Dietary Fiber and Fecal Characteristics in Humans and Animals

Abstract

We reviewed studies on the quantity and quality of feces related to the onset of various diseases including colorectal cancer, with particular emphasis on our experimental results. We attempted to determine the quantity of dietary fiber (DF) required to achieve the critical fecal output per day of 140-150g for shortening the gastrointestinal transit time (GTT), which is obtained from the relation between the GTT and the fecal output. Ten healthy young men were placed in two groups and given diets with different DF levels in two experiments. We found that a daily in take of at least 20-30 g of DF was necessary. We then analyzed the fecal secondary bile acid ratio in rats given different types of DF at 5%. The lithocholic acid/deoxycholic acid ratio, a sensitive risk index for colorectal cancer, was significantly lower in those given semipurified DF preparations obtained from several types of vegetables/fungi and apple when compared to that in those fed cellulose or corn bran. A study of rats given oil palm trunk fiber revealed that the GTT could not be shortened by simply increasing the fecal bulk, suggesting that this unique, new DF helps to explicate the mechanism of GTT shortening.