Dietary fibres are often lumped together. Yet “fibre” is really an umbrella term for a highly diverse group of substances, each with its own mechanism of action, its own indications and its own pitfalls.
Over the coming weeks we will therefore take you through a number of fibres that are commonly used in dogs and cats. What do they actually do? When are they useful? And when are they not?
We start with perhaps the best known of them all: psyllium.
Psyllium is one of the most frequently prescribed dietary fibres in veterinary medicine, and not without reason. It is highly effective at normalising faecal consistency.
That effect does not run through the microbiome. Psyllium is barely used as a nutrient source by intestinal bacteria and therefore has little prebiotic effect. Precisely because of this, its structure remains largely intact into the colon, where it binds free water into a gel-like mass.
That is all psyllium does. And that is exactly why it can help with two opposite problems.
When stools are too dry, the water held in the gel is less available for extraction by the colon. More fluid therefore remains in the intestinal content.
When stools are too loose, that same water is trapped in a matrix. The faeces become better formed and firmer in structure.
But take note. In the first case the water content of the stool changes. In the second case it is mainly the structure. A patient with diarrhoea can produce neatly formed stools on psyllium and still keep losing fluid.
Firmer stools are therefore not the same as normalised intestinal function.
When is psyllium useful?
• In mild constipation, provided the animal is well hydrated.
• In chronic large bowel diarrhoea in dogs and cats, as part of a nutritional approach.
• When stable, well-formed stools are a treatment goal in their own right.
When is caution warranted?
• In cats with (suspected) megacolon. A colon with severely reduced motility is not helped by adding more bulk to the gut.
• In animals that drink too little. Psyllium can only hold water if that water is available. With every psyllium recommendation, therefore, also discuss the importance of adequate water intake.
• In constipation: always rule out other causes first. Psyllium is not the answer in every constipated animal. Some are in pain, struggle to squat or avoid the litter box.
What you should not expect from it:
• That it resolves the cause of the complaint.
• That it steers the microbiome the way highly fermentable fibres do.
• That every constipated patient benefits from extra psyllium.
Because psyllium regulates nothing and does exactly the same thing in every gut: bind water. Whether that helps depends entirely on your patient.
🥣 Meet the Fiber: a FeedWise series on dietary fibres in dogs and cats. In each edition we discuss one fibre: its mechanism of action, its indications, its limitations and its place in clinical practice.
Next edition: FOS, the fermenter.
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