Can We Feed Our Cats & Dogs a Vegan Diet?October 6, 2018
People interested in dog and cat nutrition often point to what our companion animals would have eaten “in the wild” as an indicator of how they should eat today. While evolution does provide some dietary clues if we have a clear understanding of their domestication, it is important to realize the limited usefulness of this thinking in companion animal nutrition. Before I explain why our best friends’ survival-of-the-fittest history does not necessarily indicate their ideal diet, I will first discuss what that history is.
The dog, or Canis familiaris, has had a historical presence in nearly every human society around the world. In fact, the species’ very existence is the result of domestication by humans from wolves as early as 33,000 years ago (1, 2). Although wolves consume some vegetable and fruit matter, they primarily consume other animals (3, 4). Since early dogs were dependent on human food scraps, however, adaptation to a more human-like diet was critical to their survival as a domestic companion. In fact, genomic sequencing supports their adaptation to a starch-rich diet. Compared to carnivorous wolves, omnivorous dogs have significantly increased gene expression for pancreatic amylase, maltose to glucose conversion, and intestinal glucose uptake (5).
The cat, or Felis silvestris catus, was domesticated roughly 10,000 years ago (6). Genetic research suggests that the cat’s domestication did not depend on dietary adaptation as much as the dog’s domestication. As a result, the domestic cat’s nutrient requirements remain similar to those of its hypercarnivorous felid relatives, such as tigers and snow leopards, whose wild diets are comprised of at least 70% meat (7, 8). This is likely related to humans keeping cats to hunt animals deemed as pests as well as domestic cats being historically allowed to roam outdoors, preying on wildlife and mating with feral counterparts (9).
While understanding what food sources dogs, cats, and their ancestors relied on in the past sheds some light on their nutrient requirements, it is important to realize natural selection favors diets that allow animals to live long enough to reproduce given their current environment. It does not necessarily favor diets that help relatively sedentary, sterilized companion animals have the longest and healthiest lives possible in a world where we have access to many sources of nutrients.
For instance, an animal might evolve to prefer calorie dense foods in order to survive in the wild, but its house-bound progeny might develop obesity from consuming such foods in the same amounts. Scientific research can help fill gaps in knowledge that extrapolation from historical evidence cannot close. Since animals were and are seen as expendable by some, there have been many tightly controlled experiments in the past seventy years involving feeding nutrient deficient diets to companion animals.
Thus, we have an evolving but solid foundation of knowledge regarding the minimum nutrient requirements dogs and cats have at different stages of their lives. In the United States, the National Research Council (NRC) and the Association of American Feed Control Officials (AAFCO) set nutrient intake recommendations for dog and cats based on published research.
As a vegan veterinary student, I am often asked if our companion animals can thrive on plant-based diets. The answer is quite different for our canine friends than our feline ones. For dogs, commercial vegetarian diets have been available for decades, typically using legumes and grains to meet standards set by AAFCO and similar bodies. While there have anecdotally been many healthy dogs eating these diets, most of these diets have not been formally tested.
Those companies claiming to meet AAFCO guidelines need only test their foods on live animals if they state on their packaging they performed feeding trials. The vast majority of holistic and natural brands, meat-based or vegan, do not formally test their products. This is likely due to both the economic cost associated with the trials and the ethical dilemmas related to lab animal environments. Veterinarians commonly prescribe vegetarian diets to dogs with urate stones (most often Dalmatians) and food allergies.
The Purina HA diet, which is marketed as vegetarian, has passed AAFCO feeding trial criteria for both puppies and adult dogs. However, the vitamin D3 and possibly other supplemental nutrients are derived from non-vegan sources. Furthermore, the Purina HA diet contains trans fat. This type of fat has not been well-studied in dogs, but is known to be harmful to humans, who albeit are innately more prone to diet-induced atherosclerosis. Additional formal research was conducted on competitive sledding dogs who showed no difference in their hematological values whether eating meat-based or meat-free diets over sixteen weeks (10).
As a vegan veterinary student, I am often asked if our companion animals can thrive on plant-based diets. The answer is quite different for our canine friends than our feline ones.
Although cats are considered obligate carnivores, it seems likely that some day there will be a sound, cruelty free product that meets their nutrient requirements. Vegan sources of nutrients that were previously understood to be only animal-derived like DHA/EPA and vitamin D3 are becoming increasingly popular.
Even taurine, an essential amino acid for cats, is most commonly added to cat food from synthetic, non-animal sources. In addition, in vitro meat seems to be an ever more plausible reality. Still, a safe non-animal derived cat food product would require strict quality control and substantial evidence supporting its digestibility—both of these traits are unfortunately lacking in all current vegan feeding options for cats.
In 2004, one sample each of Evolution Vegetable Stew and Gourmet Entree and Vegecat KibbleMix were found deficient in several key nutrients (11). Without even knowing their digestibility, these products failed to contain the nutrients they claimed to on their label. A later study found that all seventeen cats eating commercial or homemade vegetarian diets had adequate blood levels of vitamin B12 and fourteen of them had adequate levels of taurine (12). Both of these nutrients are regularly supplemented in companion animal food from vegan sources.
While there is anecdotal evidence of a few veterinarians maintaining some cats on commercial vegan diets, there is also anecdotal evidence of veterinarians seeing cats eating these diets who develop dilated cardiomyopathy among other health problems. Overall, I do not see myself recommending currently available vegan cat food products once I am in practice. It is hard to say what is the most ethical way to feed your cat animal products beyond meeting his or her health needs. One possibility is feeding a homemade diet that includes shrimp if one views certain crustaceans as capable of less suffering than other animals.
Another ethically debatable choice is feeding flesh from larger animals, such as cows, so fewer lives are taken. Given the resources that beef production requires, however, there are many collateral animal casualties that should be considered. A third possibility is feeding only foods with meat by-products for which animals are not specifically slaughtered. I will let the vegan ethicists debate this topic from here.
Many animal guardians wish to cook at home for their companions. For dogs, it is possible to make a homemade plant-based diet with appropriate vegan supplements. The most reliable products currently on the market are the BalanceIt supplements, which are designed by board-certified veterinary nutritionists. Customized balanced vegan recipes for healthy adult dogs can easily be obtained for free from their website, www.balanceit.com. BalanceIt recommends regular testing of blood taurine levels for vegetarian dogs.
Although dogs do not require dietary taurine, they require adequate dietary methionine to produce sufficient amounts of taurine and carnitine. Thus, their recipes often include methionine supplementation because vegan diets can be low in methionine, which interestingly in humans, rats and mice is associated with longer lifespans (13). For healthy adult cats, balanced homemade diets that include animal products are also available from BalanceIt.
Animals with medical problems or special needs should receive a consult from a knowledgeable veterinarian or credentialed specialist. If your general veterinarian is unable to assist you, a good rule-of-thumb is to obtain a referral to a veterinarian board certified by the American College of Veterinary Nutrition or European College of Veterinary and Comparative Nutrition. These veterinarians received years of additional training in the field of clinical nutrition after earning their veterinary degrees. A list of them can be found on the BalanceIt website, and several offer consultations online.
1. Skoglund, Pontus, et al. “Ancient Wolf Genome Reveals an Early Divergence of Domestic Dog Ancestors and Admixture into High-Latitude Breeds.” Current Biology 25.11 (2015): 1515-1519.
2. Ovodov, Nikolai D., et al. “A 33,000-year-old incipient dog from the Altai Mountains of Siberia: Evidence of the earliest domestication disrupted by the Last Glacial Maximum.” PLoS One 6.7 (2011).
3. Meriggi, Alberto, et al. “Habitat use and diet of the wolf in northern Italy.” Acta theriologica 36.1-2 (1991): 141-152.
4. Salvador, A., and P. L. Abad. “Food habits of a wolf population (Canis lupus) in León province, Spain.” Mammalia 51.1 (1987): 45-52.
5. Axelsson, Erik, et al. “The genomic signature of dog domestication reveals adaptation to a starch-rich diet.” Nature 495.7441 (2013): 360-364.
6. Driscoll, Carlos A., et al. “The Near Eastern origin of cat domestication.” Science 317.5837 (2007): 519-523.
7. Montague, Michael J., et al. “Comparative analysis of the domestic cat genome reveals genetic signatures underlying feline biology and domestication.” Proceedings of the National Academy of Sciences 111.48 (2014): 17230-17235.
8. Holliday, Jill A., and Scott J. Steppan. “Evolution of hypercarnivory: the effect of specialization on morphological and taxonomic diversity.” Paleobiology 30.1 (2004): 108-128.
9. Driscoll, Carlos A., David W. Macdonald, and Stephen J. O’Brien. “From wild animals to domestic pets, an evolutionary view of domestication.” Proceedings of the National Academy of Sciences 106. Supplement 1 (2009): 9971-9978.
10. Brown, Wendy Y., et al. “An experimental meat-free diet maintained haematological characteristics in sprint-racing sled dogs.” British Journal of Nutrition 102.09 (2009): 1318-1323.
11. Gray, Christina M., Rance K. Sellon, and Lisa M. Freeman. “Nutritional adequacy of two vegan diets for cats.” Journal of the American Veterinary Medical Association 225 (2005): 1670-5.
12. Wakefield, Lorelei A., Frances S. Shofer, and Kathryn E. Michel. “Evaluation of cats fed vegetarian diets and attitudes of their caregivers.” Journal of the American Veterinary Medical Association 229.1 (2006): 70-73.
13. McCarty, Mark F., Jorge Barroso-Aranda, and Francisco Contreras. “The low-methionine content of vegan diets may make methionine restriction feasible as a life extension strategy.” Medical hypotheses 72.2 (2009): 125-128.