The importance of fibre in the diet - Veterinary Practice
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The importance of fibre in the diet

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-
Instead, the
majority of
fibres are
by micro-
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

The general effects of soluble
fibres include:

  • delaying gastric
  • the slowing of colonic
  • 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

  • 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
  • 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

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

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
  • 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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