When I was a nutrition resident, I found the topic of fibre quite confusing. The classification of fibre as either soluble or insoluble made no sense to me, because it has no real biological relevance. Fortunately, my supervisor also felt the same way, and once I started to think of fibre as either fermentable, or non-fermentable, it all became clearer.
The question of whether cats need fibre is a really important one, and also the subject of ongoing research, so be aware that this is an evolving field. Not only are pet food manufacturers exploring new and innovative fibre types, but nutritionists are also looking at how these fibres affect the microbiome, and how best to use them in diets for both healthy and unwell cats.
Unfortunately, we can’t have a good conversation about fibre without defining some terms – but these are actually great words, and they will help you to understand the potential benefits of different fibre types for cats.
So, let’s jump in (definitely get a coffee first!)
Some fibre basics (please don't skip over!)
I’m not going to spend a long time talking about the definition of fibre, and how this varies somewhat according to different references. The current definition of fibre for pet food purposes (in the USA) is: “a large class of plant carbohydrates that resist digestion hydrolysis”.
So essentially, these are plant-derived compounds or ingredients that aren’t able to be digested by the cat itself (more about the plant-derived aspect later).
There are three terms that are relevant to fibre – let’s focus only on the first two:
1) Fermentability
2) Viscosity
3) Solubility
1) Fermentability:
Fermentability is the most important term to understand, in my opinion. Fibre can
be described as rapidly to slowly fermentable. Highly fermentable fibres act as energy substrates for bacteria in the large intestine, which results in the production of short-chain fatty acids.
Short-chain fatty acids can be used by the cells of the large intestine as an energy source, as well as having a wide range of other beneficial effects. They can help to promote motility of the colon, and also have anti-inflammatory properties. However, it's important to keep in mind that many of the beneficial effects of SCFAs have only been documented in humans, and not in cats.
Slowly or non-fermentable fibres are not used (fermented) by the gut bacteria, and instead provide bulk to stools. The term “prebiotic” or “prebiotics” just refers to fermentable fibre – prebiotic fibre acts as a substrate for bacteria in the large intestine.
So, to summarise:
Fermentable fibre = used by gut bacteria to produce short-chain fatty acids and other compounds. This can affect both the host (cat), and the bacterial populations themselves.
Non-fermentable fibre = not used by gut bacteria and instead excreted from the body in stools.
Some examples of highly fermentable fibres include gums, pectins, inulin, and fructooligosaccharides (FOS).
Some examples of non-fermentable or poorly fermentable fibres include cellulose, wheat bran, and pecan shell fibre.
2) Viscosity:
Fibre sources with a high viscosity have an increased water-binding capacity that can result in softer, moister stools. This can sometimes slow the passage of food through the gastrointestinal tract, slow down the rate of digestion of nutrients (like glucose), and increase satiety, leading to decreased food intake.
Viscous dietary fibres can act as thickeners, and include gums, pectins, psyllium, chia seeds, and beta-glucans.
The ability to form gels when exposed to moisture means that viscous fibres like psyllium can be a good choice for cats experiencing constipation, because they increase the water content of stools, making them easier to pass. They can also reduce blood glucose peaks that occur after eating, because glucose is trapped in the intestine and absorbed more slowly.
As I mentioned previously, in my opinion we don’t need to discuss solubility of fibre to try and answer this question, so let’s skip that one.
One more quick thing though:
“Fillers” vs fibre
The internet loves the word “filler”, but it is really important to quickly point out that fibres are not fillers. Fibres are functional ingredients that are added for a specific purpose. “Fillers” generally refer to ingredients that have no nutritional value. Given that very few ingredients have absolutely no nutritional value, this is a term I would love people to move away from.
Do cats need fibre in their diet?
As in other species, the supplementation of feline diets with different fibres has been associated with some beneficial outcomes in numerous studies. However, many of these studies are challenging to interpret, because the significance of changes in certain bacterial species, or metabolites, is not yet well-understood. As I mentioned previously, studies in dogs and humans can't really be extrapolated to cats.
Studies in humans have shown that during chronic or intermittent dietary fibre deficiency, the gut bacteria resorts to using mucous lining of the intestine as a nutrient source, which can lead to erosion of this mucous barrier. This may increase the risk of pathogenic (bad) bacteria being able to invade and cause harm.
Other potential benefits of fibre include:
Both fermentable and non-fermentable fibre can have positive effects on stool consistency and frequency. Gel-forming fibres like psyllium can normalise stool consistency, improving both constipation and diarrhoea. Fermentable fibres like inulin can increase motility of the colon. Non-fermentable fibre like wheat bran can add bulk to stools and increase the rate of faecal passage.
Fermentable (prebiotic) fibre can promote the growth of beneficial gut bacterial species. This can increase the production of metabolites that have beneficial health effects, and decrease harmful metabolites.
Extremely low fibre diets for cats have been increasing in popularity, perhaps because fibre additives are often seen as "not species-appropriate". For example, muscle meat plus vitamin/mineral supplements is commonly recommended as an appropriate diet, and indeed, is very quick and convenient to prepare.
Many popular canned diets are almost fibre-free, apart from some fermentable gelling agents or thickeners (for example, xanthum gum, locust bean gum). However, are these diets truly "species-appropriate"? Could the lack of fibre actually be harming our cats?
These two things are not the same!
The research we do have suggests that yes, cats can benefit from fibre, and that they have evolved to consume diets that contain indigestible or poorly digestible material like fur, collagen and cartilage (i.e. fibre-supplemented diets are, in fact, species-appropriate). These "animal-derived fibres" can also be fermented by the cat's gut bacteria (similar to plant-derived fibres), and this fermentation can produce beneficial compounds (and reduce harmful ones).
When selecting fibre additives, as always, the goal is to ensure that the diet is appropriate for the individual cat – that it contains the right type/s of fibres, in the right amounts. This is especially important for cats with medical conditions like inflammatory bowel disease and chronic kidney disease. In terms of selecting fermentable or non-fermentable fibres for cats, research indicates that either moderately fermentable fibres, or complex fibre blends that include both fermentable and non-fermentable fibre, may have the most beneficial effects.
Plant-derived vs. animal-derived fibres for cats
There is an enormous range of plant-derived fibres to consider, such as gums, pectins, FOS, MOS, XOS, inulin, resistant starch, psyllium, fruit and vegetable fibres, brans, seeds, cellulose, and miscanthus grass.
Generally, slowly fermentable or non-fermentable fibres like psyllium or bran are more forgiving in terms of dosing, compared with highly fermentable fibres like FOS or inulin - so this makes them a good place to start. Similar to dogs, where we often prefer the fibre in the diet to be provided by different whole foods, for cats, we may want to try and recreate the complexity of the fibre types found in a whole prey diet, using the fibre supplements available to us.
MOS, GOS, FOS and XOS
For example, fructooligosaccharides (FOS)
Characteristics: Highly fermentable, non-viscous, soluble.
Some research shows beneficial effects from supplementation of FOS, especially for cats with gastrointestinal disease. High doses can cause soft stools, gut pain, flatulence and increased gut sounds. 250 to 500 mg per day (divided between meals) is likely adequate for most cats.
Inulin and resistant starch
For example, green banana resistant starch
Characteristics: Highly fermentable, non-viscous, soluble.
Similar to FOS but more shelf-stable. Be careful not to add too much too quickly. For highly fermentable fibres like these, it can be helpful to seek advice from a nutritionist, as they can be tricky to get right.
Psyllium seed husk
Characteristics: Slowly fermentable, viscous, insoluble.
As mentioned previously, psyllium is a viscous, gel-forming fibre that can soften stools. Powdered products are more palatable for most cats. For older cats struggling with constipation, we recommend starting with 1/4 teaspoon psyllium per meal, increasing to 1/2 teaspoon or 3/4 teaspoon over time (as needed, depending on stool consistency).
Cooked or canned pumpkin
Characteristics: Predominantly slowly fermentable, non-viscous, insoluble fibre.
Pumpkin is really a poor source of fibre, relative to other additives. It provides mainly moisture, which can also be helpful for constipation. Some pumpkins contains quite a lot of sugar (sucrose), relative to other carbohydrates, so not ideal for diabetic or pre-diabetic cats.
Fruit and vegetable fibres
For example, carrot fibre, apple fibre, tomato pomace
Characteristics: Generally provide a blend of both fermentable and non-fermentable fibre (predominantly non-fermentable).
They are not often easy to source in small quantities (to try at home), but they can work well in commercial diets and supplements.
Chia seeds, brans, beet pulp, cellulose and miscanthus grass
Characteristics: Some seeds provide a useful blend of fermentable and non-fermentable. Brans and cellulose provide non-fermentable fibre, as does miscanthus grass. Beet pulp is moderately fermentable, but it is really only used in commercial diets.
Oat bran or barley bran can be good first choices for senior cats struggling with constipation. Chia seeds and flaxseeds contain viscous fibre, so they can also increase the softness of stools. Most cats find chia seeds fairly palatable, because they don't really notice them in food.
Animal-derived fibre - the truly species-appropriate fibre?
Animal fibre is defined as poorly digestible or non-digestible protein-rich substances that are potential substrates for fermentation by gut bacteria (for example, collagen and cartilage).
Plantinga et al. hypothesised that the consumption of whole prey, which is a major source of animal fibre, might enhance gut health and affect the microbiota differently, as compared with foods of plant origin.
Fur and feathers, cartilage, collagen and hydrolyzed collagen:
Studies by Depauw et al. on the diets of cheetahs revealed some really interesting things. In one study they compared a diet of whole rabbits with raw beef. They observed that total branched-chain fatty acids and putrefactive indole and phenol were lower when fed whole rabbit. Additionally, serum indoxyl sulphate, a toxic metabolite of indole (that increases in cats with kidney disease), was analysed and showed a substantial decrease when cheetahs were fed whole rabbit.
In a second study, they looked at the fermentation of chicken cartilage, collagen, glucosamine-chondroitin, glucosamine, rabbit bone, rabbit hair, and rabbit skin. They found that rabbit hair, skin, and bone were poorly fermentable, however glucosamine-chondroitin, glucosamine, chicken cartilage and collagen were all highly fermentable, and collagen induced an acetate production comparable with FOS.
Similarly, a study by Butowski et al. looked at the fermentation of hydrolysed collagen, cat hair, and cartilage, and found that in cats that had been fed a high protein diet, these substrates were readily fermentable (especially hydrolysed collagen).
What does this mean? Cats have evolved to consume a whole prey diet, which includes collagen-rich tendons, cartilage and ligaments. These collagen-rich parts of the prey act as substrates for fermentation in the intestine, and this potentially has beneficial effects on the overall health of the cat.
Fibre for healthy cats vs. cats with medical conditions
Without getting into too much detail, it is important to point out that different medical conditions can benefit from different types and amounts of fibre in the diet. For cats, these are the most important diseases where fibre supplementation is relevant:
Obesity
Inflammatory bowel disease
Chronic kidney disease
Constipation
Hairballs
Idiopathic hypercalcaemia
Obese cats can benefit from higher levels of non-fermentable fibre, because this reduces the energy density of the diet and also promotes satiety (a feeling of fullness). Constipation is an important and common problem in older cats. Generally we recommend trialling a gel-forming fibre like psyllium husk first, because it can help to soften stools and make them easier to pass.
Chia seeds can also work well, as can fibre blends composed of inulin, psyllium and chia seeds. A small amount of fermentable fibre (like inulin) can increase motility of the colon, also helping to promote normal defecation. Make sure to also increase activity/play, promote water consumption, and increase brushing/grooming to try and reduce episodes of constipation.
Cats with chronic kidney disease can benefit from fibre in their diet, because this has been shown to reduce the formulation of (harmful) uremic toxins in the gut. Unfortunately, discussing the effects of fibre supplementation for cats with gastrointestinal disease is beyond the scope of this blog, however here's a great paper that provides a useful overview of this topic. Finally several studies have shown that higher fibre diets can increase hair passage through the intestinal tract and may reduce the incidence of hairball regurgitation or vomiting.
Key points
There are different ways to categorise fibre. Non-fermentable fibre adds bulk to stools; fermentable (prebiotic) fibre affects the gut microbiome, and subsequently the host animal.
Fibre is actually a "species-appropriate" component of diets for cats, and has beneficial effects on health.
Different fibre types and amounts suit different cats. Fibre blends and moderately fermentable fibres may be the best option for most cats.
Plant-derived fibres are a practical alternative to animal-derived fibres for most cat owners. If you would like to try adding fibre to your cat's diet, begin with psyllium husk powder, chia seeds or oat bran (1/4 level teaspoon per meal), and increase as needed (depending on stool consistency and frequency).
Animal-derived fibres like hydrolyzed collagen, fur, and cartilage may have beneficial health effects for cats. Research is ongoing. If you would like to try animal-derived fibre for your cat, consider trying whole raw prey (mice, rats, juvenile rabbits), offering dried wild rabbit ears cut into strips, or supplementing hydrolyzed collagen (same dose as per psyllium above).
If you have any questions or feedback: info@vngpets.com
Please leave any comments below, and thanks for reading. Please answer our quick poll below as well!
Do you add fibre to your cat's diet?
0%Nope, cats don't need fibre!
0%Psyllium husk
0%Cellulose
0%Oat, wheat or barley bran
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