The most important function of carbohydrates is to provide energy to the body. They are also structural components of tissues. Other functions include regulation of fat metabolism, protein sparing functions, and function in the digestive tract.
- Storage substances of potential energy. Carbohydrates are storage substances of potential energy in animals. About 60% of the total energy requirement of man is provided by the breakdown of carbohydrates. One gram of carbohydrate on oxidation yields on an average four calories. Glucose supplies the immediate energy needed by tissues. Glucose is the sole form of energy for the brain and other nervous tissue. Lack of glucose, or of oxygen for its metabolism, leads to rapid damage to the brain. Carbohydrate is stored in the body in the form of glycogen. About 100 gms of glycogen is stored in the liver and by its breakdown maintains the glucose level in he blood. Muscles contain about 200-240 gms glycogen. This glycogen is however, utilized only by the muscles and is not available for regulating the blood sugar level.
- Structural component. Carbohydrates are important components of some structural materials of living organisms. Monosaccharides are important constituents of nucleic acids, coenzymes, flavoproteins and blood group substances. Vitamin C is related to sugars. Immulnopolysaccharides play a part in the resistance of infections. Hyaluronic acid is the viscous substance in the matrix of connective tissue. Heparin prevents the clotting of blood, Glucuronic acid, which occurs in the liver acts as a detoxifying agent by combining with toxic substances and bacterial byproducts. Chondroitin sulphates are found in cornea, cartilage tendon, skin, heart valves and saliva. glycosides are components of steroid hormones, Galacolipins are constituents of nervous tissue. The cell wall of plants and the polysacchcrides in the capsule of bacteria are carbohydrates.
- Regulation of fat metabolism. Some carbohydrates are essential for normal oxidation of fats. When carbohydrates are restricted in the diet there is more rapid metabolization of fats. This results in the accumulation of incompletely oxidized intermediate products leading to ketosis. This is common in uncontrolled diabetes mellitus.
- Protein-sparing function. Carbohydrate is preferentially metabolized in the body as a source of energy as long as it is present in the required quantity. This spares protein for building of tissues. When there is a deficiency of calories in the diet, however, fat and then protein are utilized for supplying energy.
- Role in gastrointestinal function. Indigestible substances like cellulose, hemicellulose and pectins provide the the bulk or roughage of food, and thus help the peristaltic movements of he digestive tract. Lactose promotes the growth of desirable bacteria in the small intestine These bacteria synthesize certain B complex vitamins. Lactose also increases calcium absorption.