"A calorie is a calorie" is a tautology used to convey the thermodynamic concept that a "

calorie 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 of o ...

" is a sufficient way to describe the energy content of food.

History

In 1878, German nutritionist

Max Rubner Max Rubner (2 June 1854, Munich27 April 1932, Berlin) was a German physiologist and hygienist. Academic career He studied at the University of Munich and worked as an assistant under Adolf von Baeyer and Carl von Voit (doctorate 1878). La ...

crafted what he called the "isodynamic law". The law claims that the basis of nutrition is the exchange of energy, and was applied to the study of obesity in the early 1900s by

Carl von Noorden Carl Friedrich Johannes von Noorden (11 September 1833 – 25 December 1883) was a German historian who was a native of Bonn. He was a grandson to psychiatrist Christian Friedrich Nasse (1778–1851) and the father of pathologist Carl von Noorden ...

. Von Noorden had two theories about what caused people to develop obesity. The first simply avowed Rubner's notion that "a calorie is a calorie". The second theorized that

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 ...

development depends on how the body partitions calories for either use or storage. Since 1925, the calorie has been defined in terms of the joule; the current definition of the calorie was formally adopted in 1948. The related concept of "calorie in, calorie out" is contested by some, despite having become a commonly held and frequently referenced belief in

nutritionism Nutritionism is a paradigm that assumes that it is the scientifically identified nutrients in foods that determine the value of individual food stuffs in the diet. In other words, it is the idea that the nutritional value of a food is the sum of al ...

Calorie counting

Calorie amounts found on

food label The packaging and labeling of food is subject to regulation in most regions/jurisdictions, both to prevent false advertising and to promote food safety. Regulations by type Multi-faceted * Codex Alimentarius (international voluntary standard) ...

s are based on the

Atwater system The Atwater system, named after Wilbur Olin Atwater, or derivatives of this system are used for the calculation of the available energy of foods. The system was developed largely from the experimental studies of Atwater and his colleagues in the ...

. The accuracy of the system is disputed, despite no real proposed alternatives. For example, a 2012 study by a

USDA The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of comme ...

scientist concluded that the measured energy content of a sample of almonds was 32% lower than the estimated Atwater value. The driving mechanism behind caloric intake is

absorption Absorption may refer to: Chemistry and biology *Absorption (biology), digestion **Absorption (small intestine) *Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials *Absorption (skin), a route by which s ...

, which occurs largely in the

small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intes ...

and distributes nutrients to the circulatory and lymphatic capillaries by means of

osmosis Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region ...

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical ...

and

active transport In cellular biology, ''active transport'' is the movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient. Active transport requires cellul ...

Fat In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds, most commonly those that occur in living beings or in food. The term often refers specifically to triglycerides (triple est ...

, in particular is emulsified by

bile Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bi ...

produced by the liver and stored in the gallbladder where it is released to the small intestine via the

bile duct A bile duct is any of a number of long tube-like structures that carry bile, and is present in most vertebrates. Bile is required for the digestion of food and is secreted by the liver into passages that carry bile toward the hepatic duct. ...

. A relatively lesser amount of absorption—composed primarily of water—occurs in the

large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in tetrapods. Water is absorbed here and the remaining waste material is stored in the rectum as feces before bein ...

. A kilocalorie is the equivalent of 1000 calories or one dietary Calorie, which contains 4184 joules of

energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of ...

. The human body is a highly complex biochemical system that undergoes processes which regulate energy balance. The metabolic pathways for

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 ...

are less efficient than the metabolic pathways for

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 and fat. Protein contains four calories per gram, although a large part of the calories are lost as heat when metabolised by the body.

References

{{DEFAULTSORT:calorie is a calorie Nutrition Diets Food science

History

Calorie counting

See also

References