Fibre in the Diet?
Fibre is the part of plants that cannot be digested. As a result, it provides zero calories and passes through the digestive system virtually unchanged, but along the way it serves some crucial roles.
Fibre absorbs water like a sponge. This means that if there is excess water in the colon, for example during diarrhoea, any dietary fibre will soak it up and help to produce a firm stool. If, on the other hand, there is too little water in the colon, which often leads to constipation, the fibre will draw water in from surrounding tissues and help to resolve the problem. As you can see, fibre is important in maintaining intestinal health and can effectively treat both constipation and diarrhoea.
Another important function of fibre is as a prebiotic. This means that is provides a medium and a food source for "friendly" intestinal bacteria. These bacteria aid in the digestion of food and help to prevent harmful bugs from getting established.
Dietary fibre also slows down the digestion of the other foods it is consumed with. This can be particularly useful in diabetic dogs because the fibre helps to provide a slow, steady release of dietary sugar into the bloodstream. It can also help with weight loss programs as foods that are high in fibre are digested more slowly, allowing the dog to feel fuller for longer while providing less calories.
Although dietary fibre is not classed as a nutrient, and not considered an essential component of a diet, it is important and does affect the health and efficient functioning of the gut in several ways:
- It delays gastric emptying;
- It alters nutrient absorption and metabolism;
- It normalizes transit time through the gut;
- It maintains the structural integrity of the gut mucosa;
- It increases the water-holding capacity of the faeces;
- It adds bulk to the faeces.
Dietary fibre does have disadvantages:
- Flatulence and stomach rumble – particularly when large quantities are introduced suddenly into the diet;
- Increased faecal output.
In addition, decreased digestibility of protein, fat and carbohydrates, together with decreased uptake of some minerals, could lead to inadequate intake of these minerals under some circumstances.
In the wild, carnivores tend to eat all parts of their prey, both digestible and indigestible, so fibre can be regarded as a natural part of the diet. Fibre is only found in plants, so virtually all vegetables contain some, while meats contain none at all.
Dietary Fibre Requirements
Dietary fibre affects carbohydrate digestion and absorption. Typical commercial grain-based pet food dietary fibre consists of plant materials such as cellulose, hemicellulose, lignin, and pectins. Non-plant-cell-wall sources of fibre such as gums, mucilages, algal polysaccharides, and modified cellulose are also added to commercial grain-based pet foods. Dietary fibres are insoluble or soluble. Insoluble fibres consist primarily of cellulose and some hemicelluloses. They also include lignin which represents a small part of dietary total fibre. Insoluble fibres are the structural building material of cell walls. This fibre's major source is the bran part of cereal grains. Colonic bacteria do not ferment most insoluble fibres.
A. Classification of Dietary Fibre
Cellulose: whole-wheat flour, bran, vegetables
Hemicellulose: psyllium seed
Hemicellulose: bran, grains
Lignin: wheat, vegetables
Gums: oats, legumes, guar, barley
B. Ferment-ability of Dietary Fibre
locust bean gum
Water soluble fibres are all other non-structural and indigestible plant carbohydrates. Soluble fibres such as pectin, guar gum, and carboxymethylcellulose absorb water and form gels; they slow gastric emptying, reduce nutrient absorption, and increase intestinal transit rate. Increased dietary fibre reduces digestibility for carbohydrates, proteins and fats and affects absorption for some vitamins and minerals. Water insoluble fibres such as wheat cereal bran and cellulose reduce digestion and absorption the least. Fibre increases faecal volume and promotes more frequent defecation. Fibre from cereal grains also increases faecal volume by absorbing water.
Colonic bacteria vary in their ability to ferment fibre. Wheat bran and cellulose fibre are poorly fermented. Beet pulp, rice bran, and some gums are moderately fermented. Pectin, guar gum, oat bran, and some vegetable fibres are readily fermented. As mentioned, fermentation maintains greater numbers of colonic bacteria and produces short-chain fatty acids, some of which are important for colonic nutrition. Fatty acids also promote colonic salt and water absorption. Excess fermentable fibre causes diarrhoea due to the presence of large amounts of short-chain fatty acids. Fibre added to commercial grain-based diets can be completely unfermented such as cellulose flour and poorly fermented such as wheat bran. They do little more than increase faecal volume. Some added fibres are jelling agents such as guar gum, alginates, etc. which are typically added to canned commercial dog foods that contain gravy and real or simulated meat chunks. Colonic bacteria readily ferment jelling agents, but excessive amounts can cause diarrhoea.
The Fibre Debate ...
Fibre has been a component of commercial pet foods during the last 50 years as the trend developed to no longer feed owner-prepared or raw food diets. In the past, pet parents rarely add fibre to foods they prepare. The "old way of doing things" seemed to have provided adequate fibre in the diet to supply colonic nutritional needs. However, based on today's research available, as a result of the commercial pet food industry, feeding a mostly meat diet would seem to supply inadequate fibre, if we are to believe them. Most pets receive adequate fibre because they have few gastrointestinal problems. Interestingly though, dogs and cats in the wild select diets containing negligible fibre. Thus, we have to surmise that dogs and cats have low requirements for fibre. Commercial grain-based pet food manufacturers claim that optimal dietary crude fibre levels should range from 1.4% to 5%. In contrast, there is little scientific basis for any recommendation of this nature. Canine and feline nutrition books devote entire chapters to fibre but they give no recommendation on dietary fibre levels for normal dogs or cats. An owner-prepared or biologically specie appropriate diet contains less than 1.4 percent fibre, unless it contains large amounts of vegetables, beans, peas or bran-rich cereals.
Fibre is not a dietary requirement for our fur kids, but may be needed because we don't feed our fur kids animal fur (prey model) and other non-digestible sources of fibre, so they may become constipated due to their sedentary lives.
Fibre Content of Commercial Pet Foods?
The type of fibre in commercial grain-based diets has been unimportant, other than, whether it causes diarrhoea. High fibre content causing large-volume bulky bowel movements has not concerned most manufacturers. But, the pet nutrition community are in agreement that the 20 percent fibre level of some pet foods are excessive. Some manufacturers now add less fibre and use a poorly soluble (so that it does not affect digestive function) and moderately fermentable (so that it provides nutrients for the colonic mucosa but not enough fermentation of fibre to cause diarrhoea) fibre. Beet pulp and rice bran are examples of such fibres. If the need for fibre is small why give an excess that can cause impaired digestive tract function, bulky bowel movements, and diarrhoea?
Fibre is the source of energy for colonic mucosal cells. Bacteria accomplish that by producing short chain fatty acids (acetate, proprionate and butyrate). More than 70 percent of colonic cells’ energy is dependent on these fatty acids. Fibre levels needed to meet these requirements is probably low, but the lack of unbiased research make this assumption a generalisation. Many animals live on low fibre diets for years without developing colonic disease.
Fibre for Management of Disease?
Fibre is added to commercial grain-based pet foods designed for weight reduction (see our section on Pet Obesity for additional details). Commercial pet food companies claim this to be effective, because fibre reduces digestibility of other nutrients and supposedly reduces appetite or hunger by filling the stomach (McKibble or McCan effect). Sometimes veterinarians vary the dietary content of fibre for other reasons, more than often feed low fibre diets to dogs with chronic diarrhoea. Some vets recommend feeding high fibre diets to dogs with colitis. High fibre diets can help manage some animals with diabetes mellitus. Although veterinarians promote additional fibre in pet foods to treat these medical problems, there is little scientific evidence that additional fibre is of any value to the animal.
When to add fibre to the diet?
If you fur kids has dry, crumbly stools or difficulty pooping, then you would need to add a small amount of fibre to the diet. If not needed, don't add it.
Ground psyllium or coconut fibre (chips or flower) are both easy ways to add insoluble fiber if needed, but often more pumpkin, butternut or veggies will take care of the problem.
Did You Know? Tripe (and tripe-based meals) are excellent sources of natural fibre for your fur kids. A well formulated biologically specie appropriate raw food formula for dogs should also contain a small amount of vegetable fibre in the diet, typically no more than 2% as wet / 7% as dry (DM), or raw, unwashed tripe.
References and Research
Additional resources and research for you.