Grains as “fillers”

Most pet parents have heard that pet foods contain “fillers,” but few actually understand what these ingredients are, or why they are referred to in this way. Some pet owners may wonder why pet foods contain “fillers,” or wonder if they are even healthy for our pets. The term “fillers” implies a negative meaning, and many people believe ingredients that fall under its wide definition are low-quality, or even that they are a common cause of allergies. Pet food companies have certainly added to the confusion by marketing to consumers’ fear of fillers; they have created products that are grain-free or are free from corn, wheat, and soy. Pet parents are worrying they need to avoid these common ingredients, but this is unnecessary, as grains can provide pets with great sources of nutrition.

What are “fillers”?

“Filler” is a term used to describe certain ingredients in a diet. Typically, people use it to refer to sources of fiber and carbohydrates, like grains such as corn, wheat, soy, or rice. Some people even refer to by-products as fillers (see By-products and meat meal for more information). The term “filler” is often used to demonize certain ingredients, namely grains, because whomever is using the term believes these ingredients are poor sources of nutrition, or that they are just used to “bulk up” a diet to make it cheaper, without adding substance.

The term “filler” is not defined by AAFCO and therefore has no official or legal definition. People who employ this term can use it any way they want, with any connotation they choose. Generally, it is used as a derogatory term to scare consumers into believing grains or other ingredients are bad for their pets.

Grains are not “fillers.” They are not used to “bulk up” diets, and they can provide rounded nutrition to dog and cat diets.

Can dogs and cats actually digest grains?

Yes, dogs and cats can digest grains. It is a myth that they cannot digest grains or utilize the nutrients found in these ingredients.

A common argument to this fact is the apparent indigestibility of corn or other grains when fed whole. For example, a dog eats corn off the cob and the kernels come out the other end a day later, looking the same as when they were eaten. It is quite true that corn, especially if it is uncooked, is difficult to digest in its whole form. Moreover, dogs and cats do not chew very well, so the kernels are not being mechanically broken down before they enter the digestive tract. However, pet foods containing corn are not the same as a dog or cat walking into a cornfield and eating an ear of corn off the stalk. During cooking and processing, the physical structure of the corn plant changes, allowing pets (and humans!) to digest the ingredients more easily and absorb its nutrients more readily. The same can be said about other grains as well.

Remember the difference between ingredients and nutrients. When these ingredients are ground up, mixed into the diet, and cooked, they provide nutrients that are quite digestible.

Are grains good for pets?

Despite popular belief, grains can be an excellent source of nutrition for our canine and feline companions. Remember the difference between ingredients and nutrients: Nutrients are essential components of the diet such as protein, fat, water, and fiber. Ingredients are merely the sources of these nutrients. The name of an ingredient itself tells you nothing about the quality of nutrition it provides; this information can be found in a nutrition textbook, in scientific research papers, or from the pet food manufacturer if they do their own research.

Ingredients like corn, wheat, soy, and rice provide nutrients such as protein, fat, carbohydrates, fiber, vitamins, and minerals to the diet. Protein is the most desirable nutrient found in these ingredients, and it is used to complement the proteins provided by meat sources. There are a few scientific terms that are used to assess the quality of the protein found in each of these ingredients.

[Table adapted from Nutrition and Disease Management for Veterinary Technicians and Nurses, second edition.]

As you can see in the table above, corn, wheat, soy, and rice have chemical scores and biologic values that are very similar to meat. They do contain less protein than meat, which simply means they are contributing other nutrients to the diet in greater proportions, such as fiber. This is necessary for rounding out the diet and providing additional nutrition to complement the other protein and fat sources.

Why are grains in pet food?

In pet foods, different ingredients are combined to give a range of nutrition, since dogs and cats require over 40 nutrients in their diets in different proportions. Grains are added to the food to give a more diverse variety of nutrients and balance out the ratios of protein, fat, and carbohydrate in the diet. Some grains are less expensive sources of protein than meat products, for example, and when the diet is formulated properly, they can contribute similar or complementary nutrition. It is very difficult and expensive to create a diet that is made without grains. Often, diets containing common grains like corn, wheat, soy, and rice are less expensive than grain-free diets that have potatoes, lentils, or peas as a source of fiber and carbohydrate.

Carbohydrate sources are also necessary as a binding agent when making kibbles, because they are needed to give the kibble its shape. They are also found in canned or wet food diets in the form of pectins and gums, which are also binding agents.

Do grains cause food allergies?

Grains have been a scapegoat for food allergies for quite some time, but it is unclear as to why. Allergies to specific grains are extremely rare, and even these pets are not allergic to every grain.

Food allergies in dogs and cats are very uncommon; only a tiny percentage of the general pet population has a legitimate diagnosed food allergy. Most pets with allergies actually have environmental allergies. Furthermore, most food allergies are to sources of protein, because proteins are large molecules that can cause an immune response. The reason ingredients like beef, chicken, and dairy are usually implicated in food allergy cases are because they are found in many diets on the market, so these are just the most common allergies seen by veterinarians. These ingredients are not bad or toxic, and they are not allergenic to most pets, so there is no reason to avoid them unless your pet has been diagnosed with a food allergy by a veterinarian. Technically, grain proteins can be allergenic, but an animal’s immune system is far less likely to recognize these proteins than it is to recognize meat proteins; therefore, grain allergies are very rare. 

If you think your pet might have a food allergy, contact their usual veterinarian, and they can help you do a food elimination trial to determine what your pet is allergic to. Hair tests, skin biopsies, and blood tests are ineffective and not recommended to diagnose food allergies.

To learn more about food allergies in pets, click here.

Should I feed a grain-free diet to my pet?

Avoiding pet foods that contain grains is absolutely unnecessary, and is generally not recommended by veterinarians unless there is a specific medical reason for doing so. Grains provide many nutrients while helping balance out diets and complementing nutrition from other ingredients. They can also help the diet be more affordable, as stated above.

Grain-free diets are not free of “fillers” or carbohydrates; they simply contain other ingredients that are not traditionally thought of as “fillers,” but which are used for the same purpose as traditional grains (binding agents, sources of fiber and carbohydrate, etc.). These may include potatoes, sweet potatoes, lentils, peas, fruits, chick peas, quinoa, tapioca, beans, and other ingredients. The difference between these ingredients and traditional grains is that they are more sugar-dense and contain less protein and fiber; thus, they are actually poorer sources of nutrition. They also tend to be much more expensive than traditional grains, which is why grain-free diets are more expensive, not because the quality is higher!

Keep in mind that grain-free does not mean carbohydrate-free. Even if it did, feeding your pet a “carb-free” of “keto” diet is not necessary or advisable, unless there is a medical reason behind it. Carbohydrates are one of the three macronutrients (next to protein and fat), and they help balance diets out. Carbohydrates also include fiber, which can help your pet feel fuller and regulate their stool. Feeding a low-carb or no-carb diet would be very wasteful, expensive, and include higher amounts of protein and fat than the pet requires.

Grain-free diets, and the claims pet food companies make about them, are not based in science. There is no scientific evidence that they are more healthy or beneficial for your pet. The reason grain-free diets were originally created was to appeal to you, the consumer, and to earn pet food companies more money. They can charge more for grain-free formulations because their ingredients are more expensive, and because pet owners are willing to pay more for a product that they believe to be of higher quality. But, beware: it is purely a marketing ploy, and a good one, since almost 50% of the pet food market is labeled as grain free!

Grain-free diets, along with other formulations, have also been linked to a heart disease called dilated cardiomyopathy in dogs and possibly cats. The only way to reverse the heart disease caused by these diets is to switch the pet off grain-free food. The exact mechanism by which the diet causes this disease is still unknown, but it is highly recommended by veterinarians and board-certified veterinary specialists (nutritionists and cardiologists) to avoid grain-free diets at this time, until more is known about the link between diet and this disease.

Are “ancient grains” better than traditional grains?

The term “ancient grains” has no legal definition outlined by AAFCO, nor does it have a true definition by the Whole Grains Council, a human food organization. Ancient grains are usually described as grains which have not been changed by genetic modification or selective breeding over several hundred years. This describes grains like black barley, red and black rice, blue corn, sorghum, millet, quinoa, buckwheat, and wild rice.

Ancient grains are marketed to be more nutritious than traditional or refined grains, but this is usually not the case. While some of these grains may have a more balanced nutrient profile than others, this is not true for all of them. Pet food companies who advertise that ancient grains are healthier than traditional grains are perpetuating pseudoscience. Pet food manufacturers who use ancient grains also pay more for their ingredients, because these grains are expensive and hold more of the human food market share; therefore, diets made with ancient grains often cost more than diets made with traditional grains. Again, like with grain-free diets, the consumer is paying more due to the expensive ingredients and marketing.

What about diets that are advertised with “no corn, wheat, or soy”?

These types of diets are similar to grain-free diets; again, different ingredients will be used to take the place of traditional grains. Once again, this is purely a marketing ploy designed to charge pet owners more for a nutritionally similar product. Remember, there is a difference between nutrients and ingredients. Different ingredients can provide similar nutrients, but certain ingredients are not superior to others.

Manufacturers who market products with a “No” label are playing on consumers’ fears and preconceived notions about certain ingredients. This is called fear-based marketing, and it is very prevalent in the pet food industry. Pet owners should avoid pet food companies who make baseless claims about ingredients like grains, because their claims are not backed by science. Choosing a reliable pet food manufacturer will help you avoid fear-based marketing (see How to pick a pet food, part 1 for more details).