Fiber-responsive large bowel diarrhea
The author routinely adds fiber to a highly digestible diet in dogs with chronic idiopathic large bowel diarrhea, even if
irritable bowel syndrome has been diagnosed. In cases of fiber-responsive large bowel diarrhea (FRLBD), chronic intermittent
or continuous large bowel diarrhea is usually accompanied by hematochezia, excess fecal mucus, and tenesmus. Abdominal pain
and vomiting can occur in some dogs. Nervousness, abnormal personality factors, and stressors have been identified in approximately
40% of cases. However, in some of these cases, a temporal relationship to the diarrhea could not be established.
Soluble fiber, psyllium hydrophilic mucilloid (Metamucil®, Procter & Gamble), added to a highly digestible diet (i/d® Hills),
has resulted in excellent or very good results in approximately 80% of dogs with chronic idiopathic large bowel diarrhea.
In the authors' cases, the median amount of Metamucil® added to the diet was two TBSP/day which was approximately 1.3 g psyllium/kg/day.
I have not been able to identify any clinical findings that help to predict whether a dog will respond to fiber supplementation.
In some dogs, the amount of fiber added to the diet can be reduced or withdrawn entirely, while in others the highly digestible
diet can be replaced with a grocery store brand of food after the diarrhea resolves.
Some of the dogs with FRLBD have classic signs of IBS. However, many of the dogs have hematochezia, a clinical sign considered
uncommon in dogs with IBS. In addition, it has been reported that only rarely do dogs with IBS respond to dietary fiber supplementation
Dietary fiber is a collective term for a wide variety of plant polysaccharides and lignins that are resistant to mammalian
digestive enzymes. There are many types of dietary fiber, each with diverse chemical, physical, and physiologic properties.
Water soluble fibers include pectin, gums, mucilages, and some hemicelluloses. They are found in the parenchymatous portions
of fruit and vegetables, and in the seeds of leguminous plants. Water insoluble fibers include cellulose, lignin, and some
hemicelluloses. They are found in cereal grains and seed coats.
There are several potential mechanisms by which dietary fiber supplementation may result in clinical improvement in dogs with
FRLBD. Soluble fiber adsorbs a large quantity of water, improving fecal consistency. Colonic bacteria, which make up approximately
40-55% of the dry stool mass, ferment soluble fiber, which results in a vast increase in the numbers (but not types) of colonic
bacteria and quantity of bacterial byproducts. Insoluble fiber greatly adds to fecal volume. Thus, dietary fiber can increase
fecal bulk which increases colonic distention, the major stimulus for normal colonic motility. With increased colonic distention,
an improved motility pattern in dogs with FRLBD may result in resolution of clinical signs. In fact, dietary fiber has been
shown to normalize colonic myoelectrical activity and colonic motility in people. Bacterial fermentation of fiber leads to
the production of short chain fatty acids, of which butyrate serves as an energy source for colonocytes.
Psyllium comes from the seeds or husks of the plant ispaghul and consists of approximately 90% soluble fiber. Although there
are no other reported studies evaluating the use soluble fibers in dogs with diarrhea, there are in human beings. Treatment
with psyllium has been shown to be beneficial in children with nonspecific chronic diarrhea of childhood, adults with chronic
idiopathic diarrhea, patients with ulcerative colitis in remission, and some with irritable bowel syndrome. Psyllium has also
been shown to improve diarrhea in human burn patients receiving enteral nutrition and in another group of tube-fed patients.
Psyllium also improved fecal consistency in humans with experimentally induced secretory diarrhea and also reduced the acceleration
of colonic transport in those with lactulose-induced diarrhea.