Calorie

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calorie
Unit of energy
Symbolcal
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 large calorie, food calorie, dietary calorie, or kilogram calorie is defined as the amount of heat needed to raise the temperature of one liter of water by one degree Celsius (or one kelvin). [1] [3] The small calorie or gram calorie is defined as the amount of heat needed to cause the same increase in one milliliter of water. [3] [4] [5] [1] Thus, 1 large calorie is equal to 1000 small calories.

Contents

A 710-millilitre (24 US fl oz) Monster energy drink with 330 large calories Energy drink and fast food cheeseburger calorie comparison.jpg
A 710-millilitre (24 US fl oz) Monster energy drink with 330 large calories

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 kcal is not officially part of the International System of Units (SI), and is regarded as obsolete, [2] having been replaced in many uses by the SI derived unit of energy, the joule (J), [9] or the kilojoule (kJ) for 1000 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]

History

The term "calorie" comes from Latin 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 Johann T. 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 classic 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.

NameSymbolConversionsDefinition and notes
Thermochemical caloriecalth≡ 4.184  J

≈ 0.003964  BTU ≈ 1.162×10−6  kW⋅h ≈ 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] [a]
4 °C caloriecal4≈ 4.204 J

≈ 0.003985 BTU ≈ 1.168×10−6 kW⋅h ≈ 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. [b]
15 °C caloriecal15≈ 4.1855 J

≈ 0.0039671 BTU ≈ 1.1626×10−6 kW⋅h ≈ 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. [b] 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 caloriecal20≈ 4.182 J

≈ 0.003964 BTU ≈ 1.162×10−6 kW⋅h ≈ 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. [b]
Mean caloriecalmean≈ 4.190 J

≈ 0.003971 BTU ≈ 1.164×10−6 kW⋅h ≈ 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. [b]
International Steam Table calorie (1929)≈ 4.1868 J

≈ 0.0039683 BTU ≈ 1.1630×10−6 kW⋅h ≈ 2.6132×1019 eV

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

≈ 0.0039683 BTU= 1.1630×10−6 kW⋅h ≈ 2.6132×1019 eV

Defined as 1.163 mW⋅h = 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. 1 2 3 4 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 the United States, in a nutritional context, the "large" unit is used almost exclusively. [23] 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. [24] [25] 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. [26]

In the European Union, on nutrition facts labels, energy is expressed in both kilojoules and kilocalories, abbreviated as "kJ" and "kcal" respectively. [27]

In China, only kilojoules are given. [28]

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. [29] Alcohol in food contains 7 kcal/g. [30] 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. [31]

Chemistry and physics

In other scientific contexts, the term "calorie" and the symbol "cal" almost always refers to the small unit; the "large" unit being generally called "kilocalorie" with symbol "kcal". It is mostly used to express the amount of energy released in a chemical reaction or phase change, typically per mole of substance, as in kilocalories per mole. [32] It is also occasionally used to specify other energy quantities that relate to reaction energy, such as enthalpy of formation and the size of activation barriers. [33] However, it is increasingly being superseded by the SI unit, the joule (J); and metric multiples thereof, such as the kilojoule (kJ).[ citation needed ]

The lingering use in chemistry is largely due to the fact that the energy released by a reaction in aqueous solution, expressed in kilocalories per mole of reagent, is numerically close to the concentration of the reagent in moles per liter multiplied by the change in the temperature of the solution in kelvins or degrees Celsius. However, this estimate assumes that the volumetric heat capacity of the solution is 1 kcal/(L⋅K), which is not exact even for pure water.[ citation needed ]

See also

Related Research Articles

The British thermal unit (Btu) is a measure of heat, which is a form of energy. It was originally defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It is also part of the United States customary units. The SI unit for energy is the joule (J); one Btu equals about 1,055 J.

<span class="mw-page-title-main">Joule</span> SI unit of energy

The joule is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of one newton displaces a mass through a distance of one metre in the direction of that force. It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889).

<span class="mw-page-title-main">Specific heat capacity</span> Heat required to increase temperature of a given unit of mass of a substance

In thermodynamics, the specific heat capacity of a substance is the amount of heat that must be added to one unit of mass of the substance in order to cause an increase of one unit in temperature. It is also referred to as massic heat capacity or as the specific heat. More formally it is the heat capacity of a sample of the substance divided by the mass of the sample. The SI unit of specific heat capacity is joule per kelvin per kilogram, J⋅kg−1⋅K−1. For example, the heat required to raise the temperature of 1 kg of water by 1 K is 4184 joules, so the specific heat capacity of water is 4184 J⋅kg−1⋅K−1.

A nutrient is a substance used by an organism to survive, grow and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi and protists. Nutrients can be incorporated into cells for metabolic purposes or excreted by cells to create non-cellular structures such as hair, scales, feathers, or exoskeletons. Some nutrients can be metabolically converted into smaller molecules in the process of releasing energy such as for carbohydrates, lipids, proteins and fermentation products leading to end-products of water and carbon dioxide. All organisms require water. Essential nutrients for animals are the energy sources, some of the amino acids that are combined to create proteins, a subset of fatty acids, vitamins and certain minerals. Plants require more diverse minerals absorbed through roots, plus carbon dioxide and oxygen absorbed through leaves. Fungi live on dead or living organic matter and meet nutrient needs from their host.

The joule per mole is the unit of energy per amount of substance in the International System of Units (SI), such that energy is measured in joules, and the amount of substance is measured in moles.

<span class="mw-page-title-main">James Prescott Joule</span> English physicist and brewer (1819–1889)

James Prescott Joule was an English physicist, mathematician and brewer, born in Salford, Lancashire. Joule studied the nature of heat, and discovered its relationship to mechanical work. This led to the law of conservation of energy, which in turn led to the development of the first law of thermodynamics. The SI derived unit of energy, the joule, is named after him.

Food energy is chemical energy that animals derive from their food to sustain their metabolism, including their muscular activity.

<span class="mw-page-title-main">Heat capacity</span> Physical property describing the energy required to change a materials temperature

Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin (J/K).

Basal metabolic rate (BMR) is the rate of energy expenditure per unit time by endothermic animals at rest. It is reported in energy units per unit time ranging from watt (joule/second) to ml O2/min or joule per hour per kg body mass J/(h·kg). Proper measurement requires a strict set of criteria to be met. These criteria include being in a physically and psychologically undisturbed state and being in a thermally neutral environment while in the post-absorptive state (i.e., not actively digesting food). In bradymetabolic animals, such as fish and reptiles, the equivalent term standard metabolic rate (SMR) applies. It follows the same criteria as BMR, but requires the documentation of the temperature at which the metabolic rate was measured. This makes BMR a variant of standard metabolic rate measurement that excludes the temperature data, a practice that has led to problems in defining "standard" rates of metabolism for many mammals.

<span class="mw-page-title-main">K-ration</span> U.S. military three-course assault ration

The K-ration was a United States military ration consisting of three separately boxed meal units: breakfast, dinner, and supper. It was originally intended as an individually packaged daily ration for issue to airborne troops, tank crews, motorcycle couriers, and other mobile forces for short durations.

The molar heat capacity of a chemical substance is the amount of energy that must be added, in the form of heat, to one mole of the substance in order to cause an increase of one unit in its temperature. Alternatively, it is the heat capacity of a sample of the substance divided by the amount of substance of the sample; or also the specific heat capacity of the substance times its molar mass. The SI unit of molar heat capacity is joule per kelvin per mole, J⋅K−1⋅mol−1.

The kilocalorie per mole is a unit to measure an amount of energy per number of molecules, atoms, or other similar particles. It is defined as one kilocalorie of energy per one mole of substance. The unit symbol is written kcal/mol or kcal⋅mol−1. As typically measured, one kcal/mol represents a temperature increase of one degree Celsius in one liter of water resulting from the reaction of one mole of reagents.

Specific energy or massic energy is energy per unit mass. It is also sometimes called gravimetric energy density, which is not to be confused with energy density, which is defined as energy per unit volume. It is used to quantify, for example, stored heat and other thermodynamic properties of substances such as specific internal energy, specific enthalpy, specific Gibbs free energy, and specific Helmholtz free energy. It may also be used for the kinetic energy or potential energy of a body. Specific energy is an intensive property, whereas energy and mass are extensive properties.

Energy is defined via work, so the SI unit of energy is the same as the unit of work – the joule (J), named in honour of James Prescott Joule and his experiments on the mechanical equivalent of heat. In slightly more fundamental terms, 1 joule is equal to 1 newton metre and, in terms of SI base units

The insulin index of food represents how much it elevates the concentration of insulin in the blood during the two-hour period after the food is ingested. The index is similar to the glycemic index (GI) and glycemic load (GL), but rather than relying on blood glucose levels, the Insulin Index is based upon blood insulin levels. The Insulin Index represents a comparison of food portions with equal overall caloric content, while GI represents a comparison of portions with equal digestible carbohydrate content and the GL represents portions of a typical serving size for various foods. The Insulin Index can be more useful than either the glycemic index or the glycemic load because certain foods cause an insulin response despite there being no carbohydrates present, and some foods cause a disproportionate insulin response relative to their carbohydrate load.

A Guideline Daily Amount (GDA) was a nutrition facts label originally designed in 1996 in the United Kingdom (UK) as a collaboration between the government, the food industry and consumer organisations. GDAs appeared on the front and back of food packaging to help raise awareness of how much a food item represents as a proportion of a balanced intake each day in each food element. The British initiative was followed in the European Union (EU) and influenced similar systems in other countries including the United States.

"A calorie is a calorie" is a tautology used to convey the thermodynamic concept that a "calorie" is a sufficient way to describe the energy content of food.

A caloric deficit is any shortage in the number of calories consumed relative to the number of calories needed for maintenance of current body weight.

References

  1. 1 2 3 Christopher W. Morris (1992) Academic Press Dictionary of Science and Technology. 2432 pages. ISBN   9780122004001
  2. 1 2 3 4 5 6 Allison Marsh (2020): "How Counting Calories Became a Science: Calorimeters defined the nutritional value of food and the output of steam generators Archived 2022-01-21 at the Wayback Machine " Online article on the IEEE Spectrum Archived 2022-01-20 at the Wayback Machine website, dated 29 December 2020. Accessed on 2022-01-20.
  3. 1 2 "Definition of Calorie". Merriam-Webster. 1 August 2017. Retrieved 4 September 2017.
  4. 1 2 "Cambridge Dictionary: calorie" . Retrieved 9 November 2019.
  5. 1 2 "Definition of calorie noun from the Oxford Advanced American Dictionary" . Retrieved 9 November 2019.
  6. 1 2 3 U. S. Food and Drug Administration (2019): "Calories on the Menu - Information for Archived 2022-01-20 at the Wayback Machine ". Online document at the FDA Website Archived 2013-09-15 at the Wayback Machine , dated 5 August 2019. Accessed on 2022-01-20.
  7. 1 2 3 U. K. National Health Service (2019): "What should my daily intake of calories be? Archived 2022-01-21 at the Wayback Machine ". Online document at the NHS website Archived 2020-05-02 at the Wayback Machine , dated 24 October 2019. Accessed on 2022-01-20.
  8. 1 2 Conn, Carole; Len Kravitz. "Remarkable Calorie". University of New Mexico. Retrieved 1 March 2019.
  9. 1 2 Bureau International des Poids et Mesures (2019): The International System of Units (SI) Archived 2022-01-20 at the Wayback Machine , 9th edition.
  10. 1 2 Bureau International des Poids et Mesures (1998): The International System of Units (SI) Archived 2022-01-20 at the Wayback Machine , 7th edition.
  11. 1 2 United Nations Food and Agriculture Organization (2003): "FAO Food and Nutrition Paper 77: Food energy - methods of analysis and conversion factors Archived 2010-05-24 at the Wayback Machine ". Accessed on 21 January 2022.
  12. 1 2 ""Calorie."". Merriam-Webster.com Dictionary. Retrieved 2024-03-20.
  13. 1 2 Hargrove, James L (2007). "Does the history of food energy units suggest a solution to "Calorie confusion"?". Nutrition Journal. 6 (44): 44. doi: 10.1186/1475-2891-6-44 . PMC   2238749 . PMID   18086303.
  14. 1 2 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 Archived 2022-01-21 at the Wayback Machine . 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 . S2CID   4068300.
  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. Archived 2021-06-14 at the Wayback Machine .
  18. 1 2 3 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. 1 2 Rossini, Fredrick (1964). "Excursion in Chemical Thermodynamics, from the Past into the Future". Pure and Applied Chemistry. 8 (2): 107. doi: 10.1351/pac196408020095 . 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 . Retrieved 8 March 2014.
  21. ↑ International Union of Pure and Applied Chemistry (IUPAC) (1997). "1.6 Conversion tables for units" (PDF). Compendium of Analytical Nomenclature (3 ed.). Institut d'Estudis Catalans. ISBN   0-86542-615-5. Archived (PDF) from the original on 2003-10-16. Retrieved 31 August 2013.
  22. FAO (1971). "The adoption of joules as units of energy".
  23. ↑ Nutrition, Center for Food Safety and Applied (7 March 2022). "Changes to the Nutrition Facts Label". FDA.
  24. ↑ "Prospects improve for food energy labelling using SI units". Metric Views. UK Metric Association. 24 February 2012. Retrieved 17 April 2013.
  25. ↑ "SI Conventions". National Physical Laboratory . Retrieved 8 February 2016.
  26. ↑ 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.
  27. ↑ "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". EUR-Lex. Retrieved 18 April 2022.
  28. ↑ USDA (2013). "China, General Rules for Nutrition Labeling of Prepackaged Foods" (PDF). Retrieved 18 April 2022.
  29. ↑ "How Do Food Manufacturers Calculate the Calorie Count of Packaged Foods?". Scientific American. Retrieved 8 September 2017.
  30. ↑ "Calories - Fat, Protein, Carbohydrates, Alcohol. Calories per gram". Nutristrategy.
  31. ↑ 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. PMC   1319349 . PMID   16389240.
  32. ↑ Zvi Rappoport ed. (2007), "The Chemistry of Peroxides", Volume 2 page 12.
  33. ↑ Bhagavan, N. V. (2002). Medical Biochemistry. Academic Press. pp. 76–77. ISBN   9780120954407 . Retrieved 5 September 2017.
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