1. Body Distribution: The amount of carbohydrates in the adult body is about 300-500 gm. Of this 100 gm is stored as glycogen in the liver, and another 200-250 gm is present as glycogen in cardiac, smooth, and skeletal muscles and about 15 gm makes up the glucose in the blood and extracellular fluid. Carbohydrates provide the carbon skeleton for the synthesis of non-essential amino acids by the body. Very small amounts of carbohydrates are constituents of numerous essential body compounds such as Glucuronic Acid, Heparin, Chondroitin sulfates, Deoxyribonucleic Acid (DNA) Ribonucleic Acid (RNA), Galactolipid and Glycosides.
2. Providing Energy: Carbohydrates are the least expensive source of energy for the body. Each gram of carbohydrate, on oxidation, gives 4 Kcal. Glucose is the primary source of energy for the nervous system and the lungs. After absorption from the intestinal tract, the carbohydrates meet the following principal fates:
i. Immediate use to meet energy needs of tissue cells.
ii. Conversion to glycogen and storage in the liver or muscles for later release to meet energy needs.
iii. Conversion to fat as a longer reserve for energy.
3. Protein Sparing Action: The body uses carbohydrates preferentially as a source of energy when it is adequately supplied in the diet. Thus, sparing proteins for tissue building. Since meeting the energy needs of the body takes priority over all other functions, any deficiency of calories in the diet will be made up by using adipose and protein tissues.
4. Regulation of fat Metabolism: Some carbohydrate is necessary for the diet so that the oxidation of fats can proceed normally. When carbohydrate is severely restricted in the diet, fat will be metabolized faster than the body can take care of immediate products. The accumulation of these incompletely oxidized products leads to dehydration, loss of body sodium, and Ketosis. As little as 50 gm of carbohydrates in the diet will prevent Ketosis under normal conditions. In uncontrolled diabetes mellitus, ketosis is often present.
5. Roles of Gastrointestinal Functions: Lactose has several functions in the gastrointestinal tract. It promotes the growth of desirable bacteria, some of which are useful in the synthesis of B-complex vitamins. lactose also enhances the absorption of calcium. The only source of lactose is milk and it is also the richest source of calcium.
6. Role of Dietary Fibre: Dietary fiber is a negligible source of energy for the body. But it is useful in a number of ways:
i. Stimulates peristaltic movement in the gastrointestinal tract.
ii. It provides bulk to the intestinal contents and reduces the length of time that food wastes remain in the colon.
iii. Helps in the normal elimination of feces by holding water and making the stools soft.
iv. Retard gastric emptying, therefore increased satiety so that less food is eaten.
v. Helps in reducing blood cholesterol levels.