An unfermented gel component of psyllium seed husk promotes laxation as a lubricant in humans

Abstract

In addition to increasing stool weight, supplements of psyllium seed husk produce stools that are slick and gelatinous. Our purpose was to test the hypothesis that a gel-forming fraction of psyllium escapes microbial fermentation and is responsible for the characteristics that enhance laxation. Fifteen healthy adults consumed controlled diets for two 7-d periods, one of which included 8.8 g dietary fiber provided by 15 g/d of a psyllium seed husk preparation. All stools were collected and evaluated and diet was monitored throughout. Psyllium significantly increased the apparent viscosity of an aqueous stool extract, stool moisture, and wet and dry stool weights. A very viscous fraction, not present in low-fiber stool and containing predominantly 2 sugars that are also found in abundance in psyllium husk, was isolated from psyllium stool. In contrast with other viscous fibers that are fermented completely in the colon, a component of psyllium is not fermented. This gel provided lubrication that facilitated propulsion of colon contents and produced a stool that was bulkier and more moist than were stools resulting with use of comparable amounts of other bowel-regulating fiber sources.