Dietry fibre is not necessary for life and growth, but it does perform a useful role in the digestive process and may contribute other benefits.

Dietry fibre comes in two forms. Water-insoluble fibres, which make up the structural parts of plant cell walls, which are found primarily in whole-wheat products, wheat bran, and fruit and vegetable skins. Water-soluble fibers come primarily from fruits, vegetables, beans, and oats. Some of them are extracted for use as food additives.

The chemical nature of dietry fibre (especially the insoluble kind) enables it to pick up water, which adds bulk to the stool and enhances the transit time of undigested foods through the gut by stimulating the peristalsis of the gut. Also, the dietry fibre protects against a common condition in the gut called diverticulosis. This disease is characterized by pouches that develop in weak areas of the large intestine. It is believed that a low-fibre intake might increase the likelihood of this problem's developing because the muscles of the intestine become "out of shape" as a result of insufficient stimulation.