Fiber and colorectal diseases: Separating fact from fiction

Whilst fruits and vegetables are an essential part of our dietary intake, the role of fiber in the prevention of colorectal diseases remains controversial. The main feature of a high-f iber diet is its poor digestibility. Soluble fiber like pectins, guar and ispaghula produce viscous solutions in the gastrointestinal tract delaying small bowel absorption and transit. Insoluble f iber, on the other hand, pass largely unaltered through the gut. The more fi ber is ingested, the more stools will have to be passed. Fermentation in the intestines results in build up of large amounts of gases in the colon. This article reviews the physiology of ingestion of fiber and defecation. It also looks into the impact of dietary fiber on various colorectal diseases. A strong case cannot be made for a protective effect of dietary fi ber against colorectal polyp or cancer. Neither has fi ber been found to be useful in chronic constipation and irritable bowel syndrome. It is also not useful in the treatment of perianal conditions. The fiber deficit -diverticulosis theory should also be challenged. The authors urge clinicians to keep an open mind about fi ber. One must be aware of the truths and myths about fi ber before recommending it.