Food gives the human body energy. The body breaks down the carbohydrates, proteins and fats in food to provide energy to fuel its cells. Glucose, which is provided by carbohydrates, is the body's preferred source of energy.
The human digestive system easily converts carbohydrates from food into glucose, galactose and fructose. Glucose is absorbed directly into the bloodstream where insulin, a hormone produced in the pancreas, enables the glucose to move into cells and be converted into energy. If there is a shortage of carbohydrates in the diet, the body uses stored glucose from the liver for energy. When those stores are used up, the body converts fats or proteins into glucose.