Tracking carbohydrates is common among people that consider themselves healthy eaters, but it may benefit to watch the intake of fibre for your dog too. Often ignored, dietary fibre can be a key factor in your dog’s gastrointestinal health. Whether you feed a raw or kibble diet, understanding the benefits of fibre on your dog’s GI microbiota is vital for their long-term health.
Carbohydrates and dietary fibre are not the same though. Carbohydrates make up a large macromolecule family that includes sugars and starches, and they’re meant to be metabolized for energy sources. This is not the case for dietary fibre.
The exact definition of dietary fibre has been up for debate for decades. The FDA stated in 2016, “non-digestible soluble and insoluble carbohydrates (with 3 or more monomeric units), and lignin that are intrinsic and intact in plants […] determined by FDA to have physiological effects that are beneficial to human health” (Nogueira, et al, 2019). Dietary fibre, in short, consists of plant matter that you or your dog can’t digest. This is where intestinal microbes come in to aid in digesting the food that your body can’t. It’s the same for dogs, and the type of dietary fibre they have access too will alter how their GI tract will digest food.
Dietary fibre can be broken down into two categories: fermentable and non-fermentable. Let’s break down the ingredients on a common kibble from Royal Canin:
Fermentable fibre sources support intestinal bacteria by providing the nourishment they need to thrive. As microbes ferment the fibre, they produce metabolites that your dog can use. A common product of fermentation is short-chained fatty acids.
This kibble contains two fermentable dietary fibres, beet pulp and psyllium husk. The latter is a good source of fermentable fibre and promotes higher fecal moisture by absorbing water as it passes through the intestines. This increase in viscosity also increases intestinal transit time and leads to overall better nutrient absorption, but can lead to soft stool with too much water absorption. Beet pulp is more common as a fermentable dietary fibre because it also contains non-fermentable compounds that act as a stool bulking agent.
Non-fermentable fibres contribute mainly to fecal bulking. As they’re not digested by intestinal microbes, these fibres decrease transit time and increase stool mass when added to the diet (NRC, 2006). Unlike psyllium husk, a non-fermentable dietary fibre doesn’t increase water absorption in the stool while passing through the intestine. Cellulose is a very common non-fermentable dietary fibre to increase stool mass that does not contribute to overall gut health. It should be noted that these non-fermentable fibres have not shown any nutritional benefit only water retention and stool bulking capabilities (in current studies).
As non-fermentable fibres may decrease digestibility and nutrient absorption in the intestines, it’s important to combine it with a fermentable fibre source to aid in overall gut health. A blend of fermentable and non-fermentable fibres will stabilize your dog’s intestinal transit time, water retention, and stool mass. Similar to when someone takes a laxative to regulate their bowels, a combination of these fibres promotes healthy intestinal flora and stool regulation.
Including fermentable fibres has positive benefits on overall metabolism as a 2016 study showed in dogs using beet pulp and guar gum. The addition of these two fermentable fibres increased amino acid levels in blood samples taken from dogs – signalling a reduction in amino acid metabolism through the large intestine. The authors concluded that the short-chain fatty acid production induced by the fermentation of these fibres shifted the dogs to use these fatty acids, rather than protein, as an energy source. This example of metabolism change shows the benefits that dietary fibre has on your dog when including in their diet.
If your dog’s regular diet doesn’t contain a fermentable dietary fibre, you should consider adding one. Many large pet stores will have a prebiotic or probiotic supplement with these fibres added, so you don’t have to worry about finding individual ingredients yourself. For more on how carbohydrates act on your dog’s system, I would read the Nutrient Requirements of Dogs and Cats from the NRC.