Calorie

A nutrition facts label highlighting the number of calories per typical serving

General information
Unit of| energy
Symbol| cal
Conversions
1 cal in ...| ... is equal to ...
SI units|  4.184 J

The calorie is a unit of energy that originated from the caloric theory of heat.[1][2] The small calorie or gram calorie is defined as the amount of heat needed to raise the temperature of one milliliter of water by one degree Celsius (or one kelvin).[3][4][5] In the US, "large calorie" is also used to mean kilocalorie (1 kcal = 1000 cal) .[1][3]

In nutrition and food science, the term calorie and the symbol cal may refer to the large unit or to the small unit in different regions of the world. It is generally used in publications and package labels to express the energy value of foods in per serving or per weight, recommended dietary caloric intake,[6][7] metabolic rates, etc. Some authors recommend the spelling Calorie and the symbol Cal (both with a capital C) if the large calorie is meant, to avoid confusion;[8] however, this convention is often ignored.[6][7][8]

In physics and chemistry, the word calorie and its symbol usually refer to the small unit, the large one being called kilocalorie (kcal). However, the calorie is not part of the International System of Units (SI) and is regarded as obsolete,[2] having been replaced by the SI derived unit of energy, the joule (J),[9] or the kilojoule (kJ) for 1,000 joules.

The precise equivalence between calories and joules has varied over the years, but in thermochemistry and nutrition it is now generally assumed that one (small) calorie (thermochemical calorie) is equal to exactly 4.184 J, and therefore one kilocalorie (one large calorie) is 4184 J or 4.184 kJ.[10][11]

## Contents

* 1 History
* 2 Definitions
* 3 Usage
* 3.1 Nutrition
* 3.2 Food energy
* 3.3 Chemistry and physics
* 4 See also
* 5 References

## History

The term "calorie" comes from la calor 'heat'.[12] It was first introduced by Nicolas Clément, as a unit of heat energy, in lectures on experimental calorimetry during the years 1819–1824. This was the "large" calorie.[2][13][14] The term (written with lowercase "c") entered French and English dictionaries between 1841 and 1867.

The same term was used for the "small" unit by Pierre Antoine Favre (chemist) and Jean Thiébault Silbermann (physicist) in 1852.

In 1879, Marcellin Berthelot distinguished between gram-calorie and kilogram-calorie, and proposed using "Calorie", with capital "C", for the large unit.[2] This usage was adopted by Wilbur Olin Atwater, a professor at Wesleyan University, in 1887, in an influential article on the energy content of food.[2][13]

The smaller unit was used by U.S. physician Joseph Howard Raymond, in his 1894 textbook A Manual of Human Physiology.[15] He proposed calling the "large" unit "kilocalorie", but the term did not catch on until some years later.

The small calorie (cal) was recognized as a unit of the CGS system in 1896,[2][14] alongside the already-existing CGS unit of energy, the erg (first suggested by Clausius in 1864, under the name ergon, and officially adopted in 1882).

In 1928, there were already serious complaints about the possible confusion arising from the two main definitions of the calorie and whether the notion of using the capital letter to distinguish them was sound.[16]

The joule was the officially adopted SI unit of energy at the ninth General Conference on Weights and Measures in 1948.[17][9] The calorie was mentioned in the 7th edition of the SI brochure as an example of a non-SI unit.[10]

The alternate spelling calory is a less-common, non-standard variant.[12]

## Definitions

The "small" calorie is broadly defined as the amount of energy needed to increase the temperature of 1 gram of water by 1 °C (or 1 K, which is the same increment, a gradation of one percent of the interval between the melting point and the boiling point of water).[4][5] The actual amount of energy required to accomplish this temperature increase depends on the atmospheric pressure and the starting temperature; different choices of these parameters have resulted in several different precise definitions of the unit.

Name | Symbol | Conversions | Definition and notes

|
|
|

Thermochemical calorie | calth | ≡ 4.184 J

≈ 0.003964 BTU ≈ 1.162×10−6 kWh ≈ 2.611×1019 eV

| The amount of energy equal to exactly 4.184 J (joules) and 1 kJ ≈ 0.239 kcal.[18][19][20][11][lower-alpha 1]
4 °C calorie | cal4 | ≈ 4.204 J

≈ 0.003985 BTU ≈ 1.168×10−6 kWh ≈ 2.624×1019 eV

| The amount of energy required to warm one gram of air-free water from 3.5 to 4.5 °C at standard atmospheric pressure.[lower-alpha 2]
15 °C calorie | cal15 | ≈ 4.1855 J

≈ 0.0039671 BTU ≈ 1.1626×10−6 kWh ≈ 2.6124×1019 eV

| The amount of energy required to warm one gram of air-free water from 14.5 to 15.5 °C at standard atmospheric pressure.[lower-alpha 2] Experimental values of this calorie ranged from 4.1852 to 4.1858 J. The CIPM in 1950 published a mean experimental value of 4.1855 J, noting an uncertainty of 0.0005 J.[18]
20 °C calorie | cal20 | ≈ 4.182 J

≈ 0.003964 BTU ≈ 1.162×10−6 kWh ≈ 2.610×1019 eV

| The amount of energy required to warm one gram of air-free water from 19.5 to 20.5 °C at standard atmospheric pressure.[lower-alpha 2]
Mean calorie | calmean | ≈ 4.190 J

≈ 0.003971 BTU ≈ 1.164×10−6 kWh ≈ 2.615×1019 eV

| Defined as ​1⁄100 of the amount of energy required to warm one gram of air-free water from 0 to 100 °C at standard atmospheric pressure.[lower-alpha 2]
International Steam Table calorie (1929) |  | ≈ 4.1860 J

≈ 0.0039683 BTU ≈ 1.1630×10−6 kWh ≈ 2.6132×1019 eV

| Defined as ​1⁄860 "international" watt hours = ​180⁄43 "international" joules exactly.[lower-alpha 3]
International Steam Table calorie (1956) | calIT | ≡ 4.1868 J

≈ 0.0039683 BTU = 1.1630×10−6 kWh ≈ 2.6132×1019 eV

| Defined as 1.163 mWh = 4.1868 J exactly. This definition was adopted by the Fifth International Conference on Properties of Steam (London, July 1956).[18]

1. ↑ The 'Thermochemical calorie' was defined by Rossini simply as 4.1833 international joules in order to avoid the difficulties associated with uncertainties about the heat capacity of water. It was later redefined as 4.1840 J exactly.[22]
2. ↑ 2.0 2.1 2.2 2.3 The standard atmospheric pressure can be taken to be 101.325 kPa.
3. ↑ The figure depends on the conversion factor between "international joules" and "absolute" (modern, SI) joules. Using the mean international ohm and volt (1.00049 Ω, 1.00034 V),[21] the "international joule" is about 1.00019 J, using the US international ohm and volt (1.000495 Ω, 1.000330 V) it is about 1.000165 J, giving 4.18684 and 4.18674 J, respectively.

The two definitions most common in older literature appear to be the 15 °C calorie and the thermochemical calorie. Until 1948, the latter was defined as 4.1833 international joules; the current standard of 4.184 J was chosen to have the new thermochemical calorie represent the same quantity of energy as before.[19]

## Usage

### Nutrition

In North America, in a nutritional context, the "large" unit is used almost exclusively.[23][24] It is generally written "calorie" with lowercase "c" and symbol "cal", even in government publications.[6][7] The SI unit kilojoule (kJ) may be used instead, in legal or scientific contexts.[25][26] Most American nutritionists prefer the unit kilocalorie to the unit kilojoules, whereas most physiologists prefer to use kilojoules. In the majority of other countries, nutritionists prefer the kilojoule to the kilocalorie.[27]

In Europe, on nutrition facts labels, energy is expressed in both kilojoules and kilocalories, abbreviated as "kJ" and "kcal" respectively.[28]

In China, only kilojoules are given.[29]

### Food energy

The unit is most commonly used to express food energy, namely the specific energy (energy per mass) of metabolizing different types of food. For example, fat (triglyceride lipids) contains 9 kilocalories per gram (kcal/g), while carbohydrates (sugar and starch) and protein contain approximately 4 kcal/g.[30] Alcohol in food contains 7 kcal/g.[31] The "large" unit is also used to express recommended nutritional intake or consumption, as in "calories per day".

Dieting is the practice of eating food in a regulated way to decrease, maintain, or increase body weight, or to prevent and treat diseases such as diabetes and obesity. As weight loss depends on reducing caloric intake, different kinds of calorie-reduced diets have been shown to be generally effective.[32]

### Chemistry and physics

## See also

* Basal metabolic rate
* Caloric theory
* Conversion of units of energy
* Empty calorie
* Food energy
* A calorie is a calorie
* Nutrition facts label
* British thermal unit
* Satiety value
* Caloric deficit

## References

1. ↑ 1.0 1.1 Christopher W. Morris (1992) Academic Press Dictionary of Science and Technology. 2432 pages. ISBN 9780122004001
2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Allison Marsh (2020): "How Counting Calories Became a Science: Calorimeters defined the nutritional value of food and the output of steam generators " Online article on the IEEE Spectrum website, dated 29 December 2020. Accessed on 2022-01-20.
3. ↑ 3.0 3.1 "Definition of Calorie". 1 August 2017. https://www.merriam-webster.com/dictionary/calorie.
4. ↑ 4.0 4.1 "Cambridge Dictionary: calorie". https://dictionary.cambridge.org/us/dictionary/english/calorie.
5. ↑ 5.0 5.1 "Definition of calorie noun from the Oxford Advanced American Dictionary". https://www.oxfordlearnersdictionaries.com/us/definition/american_english/calorie.
6. ↑ 6.0 6.1 6.2 U. S. Food and Drug Administration (2019): "Calories on the Menu - Information for  ". Online document at the FDA Website , dated 5 August 2019. Accessed on 2022-01-20.
7. ↑ 7.0 7.1 7.2 U. K. National Health Service (2019): "What should my daily intake of calories be? ". Online document at the NHS website , dated 24 October 2019. Accessed on 2022-01-20.
8. ↑ 8.0 8.1 Conn, Carole; Len Kravitz. "Remarkable Calorie". University of New Mexico. http://www.unm.edu/~lkravitz/Article folder/remarkablecalorie.html.
9. ↑ 9.0 9.1 Bureau International des Poids et Mesures (2019): The International System of Units (SI) , 9th edition.
10. ↑ 10.0 10.1 Bureau International des Poids et Mesures (1998): The International System of Units (SI) , 7th edition.
11. ↑ 11.0 11.1 United Nations Food and Agriculture Organization (2003): "FAO Food and Nutrition Paper 77: Food energy - methods of analysis and conversion factors ". Accessed on 21 January 2022.
12. ↑ 12.0 12.1 ""Calorie."". Merriam-Webster.com Dictionary. https://www.merriam-webster.com/dictionary/calorie. Retrieved 2024-03-20.
13. ↑ 13.0 13.1 Hargrove, James L (2007). "Does the history of food energy units suggest a solution to "Calorie confusion"?". Nutrition Journal 6 (44). doi:10.1186/1475-2891-6-44. PMID 18086303.
14. ↑ 14.0 14.1 JL Hargrove, "history of the calorie in nutrition", J Nutr 136/12 (December 2006), pp. 2957–2961.
15. ↑ Joseph Howard Raymond (1894): A Manual of Human Physiology: Prepared with Special Reference to Students of Medicine . W.B. Saunders, 376 pages.
16. ↑ Marks, Percy L. (14 January 1928). "The Two Calories, Percy L. Marks". Nature 121 (3037): 58. doi:10.1038/121058d0.
17. ↑ "Resolution 3 of the 9th CGPM (1948): Triple point of water; thermodynamic scale with a single fixed point; unit of quantity of heat (joule)", BIPM. .
18. ↑ 18.0 18.1 18.2 International Standard ISO 31-4: Quantities and units, Part 4: Heat. Annex B (informative): Other units given for information, especially regarding the conversion factor. International Organization for Standardization, 1992.
19. ↑ 19.0 19.1 Rossini, Fredrick (1964). "Excursion in Chemical Thermodynamics, from the Past into the Future". Pure and Applied Chemistry 8 (2): 107. doi:10.1351/pac196408020095. http://iupac.org/publications/pac/8/2/0095/. Retrieved 21 January 2013. "both the IT calorie and the thermochemical calorie are completely independent of the heat capacity of water.".
20. ↑ Lynch, Charles T. (1974). Handbook of Materials Science: General Properties, Volume 1. CRC Press. p. 438. ISBN 9780878192342. https://books.google.com/books?id=QdU-lRMjOsgC&pg=PA444. Retrieved 8 March 2014.
21. ↑ International Union of Pure and Applied Chemistry (IUPAC) (1997). "1.6 Conversion tables for units". Compendium of Analytical Nomenclature (3 ed.). Institut d'Estudis Catalans. ISBN 0-86542-615-5. http://iupac.org/publications/analytical_compendium/Cha01sec6.pdf. Retrieved 31 August 2013.
22. ↑ FAO (1971). "The adoption of joules as units of energy". http://www.fao.org/docrep/meeting/009/ae906e/ae906e17.htm.
23. ↑ Nutrition, Center for Food Safety and Applied (7 March 2022). "Changes to the Nutrition Facts Label" (in en). FDA. https://www.fda.gov/food/food-labeling-nutrition/changes-nutrition-facts-label.
24. ↑ "Elements within the Nutrition Facts table" (in en). https://inspection.canada.ca/en/food-labels/labelling/industry/nutrition-labelling/elements-within-nutrition-facts-table#s2c1.
25. ↑ "Prospects improve for food energy labelling using SI units". UK Metric Association. 24 February 2012. http://metricviews.uk/2012/02/prospects-improve-for-food-energy-labelling-using-si-units/.
26. ↑ "SI Conventions". National Physical Laboratory. http://www.npl.co.uk/reference/measurement-units/si-conventions/.
27. ↑ Kevin T. Patton; Gary A. Thibodeau (11 January 2017). The Human Body in Health & Disease - E-Book. Elsevier Health Sciences. p. 537. ISBN 978-0-323-40206-4. https://books.google.com/books?id=JtDwDQAAQBAJ&pg=PA537.
28. ↑ "EU Regulation No 1169/2011 of the European Parliament and of the Council of 25 October 2011 on the provision of food information to consumers" (in en). https://eur-lex.europa.eu/eli/reg/2011/1169/oj#d1e2548-18-1.
29. ↑ USDA (2013). "China, General Rules for Nutrition Labeling of Prepackaged Foods". https://apps.fas.usda.gov/newgainapi/api/report/downloadreportbyfilename?filename=General Rules for Nutrition Labeling of Prepackaged Foods _Beijing_China - Peoples Republic of_1-9-2013.pdf.
30. ↑ "How Do Food Manufacturers Calculate the Calorie Count of Packaged Foods?" (in en). Scientific American. https://www.scientificamerican.com/article/how-do-food-manufacturers/.
31. ↑ "Calories - Fat, Protein, Carbohydrates, Alcohol. Calories per gram". http://www.nutristrategy.com/nutrition/calories.htm.
32. ↑ Strychar, I. (3 January 2006). "Diet in the management of weight loss". Canadian Medical Association Journal 174 (1): 56–63. doi:10.1503/cmaj.045037. ISSN 0820-3946. PMID 16389240.

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