Written By: Tiffany Ruiz Dasilva, VMD, cVMA | Professional Services Veterinarian, Wild Earth

Walking through the aisles at a pet store or shopping online for dog food can seem overwhelming with choices ranging from conventional meat-based kibble, to raw meat, to plant-based. Each comes with benefits and drawbacks, but all will claim to be the best. The sad reality is, of the many factors that play a role in what food a person decides to feed their dog, most of them do not take proper nutrition into account. Regardless of what they are feeding, they likely feel strongly about the benefits of their decision. Feeding our pets is a way that we are able to strengthen the human-animal bond, and even better, providing our pets with food is an easy way for us to directly influence their health. In this article, I will discuss the benefits and drawbacks of many of these feeding choices, illustrating why plant-based diets were found to be the “healthiest and least hazardous dietary choices for dogs” (Knight, 2022).

Traditionally, the most common diet choice has been meat-based kibble, and many people still believe that this is the “best” option. Ultimately, the reason meat is often a large part of a dog’s diet primarily rests on the misconception that dogs are carnivores like wolves, and therefore need animal-based ingredients to thrive. The same rationale applies to those that feed their dogs raw meat-based diets. What people have failed to realize is that just because dogs have evolved from wolves, doesn’t mean they are wolves.

In fact, dogs diverged from wolves over 15,000 years ago (that’s a long time ago!), and evolved alongside humans, eating their scraps which included grains, fruits, and vegetables. During domestication, dogs gained many copies of the gene responsible for starch digestion, just as humans did during the agricultural revolution. This makes dogs more accurately classified as omnivores rather than carnivores. This means that dogs can obtain nutrients from both plant and animal matter, and therefore they can thrive on a plant-based or meat-based diet. Compared to true carnivores, dogs have lower protein and amino acid requirements and can more easily utilize vitamins A and D from plant sources, for example.

This is just one of the many myths surrounding dog nutrition, and while it is easy to access information, what is often overlooked is that it is just as easy to access misinformation. As such, it remains important to think critically when evaluating a pet food or feeding style. Let’s dive in and compare plant-based diets to traditional meat-based diets and raw meat-based diets. Please keep in mind I am discussing only commercially-available diets. I will not be discussing homemade diets as these are often nutritionally incomplete and unbalanced, and may pose additional health risks.

Raw Meat-Based Diets: Potential Benefits

Let’s begin with raw meat-based diets (RMBDs). Types of commercially available RMBDs include (Stogdale, 2019):

1. Commercial raw frozen, freeze-dried, or dehydrated meat diets that are not complete and balanced. These require the addition of a com- bination of bones, a vitamin and mineral mix, vegetables, and fruit.
2. Commercial raw frozen complete and balanced diets with a variety of protein sources. Some are limited to one protein source, especially those using exotic meats. Freezing kills a variable percentage of bacteria.
3. Commercial freeze-dried complete and balanced diets that have been frozen under vacuum to remove nearly all moisture. Freeze-drying leaves the food nearly unchanged compared with raw frozen diets, and kills a percentage of bacteria.
4. Commercial dehydrated complete and balanced diets that have been heated slowly to remove nearly all the moisture. Whether the low heat has a significant effect on the nutritional quality of the food is un- known. The drying results in a reduction of microbial numbers but Salmonella and other pathogenic bacteria can survive.
5. Commercial high pressure pasteurized (HPP) complete and balanced diets that have been subjected to high pressure without heating. This process kills most bacteria including Salmonella and Listeria without altering nutritional quality.

When compared to meat-based kibble diets, a 2021 study based on data from a questionnaire found that dogs fed a RMBD in their postnatal period (1–6 months of age) had a lower risk of developing inflammatory bowel disease later in life, whereas those fed kibble had a higher risk (Hemida et al., 2021). The authors attributed this to a change in the microbiome of RMBD- fed dogs, however these same possible alterations in the microbiome led to adverse effects in another study. In the study, 33 dogs were fed either a “sensitive skin” meat-based kibble diet or a commercial raw food diet (Anturaniemi et al., 2020). While those fed a RMBD had several positive changes on blood work such as a lower serum cholesterol, alkaline phosphatase and glucose, they also experienced a significant decrease in folate, B12 and iron. Based on the current evidence to date, research on RMBDs does not show a clear ben- efit on the gut microbiome, and may increase the risk of pathogen exposure (Wernimont et al., 2020).

Anecdotes surrounding RMBDs include that they have anti-inflammatory and/or anti-oxidative effects as they theoretically contain higher levels of antioxidants and lower levels of heterocyclic amines (HAs). HAs are produced when muscle meat is cooked at a higher temperature such as during the production of meat-based kibble diets. Furthermore, those who choose RMBDs often claim that these diets are nutritionally superior and provide many benefits such as a shiner coat and improvement in energy and immunity. Unfortunately, many of these health benefit claims have not been scientifically evaluated and therefore remain unproven. Moreover, there exist many risks associated with feeding RMBDs.

Raw Meat-Based Diets: Potential Drawbacks

First, upon evaluation, many commercial RMBDs have had nutritional imbalances such as incorrect calcium to phosphorus ratio (Stogdale, 2019). This is especially true for those produced by small companies avoiding synthetic nutrient supplements. Many RMBDs are also high in fat—while potentially leading to coat improvements, higher fat diets can also cause gastrointestinal issues and increase the risk for obesity as they are easy to overfeed due to in- creased palatability. Third, RMBDs that require the addition of bones, pose a risk for intestinal obstruction and/or perforation. Many RMBDs are also often grain-free, and investigations between the potential link of grain-free diets to canine dilated cardiomyopathy are ongoing.

Next, due to the nature of raw diets, they are inherently prone to bacterial contamination. In fact, reports of raw meat pet food containing zoonotic foodborne bacteria, including Salmonella, Escherichia coli, and Listeria monocytogenes, are increasing (Jones, 2019). While many dogs may tolerate pathogens, others succumb to illness, and some have even died due to infec- tion with pathogens in their raw food diets. Prevalence rates for contamina- tion with Salmonella in commercial RMBDs ranges from 20% to 48% (Freeman, 2013). As for other pathogenic bacteria, according to a report published by Public Health England in 2017, of four individuals (one of which died) infected with multidrug-resistant (MDR) E.coli O157, three were feeding a raw commercial frozen diet to their dog (Byrne et al., 2018). All were positive for shiga toxigenic E.coli, and in one case the bacteria was cultured out of the freezer. This clearly demonstrates that although freezing and freeze-drying may reduce the number of bacteria, it does not destroy all pathogens. These pathogens will continue to be shed in the feces even if the dog consuming the RMBD does not show signs of illness. This poses a risk for humans who come into contact with the dog, especially people who are young, old, pregnant or immunosuppressed. Another human health risk associated with feeding RMBDs is exposure to resistant bacteria which can provide a source of antibi- otic resistance in humans. Several studies published in the United Kingdom and the Netherlands have provided clear and compelling evidence that dogs fed RMBDs are shedding significantly more antibiotic-resistant bacteria than those fed cooked diets (Baede et al., 2017, Wedley et al., 2017, Schmidt et al., 2015).

Based on overwhelming scientific evidence, The American Veterinary Medical Association and the American Animal Hospital Association oppose the unregulated feeding of raw foods and discourage “the feeding to cats and dogs of any animal-source protein that has not first been subjected to a process to eliminate pathogens, because of the risk of illness to cats and dogs, as well as humans.”

Meat-Based Kibble: Potential Drawbacks

Moving on to meat-based kibble. Traditional meat-based kibble typically contains the parts of animals that may be unfit for human consumption, ranging from organs to those animals that are down, dead, dying, and diseased (4D). While the use of “byproducts,” the non-rendered parts of the animal other than the meat, is environmentally responsible, it adds a question mark to what is actually in the food. Essentially it is often used as a method to keep protein levels high (but not always high quality), and food production costs low. The more problematic meat ingredients are those designated as “meal,” which are the result of rendering. Rendering is defined as “an industrial process of ex- traction by melting that converts waste animal tissue into usable materials.” In other words, it is a process by which animal parts that are often unfit for hu- man consumption (including expired meats, the 4D meats, and even animals who have drowned after a flood) are chopped up and boiled into a stew which is then dehydrated. The fat and protein portions are then removed and used as animal fat or ground up into “meal,” respectively. To further compound the problem, if the general term “meat meal” is used, the animal the parts came from is not disclosed. Even if a specific animal is named on the label such as “chicken,” for example, meat is often mislabeled, meaning what is on the bag isn’t necessarily what is inside. In 2015, a Chapman University research team looked at 52 commercial pet foods, and found that 40% of those tested contained mislabeled meat products (Okuma et al., 2015).

To add to concerns surrounding meat-based dog food, meat is much more likely to become contaminated with bacteria such as Salmonella. There have been over 180 dog food recalls since 2009, and major ones from bacterial con- taminants from meat sources. In fact, 49% of all pet food recalls in the past ten years have been from pathogenic bacteria. The second leading cause of pet food recalls is pentobarbital, a euthanasia drug. In 2018, the director of FDA Center for Veterinary Medicine addressed this, stating “we have reason to believe rendered products can be a source for pentobarbital” (FDA.gov, 2018).

Meat-based pet food has not only been found to contain pentobarbital, but it has also been found to contain hormones, antibiotics, and toxic amounts of heavy metals. The Clean Label Project, a national nonprofit focused on health and transparency in labeling, tested the top pet foods and found lead in some pet foods at 16 times the concentration of lead in Flint, Michigan’s tainted drinking water. They also found arsenic in concentrations of 555 times higher than the maximum contaminant level for human drinking water set by the Environmental Protection Agency.

Furthermore, kibble is made using the same process used to make breakfast cereals, high heat extrusion. During this process, wet and dry ingredients are mixed together to form a dough. The dough is then cooked under high pressure and high temperature and pushed through a ma- chine to cut the kibbles. The kibble is then dried, cooled and spray coated. On the surface this process seems benign—after all, who doesn’t love cereal? However, the problem lies in what happens to the meat when it is subjected to high temperature. Heterocyclic amines are compounds formed when muscle meat is cooked at a high temperature, and have been associated with cancer in research animals when consumed in high concentrations (Sugimura et al., 2004). It is important to note here that while heat processing of moist or dry extruded pet foods may have a negative impact on animal tissue proteins, heat processing improves the bioavailability of some plant proteins.

Meat-Based Kibble: Potential Benefits

As for the benefits of meat-based kibble diets, these diets have the most amount of research behind them because the largest companies in the pet food industry make mostly meat-based kibble and have the money to fund studies including feeding trials to support nutritional adequacy. Furthermore, these diets offer convenience to pet parents, while also usually being lower in cost when compared to both RMBDs and plant-based kibble diets. Proponents of feeding meat-based kibble also claim reduced dental tartar and improved gum health. While this claim is supported by research, kibble size does matter (and this likely applies to plant-based kibble diets as well). A study published in 2007 concluded that increasing the kibble size by 50% resulted in a 42% decrease in the accumulation of dental tartar (Hennet et al., 2007).

How Do Plant-Based Diets Compare?

Plant-based diets are inherently free of many of the risks associated with RMBDs and meat-based kibble diets described above. They are also free of the most commonly reported food allergens for dogs, making plant-based diets a great option for dogs with food allergies, and why many food-allergic dogs have experienced symptom relief on plant-based diets. Plant-based diets also offer many other benefits, and when compared directly to conventional meat- based kibble and RMBDs, a recent study found that “the pooled evidence to date indicates that the healthiest and least hazardous dietary choices for dogs are nutritionally sound plant-based diets” (Knight, 2022). To learn more about the benefits of plant-based diets for dogs, click here.

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