Dog Food, Fillers & Science: Here’s What You Need to Know

What is a Filler, Anyways?

The term “filler” in dog food refers to low- or non-nutrient ingredients that are used in pet food primarily to add bulk and reduce production costs. These ingredients are a cheaper way to make food look larger or meet nutritional content requirements for food testing, and are used in place of higher quality, more nutritious components.

It’s important to know that the term fillers isn’t defined by any regulatory body or nutritional text, which means that it’s a bit of the Wild West in terms of what gets classified as a filler, or how the term is used in product marketing. The Association of American Feed Control Officials (AAFCO), a private, nonprofit organization that sets guidelines for pet foods, doesn’t define the term “fillers,” as they say all ingredients should serve a purpose in a balanced formula.

Common Fillers & Why to Avoid Them

Commonly used fillers include corn, wheat, soy and other plant-based materials. These ingredients are often used in place of meat-based ingredients to increase the volume of food. In comparison, these plant-based fillers may not offer as much protein or essential nutrients as meat and meat products do. In some cases, excessive fillers may lead to digestive issues or allergies in dogs, especially if they have sensitivities to these ingredients.

Here’s a list of the most common fillers, and why pet parents might want to avoid them:

• Corn: Frequently used as a cheap filler in dog food. While not inherently harmful, it provides limited nutritional value for dogs and can be difficult to digest for some.
• Wheat: Like corn, wheat is used as a filler to add bulk in many dog foods. Some dogs may have allergies or sensitivities to wheat, which can lead to digestive issues.
• Soy: Soy is another common filler that may not provide significant nutritional benefits and can cause allergies in some dogs.
• Rice Bran: While rice is generally safe and digestible for dogs, rice bran is different. It’s a byproduct that can be used as a filler, and it has less nutritional value than whole rice.
• Beet Pulp: This is often used as a source of fiber in dog food, but excessive amounts can lead to digestive upset.
• Meat & Bone Meal: While not necessarily a filler, some dog foods use meat and bone meal as a primary protein source. It’s important to choose foods that specify the type of meat meal, like chicken meal, and ensure it comes from a high quality source.
• Byproducts: Some byproducts can be nutritious, but others may consist of less desirable parts of animals, like feathers, feet or intestines, with questionable nutritional value. Look for specific, named byproducts, like chicken byproduct meal, and avoid foods with vague descriptions.
• Artificial Fillers: Some dog foods may contain artificial fillers like cellulose, which are used to add bulk to the food and have no nutritional value.

This list is not the final authority on the topic, because fillers are more nuanced than that. But it is a good starting place to help educate you so that you can make the best decision for your dog.

Are All Fillers Harmful?

You may already know the answer by now, but let’s be clear: No, not all fillers are harmful. However, they can dilute the nutritional quality of the food and may not provide the essential nutrients that dogs need for overall health and longevity. Fillers can also cause potential digestive issues and trigger allergies.

It pays to know what fillers are, what they’re used for and what sensitivities or allergies your pup has so that you make informed decisions accordingly. A good rule of thumb is to consider whether a filler is being used to crowd out other, more healthful, ingredients. This can be achieved by a thorough look at the ingredient label. Ingredients that appear higher on the list are present in higher proportions, so look for whole food sources higher at the top of the list, and fillers (if any), lower on the list.

Additives & Preservatives to Avoid

Additives in dog food refer to substances that are added to the food to serve specific functions. They can include various ingredients used to enhance nutritional content, flavor, texture, appearance or shelf life, and are either natural or synthetic. 

Here are some additives to look out for:

• Preservatives: BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene) and ethoxyquin are artificial preservatives that some people prefer to avoid due to potential health concerns. Natural preservatives like vitamin E (tocopherols) are a better choice.
• Propylene Glycol: A chemical linked to antifreeze; touted as safe but offers no benefit.
• Melamine: A plastic derivative used to artificially inflate protein content, which can lead to kidney failure in some dogs.
• Sugar & Corn Syrup: Provides empty calories and can lead to obesity and dental problems.
• Carrageenan: A thickener linked to digestive inflammation and cancer.
• Artificial Flavors & Colors: Added to enhance the taste or appearance of food, but provide no nutritional benefit. Artificial colors are linked to allergies and sensitivities in some dogs.

What to Look for Instead

Sourcing the best nutrition for your dog involves carefully reading the ingredient list. Look for foods with high quality, whole protein sources high on the list, like chicken, turkey and salmon. Avoid foods with excessive fillers, artificial additives and other low-quality ingredients. Be sure to consult with your vet to incorporate any dietary needs specific to your pup.

Many fresh dog food brands have hit the market recently with a mission to create vet-developed, human-grade food for dogs that meets or exceeds AAFCO nutrition standards.  One particular company stands out in the crowd—The Farmer’s Dog—and next, we’ll cover what they’re doing differently.

What Recent Research Says About Fillers & Fresh Food

The Farmer’s Dog is leading the pack on research around fresh dog food and its impacts on dogs’ health and longevity. Until recently, there’s been a limited body of research to back up the idea that fresh, human-grade dog food is as beneficial for our pups as brands claim. But The Farmer’s Dog is changing that, pouring an additional $10 million into research this year, including new studies pitting fresh dog food against its kibble counterparts—and the research that’s unfolding is noteworthy.

Dr. Jim Berry, president of the World Small Animal Veterinary Association (WSAVA), underscores the importance of brands conducting research on their own products. “I think every company should be doing research on their own food. If it doesn’t have good peer-reviewed science behind it, then it’s an anecdote,” Dr. Berry said.

Here are some takeaways from key studies involving fresh, filler-free dog food:

• Research published in the AVMA Journals in 2002 showed that a 25 percent reduction in commercial pet food intake increased dogs’ median lifespan and delayed the onset of chronic disease.
• A study published in 2005 in the AVMA Journals showed that vegetables can provide your pup with an array of key vitamins, minerals and nutrients, including antioxidants that help promote a healthy immune system. The Farmer’s Dog’s recipes, in addition to being filler-free, include vegetables like Brussels sprouts, broccoli, carrots and green beans.
• According to research published in 2018 in the Journal of Veterinary Internal Medicine, keeping your dog at an ideal weight has been shown to increase their lifespan by an average of two and a half years. This is why it makes sense to avoid fillers that can lead to weight gain, and is easily achieved by feeding a fresh, filler-free diet like The Farmer’s Dog that comes pre-portioned for your pup’s weight, lifestyle and nutritional needs.
• Peer-reviewed research published in 2021 in the Journal of Animal Science showed that feeding fresh, lightly cooked food from The Farmer’s Dog led to greater nutrient digestibility compared to extruded kibble diets. Better digestion means your pup absorbs more of the nutrition the food contains, which leads to less gas and bloating, and healthier poops—a win for your pup (and, let’s be honest, for you too).
• A 2025 study published in the journal Metabolites revealed that feeding dogs food from The Farmer’s Dog can meaningfully support healthier aging, reinforcing that minimally processed, filler-free foods have the potential to enhance metabolic function and overall health.

So, is The Farmer’s Dog Safe?

The Farmer’s Dog has published multiple long-term feeding studies that show their recipes are complete and balanced, meeting or exceeding AAFCO standards, and moreover, bioavailable, meaning that your pup can actually take in all the nutrients that the food contains.

So if you’ve had this question yourself, about The Farmer’s Dog specifically, or fresh dog food in general, we hope this article helps you feel informed on the topic. 

Bridging the gap between science and marketing is difficult and requires pet owners to be proactive. However, helping pet owners understand the difference, including what new research has shown, can lead to more educated choices and being an informed advocate for your pet’s health and well-being.