Food is an energy source for humans, in the same manner as the fuel for the steam engine. Food provides the fuel supply to the human engine. It varies such that it can be dissolved in blood and a very slow process of burning takes is carried out in humans. The energy that is released to help the human body to perform the functions and the heat keeps body warm.

Food is essential to maintain the body. Different people have different caloric requirements, but each requires a food to stay alive.