The effect of wheat bran on intestinal transit

In 18 students and two members of staff at a boys' boarding school, the time taken to pass 20 out of 25 radiopaque pellets varied from one to seven days while the subjects were eating a normal English diet. After the additon of bran, about 20 g daily, to this diet transit time fell from 2-75 plus or minus 1-6 to 2-0 plus or minus 0-9 days (P smaller than 0-025). Transit became faster in all nine subjects who had an initial time of three days or more, and in three of seven with an initial time of two days, but became slower in all four boys with an initial one-day transit. Frequency of defaecation correlated poorly with transit time (a once daily bowel action being found with transit times ranging from one to four days), and did not increase significantly with bran. In 10 additional adults with slow initial transit (three or four days) the effect of bran was compared with that of an equal volume of ground oatflakes in a double-blind crossover trial. Bran caused a significant acceleration of transit, wherease oatmeal had no effect. These studies confirm that bran accelerates slow intestinal transit and show that this is not simply a psychological effect. Bran may also slow down fast transit.