The practical and ethical problems of feeding cats a vegan diet have been fairly contentious issues among both veterinarians and vegan activists alike and I myself have jumped into the fray a number of times. While reasons vary among those that advocate or are interested in the idea of animal product-free diets, most express ethical reasons and the desire to avoid contributing to animal slaughter. These advocates claim that cats can get all their nutrition from a properly formulated vegan diet and point to their own personal stories of cats that have lived long term on a vegan diet. The other side claims that cats are obligate carnivores and need meat to survive and often cite personal anecdotes of cats that developed medical problems.
So what does the published science on this issue say? A little bit, but not a whole lot really. An early study from 1992 touched on the issue but its findings are not too impressive scientifically (and sound pretty cruel), notably that cats fed a potassium deficient diets developed a muscle condition typical of potassium deficiency, while cats given supplemental potassium did not develop the condition. Another study in 2001 from Germany titled, “A field study on the nutrition of vegetarian dogs and cats in Europe”, was not encouraging. However this study only looked at eight cats and is at best preliminary.
A 2004 study published in the Journal of the American Veterinary Medical Association (JAVMA) examined the nutrient content of two commercial brands of vegan cat food (Evolution Diet and Vegepet) and found them to be lacking in key nutrients. With its small sample size this study is hardly a slam dunk for those that argue against the idea of vegan cat food but it is worrying nonetheless. The manufactures of both foods responded that they felt that it was likely the result of a mixing error at the factory. But if researchers found such an error in two independent products it leads one to wonder how often such mixing errors occur. The makers of Vegepet promised to look into it and reformulate. The owner of Evolution Diet, Eric Weisman, for his part dismissed the finding altogether as unimportant.
I would be amiss if I were to not also mention that Mr. Weisman has had a history of shady conduct. Aside from lying about the benefits of his products and practicing medical quackery, he has also been accused of some not-so-ethical treatment of animals. And for a taste of Weisman’s argument style listen to his teeth-grating interview on The Vegan Option podcast. Take it for what you will but he certainly doesn’t sound like someone I would trust.
A 2006 study titled, “Evaluation of cats fed vegetarian diets and attitudes of their caregivers”, found that most of the cats in the study were quite healthy. However the sample size was on the small side (34 cats in the vegetarian diet group) and the only objective measures taken were cobalamin and taurine levels. Ian MacDonald (with guest Erin Red) of The Vegan Option podcast speaks with the lead author of this last study in what I consider to be one of the best examples of engaging the issue for a popular audience in their episode Cats: Can they be vegan? and further explores the issue in the follow-up episode Cats: Ethics.
Aside from micro-nutrient balance, the main medical issue that comes up when discussing feeding cats a commercially formulated vegan diet is that of urinary tract obstruction from the formation of small struvite crystals, particularly with male cats. Dr. Armaiti May explains,
Cats on a vegan diet can develop abnormally alkaline (high pH) urine due to the more alkaline pH of plant based proteins in comparison to the acidic pH of meat-based foods which cats have evolved to eat. When the urine pH becomes too alkaline, there is an increased risk of formation of struvite (also known as magnesium ammonium phosphate) bladder crystals and/or stones. Calcium oxalate stones can also occur, but these do not occur if the urine is too alkaline, but rather if it is too acidic. Such stones can create irritation and infection of the urinary tract and require veterinary treatment. In male cats who form such crystals or stones, they can suffer more severe consequences than simply irritation or infection of the urinary tract because the stones can actually cause an obstruction of the urethra so the cat cannot urinate. This is a life-threatening emergency requiring immediate veterinary care…
Thats about it, a little bit of published science and a whole lot of anecdote. So where does that leave us? I myself have serious reservations about feeding cats a vegan diet. I simply don’t think that we have enough information or research. It appears that many cats do quite fine on a vegan diet for much or all of their life. But there also appears to be a potentially serious health risk to a certain subset of cats. Perhaps better food formulations are all that’s needed to do the job, maybe not. And if not then perhaps alternatives such as farmed sessile bivalves or insects may be a route to reduce suffering.
I don’t really have any solid answers here. All I can say is, think critically and think compassionately.
Further Resources:
Cats: Can they be vegan? on The Vegan Option
Cats: Ethics on The Vegan Option
Vegan Cats & Dogs with Jed Gillen, Author of Obligate Carnivore on Animal Voices
Vegan Pet Food: A Discussion on Animal Voices
Evolution Diet – Selling Food with Fear and Lies by Skeptvet
Evolution Diet Update: Selling Food with Fraud by Skeptvet
Mr. Eric Weisman, Promoter of Evolution Diet, Finally Prosecuted by Skeptvet
Eric Weisman Gets Fine and Probation for Violating Court Order by Skeptvet