Calorie

The term calorie (symbol: cal) is the name of various units of energy based on the specific heat capacity of water. Since there are several units with the name calorie, expressing a quantity as “X calories” leaves the unit used ambiguous. Furthermore, all variants of the calorie are units inconsistent with current unit systems (i.e., they have no natural relationship to any other base unit in use, but all variants of the calorie require arbitrary conversion factors).). Therefore, instead of the calorie, the joule (symbol: J) and its multiples and submultiples should be used.

An energy drink of 710 milliliters (24 American liquid ounces) with 330 kilocalories

For historical reasons, two main definitions of calories are widely used. The small calorie or gram calorie (usually denoted cal) is the amount of heat required to raise the temperature of one gram of water by one degree Celsius (or kelvin). The great calorie, food calorie or kilocalorie (Cal, Calorie or kcal), more commonly used in nutrition, is the amount of heat necessary to cause the same increase in a kilogram of water. Therefore, 1 kilocalorie (kcal) = 1000 calories (cal). By convention in food science, the large calorie is commonly called the Calorie (some authors with a capital C to distinguish it from the smaller unit). In most countries, industrialized food product labels must indicate the calorie. nutritional energy value in calories (kilo or large) per serving or weight.

The calorie is directly related to the metric system and therefore to the SI system. It has been considered obsolete within the scientific community since the adoption of the SI system, but is still used in some form. The SI unit of energy is the joule (J). A calorie is defined exactly as 4,184 J, and a kilocalorie is 4,184 J.

Definitions

The most exact definition of the calorie is the amount of heat (which is a form of energy) required to produce a 1 °C increase in temperature in a sample of water with a mass of 1 g from 14.5 ° C up to 15.5 °C; it is also called "gram-calorie" and "small calorie".

A variant used in the study of nutrition was to substitute the amount of water referred to by 1 kg; this was the first source of ambiguity. These kilogram-based variants are called "kilogram-calorie," "kilocalorie," "large calorie," or "calorie" (symbol: Cal; note the capital "C").^{[citation needed ]}

The second source of ambiguity was that the specific heat capacity of water is not constant, but depends on temperature and isotopic composition, which was fixed by setting the temperature at which it was to be measured, as shown in Fig. Initial definition of this section.

There are several mutually incompatible definitions. Some of them are listed below. Exact conversion factors are shown in bold; those not shown in bold are approximations. Data published by NIST in 2008.

Origin

The calorie was first defined by Professor Nicolas Clément in 1824 as a calorie-kilogram and thus entered French and English dictionaries during the period between 1842 and 1867.

The calorie arose as a consequence of the caloric theory: it was supposed that the transmission of heat was produced by the passage of a certain fluid (the caloric) of a body to another. That amount of caloric would be measured in calories. Once the caloric theory was discarded, and the physical fact that heat is a manifestation of energy recognized, the calorie was defined as a unit of energy in the metric system of units (and later on in the Technical System). Of units).

The "little" (modern calorie) was introduced by Pierre Antoine Favre (chemist) and Johann T. Silbermann (physicist) in 1852. In 1879, Marcellin Berthelot distinguished between gram-calorie (modern calorie) and kilogram-calorie (modern kilocalorie). Berthelot also introduced the convention of writing the kilogram-calorie in upper case, as Cal.

The use of the kilogram-calorie (kcal) for nutrition was introduced to the American public by Wilbur Olin Atwater, a professor at Wesleyan University, in 1887.

The modern calorie (cal) was first recognized as a unit of the cm-g-s (cgs) system in 1896, together with the already existing cgs unit of energy, the erg (first suggested by Clausius in 1864, under the name erg, and officially adopted in 1882).

As early as 1928, there were serious complaints about possible confusion arising from the two main definitions of the calorie and whether the idea of using a capital letter to distinguish between them was sound. The use of the calorie was officially disapproved by the 9th General Conference of Weights and Measures in 1948.

Calories are not currently included in the International System of Units.

Metabolism and calories

The calorie that was formerly used in Biology, Medicine and Nutrition, had the value of one kilocalorie, was assigned the symbol «Cal» (with a capital C) to differentiate it from the calorie itself, symbol cal and was sometimes called a big calorie. This custom was replaced in favor of the kilocalorie (kcal) and calorie (cal) which in turn is now present and as a consequence of the application of regulations regarding food labeling, at least in the most developed countries. The information that appears on the labels is indicative of the energy value of the food in question for a predetermined amount of food (100 grams) and is usually expressed in joules (J) and still, between parentheses, in calories (cal); little by little the kilocalorie will disappear from the labels.^{[citation needed]}

The calorie is still used as a unit of measurement for the energy of the food ingested and thus prepare adequate and often "low-calorie" diets (they usually mean a reduction of 30%) that allow the loss of body weight.

In some foods we also talk about junk calories (also called empty calories), which are calories from foods with very little nutritional value, such as sugary soft drinks or alcoholic beverages.

Nutrition

In a nutritional context, the kilojoule (kJ) is the "SI" unit of food energy, although calorie is commonly used. The word calorie is commonly used with the number of kilocalories (kcal) of nutritional energy being measured.

In the United States, most nutritionists prefer the unit kilocalorie to the unit kilojoule, while most physiologists prefer to use the kilojoule. In most other countries, nutritionists prefer the kilojoule to the kilocalorie. US food labeling laws require the use of kilocalories (under the name "Calories"); Kilojoules are allowed to be listed on food labels next to kilocalories, but most food labels do not. In Australia, kilojoules are officially preferred to kilocalories, but kilocalories retain some degree of popular usage. Australian and New Zealand food labeling laws require the use of kilojoules; kilocalories are allowed on labels in addition to kilojoules, but not required. EU food labeling legislation requires both kilojoules and kilocalories on all nutrition labels, with kilojoules first.

For ease of comparison, specific energy or energy density figures are often quoted as "calories per serving" or "kcal per 100 g". Nutritional requirements or consumption are usually expressed in calories or kilocalories per day.

Dietary nutrients such as fats (lipids) contain 9 kilocalories per gram (kcal/g), while carbohydrates (sugar) or protein contain approximately 4 kcal/g. Alcohol in food contains 7 kcal/g. Nutrients in food are also often quoted "per 100 g".

Chemistry

In other scientific contexts, the term calorie almost always refers to the small calorie. Although it is not an SI unit, it is still used in chemistry. For example, the energy released in a chemical reaction per mole of reactant is occasionally expressed in kilocalories per mole. Typically, this use was largely due to the ease with which it could be calculated in laboratory reactions, especially in aqueous solution: a volume of reagent dissolved in water forming a solution, with the concentration expressed in moles per liter (1 liter weighs 1 kilogram), it will induce a temperature change in degrees Celsius in the total volume of water solvent, and these quantities (volume, molar concentration, and temperature change) can then be used to calculate energy per mole. It is also occasionally used to specify quantities of energy that are related to the energy of reaction, such as the enthalpy of formation and the size of activation barriers. However, its use is being replaced by the SI unit, the joule, and its multiples as the kilojoul.

Other energy measures

The SI unit of energy, which in most countries is the legal system of units, is the joule (J). The BIPM (International Bureau of Weights and Measures), ISO (International Organization for Standardization) and CIE (International Commission on Illumination) recommend using the joule, its multiples and submultiples.

Other units of measure for energy are:

• The kilowatt-hour (kWh), usually related to electricity, and its megawatt-hour multiples (MWh), megawatt-year. (1 kWh = 3.6 × 10⁶J)
• Refrigeration is an obsolete energy unit, used in cooling systems and is equivalent to a negative kilocalorie.
• The term. 1 term = 10⁶cal = 1Mcal (megacalorie)
• Oil equivalent to 41,84 GJ = 11,622 MW h
• Coal equivalent to 29.3 GJ = 8,1389 MW h