Dietary fiber (fibre) is a food substance which is derived from plants and cannot be digested by humans. Fiber changes the nature of the contents of the gastrointestinal tract and affects the absorption of nutrients and chemicals. In addition, the fermentation of fiber in the colon produces short chain fatty acids. For this reason, while fiber itself is non-digestible, its presence in the diet is important for the proper functioning of the digestive system and thus for the health of the whole body.
Significant amounts of fiber are found in natural cereals such as wheat bran, muesli, brown rice, wholemeal and wholegrain bread as well as fruits and vegetables. Food sources of dietary fiber are commonly divided into two groups, depending on whether they contain soluble (or predominantly soluble) or insoluble fiber.
Both types of fiber are found in plant products in amounts that vary depending on the properties of the particular plant.