Carbohydrates are mainly sugars and starches,which are found in a variety of foods,eg.sugar,jam,cereals,bread,biscuits, pasta,fruits and vegetables. They consist of carbon,hydrogen and oxygen,the hydrogen and oxygen being in the same proportion as in water. Carbohydrates are classified according to the complexity of the chemical substances from which they are formed.
MONOSACCHARIDES.
Carbohydrates are digested in the alimentary canal and absorbed as monosaccharides. Examples include glucose,fructose and galactose. These are,chemically,the simplest form in which a carbohydrate can exist.
DISACCHARIDES.
These consist of two monosaccharide molecules chemically combined,eg.sucrose,maltose and lactose.
POLYSACCHARIDES.
These consist of complex molecules made up of large numbers of monosaccharides in chemical combination,eg.startches,glycogen,cellulose and dextrins.
Functions of digestible carbohydrates.
These include:
- Provision of energy and heat;the breakdown of monosaccharides,preferably in the presence of oxygen,releases energy for metabolic work-glucose is the main fuel molecule used by body cells.
- ‘protein sparing’ . When there is an adequate supply of carbohydrate in the diet,protein does not need to be used to provide energy and heat.
- Provision of a store of energy when carbohydrate is eaten in excess of the body’s needs as it is converted to:- glycogen and fat and stored in the fat depots
