Dietary fibre or roughage is the elements of food which cannot be digested. It consists of:
Poor dietary fibre consumption has been linked with the onset of a number of disease states in the 'developed' western world:
- irritable bowel syndrome
- chronic constipation
- diverticular disease
- hiatus hernia
- colonic carcinoma
The amount of fibre in the diet has a direct influence on the quantity and consistency of stool produced, and the stool transit time. In the Western world, an adult produces between 80 g and 120 g of firm stool each day with a stool transit time of about 3 days. This is in contrast with an adult in the third world, who has a diet that is similar to that of the hunter-gatherer, i.e. whole grains, cereals, legumes and nuts, supplemented by small quantities of meat and fish, who produce between 300 g and 800g of stool per day with a stool transit time of about one and a half days.
Dietary fibre also influences bile salt metabolism: an increasing amount of deoxycholate is formed from cholate.