FIBRES are naturally found within plants (often as structural components), and they are 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 shortchain fatty acids (SCFAs). Some of the most common fibres include cellulose (and hemicellulose), pectins, 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. This article explores the potential benefits of using supplementary fibre within the diet of dogs and cats.
The classification of fibre
Fibres can be classified by their structure, rate of fermentation, solubility in water, digestible and indigestible fractions, water-holding capacity and viscosity. Table 1 summarises some of these categories: Most rapidly fermentable fibres (such as pectins and fructooligosaccharides) are soluble, whereas slowly fermentable fibres (such as cellulose) tend to be insoluble.
The general effects of soluble and insoluble fibre sources2 are shown below:
- Slow gastric emptying.
- Colonic transit slowed.
- Colonic pH decreased.
- Fermentation to SCFAs providing energy for colonocytes.
- May hasten gastric emptying.
- No effect on, or hastening of, colonic transit.
- Faecal bulk increased.
It has been found that soluble fibres can attract water, form gels and slow gastric emptying. In contrast, insoluble fibres tend to hasten gastric emptying, they do not often form gels and they are less fermentable than soluble fibres. Insoluble fibres are often used to provide bulk within the colon, which is important for the maintenance of normal faecal consistency. Slowly fermentable fibres (such as cellulose) are the most effective stool bulking agents because they retain their structure for a long period of time and they are therefore able to bind greater amounts of water. Efforts to increase faecal bulk have been recommended for the treatment and prevention of irritable bowel syndrome (IBS) and other gastrointestinal disorders.
Examples of commonly used fibres
Cellulose. Cellulose consists of glucose units bound together by beta1,4- linkages (rather than the á-linkages in starch). The beta1,4-linkages can only be broken apart by microbial enzymes, and this results in cellulose being fermented in the colon by microorganisms. Cellulose is an effective stool bulking agent. Pectins. Pectins consist of linear chains of galacturonic acid linked together by alpha1,4-glycosidic bonds which are interrupted by other sugars e.g. galactose and rhamnose) to form branches. Pectins can be found in the skins of citrus fruits and they are water soluble and rapidly fermentable. Gums. Gums are viscous and sticky polysaccharides that can be found in the seeds and exudates of plants. Gums tend to have variable fermentation rates and commonly used gums include acacia gum and psyllium gum. Psyllium husk. Psyllium 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 management of large intestinal disease.
Oligosaccharides are polymers that contain up to nine sugars; fructooligosaccharides (FOS) are oligosaccharides that contain fructose. FOS 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.3,4 Bifidobacteria ferment FOS into SCFAs and the resulting reduction in intestinal pH can inhibit the growth of pathogenic bacteria such as E. coli and Salmonella species. In addition, the more acidic environment can inhibit the sporulation of Clostridium perfringens.
The beneficial effects of fibre
The main function of insoluble fibre is to increase faecal bulk and the level of water in intestinal contents.5 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.6 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.7 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.5,6 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 (see fructooligosaccharides). The addition of fibre may not be suitable for every animal with small intestinal disease due to the potentially abrasive properties of certain fibres. However, soluble fibres which form gels can bind to deconjugated bile acids, and therefore could confer a benefit in certain cases.
The use of fibre for specific conditions
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, pectins or FOS) to 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. It is important that an adequate fluid intake should be encouraged alongside fermentable fibres to prevent dehydration occurring.
Manipulation of the fibre content of an animal’s diet has been recommended for the management of colitis. Increasing the amount of fibre in a diet can help to bind bile acids and prevent bacterial deconjugation of the bile acids. 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.8 The addition of insoluble fibre (e.g. cellulose) 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. Soluble fibres (such as pectin and soya fibre) are fermented into SCFAs which can provide the benefits described previously.
Irritable bowel syndrome (IBS)
It has been reported that patients with IBS improve clinically when the fibre content of their diet is increased. An increased dietary fibre intake can alter faecal water content, colonic motility and intestinal transit rate. Psyllium husks have been used successfully in the management of IBS.9
Obesity and body weight management
The addition of slowly fermentable fibre (e.g. cellulose) to a pet’s diet can be effective for controlling body weight and treating obesity. Cellulose increases bulk in the stomach and intestines and helps to promote the feeling of satiety whilst fewer calories are consumed.10 In dogs, diets supplemented with high levels of both protein and fibre have a greater effect on satiety than those supplemented with either protein orfibre alone.11
Although fibre is not considered an essential component in the diets of dogs and cats, the use of fibre as an aid in the management of various GI diseases is gaining much interest.
Undoubtedly, this interest will continue to increase in the future.
- Hand, M.S., Thatcher, C. D., Remillard, R. L. et al. Eds. (2010) Small Animal Clinical Nutrition, 5th Edition. Mark Morris Institute.
- Chandler, M. (2002) Essentials of nutrition in dogs and cats with gastrointestinal disease. In Practice 24: 528-533.
- Gibson, G. R. and Roberfroid, M. B. (1993) Dietary modulation of human colonic microbiota: Introducing the concept of prebiotics. Journal of Nutrition 125: 1,401-1,412.
- Roberfroid, M., Gibson, G. R. and Delzenne, N. (1993) The biochemistry of oligofructose, a nondigestible fiber: an approach to calculate its caloric value. Nutrition Reviews 51: 137-146.
- Twedt, D. C. (1993) Dietary fibre in gastrointestinal disease. In: Proceedings, Eleventh Annual Veterinary Medical Forum, American College of Veterinary Internal Medicine, Washington DC, pp225-229.
- Burrows, C. F., Kronfeld, D. S., Banta, C. A. et al (1982) Effects of fibre on digestibility and transit time in dogs. Journal of Nutrition 112: 1,726- 1,732.
- Roediger, W. E. (1982) Utilisation of nutrients by isolated epithelial cells of the rat colon. Gastroenterology 83: 424-429.
- Bush, B. (1995) Colitis in the dog. In Practice 17: 410-417.
- Leib, M. S., Saunders, G. K., Willard, M. D. et al (1997) Fibreresponsive large bowel diarrhoea. In: Proceedings. Fifteenth Annual Veterinary Medical Forum, American College of Veterinary Internal Medicine, Lake Buena Vista FL, pp319-321.
- Jewell, D.E. and Toll, P.W. (1996) Effect of fibre on food intake in dogs. Veterinary Clinical Nutrition 3: 115-118.
- German, A. (2010) Obesity in companion animals. In Practice 32: 42- 50.