Dietary fiber

The term "fiber" refers mostly to complex carbohydrates which are not digested by the endogenous enzymes in the small intestine of dogs (digestion and absorption increases if these enzymes are supplemented). Some fibers are partially digested by beneficial bacteria present in the healthy large intestine. Cellulose, hemicellulose and pectin are three major carbohydrate based components of fiber, the fourth, lignin, is the only one that is not carbohydrate based. The properties of fiber are classified as follows:

Solubility: the ability of fiber to hold water and form a gel-like substance. Highly soluble fibers can hold a lot of water, decrease gastrointestinal transport and slow nutrient absobtion. Insoluble fibers do not hold much water and increase gastric emptying.

Fermentability: the extent of bacterial digestion in the large intestine, which results in various end products that can in turn be metabolized by the dog's body.

Examples:

Cellulose: low solubility and fermentability
Beet pulp: low solubility, moderate fermentability
Pectin: low solubility, high fermentability
Guar gum: high solubility and fermentability
Gum arabic, Xanthan gum: high solubility, moderate fermentability
Locust bean gum: high solubility, low fermentability

Herbivores (especially ruminants) with their elaborate digestive system are able to draw a high amount of energy from short chain fatty acids (SCFAs) produced by bacterial fermentation of fiber. Dogs with their short and simple digestive tract do not have this ability, but still benefit in a different way - the enterocytes and colonocytes lining the gastrointestinal walls are active cells with a very high turnover rate that utilize short chain fatty acids as a significant energy source.

A moderate amount of fiber in the diet aids in the transport of the stomach contents through the intestines and promotes regular elimination. Excessive amounts often cause loose stools, gas and increased stool volume and frequency. High fiber diets are often used for management of diabetes mellitus and/or obesity in dogs.