Bran is widely used to treat a variety of gastrointestinal disorders. With few exceptions, investigative work has focused on the effect of bran in normal subjects. Despite its widespread use, there have been no systematic studies of bran in constipation. Wheat bran is the "gold standard" because no other natural fiber has yet been shown to be as effective in increasing fecal bulk. We evaluated the effect of two brans, wheat and corn (20 g/day), on fecal weight, fecal moisture content, bowel movement frequency, intestinal transit time, and symptoms in 10 constipated (less than or equal to 3 movements/wk) but otherwise healthy women. The administration of bran was associated with a significant increase in fecal weight (157%), bowel movement frequency (55%), and decrease in intestinal transmit time (50%). Percentage fecal moisture increased only with wheat bran (67.4-72.1%), whereas corn bran was significantly better than wheat bran in relieving symptoms of constipation.