Energy is the capacity to do work. The energy to perform work is derived from the carbohydrate, fat and protein in the diet. The source of energy in diets varies depending on agricultural, cultural, social and economic factors.
The body needs energy for maintaining body temperature, metabolic activity, supporting growth, for physical work, to maintain constant body weight and good health.
The body' s storage energy or potential energy is continuously available in the body from the glycogen in muscle and liver. This stored energy is transformed to other forms to accomplish the work of the body. Examples are
I. Osmotic Energy - Maintain transport of nutrients.
II. Electrical Energy - Transmission of nerve impulse.
III. Chemical Energy - Synthesis of new compounds.
IV. Thermal Energy - Heat regulation.
Whenever one form of energy is produced another form is reduced by exactly the same amount as stated by the Law of Conservation of Energy.
This law states that energy can neither be created or destroyed it can only be transformed from one form to another.
UNITS OF ENERGY - CALORIE AND JOULE
The unit of energy, kilocalorie (Kcal) was used for a long time. Recently the International Union of Sciences and International Union of Nutritional Science (IUNS) have adopted ' Joule' as the unit of energy in place of Kcal. These units are defined as follows.
A joule is defined as the energy required to move 1kg mass by 1 metre by a force of 1 Newton acting on it.
One Newton is the force needed to accelerate 1 kg mass by less than a second.
Kcal is defined as the heat required to raise the temperature of 1kg of water by 1 o C. (From 14.5 o C to 15.5 o C)
1Kcal = 4.184 KJ (Kilo Joules)
1000 Kcal = 4184 = 4.18 MJ ( mega joules )
1 KJ = 0.239 Kcal.