Carbohydrates form the major bulk of human diet and are also the chief sources of energy. Carbohydrates are easily digested and broken down by enzyme action into glucose and are easily absorbed, Starches and sugars are converted to glucose. Glucose is absorbed by the stomach and small intestine and then stored in liver as glycogen. This glycogen is reconverted into glucose and is used by tissues. Carbohydrate metabolism plays an important role in both types of diabetes mellitus. The entry of glucose into most tissues-including heart, muscle, and adipose tissue is dependent upon the presence of the hormone insulin. Insulin controls the uptake and metabolism of glucose in these cells and plays a major role in regulating the blood glucose concentration. The reactions of carbohydrate metabolism cannot take place without the presence of the B vitamins, which function as coenzymes.
Phosphorous, magnesium, iron, copper, manganese, zinc and chromium are also necessary as cofactors. When the concentration of glucose rises in the blood, insulin is secreted by the pancreas. Insulin stimulates the transfer of glucose into the cells, especially in the liver and muscles, although other organs are also able to metabolize glucose. In whatever form carbohydrates have been ingested in food, it is converted to the monosaccharide glucose and absorbed into the blood. Some of the glucose my enter the systemic circulation to supply the requirement of the other tissues. The surplus glucose is converted to glycogen and stored by the liver.