Energy drink and fast food cheeseburger calorie comparison

The calorie is a unit of energy. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

of one kilogram of

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

by one degree Celsius (or one

kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and ...

). The small calorie or gram calorie was defined as the amount of heat needed to cause the same increase in one gram of water. Thus, 1 large calorie is equal to 1000 small calories. In

nutrition Nutrition is the biochemical and physiological process by which an organism uses food to support its life. It provides organisms with nutrients, which can be metabolized to create energy and chemical structures. Failure to obtain sufficient ...

and food science, the term ''calorie'' and the symbol ''cal'' almost always refers to the large unit. 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,

metabolic rate Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

s, etc. Some authors recommend the spelling ''Calorie'' and the symbol ''Cal'' (both with a capital C) to avoid confusion; however, this convention is often ignored. In

physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which ...

and

chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...

the word ''calorie'' and its symbol usually refer to the small unit; the large one being called ''kilocalorie''. However, this unit is not officially part of the metric system (SI), and is regarded as obsolete, having been replaced in many uses by the SI unit of energy, the

joule The joule ( , ; symbol: J) 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 1 newton displaces a mass through a distance of 1 metre in the direction of the force appli ...

(J). 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.

History

The term "calorie" was first introduced by

Nicolas Clément Nicolas Clément (12 January 1779 – 21 November 1841) was a French physicist and chemist. He was a colleague of Charles Desormes, with whom he conducted the Clément-Desormes experiment. The two chemists are also credited with determining a ...

, as a unit of

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

energy, in lectures on experimental

calorimetry In chemistry and thermodynamics, calorimetry () is the science or act of measuring changes in ''state variables'' of a body for the purpose of deriving the heat transfer associated with changes of its state due, for example, to chemical re ...

during the years 1819–1824. This was the "large" calorie. The term (written with lowercase "c") entered French and English dictionaries between 1841 and 1867. It comes . The same term was used for the "small" unit by Pierre Antoine Favre (Chemist) and Johann T. Silbermann (Physicist) in 1852. This unit was used by U.S. physician Joseph Howard Raymond, in his classic 1894 textbook ''A Manual of Human Physiology''. He proposed calling the "large" unit "kilocalorie", but the term didn't catch on until some years later. In 1879, Marcellin Berthelot distinguished between gram-calorie and kilogram-calorie, and proposed using "Calorie", with capital "C", for the large unit. 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. The small calorie (cal) was recognized as a unit of the CGS system in 1896, alongside the already-existing CGS unit of energy, the

erg The erg is a unit of energy equal to 10−7joules (100 nJ). It originated in the Centimetre–gram–second system of units (CGS). It has the symbol ''erg''. The erg is not an SI unit. Its name is derived from (), a Greek word meaning 'work' o ...

(first suggested by Clausius in 1864, under the name ''ergon'', and officially adopted in 1882). Already in 1928 there were 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. The joule was the officially adopted SI unit of energy at the ninth General Conference on Weights and Measures in 1948. The calorie was mentioned in the 7th edition of the SI brochure as an example of a non-SI unit. According to Wiktionary the alternate spelling is dated.

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). The amount depends on the atmospheric pressure and the starting temperature, and different choices of these parameters have resulted in several different precise definitions of the unit. 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.

Usage

Nutrition

In a nutritional context, the "large" unit is used almost exclusively. It is generally written "calorie" with lowercase "c" and symbol "cal", even in government publications, although the capitalized form "Calorie" (with symbol "Cal") or the name "kilocalorie" (with symbol "kcal") are also used, and may be mandated by law. The SI unit of energy kilojoule (kJ) may be used instead, in legal or scientific contexts. In the United States, most 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. On nutrition facts labels in the European Union, energy is expressed in both kilojoules and kilocalories. In the United States and Canada, labels use "Calories", referring to the large unit. In China, only kilojoules are given.

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 (lipids) contains 9 kilocalories per gram (kcal/g), while

carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may o ...

s (sugar and starch) and

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

contain approximately 4 kcal/g. Alcohol in food contains 7 kcal/g. 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 Human body weight is a person's mass or weight. Strictly speaking, body weight is the measurement of weight without items located on the person. Practically though, body weight may be measured with clothes on, but without shoes or heavy accessor ...

, or to prevent and treat diseases such as

diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...

and

obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's ...

. As weight loss depends on reducing caloric intake, different kinds of calorie-reduced diets have been shown to be generally effective.

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 A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking ...

or phase change, typically per mole of substance, as in kilocalories per mole. 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 barrier In chemistry and physics, activation energy is the minimum amount of energy that must be provided for compounds to result in a chemical reaction. The activation energy (''E''a) of a reaction is measured in joules per mole (J/mol), kilojoules p ...

s. However, it is increasingly being superseded by the SI unit, the joule (J); and metric multiples thereof, such as the kilojoule (kJ). 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 kelvin 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.

References

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ISO 31-4 ISO 31-4 is the part of international standard ISO 31 that defines names and symbols for quantities and units related to ''heat''. It is superseded by ISO 80000-5. Its definitions include: Annex A of ISO 31-4 lists units of heat based on the ...

: Quantities and units, Part 4: Heat. Annex B (informative): Other units given for information, especially regarding the conversion factor.

International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in A ...

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UK Metric Association The UK Metric Association, or UKMA, is an advocacy group in the United Kingdom that argues for metrication in the United Kingdom and advocates the use of the metric system among the general public in the UK. UKMA argues that the continued use of ...

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