what are calories

Calorie - Wikipedia, the free encyclopedia


** Calorie **

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This article is about the units of energy. For other uses, see Food energy
and Calorie (disambiguation).

The name *calorie* is used for two units of energy.

· The *small calorie* or *gram calorie* (symbol: cal) is the approximate
amount of energy needed to raise the temperature of one gram of water by
one degree Celsius.^[1]
· The *large calorie*, *kilogram calorie*, *dietary calorie*,
*nutritionist's calorie* or *food calorie* (symbol: Cal, equiv: kcal),
which is the amount of energy needed to raise the temperature of one
kilogram of water by one degree Celsius. The large calorie is thus equal to
1000 small calories or one kilocalorie (symbol: kcal).^[1]

Although these units are part of the metric system, they now have been
superseded in the International System of Units by the joule. One small
calorie is approximately 4.2 joules (one large calorie or kilocalorie is
therefore approximately 4.2 kilojoules). The factors used to convert
calories to joules are numerically equivalent to expressions of the
specific heat capacity of water in joules per gram or per kilogram. The
conversion factor depends on the definition adopted.

In spite of its non-official status, the large calorie is still widely used
as a unit of food energy in the US, UK and some other Western countries.
The small calorie is also often used in chemistry as the method of
measurement is fairly straightforward in most reactions, though the amounts
involved are typically expressed in thousands as kcal, an equivalent unit
to the large calorie.

The calorie was first defined by Nicolas Clément in 1824 as a unit of
heat,^[2] and entered French and English dictionaries between 1841 and
1867. The word

Source: en.wikipedia.org/wiki/Calorie

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