Calorie

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A calorie is a unit of measurement for energy. Calorie is French and derives from the Latin calor (heat). In most fields, it has been replaced by the joule, the SI unit of energy. However, the kilocalorie or Calorie (capital "C") remains in common use for the amount of food energy.

Definitions for calorie fall into 3 classes:

In scientific contexts, the name "calorie" refers strictly to the gram calorie, and this unit has the symbol cal. SI prefixes are used with this name and symbol, so that the kilogram calorie is known as the "kilocalorie" and has the symbol kcal. In non-scientific contexts the kilocalorie is often referred to as a Calorie (capital "C"), or just a calorie, and it has to be inferred from the context that the small calorie is not intended.

The conversion factor among calories and joules is numerically equivalent to the specific heat capacity of liquid water (in SI units). See "Versions" below for explanation of units.

1 calIT = 4.1868 J (1 J = 0.23885 calIT) (International Steam Table calorie, 1956)
1 calth = 4.184 J (1 J = 0.23901 calth) (Thermochemical calorie)
1 cal15 = 4.18580 J (1 J = 0.23890 cal15) (15°C calorie)

Contents

  • 1 Versions
  • 2 Nutrition
  • 3 Trivia
  • 4 See also
  • 5 References
  • 6 External links

[edit] Versions

The energy needed to increase the temperature of 1 g of water by 1 Celsius varies depending on the starting temperature, and is in any case difficult to measure precisely. Accordingly there have been several definitions of the calorie:

The two perhaps most popular definitions used in older literature are the "15 °C calorie" and the "thermochemical calorie". Since the many different definitions are a source of confusion and error, all calories are now deprecated in favour of the SI unit for heat and energy: the joule (J).

[edit] Nutrition

In nutrition, the difference between these calorie definitions is of no practical relevance. This is because nutritional calories are not measured amounts of energy, but are calculated from food composition. Such calculations use internationally agreed conventional conversion factors, which are generously rounded values that roughly approximate the average energy density of a large number of different food samples. The exact composition of agricultural products varies far more than the 0.1% difference between the above definitions of the calorie as a physical energy measure.

Human fat tissue contains about 87% lipids, so that 1 kg of body-fat tissue has roughly the caloric energy of 870 g of pure fat, or 7800 kcal. In principle one has to create a 7800 kcal deficit or surplus between energy intake and use to lose or gain 1 kg of body-fat. (or 3500 kcal per pound). [1] However, if one eats 7800 kcal more than the body needs, one won't necessarily gain 1 kg of fat, since muscle and other tissues may be built. The same way, if one eats 7800 kcal less than their maintenance level, they may not lose 1 kg of fat, since muscle and sugars may be metabolized to generate energy.

[edit] Trivia