The Dog Days Blog

If you’ve spent more than a few minutes reading about nutrition for dogs, you know that the subject of dietary fibre is a controversial one. In fact, the jury still seems to be out on some of the topics related to fibre, such as increasing the feeling of being satiated during a weight-loss program, but other areas are on more solid ground.

For the purposes of discussing nutrition, fibre is a specific type of carbo-hydrate, one that is “insoluble” (not easily digestible). “Soluble” (easily digestible) carbohydrates can be a source of energy in the diet, but insoluble carbohydrates – fibre – are not broken down by the enzymes in the small intestine and thus do not provide any usable energy. They may, however, have other benefits.

Fibre in dog foods comes mainly from the cell walls of plants or grains included in the food. Sources might include corn and corn by-products, beet pulp, bran, apple or tomato pomace, pectin, rice hulls, soybean hulls or peanut hulls.

These obviously do not sound like foods that wild canines would be eating, so why are they in dog food? On a practical level, the process of extrusion for manufacturing dry dog food requires a binding agent, and carbohydrates, whether soluble or insoluble, fill that need. But research has shown that low levels of fibre also provide some benefits to the dog.

Just as it does in humans, fibre can help ease symptoms of both diarrhea and constipation. Fibre provides bulk to the contents in the intestine, and has the ability to hold onto water. So it works to absorb the extra water in loose stools, and to provide water to help prevent constipation. This also helps slow nutrients that are travelling through the intestinal tract too quickly and speed up those that are taking too long.

Iams claims their research shows that crude fibre levels should be between 1.4 and 3.5 per cent for maximal nutrient digestibility. Joe Bartges, D.V.M., Ph.D., Diplomate of the American College of Veterinary Nutrition, points out, however, that crude fibre (the numbers shown on the dog food packaging) is only a rough, and generally low, estimate of the actual fibre in the diet. Overprocessing can also alter the amount and type of fibre. So numbers can be misleading.

Still, Bartges agrees with Iams that fibre can have a variety of beneficial effects. Fibre can help manage diabetes, play a role as an antioxidant and help prevent cancer. The moderation of both diarrhea and constipation has already been mentioned. Fibre can also promote colon health by virtue of its fermentability.

The lining of the gastrointestinal tract renews itself rapidly, and much of the energy for this constant renewal comes from short-chain fatty acids (SCFAs), which are produced by bacterial fermentation of fibre. Iams research showed that a moderately fermentable fibre provided the optimum nutrition for the GI tract without causing diarrhea. Their publication Topics in Practical Nutrition (Vol. 4, No. 2, June 1994) provided the following table of fibre characteristics.

So both beet pulp and rice bran offered the low solubility and moderate fermentability their studies indicated as the best choice.

Humans seem to have a tendency to think that if a little is good, more is better, but this definitely isn’t the case with fibre. Some weight-reduction dog foods rely on greatly increased fibre content to ‘bulk up’ the food and decrease caloric content per serving. The dog has no choice about ingesting fewer calories, but studies have shown that the increased fibre does not help the dog feel less hungry.

Investigation continues on this subject. Higher fibre levels can result in a variety of unwanted side effects such as increased stool volume, loose stools and more flatulence. A potential effect owners can’t see directly is decreased digestibility of the nutrients in the food.

One of the most-studied diseases in relation to fibre is diabetes. In a small study of dogs with insulin-dependent diabetes, researchers found that a high-fibre diet using only insoluble fibre resulted in significantly lower mean and maximum blood-glucose concentrations. High-fibre diets have been a component of treatment of diabetic dogs for some time.

But dietary fibre can also contribute to improved nitrogen metabolism in dogs with renal dysfunction, through regulation of transit time. There is increasing evidence that fibre fermentation contributes to overall intestinal health, helping to avoid megacolon, colitis and irritable bowel syndrome. Fibre binds to potentially carcinogenic bile acids and may thus play a role in preventing colon cancer.