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The importance of fibre in the diet

01 January 2014, at 12:00am

Ian Williams presents the first in a new series of monthly columns from Royal Canin, focused on the latest knowledge behind nutrients that can be of benefit to cats and dogs

WHAT is fibre? It is naturally found within plants (often as structural components), and it is resistant to digestion by the enzymes secreted within non- ruminant, monogastric animals. Instead, the majority of fibres are fermented by micro- organisms within the colon into short-chain fatty acids (SCFAs).

Some of the most common fibres include cellulose (and hemicellulose), gums and mucilages. In addition to this, other plant polysaccharides can also be considered as fibres – these include fructans (e.g. inulin, which contains fructo-oligosaccharides) and mannans. Fibres can be classified by their structure, rate of fermentation, solubility in water, digestible and indigestible fractions, water-holding capacity and viscosity. Most rapidly fermentable fibres (such as fructo- oligosaccharides) are soluble, whereas slowly fermentable fibres (such as cellulose) tend to be insoluble.

The general effects of soluble fibres include: 

  • delaying gastric emptying; 
  • the slowing of colonic transit; 
  • a decrease in colonic pH; 
  • and the fermentation to SCFAs providing energy for colonocytes.

Conversely, insoluble fibres may hasten gastric emptying; they have no effect on, or hastening of, colonic transit; and they may result in an increase in faecal bulk. Efforts to increase faecal bulk have been recommended for the management of irritable bowel syndrome (IBS) and other gastrointestinal disorders. 

Commonly used fibres 

Examples of commonly used fibres include: 

  • Cellulose – which consists of glucose units bound together by β1,4-linkages (rather than the α-linkages in starch). The β1,4-linkages can only be broken apart by microbial enzymes, and this results in cellulose being fermented in the colon by micro-organisms. Cellulose is an effective stool bulking agent. 
  • Psyllium – this is a good source of soluble fibre. The seed husks contain glycosides and mucilages which swell when in contact with fluid, forming a gel-like substance. Psyllium can help to improve faecal consistency and for this reason it is often useful for the nutritional management of animals with large intestinal problems.
  • Fructo-oligosaccharides (FOS) – this is able to enter the colon intact because it is not digested by enzymes in the small intestine. In the colon, certain beneficial bacteria (bifidobacteria and Lactobacillus spp.) ferment FOS readily, which leads to an increase in their numbers. The resulting reduction in intestinal pH can minimise the growth of pathogenic bacteria such as E. coli and Salmonella.


The main function of insoluble fibre is to increase faecal bulk and the level of water in intestinal contents.1 Fibre has been shown to shorten intestinal transit rate in dogs with normal or slow transit time and to prolong transit rate in dogs with rapid transit time.1 These factors help to promote and regulate normal colonic motility and faecal consistency.

Soluble fibre is rapidly fermented by micro-organisms within the colon into SCFAs (acetate, propionate and butyrate). Colonocytes preferentially use butyrate as their source of energy, rather than obtaining energy from glucose or amino acids.1 In addition, SCFAs facilitate the reabsorption of sodium, chloride and water in the colon.

Finally, the production of SCFAs lowers the pH of the colonic contents, which can result in decreased numbers of pathogenic bacteria and an increased colonisation resistance against pathogenic bacteria.1 As can be seen, SCFAs (in particular butyrate) are vital for the health of the colon.

Fermentable fibres that can stimulate the growth of intestinal bacteria, such as lactobacilli and bifidobacteria, are often called prebiotics. Prebiotics have been shown to limit the growth of intestinal pathogens.

The addition of fibre may not be suitable for every animal with small intestinal disease due to the potentially abrasive properties of certain fibres and so it is important to evaluate each patient’s needs on a case by case basis.

Specific conditions

Fibre can assist in the nutritional management of pets with the following specific issues:

  • Diarrhoea and constipation Fibre can normalise intestinal water content by absorbing water from the luminal contents if an animal has diarrhoea and adding moisture to the faecal matter in animals with constipation. The addition of fermentable fibre (psyllium and FOS) within the diet of dogs and cats with constipation is recommended, since the gas produced by the fermentation of these fibres can help to break up the faecal mass. Psyllium is also able to absorb water which increases the volume of the faeces. The softer stools that are created are then easier to pass. 
  • Colitis Increasing the amount of fibre in a diet can help to bind bile acids and prevent them being deconjugated by bacteria. Deconjugated bile acids are toxic to the colonic mucosa and they can also increase permeability and fluid secretion in the colon as well as stimulating mucus output.1 The addition of insoluble fibre can help to bind water, producing better formed, softer faeces. This leads to stretching of the colonic smooth muscle, helping to restore normal peristalsis and reduce straining.
  • Obesity The addition of fibre to a pet’s diet can be effective for controlling body weight and managing obesity. A carefully balanced level of soluble and insoluble fibre in the diet can increase bulk in the stomach and intestines and helps to promote the feeling of satiety whilst fewer calories are consumed.1

In conclusion, although fibre is not considered an essential component in the diets of dogs and cats, the use of fibre as an aid in the nutritional management of pets with various GI issues is gaining much interest. Undoubtedly, this interest will continue to increase in the future.

  1. References on file. For more details, visit (or for Ireland). 
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