Particle Size of Wheat Bran in Relation to Colonic Function in Rats

Abstract

Wheat bran is widely used in the treatment of constipation and may be beneficial in preventing a range of diseases including colorectal cancer. However, the results of different studies show variability in the effects of wheat bran. This could be a consequence of different brans having different ranges of particle sizes which may affect the transit time through the gastrointestinal tract. This possibility was tested using male Fisher 344 rats which have been widely used in carcinogenicity studies. The effects on transit time of supplementing the diet (a high fat modification of the AIN-76™ diet) with wheat bran fractions with particle size ranges of 212–710 μm, 710–1000 μm, and 1000–1700 μm was examined. Fractions were obtained by sieving wheat bran obtained from a hard bread wheat (cv. Otane). Transit times were measured using glass beads (diameter 150–170 μm). Supplementation of the diet with each of the wheat bran fractions significantly reduced transit times ( P< 0.05), but the fraction with the largest particles was the most effective. Similarly, each fraction increased the rate of excretion of faeces (on a dry weight basis), the fraction with the largest particles producing the greatest effect. These results are consistent with human studies which showed that shorter transit times resulted from supplementing the diet with large compared with small wheat bran.