The effects of dietary fiber on gastrointestinal motor function.

For normal individuals and probably for persons with diverticular disease, dietary fiber affects stool bulk and decreases transit time. The unproven rationale for the use of fiber in irritable colon and diverticular disease assumes that these diseases are the result of increased intraluminal pressure caused by excessive segmentation over a period of years. In short-term experiments, certain fibrous materials do decrease intraluminal pressures, usually in response to a stimulus such as food but sometimes under resting conditions as well. It seems likely that the physical and probably chemical characteristics of fiber influence the motor responses of the alimentary tract. Anecdotal testimonials to the merits of fiber abound, but firm evidence that even wheat bran, the most commonly studied fiber, is effective is difficult to obtain. Controlled clinical trials have been attempted and to date have given conflicting results. Careful studies using a number of well-defined fibrous materials are urgently required to determine the physiological mechanisms of action of different fibers on gastrointestinal motor activity.