Addition of fiber to the diet could alleviate chronic large bowel diarrhea for several reasons. Insoluble fiber alters the colonic myoelectrical activity of normal dogs, purified cellulose decreased, and coarse wheat bran increased, activity. If these effects occur in dogs with diarrhea, choice of the appropriate fiber might normalize feces consistency if altered motility was the cause of diarrhea. Some dietary fibers also can adsorb water or trap it within the fiber matrix, reducing the amount of free water in the feces. This property, which is beneficial in diarrhea, is dependent on the physical and chemical properties of the fiber.
Soluble fibers prolong intestinal transit time, allowing greater water absorption.
And some dietary fibers, such as carob, contain significant amounts of tannin, which may be useful in secretory or osmotic diarrhea by adsorbing toxins within the intestinal lumen. Finally, fiber fermentation alters intestinal microflora, and may reduce the numbers of pathogenic bacteria in cases of primary bacterial diarrhea or secondary bacterial overgrowth. Although controlled studies have not been performed, some veterinary gastroenterologists believe that dietary fiber can be of therapeutic benefit in inflammatory and idiopathic colitis in the dog and cat. Empirical addition of fiber to a hypoallergenic diet also has been advocated. One to four tablespoons of coarse wheat bran is recommended by some, and one to two tablespoons of psyllium husk by others, to be added per 500 kilocalories.