1. They are the main constituents of diet.
2. They are the main source of energy (4 K cals per gram).
3. They are essential for the oxidation of fats.
4. They are required for the synthesis of some non – essential amino acids.
Sources of carbohydrates
The main sources of carbohydrates are 1. sugars 2. starch 3. cellulose.
Sugars: They are the simplest form of carbohydrates. The important sugars are:
1. Glucose: All carbohydrates are ultimately converted to glucose in the body. Glucose is the chief source of energy.
2. Fructose: It is the sweetest of all sugars. It is found in cane sugar, fruit juices and honey.
3. Sucrose: It is a disaccharide. It contains glucose and fructose. Sucrose is a constituent of beat sugar and cane sugar.
4. Lactose: It is the sugar of milk. It contains glucose and galactose.
5. Maltose: It is made of two glucose molecules. It is formed from starch during germination of barley or wheat.
6. Starch: It is a polysaccharide. It forms the basic human diet. Rice and potatoes are rich sources of starch.
7. Cellulose: It is the indigestible constituent of carbohydrate. It does not have any nutritive value but it contributes to dietary fibre. The fiber absorbs water and increases the bulk of stools. This increases bowel movements and prevents constipation.