Fillers in Dog Food

When grain-free diets were found in some recent research to be linked to DCM in dogs and cats, fillers such as corn have started to get the attention they deserve. The study revealed that pets benefit from grain diets and that fillers may actually be the cause of some health problems in pets.

So, what are fillers?

Fillers are ingredients added to food to bulk it up and make it cheaper to produce. They have no nutritional value and are often made from leftover scraps or by-products of other industries. Common fillers include corn, wheat, soy, and rice.

Fillers are often used in pet food because they are cheap and easy to source. They help to keep the cost of production down, which can be important for mass-produced brands that need to make a profit. Unfortunately, fillers provide no nutritional value for your pet and can actually cause health problems.

Below is a chart showing different nutrient compositions on a dry matter basis. As shown in the table below, starch sources and specifically barley flour, corn flour, potato flour, rice flour, sorghum flour, and wheat flour had DM% of 51.9%, 43.6%, 50.4%, 44.1%, 44.2% and 49.1% respectively.

Murray S. M. et al.,(1999) Study demonstrates that none of the starch sources mentioned above qualify to ‘have no nutritional value’ as we have seen their nutritional composition in DM basis to be in the upwards of 50%.

Which ones are the true fillers?

As shown in the table above, any ingredient with a DM basis % of less than 10 can be considered fillers as they have minimal contribution to the overall nutrient composition of the food. This would include ingredients such as Brewer’s dried yeast, cellulose, carob bean gum, dextrose, dried beet pulp, and so on.

While some fillers may not be harmful in small amounts, others can cause health problems for your pet.

It is possible that some ingredients such as corn are often added in proportionately high amounts to pet food diets to increase the weight but corn, wheat, rice and other common ingredients normally shamed as fillers actually contain some great nutritional value.

A high percentage of Fillers in the diet may result in:

  • – Unhealthy weight gain from the increased calories
  • – Increased risk of gastrointestinal issues such as bloat
  • – Allergies
  • – Poor nutrient absorption
  • – Nutritional deficiencies

Types of True Fillers:


Cellulose is a plant-based fiber that is often used as a filler in pet foods. It is safe for pets and helps to add bulk to their diet. However, it has no nutritional value and can cause digestive issues if used in large amounts.

Cellulose is only poorly fermented in the colon after it has passed through. The water-retaining capabilities of these fibers result in a stool-bulking effect, which causes reduced transit time and greater feces mass.

The short-chain fatty acids produced by the fermentation of cellulose stimulate colonic motility and have a laxative effect.

Aside from its water-binding, bulking capacities, cellulose which is extensively fermented has a minimal caloric contribution and this is what makes it a true filler.

Wheat bran:

Wheat bran is another insoluble fiber made from the outer layer of wheat kernels and is high in fiber. While it is safe for pets, it has no nutritional value and can cause digestive issues if used in large amounts.

The water-binding capacity of wheat bran results in an increase in stool bulk and softer stools.

Wheat bran is not as extensively fermented as cellulose and its qualities makes it the ideal bulking agent which increased transit time in the gut “by 28 percent, while cellulose caused a 900 percent increase in transit time and a 50 percent reduction in the flow of digesta in dogs (Bueno et al., l980)”

Dried plain beet pulp :

Traditionally added to livestock diet for horses, dried plain beet pulp is now getting added to pet food diets. Beet pulp is a by-product of sugar beet processing and is made up of the residual pulp and fiber from the sugar beet.

The dried plain beet pulp contains almost no sugar and has no real nutritional value other than other bulk to the dog’s stool

Dried plain beet pulp is an excellent source of dietary fiber with a high water-binding capacity. This results in an increase in stool bulk, softer stools and increased transit time.

There have been problems linked to dried beet pulp such as stomach swelling, villi plugging, and lack of palatability. It can also lead to weight gain, and hyperactivity and feeds arthritis.

Rice hulls:

Rice hulls are the hard outer shells of rice grains and are often used as a filler in pet foods. They contain no nutritional value and can cause digestive issues if used in large amounts.

Rice hulls are not digested or absorbed and act as insoluble fiber. This results in an increase in stool bulk, softer stools and increased transit time.

Rice hulls can also cause gastrointestinal issues such as diarrhea, bloating and gas as it can be harsh on the intestines.

Soybean Hull:

Soybean hulls are the hard outer shells of soybeans and are often used as a filler in pet foods. They contain no nutritional value and can cause digestive issues if used in large amounts.

As an insoluble fiber, soybean hulls increase stool bulk, soften stools and increase transit time.

Soybean hulls can also cause gastrointestinal issues such as diarrhea, bloating and gas as it can be harsh on the intestines.

Types of False fillers

False fillers are ingredients that have some nutritional value, but also has qualities such as their ability to add bulk to pet food diets and its low cost that make it a filler.


Corn is the most common filler used in pet food. It is cheap and easy to source, but it has no nutritional value for your pet. Corn can actually be hard for your pet to digest and can cause allergies if you give it to your dog in a minimal-processed form.

Corn gluten meal, corn meal, or maize flour are actually 90+% digestible and it is important to differentiate between the two.I found a table showing the different digestibility of corn in different forms;

At its best, the digestibility of corn meal or extruded kibbles is about 92% and is higher than the digestibility of various forms including ground corn. In addition, the digestibility of most carbohydrate sources increases drastically when processed by methods such as cooking, rolling, grinding, and flaking as witnessed by Walker JA, et al,., (1994 Study) who found digestibility to be above 97%.

This other chart shows digestibility of corn;

pet nutrition chart

As a source of carbs, corn contains less sugar than rice or potato and is a rich source of the richest sources of linoleic acid. In addition, corn also contributes protein, fiber, vitamins, minerals and highly digestible carbohydrates to pet diets. 

Verlinden et al.,(2006) noted that corn is actually a very uncommon cause of gastrointestinal distress(chronic vomiting or diarrhea) and dermatological problems(e.g., pruritus, otitis, pyoderma) in cats and dogs.

Their study estimated that only 1% of all skin diseases can be attributed to food allergies with flea-allergy(as opposed to food allergens) and atopy account for the vast majority of dermatological signs.

In the research, they also noted that animal food diets are linked to more dog and cat allergies than corn diets. They specifically listed chicken, beef, and dairy as more common causes of allergies than corn.

This brings us to an interesting question: Despite the compelling data, why do so many pet owners blame corn more than some more probably offenders?

The reasoning behind some pet owners is that corn causes allergens in humans and must also cause them in cats. In addition, a lot of misinformation is available on the internet and some pet owners have likely fallen for or are influenced by various inaccurate marketing materials.

So is corn a filler?

Corn is not a true filler as true fillers do not contribute any nutritional value. As seen above, corn is a source of calories(sugar), protein, carbs, fiber, and linoleic acid. It also contributes Vitamin E, beta carotene, and lutein. These all contribute to your pet’s diet and from these observations, corn does not fit the definition of a cheap filler.

Should you avoid corn in your pet’s food? No, as corn is a healthy source of nutrients. However, you should be aware of the different types of processing methods used to make kibble as they can affect the digestibility of corn. In addition, you should avoid any pet foods that list “corn gluten meal” or “corn syrup” as these ingredients are indigestible fillers that can cause dogs and cats to develop severe allergies.


Like corn above, wheat is not a true filler in that it contains some essential ingredients that are beneficial to dog and cat health. Wheat is a source of protein, carbs, fiber, and essential vitamins and minerals.

Similar to corn, the digestibility of corn increases with any form of processing. According to this 2004 Study, “whole wheat might be expected to have a digestibility of 65–75% which contrasts with the 85–90% of processed wheat.”

When compared to barley, corn, potato, rice and sorghum, wheat appears to have some of the highest digestibility scores of up to 99.88% for wheat starch and 93.7% for wheat fat – according to Murray S. M et al.,(1999). see the chart below;


Q: Do all pet foods contain fillers?

A: No, not all pet foods contain fillers. However, most commercial pet foods do contain some form of filler.

Q: Are all fillers bad?

A: No, not all fillers are bad. Some fillers such as corn and wheat flour can provide some essential nutrients that are beneficial to your pet’s health. However, other fillers such as corn gluten meal and wheat gluten can be indigestible and can cause allergies in dogs and cats.

Q: How can I avoid fillers in my pet’s food?

A: The best way to avoid fillers is to feed your pet a diet of whole, unprocessed foods. However, this can be expensive and time-consuming. Another option is to feed your pet a commercial pet food that does not contain any fillers or uses only healthy fillers such as corn and wheat flour.

Q: What are some alternative names for fillers?

A: Some common alternative names for fillers include “grain fractions”, “by-products”, and “processed grains”.

Q: can you feed dogs pasta?

A: Pasta is made from wheat flour which is a healthy filler for dogs. However, pasta is processed food and should only be fed to your dog in moderation. Studies have shown that it causes allergies and feeds arthritis and should not feed it to your dog.