This article is a review of the effects that ingested dietary fiber has on gastrointestinal transit time. The various phases of gastrointestinal motility are considered, and the effect of fiber on these various components is explored. Fiber affects each phase of gastrointestinal motility differently; however, the most dramatic effect on decreased transit time and frequency of bowel movements results from the variations it causes in colonic transit time. The mechanisms of defecation in children and the ways in which fiber affects the frequency of bowel movements are emphasized. All types of fiber do not affect gastrointestinal transit in a similar manner, and different preparations of the same fiber either may delay or may increase the time of intestinal transit. In general, fiber is found to increase the frequency of bowel movements and may prove to be of considerable benefit in treating constipation, a common childhood disorder.
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