It hasn’t been very long since I last wrote about vegetarian diets for pets, but a new study is out that touches on the issue, so I thought it was time for an update.
Dodd, S. A. S. et al. (2021) ‘A cross-sectional study of owner-reported health in Canadian and American cats fed meat- and plant-based diets’, BMC Veterinary Research. BioMed Central, 17(1), p. 53. doi: 10.1186/s12917-021-02754-8.
This study specifically addresses vegetarian diets for cats, so let’s start with the conclusions from my most recent article on the subject:
Cats have been more lightly touched by domestication and artificial selection than dogs, and they are clearly still obligate carnivores.34,35 This does not mean they are healthiest when fed only raw birds and small mammals, and in fact the evidence indicates this is not the safest or healthiest diet for domestic cats.36,37 However, domestication has had limited effects on the physiology of cats, and their dietary requirements are unlikely to be effectively met by plant-only diets. The need for preformed vitamin A, taurine and other specific amino acids lacking in plant-based foods, and other specific and known dietary requirements of cats makes it unlikely that long-term feeding of vegan diets will support good health in this species.35,38
There are few studies evaluating the health effects of plant-based diets on cats. Some research on cats fed commercial vegetarian diets by their owners have found deficiencies in some nutrients in some cats, but the evidence is limited and of low quality, so no robust conclusions can be drawn.9,39–41
This new study appears to suggest that the jury is in and that plant-based food for cats has no health risks and may even have health benefits. Here are some of the key results:
* No differences in reported lifespan were detected between diet types.
* Fewer cats fed plant-based diets reported to have gastrointestinal and hepatic disorders.
* Cats fed plant-based diets were reported to have more ideal body condition scores than cats fed a meat-based diet.
* More owners of cats fed plant-based diets reported their cat to be in very good health.
However, even the authors recognize that these findings don’t just the general conclusion that vegetarian diets are safe or health for cats. Here is their more measured assessment:
Cat owner perception of the health and wellness of cats does not appear to be adversely affected by being fed a plant-based diet. Contrary to expectations, owners perceived no body system or disorder to be at particular risk when feeding a plant-based diet to cats. This study collected information from cat owners and is subject to bias, as well as methodological limitations. Further research is warranted to determine if these results are replicable in a prospective investigation.
The key point here is that this study didn’t actually evaluate the effect of plant-based vs. meat-based diets on health or longevity in cats. What the study evaluated was the perceptions of owners about their cats’ diet and health. The difference is crucial.
The study was essentially an online survey distributed through a pet store and cat-centered social media. The owners surveyed were those who voluntarily chose to go to the web site and fill out the survey. This already introduces a selection bias since the people willing and able to do this differ in various ways from the rest of the population. People who respond to web surveys, for example, are younger, whiter, and richer, than people who are more likely to respond to mail or phone surveys. And people tend to respond to surveys when they have a higher level of interest in the subject than the average person. Surveys touching on unconventional diet and medical beliefs tend to be biased towards people with the strongest feelings on these issues, which biases the results.
The other major problem with such a sample is that the health status of the cats was determined entirely based on the opinions and reports of owners. No medical evaluation or records were involved. Owners, however, are neither medical professionals nor objective about their cats’ health, and they are likely to report their beliefs, which often doesn’t line up with the reality.
For example, 55% of cats in the study were reported to be a health weight. However, previous research has shown that owner assessment of body condition is inaccurate and tends to underestimate weight in overweight cats. People who fed a plant-based diets were much more likely to report that their cats were a healthy weight (71% compared with 54% of those on meat-based diets) and less likely to report they were overweight (22% compared with 34% of those on meat-based diets). Proponents of plant-based diets will likely conclude that this means such diets lead to a healthier weight than meat-based diets. This is possible, but it isn’t a conclusion we can reach based on this survey. All we can say is that owners who choose to feed a plant-based diet believe their cats are a healthier weight than owners who feed meat-based diets. Since plant-based diets are fed to a small minority of cats (only 18% in this survey, which likely overestimated the true popularity), the people who feed these diets must choose to do so based on pre-existing beliefs about their health value. Such individuals already believe these diets are healthier, and they are likely to see and report what is consistent with these beliefs, whether or not it is the reality of their cats’ condition.
The same sorts of biases create a problem for all of the other measures of health assessed in this study. Again, it didn’t really evaluate diet and health, only diet and owner beliefs about health. As the authors suggest, prospective, blinded, randomized feeding studies would be needed to allow any strong conclusions about whether or not plant-based diets are safe and healthy for cats.
9. Knight A, Leitsberger M, Knight A, Leitsberger M. Vegetarian versus Meat-Based Diets for Companion Animals. Animals. 2016;6(9):57. doi:10.3390/ani6090057
34. MacDonald ML, Rogers QR, Morris JG. Nutrition of the Domestic Cat, a Mammalian Carnivore. Annu Rev Nutr. 1984;4(1):521-562. doi:10.1146/annurev.nu.04.070184.002513
35. Morris JG. Idiosyncratic nutrient requirements of cats appear to be diet-induced evolutionary adaptations. Nutr Res Rev. 2002;15(01):153. doi:10.1079/NRR200238
36. Glasgow A, Caver N, Marks S, Pedersen N. Role of Diet in the Health of the Feline Intestinal Tract and in Inflammatory Bowel Disease.; 2002. http://www.vetmed.ucdavis.edu/ccah/530-752-7295. Accessed December 28, 2018.
37. Schlesinger DP, Joffe DJ. Raw food diets in companion animals: a critical review. Can Vet J = La Rev Vet Can. 2011;52(1):50-54. http://www.ncbi.nlm.nih.gov/pubmed/21461207. Accessed October 27, 2018.
38. Weeth L, Chandler M. Vegetarian Diets. Clin Br. 2015;(January):61-63. https://www.cliniciansbrief.com/article/vegetarian-diets. Accessed April 29, 2019.
39. Leon A, Bain SA, Levick WR. Hypokalaemic episodic polymyopathy in cats fed a vegetarian diet. Aust Vet J. 1992;69(10):249-254. http://www.ncbi.nlm.nih.gov/pubmed/1359869. Accessed April 29, 2019.
40. Wakefield L, Michel KE. Taurine And Cobalamin Status of Cats Fed Vegetarian Diets. J Anim Physiol Anim Nutr (Berl). 2005;89(11-12):427-428. doi:10.1111/j.1439-0396.2005.00611_2.x
41. Gray CM, Sellon RK, Freeman LM. Nutritional adequacy of two vegan diets for cats. J Am Vet Med Assoc. 2004;225(11):1670-1675. http://www.ncbi.nlm.nih.gov/pubmed/15626215. Accessed April 29, 2019.
Thank you for this!!
Btw, could this be one of the articles you might publish on dvm360 magazine? 🙂
I was a volunteer for a free spay and neuter program in a very poor area. I encountered a woman who had what appeared to be an apartment full of 4 – 5 month old kittens. We managed to build a bridge with her and got all her cats fixed. Imagine my surprise when I discovered the kittens weren’t kittens but FULL GROWN CATS. This woman was somewhat challenging to deal with, and had significant mental health issues. She “didn’t believe” in feeding her cats commercial cat foods, or anything containing meat, poultry or fish. All of the cats in this household had severe nutritional deficiencies, which is why their growth was so stunted. Some of the older cats had died suddenly, probably from heart issues from a complete lack of taurine in their diet.
In contrast to many of the owners surveyed in the study you cited, this woman had no internet access, and did not even have a phone. She was not from an educated background. I do not know where her beliefs came from. She was given donated cat food, and was gently spoken to about cat’s nutritional needs. There was nothing else that could be done but it was a very worrisome situation.
It’s an interesting study nonetheless. My understanding is that cats require certain nutrients, not certain ingredients – the two are often confused. There appears to be a growing body of evidence that cats do not, in fact, need to eat meat (and no evidence to date that they do – despite the widely held belief that this is the case).
It is true that nutritional requirements are described in temp software nutrients rather than ingredients. However, ingredients differ in the amount and quality and bioavailability of nutrients, so the two are not entirely unconnected. Whether, for example, plant sources of taurine are as effective in cat food as animal sources is not completely clear. I’m not sure what the “growing body of evidence” you refer to is, so please share sources if there are specific studies you are referring to. Thanks!
Very interesting. Although I’ve been vegan for almost nine years, I’ve never considered putting my dogs or cat on a plant based diet. Maybe I’m being a hypocrite, but despite a plant based diet that would make a nutritionist proud, I’ve experienced more than one nutrient deficiency. So yes, the bioavailability issue is very real. Although it’s been easy enough for me to remedy with the appropriate supplements, it concerns me that these companies jumping on the plant based bandwagon, know more about how to appeal to my personal convictions than they do about the long term health ramifications of say a cat being on a plant based diet for 10 or 12 years.
Here’s a review of several relevant studies https://doi.org/10.3390/ani6090057
This is a study addressing uncritical reliance on the ‘cats are carnivores’ argument https://www.mdpi.com/2306-7381/4/4/55/htm.
Here’s an example from dogs: https://www.vegepets.info/resources/Publications/Veg-dogs-Brown-et-al-Br-J-Nutr-2009.pdf?fbclid=IwAR27d8zcG7wNKX1R8k245vzLwmmmKeWt6ARtSvnzGMj_5ksueU4yYtfYim8
At present there are several studies showing balanced plant-based diets in cats and dogs are as healthy as meat-based diets, and none showing the opposite. It would be good to mention this if you are aiming to have a balanced, well-informed scientific discussion of this subject.
This post was a review of a single study, not a “balanced” discussion of the general subject, so you are criticizing it for not being something it doesn’t claim to be. Nevertheless, I always appreciate being offered specific citations, so let’s see what we have.
This is a narrative review with a clear intent to show that vegetarian/vegan diets are acceptable, so no objective study selection or evaluation methods and no control for bias. Here are the studies mentioned in this review involving cats-
Study by Kanakubo et al. (2015) 
An evaluation of vegetarian diets sold in the US for cats and dogs. 25% did not meet minimum AA requirements. No information about health outcomes.
Study by Semp (2014) 
An evaluation of two diets for cats in an unpublished thesis. Some nutritional inadequacies found, no obvious clinical abnormalities, but it’s not clear how this was determined.
Study by Gray et al. (2004)
Evaluated commercial vegan cat foods and found them to be inadequate. The manufacturers claimed only the samples tested were inadequate and the rest of the food they sold was fine, but there’s no explanation of why this should be accepted as an explanation for the findings. No assessment of clinical status in cats fed the diets.
Study by Kienzle and Engelhard (2001)
Nutritional analysis of various diets, most judged to have some inadequacies, especially in taurine levels. No assessment of clinical status in cats fed the diets.
“A growing body of evidence appears to indicate that dogs and cats can survive, and indeed thrive, on nutritionally-sound vegetarian and vegan diets. Numerous cases are described on various websites and in a small number of books”
A collection of case reports from websites and books is hardly reliable evidence to justify this conclusion. The authors acknowledge this subsequently, but the studies they then cite are hardly rigorous controlled research.
Study by Semp (2014)
Survey of owners to ask about diet and then single exam and labwork on 15 cats which found no obvious abnormalities. Again, this hardly constitutes proof that there are benefits or no long-term harm from feeding cats vegetarian diets.
Study by Wakefield et al. (2006)
Owner survey used to determine diet and feeding practices (e.g. length of time on vegetarian diet).
Taurine and cobalamine were sampled from 17 cats and while some values were low for taurine for a few cats, none were considered dangerous.
Study by Kienzle and Engelhard (2001)
8 cats on vegetarian diets were evaluated. Nutritional deficiencies were identified, and three cats had potentially related clinical problems.
And that’s pretty much it. Not even close to a robust body of evidence showing equivalence or superiority of plant-based diets for cats.
Not a “study” but another narrative literature review. This focuses on the fact that carbohydrates are not inherently bad for cats, which you will see is a point I make repeatedly on this site. Not, however, evidence for or against the health effects of vegetarian diets.
I won’t address the dog literature since this post was about a single study in cats, and I have said elsewhere that I suspect vegetarian may be perfectly fine for dogs if properly formulated, though the evidence is not that strong either way on that point.
The bottom line is that there is no strong or reliable evidence allowing us to conclude that vegetarian diets are health for cats. There are studies showing they can be harmful if not properly formulated, but we don’t have enough evidence to determine conclusively if they could be made in a way that is safe or even has health benefits.
I didn’t find the results that surprising given that it was based on owner-supplied information. The problem is that many people will misinterpret the study to mean a plant-based diet is beneficial.
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Hi! Sorry for another pet food question, but have you written an article on low carb foods specifically for cats? I’m a pet owner that’s always fed Royal Canin wet and dry food, but recently I’ve been seeing more and more people cite Catinfo.org, a site written by a DVM as the holy grail on pet nutrition.
It seems to be full of misinformation (from a laymans perspective) and falls victim to the naturalistic fallacy, but it also has a seemingly balanced perspective on by-products and commercial food. A few veterinary technicians have even recommended this site to me on forums! It’s making me question if the vet who wrote it has a point after all.
Thank you for the work you do writing this blog and debunking alternative medicine fads!
Thanks for the feedback!
Here are a couple of articles addressing the issue of carbs and cats.
I should’ve done a simple search before commenting. I’m facepalming right now! Thank you for the information. I’ve now got articles to refer people to when they preach the virtues of canned only, no carb diets for cats. I hope no cats are harmed because of the writing of Dr. Pierson, who says to reduce carbs and insulin dosage, and knowing most people they won’t contact their vet first.
I would add that there are many things that we simply don’t understand about the complexities of feline nutrition, especially at the cellular level. Even info on human nutrition is sorely lacking. So why risk changing the diet of our feline friends in order to satisfy our own human desire to control them and to try and force their needs to conform to our arbitrary values? Biology trumps human desires as far as I’m concerned. I’m a vegan but my cats are obligate carnivores. If I didn’t want to feed them the meat they need, I shouldn’t have adopted cats.