What is dietary fibre?
The word ‘fibre’ maybe makes us think of string! However, dietary fibre is not string or even stringy, but a group of carbohydrate compounds with rather special physiological actions. It includes:
- non-starch polysaccharide (NSP) – the structural carbohydrate from plant cell walls; and
- Resistant starch – starch which has been altered by cooking. Both of whose structures are not digested by the enzymes in our intestines.
- Resistant oligosaccharides -another form of indigestible carbohydrate, such as lactose.
Did you know? Lactose from cow’s milk is partly undigested, so it functions as dietary fibre for babies.
Types of dietary fibre
There are two categories of fibre: insoluble fibre or soluble fibre:
- Insoluble fibre binds water and increases stool bulk. It increases the contraction and relaxation (peristalsis) which moves materials through your intestine. An example is cellulose in cereal foods.
- Soluble fibre forms a viscous gel in the presence of water, which has particular value for smoothing out the absorption of nutrients after meals. Once in the large intestine, soluble fibre is almost entirely fermented by bacteria. Examples are pectin and guar gum, from fruits and beans respectively.
All types of dietary fibre are fermented, by the natural and healthful bacteria which live in our large intestines. Without them we would soon become ill. From dietary fibre the bacteria release small molecules called volatile fatty acids which are important as energy sources for our large bowel, and may reduce cancer risks. Eating more dietary fibre increases the bulk of our stools, mainly by increasing the number of healthy bacteria.