There is increasing evidence that dietary fiber is important in maintaining the overall health of dogs and cats. Fiber in petfoods plays a significant role in the prevention and mitigation of several illnesses, including:
- Irritable bowel syndrome,
- Megacolon and
- Colon carcinoma.
Other possible clinical nutrition uses of fiber include blunting of postprandial glycemia, preventing the growth of pathogenic microorganisms and improving nitrogen metabolism in pets with renal dysfunction. Although the contribution of energy from fiber fermentation is minimal in dogs and cats, increasing evidence indicates that this fermentation contributes to their intestinal health.
Fiber's impact on nutrition
As dogs and cats have become domesticated, their diets have changed from being largely meat-based to ones containing a substantial amount of carbohydrate. Indeed, many commercial dog and cat diets contain 30% or more carbohydrate, of which dietary fiber can be an appreciable component.
Including fiber in petfoods can impact nutrition in several ways. Moderate to high concentrations of dietary fiber can decrease food intake and help improve appetite regulation. Depending on the fermentability and viscosity characteristics of a particular dietary fiber source, fibers can slow gastric emptying, decrease intestinal transit time and decrease total tract nutrient digestibility (see Table 1). However, more recent data indicate that ileal nutrient digestibility is not compromised. Other physiological responses attributed to fiber include fecal bulking, production of short chain fatty acids (SCFA), enhanced colonic morphology and intestinal function and a positive influence on the distribution of colonic microflora (see Table 2).
The ideal dietary fiber
An ideal dietary fiber or fiber blend should provide good stool characteristics without significantly decreasing nutrient digestibility.
The fermentation compartments of companion animals occur posterior to the stomach. The fermentative role of the cecum is likely more important in the dog than in the cat. The cecum is a blind ended sac of the proximal colon in the dog whereas it is considered a vestigial organ in the cat.
Dogs are capable of fermenting a significant quantity of dietary fiber. Total tract digestibility of lignocellulose, hemicellulose and cellulose of 33%, 47% and 18%, respectively, have been reported in dogs. Swanson et al. investigated the fermentability of several alternative fiber sources using a canine in vitro fermentation model.
Fiber sources tested included several pomaces (apple, carrot, grape, tomato), flaxseed, pea hulls and pistachio. On a dry matter basis, substrates contained between 55% and 86% total dietary fiber (TDF) and had varying rations of insoluble:soluble fiber. Accordingly, fermentation characteristics also varied greatly, resulting in a range of organic matter disappearance values (9.3% to 51.7% after 24 hours of fermentation).
Cats and fiber
The carnivorous nature of cats, their relatively small colon and their lack of a functional cecum suggest that they may not utilize dietary fiber as extensively as do other non-ruminants. However, Kienzle noted reduced pH values of large bowel digesta and feces after cats ingested raw corn starch. The change in pH was undoubtedly a result of SCFA produced from microbial hindgut fermentation of starch.
Sunvold et al. fed domestic shorthair cats diets containing 0% or 9.5% supplemental TDF from either beet pulp (a moderately fermentable fiber), cellulose (a nonfermentable fiber), a 3:1 cellulose:gum Arabic mixture or two different blends of fibers:
- 35% pectin + 30% locust bean gum + 20% carob bean gum + 15% guar gum or
- 60% beet pulp + 22% rice bran + 10% pectin + 8% carob bean gum.
Total tract disappearance of TDF was increased by consumption of beet pulp (38.2%) and fiber blends (50.6% and 41.1%, respectively) compared to the control diet (5.3%) However, TDF digestibilities of cellulose (8.9% and the 3:1 cellulose:gum Arabic mixture (5.7%) were similar to the control diet. These data refute the assumption that cats are incapable of utilizing fermentable carbohydrates.
Better knowledge base needed
To further define the role of dietary fiber for companion animals, research is needed in several areas. For example, the role of fiber in the longevity of dogs and cats is virtually unknown. Also, the role of fiber in diets to aid treatment of specific disease is promising but needs further study. Finally, although evidence exists as to the potential benefit of SCFA production in the intestine of other species, information regarding the role of SCFA in the dog and cat is scarce. Development of a better knowledge base in these areas would further refine our ability to develop diets for companion animals that would optimized their health and well-being.
Online extra!This article is based on a 33-page paper by Fahey et al., which includes references, and is titled The role of dietary fiber in companion animal nutrition. It is available online at www.petfoodindustry.com/fiber.aspx .