ''calere'' (to be warm).</small>
<small>Etymology: French ''calorie'', from Latin ''calor'' (heat).</small>




A '''calorie''' is a unit of measurement for [[energy]]. In most fields, it has been replaced by the [[joule]], the [[SI]] unit of energy. However, the kilocalorie or calorie remains in common use for the amount of [[food energy]]. The calorie was first defined by Professor [[Nicolas Clément]] in 1824 as a kilogram-calorie and this definition entered French and English dictionaries between 1842 and 1867.
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 1842 and 1867.


The word has two conflicting definitions, one used (now rarely) in physics, and one used quite commonly in nutrition and physiology.
The calorie was never an SI unit. Modern definitions for calorie fall into two classes:


* The '''small calorie''' or '''gram calorie''' approximates the energy needed to increase the temperature of 1 [[gram]] of [[water]] by 1&nbsp;[[degree Celsius|°C]]. This is about 4.184 [[joule]]s.
* 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&nbsp;[[degree Celsius|°C]] to 15.5&nbsp;°C at standard atmospheric pressure - approximately 4.184 [[joule]]s. (/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Dictionary of the English Language/, Library of Congress Catalog Card Number 67-12237, s.v.) It is rarely used, having been replaced by the SI unit.
* The '''large calorie''' or '''kilogram calorie''' approximates the energy needed to increase the temperature of 1 [[kilogram|kg]] of water by 1&nbsp;°C. This is about 4.184 [[kilojoule|kJ]], and exactly 1000 small calories.


* In physiology, (also called '''kilocalorie,''' '''kilogram calorie,''' or '''large-c Calorie''') the energy needed to increase the temperature of a [[kilogram|kg]] of water by 1&nbsp;°C, exactly 1000 small calories, or about 4.184 [[kilojoule|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.
In some scientific contexts such as physics and chemistry, the name "calorie" refers strictly to the gram calorie, and this unit has the symbol '''cal''' (a symbol also used by many for the large calorie). [[SI prefix|Prefixes]]<!--these existed long before here was an SI; we didn't borrow this from a system that was only invented in 1960, but rather had used them for many years before them. There should be no "SI" in the visible text here--> are used with this name and symbol, so that the kilogram calorie is often known as the "kilocalorie" and has the symbol '''kcal'''.


⚫
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 unit]]s. See "Versions" below for an explanation of the units.
In the medical sciences and non-scientific contexts the calorie<!--not a shortening of kilocalorie, just a parallel system that came into use based on the kilogram rather than the gram--> is equal to a kilocalorie in the physics or chemistry sense, and is occasionally referred to as a Calorie (capital "C") in an attempt to distinguish it. This has been somewhat ineffective, partly because the convention is not used outside this context, and partly because it results in ambiguity when the word appears at the beginning of a list or sentence. Thus it has to be inferred from the context that the small calorie is not intended.

⚫
The conversion factor among calories and joules is numerically equivalent to the [[specific heat capacity]] of liquid [[water]] (in [[SI unit]]s). See "Versions" below for explanation of units.
:1 cal<sub>IT</sub> <!--(international)--> = 4.1868 J (1 J = 0.23885 cal<sub>IT</sub>) (International Steam Table calorie, 1956)
:1 cal<sub>IT</sub> <!--(international)--> = 4.1868 J (1 J = 0.23885 cal<sub>IT</sub>) (International Steam Table calorie, 1956)
:1 cal<sub>th</sub> <!--(thermo)--> = 4.184 J (1 J = 0.23901 cal<sub>th</sub>) (Thermochemical calorie)
:1 cal<sub>th</sub> <!--(thermo)--> = 4.184 J (1 J = 0.23901 cal<sub>th</sub>) (Thermochemical calorie)
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==Versions==
==Versions==
The energy needed to increase the temperature of 1 [[gram|g]] of water by 1 [[degree Celsius]] varies depending on the starting temperature, and is in any case difficult to measure precisely. Accordingly there have been several definitions of the calorie:
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&nbsp;°C calorie (cal<sub>15</sub>): the amount of energy required to warm 1&nbsp;g of air-free water from 14.5&nbsp;°C to 15.5&nbsp;°C at a constant pressure of 101.325&nbsp;kPa (1 [[atmosphere (unit)|atm]]). Experimental values of this calorie ranged from 4.1852&nbsp;J to 4.1858&nbsp;J. The [[CIPM]] in 1950 published a mean experimental value of 4.1855&nbsp;J, noting an uncertainty of 0.0005&nbsp;J.
* 15&nbsp;°C calorie (cal<sub>15</sub>): the amount of energy required to warm 1&nbsp;g of air-free water from 14.5&nbsp;°C to 15.5&nbsp;°C at a constant pressure of 101.325&nbsp;kPa (1 [[atmosphere (unit)|atm]]). Experimental values of this calorie ranged from 4.1852&nbsp;J to 4.1858&nbsp;J. The [[CIPM]] in 1950 published a mean experimental value of 4.1855&nbsp;J, noting an uncertainty of 0.0005&nbsp;J.
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Human fat tissue contains about 87% [[lipids]], so that 1 kg of body-fat tissue has roughly the caloric energy of 870 g 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 (mass)|pound]]. <ref>{{cite web | url=http://www.nlm.nih.gov/medlineplus/ency/article/001940.htm | title=Medical Encyclopedia: Losing weight | publisher=[[MedlinePlus]] | accessdate=2007-08-28}}</ref> 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.
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 (mass)|pound]]. <ref>{{cite web | url=http://www.nlm.nih.gov/medlineplus/ency/article/001940.htm | title=Medical Encyclopedia: Losing weight | publisher=[[MedlinePlus]] | accessdate=2007-08-28}}</ref> 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==
==External links==

Revision as of 21:58, 27 February 2008

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 1842 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

Nutrient Calories per gram
Carbohydrate 4 kcal
Protein 4 kcal
Fat 9 kcal
Alcohol 7 kcal

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.

  • USDA National Nutrient Database for Standard Reference - Release 19 Official, publicly available reference database and online search site. Includes 7,293 foods and is free to download and use. This database is the one used by most websites that provide calorie information, and forms the basis of the Canadian national nutrient database and others
  1. ^ "Medical Encyclopedia: Losing weight". MedlinePlus. Retrieved 2007-08-28.
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