Ultimate Dog

By Luna Lupus - Reading Time: 13 minutes
Can dogs be vegetarian?

Can Dogs Be Vegetarian? Biology, Nutrition, and Dietary Evolution

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A few decades ago, the question of dogs on a vegetarian diet would hardly cross anyone’s mind. Dogs are the descendants of domesticated wolves, so a meat-based diet is what they would choose for themselves. It’s been many centuries since dogs could pick their own diet, though, so the responsibility for their nutrition now lies solely with their guardians. The diet of any modern dog is shaped significantly by his owners’ personal beliefs and lifestyle practices. 

It's estimated that there are around 20 million pet owners in the USA alone who eat a plant-based diet. Many find themselves in a moral dilemma, trying to live a life where no animals die for their consumption while also sharing their home with little furry carnivores. The seeming solution to this dilemma is plant-based dog food — a completely meat-free diet that could be nutritionally whole. But is that a safe, ethical option? Or is it a biologically inappropriate risk to optimum canine nutrition?

The objective of this article is to take a closer look at canine physiology, examine the biology that dictates nutritional needs, and consider the dietary evolution of dogs that took place over the long course of history and is indeed still in progress today. 

Dietary Changes in Dog Evolution

From Wolves to Dogs — The Domestication 

The process of domestication began thousands of years ago when humanity was at the hunter-gatherer stage. Humans in that era marveled at the sight of wolves, who were incredible predators. Whether wolves made contact with humans first or was it the other way around will always be up for debate, but what we know for sure is that we eventually gained each other's trust and began to live, and hunt together.

Here lies the first uncomfortable truth: we didn't domesticate wolves because they were cute and fluffy; we domesticated them because they were hunters. They were faster than any human, with sharper teeth than any weapon of that time, and had invaluable instincts for danger and prey. They elevated humanity’s hunting skills, protected their communities, and helped us reach the next stage in our own evolution. 

Carnivores to Omnivores — The Introduction of Starch 

This next stage was the discovery of agriculture. By this time, dogs were already a species of their own with several different breeds, as humans wasted no time by carefully breeding their canines to enhance the desired characteristics in each new generation. Those characteristics were confidence around humans (no fear aggression), vocalizations (to alert for danger), and strong prey instincts (their main job).

When humanity discovered agriculture, the hunting model we lived on before changed drastically. We began organizing into first civilizations and experiencing more food security when the harvest was good. Although we still hunted for meat, the bulk of our diet became grains and other plants that we could grow by ourselves. We realized that grains are a fantastic source of energy and satiety. This big turning point in our evolution was incredibly significant for our dogs, too. For the first time in history, we began to feed them starch and made it a regular part of their diet. This dietary shift changed their biology forever. 

In order to survive on this new diet, dogs needed to evolve into having more genes for processing starch than their wolf ancestors. Circumstances force the species to evolve or die out — for dogs, the introduction of starch was that circumstance. It was simply what humans were able to feed them. They still ate meat and even dairy … but bread and various porridge became new staples in their daily meals. They adapted to omnivores. For a very long time after that, the canine diet remained unchanged. Dogs continued to eat a combination of fresh meat, animal products, and grains … until the Industrial Revolution led the way for our lives to become more and more urban. 

The Birth of Commercial Dog Food 

With urbanization came the demand for convenience. Kibble was invented during the Second World War and popularized in the 1950s. This stage of canine dietary evolution is still very new. We stopped feeding dogs fresh ingredients and switched to a completely different dietary model, one that was better suited to our urban lifestyle.

The idea of feeding dogs a nutritionally complete meal that only needed to be tossed into their bowl once or twice a day with zero preparation and an almost unlimited storage time was groundbreaking. It made life easier, and it kept dogs fed. Once again, this mimicked our own dietary evolution, as canned, pre-made, and processed foods took the world by storm. 

Next, Meat-Free Evolution?

Where do plant-based diets fit within the frame of canine evolution? Reflecting on the historic journey dogs have walked alongside us, one thing is very obvious: the changes in the human diet have been shaping the changes in the canine diet for thousands of years. Each time we changed the canine diet, though, we did it because it met a human need. Those changes were initially required for our mutual survival, but it’s interesting to see how they have stuck even after survival wasn’t in question anymore. 

Shifting the canine diet to a meat-free model because of personal beliefs is not unexpected, nor does it diverge from anything else we’ve done before. We have always adapted their diets to our needs and preferred lifestyles. What would actually be completely new is if we adapted our lifestyle and beliefs to their biology. After thousands of years of asking them to live by our rules, do we not owe them this much?

Canine Biology — The Order of Carnivores 

Despite their historic dietary evolution, dogs are still classified in the order of carnivores. They have successfully adapted to an omnivore diet, yes, but they have retained the physiology of a carnivore. That's an important distinction! Dogs can live and survive as omnivores … but they are carnivores. 

We don’t need a degree in biology to know what type of food nature intended for dogs to eat — one look at their teeth gives away the answer. Dogs have teeth designed to cut, tear, gnaw, and grind raw meat. They have the teeth of a predator that needs to work its way through the skin, bones, and inner organs of their prey. The sole purpose of those sharp and pointy canine teeth is to grind the meat down to smaller, swallowable chunks so they can travel to the stomach as soon as possible.

This is another key part of their carnivorous biology — their digestion begins in the stomach, NOT in the mouth, as it does with humans. The canine saliva doesn’t contain any enzymes for breaking down starch! In herbivores and omnivores, digestion begins in the mouth, where the enzymes help break down the starches while the animal is chewing. This does not happen in dogs. Carnivores have no use for those enzymes because they nutritionally don't need carbohydrates. Once the meat reaches the stomach, that's when the carnivore's digestion begins.

The canine stomach is spacious and acidic, accommodating for the fact that, in nature, they don’t eat frequent meals on the clock. They tend to eat a big meal when they get the chance and then experience a period of fasting afterward. The acid in the stomach helps with the quick breakdown of meat, and their short, simple digestive tract enables them to constantly live on the move. This physiology shows us that dogs could live on a diet solely composed of meat (prey). They need quality protein and fat in order to survive. Carbs, on the other hand? Purely optional. 

The Genes Behind Digesting Starch

Omnivorous traits in dogs are related to their unique ability to digest starches despite having a carnivorous biology. Evolution has granted them several genes that play an important role in processing starch, most notably AMY2B, which influences the enzyme called amylase. Amylase is crucial for the breakdown of carbohydrates, so the more copies of the AMY2B gene a dog has, the easier they will break down starches. As a testament to their omnivore diet adaptation, dogs have more copies of this gene than wolves, who generally only have two.

There is only one problem — we don’t know how many copies of this gene are in any individual dog because the number differs so greatly between breeds and individuals. One study looked at 20 different dog breeds and found they all had different numbers of the AMY2B gene, which means that some of them are biologically better at processing carbohydrates than others. Samoyeds, for example, had around 7 copies on average, while English Springer Spaniels had 17! 

Without genetic testing, we can’t really know how well individual dogs metabolize starch. But we do know they have no problems metabolizing meat. This is why it’s so important to keep in mind your dog’s biology. Vegetarian diets are high in carbohydrates because most plant-based sources of protein also contain starch.

This kind of protein is nutritionally incomplete and contains the wrong ratio of essential amino acids necessary for the health of dogs. Their body then needs to work overtime to make up for the non-optimal nutrition source, resulting in a longer digestive process, lower energy levels, weight gain, loss of muscle mass, and weaker bones. Animal sources of fat and protein, on the other hand, don’t contain starch and are biologically appropriate for dogs. 

Nutritional Adequacy of Vegetarian Dog Food

The controversies around vegetarian diets for dogs have drawn the attention of many researchers who examined the nutritional profiles of plant-based dog foods in several studies over the past 20 years. The vegan pet food market, growing rapidly, is currently valued between 9-13 billion dollars. One study showed that 78% of questioned vegans would switch their pets to a meat-free diet if there was a safe option available. Among those who already feed their pets a vegan diet, 91% said they depend on a commercially available option. How adequate are those options?

The general consensus is that plant-based kibble can be nutritionally complete if all important parameters are met. Kibble, by design, favors nutrients over ingredients. Most commercial dog foods are nutritionally completed with added synthetic nutrients, not with specific ingredients that naturally provide those nutrients. Vegan dog food is no different in this respect and can rival meat-based kibble on the market.

Many of the studied plant-based dog foods were considered nutritionally adequate, meeting the minimum nutrient requirements. That said, they were still often nutritionally imbalanced. This is a common issue in commercial dog food (including meat-based), which is why rotational feeding is recommended to make up for the nutritional inconsistencies within the individual kibble brands. 

For example, one study looked globally at 19 meat-based and 10 plant-based dog foods. They found that both categories met equal standards, including when it came to diet formulation, where all examined brands used nutritional specialists of varying expertise. However, a different study that looked at 26 vegetarian pet foods in Canada found that only four met the AAFCO (Association of American Feed Control Officials) nutritional recommendations. The foods were mainly insufficient in taurine, omega-3 fatty acids, and vitamin D, among other nutrients. In the USA, 18 out of 24 examined plant-based pet foods met the minimum requirements in a 2015 study. 

It’s clear that the concept of vegan dog food isn’t the “perfect solution” to people’s moral dilemma after all. It’s nearly impossible to know whether the vegan kibble on the shelf of your pet store could meet your dog’s nutritional needs or not. 

To be completely fair, the same can be said of any kibble, meat-based or not. A study that took under a microscope 2208 pet foods from 204 different companies revealed that most of them contained discrepancies between the % of nutrients listed on the label and the % actually in the food! It's, therefore, unfair to have a conversation about plant-based dog food without acknowledging the larger issue in the dog food industry, which is the blind trust most of us are putting in commercial kibble.

The Risks of a Vegetarian Dog Diet

Even if you find a nutritionally sound vegan kibble on the market, you have to consider the additional risks you are taking with your pet’s long-term health and development. Some have already been mentioned in this article, such as low energy and the loss of muscle mass caused by the lack of animal protein. Weight gain is also possible because of the high carbohydrate content and a deficiency in animal fat, which biologically gives dogs the feeling of satiety.

Another concern is that a plant-based diet will make the canine urine too alkaline. As biological carnivores, dogs are supposed to have acidic urine. A drastic change in that pH can lead to the formation of crystals, a very painful experience for dogs who then find it difficult to urinate and can potentially develop dangerous urinary blockages. Male dogs are especially predisposed to this condition! It is strongly recommended that pets on a vegetarian diet have their urine pH monitored regularly.

Other risks of vegetarian diets are related to the lack of necessary nutrients that dogs can only get through animal protein, such as:

  • Omega-3 fatty acids essential for brain functions and the immune system
  • Taurine vital for the strength of the heart muscle
  • Vitamin D important for the health of bones 

In vegan kibble, these nutrients could be artificially added into the mix, but because they are inevitably sourced from plants, the dog’s ability to absorb them could be questionable. Within a biologically-appropriate diet, the only complete dietary source for all of these nutrients is meat.

Final Thoughts on Feeding Dogs Vegetarian

Dogs are domesticated carnivores that have evolved into omnivores as a consequence of their symbiotic companionship with humans. Evolution has granted them the ability to metabolize starch as a survival mechanism. Their digestive system didn't evolve to accommodate our moral needs; it evolved to accommodate for nutritional scarcity! Starch was on the menu when meat wasn’t available. Now, in an era of plenty, we are living out the irony by putting our dogs on a diet that historically meant they were living in deprivation. 

Canine biology can’t tell the difference between eating grains when the owner can’t supply meat versus when the owner is choosing to be vegan — to their biology, it’s all the same! Biological carnivores to this day, dogs are meant to eat meat. Nature doesn’t have morality, and it is unethical on our part to neglect & negate the biology of an entire species that has so loyally run beside us for thousands of years.


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Luna Lupus

Luna’s passion for learning about canine psychology and behavior began when she adopted a severely reactive puppy from a local shelter. She is now a big advocate for positive reinforcement and compassionate training. As a writer, she strives to spotlight the topics that fly under the radar and be the voice for all who cannot speak for themselves.

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