Does it help to include fiber in my dog’s diet?  If so, what types of fiber?  What are the benefits of including fiber in a dog’s diet?

A Dog’s Intestinal System

Once a dog eats something, the food travels down the esophagus and into the stomach.  The stomach serves as a reservoir for a powerful acid produced by the body to break down the food pieces into smaller particles.  Eventually, the stomach’s contents are emptied into the small intestine where digestive enzymes and bile acids are added to further break down the food and aid its absorption into the body.  But there always are undigested food residues that are not absorbed from the diet and must be eliminated from the body.

The Role and Benefits of Dietary Fiber

Proper sources of levels of dietary fiber aid removal of undigested food residues by producing a well-formed stool.  Not only does this make stool clean-up easier, it can also aid ease of bowel elimination by the pet.  Another important benefit of proper sources of dietary fiber is their ability to nourish the intestinal lining of the pet.  Moderately fermentable fiber sources such as beet pulp, tomato pomace, and psyllium are partially broken down (fermented) by intestinal bacteria to produce short-chain fatty acids.  These small fatty acids are not normally available in large quantities from other dietary ingredients making fermentable fiber sources very unique to the pet for maintaining health.  The acids produced from fermentation also limit pathogen (bad bacteria) growth. 

Dietary fibers can also help slow the digestion of food to reduce the sugar (glucose) spike following a meal.  This is metabolically advantageous to the pet.  In cats, certain non-fermentable fibers (eg, cellulose, miscanthus grass) help bind hair to aid it being defecated rather than vomited out of the animal.  Other research suggests that dietary fibers, likely through their fermentation to short-chain fatty acids, modulate the immune response and promote gut-derived hormones helpful in promoting satiety and insulin secretion.  Insulin secretion is useful in storing the increased sugar in the blood in response to a digesting a meal.

What are the downsides to Dietary Fiber?

Highly fermentable fibers, such as guar gum or pectins (such as those found in fruit), when included in high amounts will be fermented extensively.  This becomes too much of a good thing and can be disruptive to the gut causing osmotic diarrhea (pulling water into the gut), an undesirable condition for both the owner and the pet.

Another inappropriate dietary attribute that has been perpetuated by some is the over-inclusion of fiber to dilute the diet’s calories to induce weight loss.  Without other changes to the product, such diets will just result in the pet eating more of the food and increasing its stool output.  Again, an inconvenience for the pet owner.

What’s the bottom line?

Look for a product that does contain an added source of dietary fiber.  Unfortunately, many new product formats (eg, lightly processed, raw) products do not contain added fiber.  Then verify that the source of dietary fiber is a moderately fermentable source.  Finally, refrain from using a high fiber diet for weight loss.