Human body is actually a living machine and is like all other machines. This living machine needs fuel to supply it with energy. The fuel is provided by the food which we eat. However do we know how much we need to stay healthy?
The energy value of food is usually measured in calories. A calorie is the amount of heat which is required to raise the temperature of 1 kg of water by 1 degree C. The number of calories which people need per day varies. It depends on the activity which the people are involved in. For example; people will need more calories for standing than for sitting, people need more for running than for walking, etc.
The energy which is provided by food is in the form of three kinds of chemical substances. They are carbohydrate, protein and fat. Carbohydrate provides 8.8 calories per gram (cal/gm) of energy, protein 4.0 cal/gm and fat 8.0 cal/gm. Each food contains different proportion of these substances.These three chemical substances are all important for body staying healthy.