What is Calorie ?
The
calorie is a unit of energy defined as the amount of heat needed to raise the temperature of a quantity of water by one degree.
For historical reasons, two main definitions of
calorie are in wide use. The
small calorie or
gram calorie (usually denoted cal) is the amount of heat needed to raise the temperature of one gram of water by one degree Celsius (or one kelvin).
The
large calorie,
food calorie, or
kilocalorie (Cal, Calorie or kcal), most widely used in nutrition,is the amount of heat needed to cause the same increase in one kilogram of water.
Thus, 1 kilocalorie (kcal) = 1000 calories (cal).
By convention in
food science, the
large calorie is commonly called
Calorie (with a capital C by some authors to distinguish from the smaller unit).
In most countries, labels of industrialized food products are required to indicate the
nutritional energy value in (kilo or large) calories per serving or per weight.
Calorie relates directly to the metric system, and therefore to the SI system. It has been regarded as obsolete within the scientific community since the adoption of the SI system, but is still in some use.
The SI unit of energy is the
joule. One calorie is defined as exactly 4.184 J, and one
Calorie (kilocalorie) is 4184 J.
