The Problems With Dietary Fiber in Pet Foods

Analysis by Dr. Karen Shaw Becker

miscanthus grass

Story at-a-glance

  • Pet parents may soon discover a new fiber source in their bag or can of dog or cat food: miscanthus grass
  • In pet food, miscanthus grass is somewhat similar to powdered cellulose, an ingredient the pet food industry loves, but pet parents try to avoid
  • In dog and cat diets, a small amount of species-appropriate fiber is very important, but foods loaded with fiber are very detrimental

Soon you’ll very likely see yet another new “alternative fiber source” in pet food — miscanthus grass. At least it’s a step up from peanut hulls and other mycotoxin-filled Ag leftovers that have been served to pets in “premium” pet food brands the last 50 years.

In an article discussing big pet food’s interest in miscanthus grass, online publication acknowledges the following:

“While not an essential nutrient for dogs or cats per se, fiber can provide benefit to their gastrointestinal health and daily elimination products. Further, because fiber is by definition indigestible, it provides a mechanism to lower the caloric density of the diet. Given that over 50% of dogs and cats in the U.S. are overweight or obese, energy dilution with fiber has proven to be a valuable tool to help in weight control.”1

While it’s certainly true we have a pet obesity epidemic in this country, the pet food industry fails to admit its significant role in creating the problem. And certainly, there’s a better approach to keeping dogs and cats lean than adding cheap filler ingredients to pet food to lower calorie counts.

Miscanthus Grass

“… Miscanthus giganteus … is a C4 [perennial] grass that was originally propagated for landscape cover. It has a rapid growth pattern growing to 8 feet or more and produces substantial tonnage every year. The plant grows from rhizomes and once a stand is established will persist for 20 years or more.”2

Miscanthus grass grows fast and tall and in huge quantities. The stems of the plant are harvested and baled, and when used for animal feed, the bales are ground into fine particles. The finished product is extremely high in fiber (90%), and most of it is insoluble fiber (83%). Beyond fiber, there are no significant nutrients in miscanthus grass.

The plant was originally farmed “to capitalize on its cellulose biomass for the ethanol industry,” according to However, the economics didn’t work out, but “Given its similarity to cellulose, the growers thought it might be a viable candidate as a fiber source for animals.”

The cellulose mentioned just above is actually wood pulp (sawdust), primarily from pine trees. Since sawdust just doesn’t cut it with pet parents looking for more natural ingredients in their dog’s or cat’s diet, pet food companies are motivated to find alternative filler fibers to replace it.

Like miscanthus grass, powdered cellulose has a tremendous amount of insoluble fiber, too much of which can interfere with your pet's ability to digest and assimilate the nutrients his body actually needs, like protein and minerals. High levels of cellulose can also rob cells in the colon of critical fuel, like butyrate, due to reduced fermentation. Excessive powdered cellulose in your pet's food will also cause him to produce a bigger volume of poop.

Healthy Pets Need Healthy Guts

The ultra-processed pet food industry is very invested in whatever it takes to create good poo. The industry knows the main way pet parents judge whether they will purchase a second bag of food or not is what their animal’s poop looks and smells like.

And while I agree bowel health is of critical importance, I want animals to truly have a healthy and resilient gastrointestinal (GI) tract, not an artificially created one. I don’t agree with masking a dysbiotic digestive tract with a plethora of food additives that result in firm poop but do nothing to nourish or maintain the rest of the body.

Looking at the vast majority of ultra-processed pet food labels and the overall health status of the animals eating kibble, I would not say we’re having an epidemic of thriving, long-lived pets that age free of disease and degeneration.

I would say we have millions of pets and people with dozens of symptoms, including “sensitive stomachs” and gut disorders, recurrent ear and skin issues, allergies, cancer, cognitive and auto-immune disease that require a whole lot more real nutrition from real foods to spark an adequate and appropriate immune response. In the U.S., 50% of the calories people consume are from ultra-processed food and nearly 100% for pets.3

There simply aren’t enough nutrients, polyphenols, antioxidants, amino acids and essential fats in cereal or kibble to sustain health. Highly processed foods contain an abundance of empty, great-tasting calories, laced with phthalates, endocrine disrupters, glyphosate, heavy metals and mycotoxins that further burden our struggling bodies. If humans and their pets only ate highly processed foods on occasion, we wouldn’t have the issues we have today.

Part of our current health crisis for both people and pets is the dramatic increase in consumption of fast food (ultra-processed foods and snacks) and the reduction of unprocessed, fresh food which fuels our bodies optimally. At least humans have the choice to eat some real, healthy food when the urge strikes. Most pets never get the opportunity to choose the foods they crave or need to help nourish their bodies the way nature intended.

You can thank or curse the bulk of your pet’s immune system for being in her gut. Many pets (and people) can regain their health by reducing consumption of “fast food” and increasing consumption of fresh foods. When I interviewed Finnish veterinarian and researcher Dr. Anna Hielm-Bjorkman, I was encouraged to learn that as little as a 20% swap of kibble for fresh food (including dark green leafy vegetables) led to improved metabolomic markers in dogs.

The good news is you can intentionally focus on creating gut health by addressing leaky gut and removing contaminants and metabolic stressors from your pet’s food or, by default, allow the ultra-processed pet food industry to make these nutrition choices for you.

Over the last 40 years pet food companies have convinced most pet lovers their brand is the healthiest food (aka healthiest breakfast cereal) on the market. Just remember, you’re fueling your pet’s entire health response on the equivalent of cereal; cool for a meal, bad for a lifetime of nutrition.

Good and Bad Fiber in Pet Food

The quality of fiber and amount of fiber is pet food is what determines how beneficial or detrimental it is to your pet’s body. Unfortunately, the pet food industry has historically relied on contaminated, very poor-quality fiber sources left over from human food processing, including soy, rice, pecan and peanut hulls, and in amounts that can be nutritionally problematic (in addition to the risks of mycotoxins).4

“Diet” or lower calorie pet foods can be particularly risky to feed pets, long term. To reduce calories and make pets feel full, companies add excessive fiber in an attempt to “fill pets up,” but in reality nutrient-dense foods have been swapped for filler (fiber content above 6% is considered filler) and the excess fiber traps the minimal nutrients present, resulting in micronutrient deficiencies and extra-hungry pets. 

Poorer quality pet foods use extra fiber in their regular dog and cat food formulas because it’s plentiful and cheap. When it comes to grain-free kibble, there’s a double risk: the phytates and lectins (or “anti-nutrients”) naturally present in legume-based foods decrease the absorption of critical minerals, with excessive fiber making it extra difficult to nourish carnivores on a cellular level.

Over time, the excessive “anti-nutrient” starch and fiber not only have the potential to create metabolic disease, but organ degeneration as well. 

Although the amount of fiber in the diet of wild dogs and cats is small (less than 5% in most cases), it serves a critical role. In fact, research shows “prey model” raw food diets devoid of additional sources of fiber actually deplete the microbiome, which is one reason most fresh-feeding veterinarians have marked hesitations about the long-term feeding of “80/10/10” or “prey model” diets; we see animals do poorly on them long-term.

The key to a healthy microbiome and in turn, a healthy immune system for any species, is an optimal amount of nutrients coming from minimally processed, whole food sources. I’m very pro-plant fiber for pets, as it builds the microbiome and provides roughage for bowel health. But fiber should be provided in appropriate amounts, and not added to highly processed diets as a means of keeping stools artificially firm or tricking animals into thinking they are satiated.

That said, out of all the AAFCO-approved fiber sources the pet industry has to choose from, miscanthus grass is among the healthiest; it’s grass, which dogs and cats naturally consume.

The problem I see is that none of the current suppliers produce a human grade version (unlike cellulose), so it can’t be used by quality pet food manufacturers insisting on human grade raw materials. There also is not a spray-free version on the market, so we can assume there are probably pesticide residues that will be passed up the food chain.

The takeaway here is that a small amount of fiber is very important, but a diet loaded with fiber is very detrimental (unless you are feeding a cow or horse). If you're feeding your dog or cat a nutritionally optimal, species-specific diet, which includes low-glycemic vegetables, along with appropriate supplementation, including pet probiotics and digestive enzymes, she’s probably producing small, firm stools, which means she's getting the amount of fiber she needs.

If Your Dog or Cat Needs Additional Dietary Fiber

Wild dogs and cats consume about 4% fiber, or roughage, coming from whole food sources (including foraging on grasses and consuming predigested stomach contents of prey animals, along with feathers and fur). I’ve found that several brands of commercially available raw food diets are constipating for some pets, most likely due a lack of fiber (veggies) in the food.

Generally speaking, nutritionally balanced raw diets should contain low glycemic, fibrous veggies to meet pets’ fiber needs naturally. Vegetables also provide critical nutrients, polyphenols, antioxidants and phytonutrients not found in meat, bones and organs.

Raw food diets without appropriate vegetables are more likely to cause constipation in your dog or cat. Raw pet foods that contain excessive bone or bone meal is another reason pets can become constipated. I recommend only feeding diets that have been formulated to meet minimum nutrient requirements, including fiber, and are not excessive in calcium and phosphorus.

Because of the popularity of raw food diets, there’s a rash of poor quality, poorly formulated (or completely unformulated) raw food manufacturers now selling risky raw food formulas. Ask your manufacturer to send you their nutritional analysis so you know what you’re buying falls into safe nutritional parameters. If you make fresh food at home, follow a recipe that has a nutritional analysis, so you aren’t guessing at trying to create health.

Just like some humans, some pets need a little more fiber than others to maintain healthy gut function. If this is the case with your dog or cat, I recommend adding extra ground leafy veggies to their meals — about a teaspoon for every 10 pounds of body weight, given once or twice a day.

If that isn’t effective, try adding organic psyllium husk powder at one-half teaspoon for every 10 pounds of body weight, or go with coconut or organic acacia fiber at one teaspoon for every 10 pounds of body weight, once or twice a day.

If your pet is consistently producing narrow, loose stools, he may benefit from the addition of a soluble fiber called slippery elm bark to his food. When slippery elm combines with digestive juices, it produces a gel-like material called mucilage, which coats and soothes the GI tract and helps to firm the stool. About one-half teaspoon for every 10 pounds of body weight per meal should do the trick.

Another very beneficial add-in to pet meals is canned or freshly steamed 100% pumpkin at about one teaspoon for every 10 pounds of body weight, one to two times a day. Pumpkin is low in calories, rich in potassium, can resolve both constipation and loose stools, and also helps with regularity. You can learn more about all the different types of fiber for pets here.



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