The Role of Fibre in Pet Foods

Although not often considered by consumers as an essential ingredient of a balanced pet food, the role of fibre is both complex and important.

The term "fibre" which appears on a pet food label refers to "crude fibre" (defined as that portion of a diet which is not soluble in either hot alkali or acid). However, it is often times easier to think of fibre as either insoluble and relatively inert (e.g. cellulose) or soluble (e.g. pectins, carrageenan and other gums) in water. Ingredients commonly found in dry per foods, which are high in soluble fibre, would include oats and oat bran, whereas insoluble fibre is commonly associated with the cereal grains such as wheat and wheat bran. Typical crude fibre levels in pet foods range from 2.5 - 5 per cent and can vary as high as 24 per cent in some specialized therapeutic foods. Levels below 2.5 per cent would likely impeed normal bowel function. The CVMA's recommended levels of fibre for optimum nutrition in a healthy pet vary between 3.5 per cent and 6.0 per cent.

Fibre serves many functions in a diet. One important role is the absorption of water with soluble fibre having a greater capacity than insoluble. Fibre also acts as a bulking agent, both on its own and in conjunction with its water holding capacity, which increases muscle tone and movement in the large intestine (colon) with the presumption of healthier tissue. Consequently, fibre may be helpful in the resolution of constipation in some pets by increasing fecal mass and by softening stool through increased water absorption and retention.

Traditional thinking allowed that dietary fibre had no nutritional value. However, research in dogs has shown that, through the process of fermentation in the colon, soluble fibre can, to varying degrees, provide a source of metabolizable energy. In addition to energy, this fermentation produces a variety of short chain fatty acids (SCFA) which may play a role in the treatment of inflammatory bowel disease. SCFAs also lower the pH of the fluid within the large intestine, thus minimizing certain bacterial overgrowths, such as Salmonella, and minimizing the uptake of ammonia through the cells of the colon.

It is important to appreciate that many of the properties associated with fibre have been based upon work done in humans and rats. The inclination to draw inter-species conclusions may be unreliable, as there are significant differences involved. For example, there are claims that excessive fibre levels potentially compromise the availability to the body of certain micronutrients, such as zinc, calcium and iron. Yet some studies have contradictory conclusions and the implications for pet foods have been largely uninvestigated. Research in dogs has shown cellulose tolerance levels of 10 - 15 per cent of the diet without any adverse effects on the digestion of nutrients. However, fibre can tie up the availability of the amino acid taurine in cats, which may suggest the need for a higher dietary taurine content in cats on high fibre diets.

Studies on humans have implicated fibre as compromising the activity of digestive enzymes produced by the pancreas, although fibre appears not to impair enzyme secretion. While research in dogs is limited, at this time, high fibre diets are considered inappropriate for dogs who have a poor ability to produce pancreatic digestive enzymes.

Fibre affects the transit time of food through the gastrointestinal tract, although the impact varies with fibre type. The use of higher than normal fibre content in the diets of diabetic cats is based, in part, upon the assumption that, by utilizing a fibre source that adds bulk to the food and increases retention time within the intestine, the result will lead to lower peaking of blood sugar levels after eating a meal. Again, such assumptions are based largely upon human research and the effectiveness in human diabetics is coming under greater scrutiny.

High fibre, low caloric density pet foods have been traditionally advocated for use in weight reduction programs based upon the principle of low caloric intakes and the feeling of fullness achieved by the bulk of fibre physically bloating the stomach. However, the resultant fecal mass achieved from some very high fibre diets can severely compromise owner compliance in the feeding of such diets.

For many pets, a diet with greater emphasis on restricted caloric density levels and less on insoluble fibre levels may be more successful in achieving the long term goal of weight reduction.