Studies/Surveys Purportedly showing benefits of Vegan Pet Food

Vegan Dog Diet Could Save you Massive Vet Bills Study- NY Post

Vegan diets are healthier and safer for dogs, study suggests- The Guardian

Now even DOGS are being told to go vegan! Pooches who follow meat-free diets have fewer health disorders and are less likely to need medication, study claims – The Daily Mail

Vegan diets for dogs may be linked with better health, and could be less hazardous, than meat-based diets- Science Daily

Vegan Diet For Dogs May Be “The Healthiest And Least Hazardous” Choice, Study Claims- IFLScience

These are all recent headlines about Vegan Dog Food.

In an earlier post on Vegan Dog and Cat food, we briefly discussed that the surveys/studies conducted so far should not be relied on as evidence that these diets are safe for long-term feeding o provide any health benefit.

This post will go into much greater detail about why these studies do not tell us much about vegan pet foods’ long-term safety or health benefits.

Just because something was peer-reviewed does not mean that it is good science or that there are no severe limitations to the study.

While there are many commonalities between the two studies, it is best to go through them separately.

Study 1: A cross-sectional study of owner-reported health in Canadian and American cats fed meat- and plant-based diets

Study 2: Vegan versus meat-based dog food: Guardian-reported indicators of health

General Issues

The First thing we want to look at is who designed the study and the conflicts of interest.

Researchers-

Study 1: Lead Author is Dr. Sarah Dodd; while Dr. Dodd was not a veterinary nutritionist at the time of publication, she has become a board-certified veterinary nutritionist. The other Authors are Dr. Cate Dewey and Dr. Deep Khosa, both members of the Department of Population Medicine. Dr. Adronie Verbrugghe is a member of the Department on Clinical Studies and is a board-certified veterinary nutritionist. They are all Veterinarians located at the Ontario Veterinary College, University of Guelph.

Study 2: Lead Author and designer of the study is Dr. Andrew Knight. His qualifications are in Animal Welfare and Ethics as well as Veterinary Surgery. None of the other authors appear to have any specialization in animals. The other authors are Hazel Brown, part of the Centre for Animal Welfare, Faculty of Health and Wellbeing, Nicholas Rai affiliated with the Menzies Health Institute (Human), and Eason Huang, an independent consultant.

Conflict of Interest                           

Study 1: Some have received grants or have consulted with various pet food companies, both conventional foods, and plant-based foods.

Study 2: The study was directly Funded by Proveg International, an organization advocating for Vegan diets for humans and animals. Dr. Andrew Knight also runs a website called sustainablepetfood.info, which advocates for feeding animals vegan diets.

Study 1Study 2
Population Medicine and Nutrition, All DVMsAnimal welfare and Ethics- One DVM
Have Received funding or consulted for the Pet Food Industry, both Meat, and plant based.Funding from an Organization Advocating for Vegan Diets. One Author advocates for Vegan Pet Foods

There is nothing inherently wrong with the fact that he is advocating for a specific feeding method. Still, it does create, at the very least, the appearance of bias towards a particular result. This would be no different than if any of the Veterinarians that have advocated for raw diets over the year decided to publish a similar Study (Survey) on Raw Food Diets.

Results of the Studies

Study 1

Diets Fed- Cat Characteristics

The Diets fed are 187 (18.2%) Plant-Based (PB) , 667 (65%)  Meat Based (MB), and 69 (6.7%) a combination of Plant-Based and Meat Based.

Most cats lived exclusively indoors (60%). At the same time, 30% had unlimited access to the outdoors, and 9.1% had limited access. Less than 1% lived outdoors exclusively.

Most owners indicated that their cats did not hunt prey. However, 35% of the Plant-Based had unlimited access to the outdoors, so it is possible that the cats hunted without the owner’s knowledge, So they were classified as PB+MBH. This resulted in

Meat Based667(65%)
Plant Based117(11%)
Plant Based + Meat Based/Hunted139(13%)

53% of the cats had been fed their current diet for their whole life, while 48 % had at least one previous diet. Most have been fed the same diet for 3.8 years. Less than half of the cats received treats or table scraps. More MB received treats while more PB Cats were given table scraps. More PB received supplements.

There was No Deviation between Diet type and age. The Meat-based were more likely to be domestic longhairs while Plant-Based were more likely to be mixed.

Evaluation of Cat’s Health

Most Cats were reported to be in ideal condition, with more cats being overweight than underweight. The PB owners reported a better Body Condition Score than the MB. It must be noted that this is not consistent with the data regarding the prevalence of obesity in cats.

The Survey also looked at the fecal score between diet groups, and there was no difference detected. Half of the cats were reported to have no health disorders.

Both Plant-Based groups were associated with fewer disorders than the Meat Based group, but it was not significantly different. Furthermore, owners were more likely to report them as having very good health and wellness based on the metrics used: 

Frequency of Vomiting, Frequent inactivity, happy appearance, distress vocalization, demonstration of affection, contact avoidance, and curious behavior.

Comfortable, Soft, Shiny Fur, Friendly, Good Appetite, Playful,

Stiff and or slow, Lethargic, and Slow/Painful.

There was no difference in reported lifespan between the diet groups

Issues:

Owner Beliefs and Biases

The Survey was not random; participants were invited to participate in the study. The Survey was advertised online and in pet stores. This leads to self-selection biases. This is a limitation represented by many surveys.

The Survey also relies on the pet owners’ accurate memory, especially those that involved a previous cat.

The fact that research indicates that those feeding vegan diets to cats are also vegan themselves suggests that there is probably a level of bias in their responses. Diets, especially alternative diets, can often lead to powerful beliefs about the benefits of their chosen diet. This causes both conscious and unconscious biases. In addition, Owners might report positive effects as a result of the caregiver effect, which is fairly well documented. This is something that needs to be taken into consideration when evaluating the results of the Survey.

There is a reason the gold standard is double-blinded studies and baring those single-blinded studies. This is done to reduce the effect of conscious and unconscious bias of both the researcher and participant.

This could influence owners to believe that the cat is healthy or very healthy when they are not. One other consideration not addressed is that cats can be very good at hiding whether they are not feeling well.

This is why independent evaluations are so critical in evaluating the health effects of a particular feeding method.

Given that the owners are also consuming a vegan diet, any possible health problems associated with vegan pet food would partially impugn their own dietary choices. This presents a strong unconscious motivation for them to believe and see that a vegan diet is beneficial(Confirmation Bias).

Owner Source of Information Distrust of Veterinarians

In the present study, the owner’s sources of information were 64% Veterinarians, while 62% relied on the internet and social media. 58% of those indicating the internet did also use a vet as a source of information

However, Like Many raw feeders, the plant-based owners were less likely to rely on veterinarians regarding the diet.

They are both more likely to rely on the internet and social media. Research indicates that raw feeders have a decreased level of trust in Veterinarians and seek nutritional information from the internet and social media. The same level of distrust may also be found among those feeding Vegan Diets to dogs and cats.

Unknown Effects

Owners, especially those with alternative diets, place much value on taking care of their pets. This likely would have some effect as they are likely to be more perceptive of their pet’s health or behavior changes. One possible effect is early diagnosis of conditions. This would lead to an increase in the number of disorders among the Plant-Based group. The other effect could be that it allows for more preventative strategies to lower the number.

The study was also unable to determine whether the lower rate of health disorders in the plant-based groups resulted from cats being switched to therapeutic diets due to a diagnosis. Most owners, however, did not change diets from a previous cat. Indicating that it is unlikely, among those currently feeding a plant-based cat food, but it is something that can’t be ignored entirely;

Study 2

The Second study suffers from many of the same problems as the above study but does have some additional issues.

Statistical Power

Owner Information

The survey response was primarily female, 92%. The age brackets were well represented except on the extremes. The diets of the respondents were:

Omnivore40%
Vegan23%
Reductatarian (Omnivore Reducing Meat Consumption22%
Vegetarian10%
Pescatarian5%

While most of the responses coming from females isn’t ideal, it’s not that big of an issue. Given the uniqueness of Vegan Pet food, it’s probably safe to assume that most if not all of the vegan diet group came from those also eating a vegan diet. This is supported by other research indicating that those consuming no meat are the only ones to feed plant-based diets to cats. This introduces strong biases, As we discussed earlier.

The other feeding groups are subject to the same bias related to their feeding decisions, probably the raw-fed group more so than the conventional. After all, some vegans still feed their dog or cat a raw diet.

Diets Fed

76% of all responses received treats. While 37% received supplements, This slightly complicates matters but isn’t that big of a deal.

Diet TypeResponse (Percent of Response)
Conventional Diet1370 (54%)
Raw Diet830 (33%)
Vegan Diet336 (13%)

While the total responses are better than the first Survey, when the responses are broken down into each group, the issue with drawing conclusions becomes apparent. This is especially true for the vegan group and the raw group to a significantly lesser extent.

The fact that only 13% of the total responses came from the vegan groups means that as it relates to the vegan group, it lacks statistical and thus predictive power compared to the other groups. The Total number of Vegan Dogs is also not significantly more than the number of cats on plant Based diets in the earlier study. The significant difference between Vegan/Conventional, Vegan/Raw, and Raw/Conventional could very well skew the results.

Vegan vs Conventional.2455
Vegan vs Raw.4048
Raw vs conventional.6058

The other issue that arises is that

“In anticipation of lower levels of unconventional diets, and the need to achieve group numbers sufficient for statistical analysis, volunteers and the authors made some efforts to reach unconventional pet food interest groups, as well as conventional dog and cat interest groups. However, by careful wording choice, no bias for or against any particular diet choice was implied within advertising materials, or within the survey questions or explanatory text.” (Knight, 2022)

I.e. people with interest in either Raw or Vegan Feeding.  

One more issue is that the study’s only requirement was that they were on the diet for at least a year. This becomes an issue when drawing conclusions about the long-term health impacts.

Breed and Weight

The Survey did take age into account, as age may provide a certain level of protective effect.

Diet TypeAverage Age
Overall6.18
Raw5.552
Conventional6.31
Vegan7.30

The smaller sample size of both the Vegan, and Raw could have skewed the age results, with the Vegan having a greater impact as they had far fewer responses.

However, this information is ultimately useless without accounting for the size and breed. A 12-Year-old Vegan Fed Yorkie is not that different from a 5-year-old conventionally or raw-fed English Mastiff. So the one or two-year difference between the groups could have an effect, or it could not.  

They did collect breed information (toy, small, medium, large and giant) but did not use this information in the analysis.

The fact that breed and size weren’t considered is another major flaw as some breeds are relatively healthy while others are less so.

Given the substantially smaller sample size of the Vegan and Raw to a much smaller extent, Each healthy, unhealthy, Intact, fixed, big, small, toy-sized dog has a greater impact on the overall numbers.

If the vegan fed dogs were skewed more towards toy breeds, and the raw fed group skewed towards medium-sized breeds, and the conventional large breeds, this would have a sizeable impact on the effect of age. The same would go for relatively healthy breeds.

This also impacts the use of vet visits as a metric because it doesn’t account for the fact that some breeds, and also breeders commonly see specialists. Some go see reproductive vets. Dobermans will commonly go see a cardiologist each year in addition to a regular check-up.

When it comes to health issues, some of them are not even related to nutrition or diet.

Entropion eye is not influenced by diet. Environmental allergies are not controlled by diet; the dog being over or underweight is likely due to over or underfeeding, not a particular feeding method. Many health issues have a strong genetic component.

These can’t be ignored when attempting to draw conclusions about the effects of a particular feeding method on a dog’s health. These issues would be exacerbated in the Vegan fed and the raw fed groups to a lesser extent as each small, relatively healthy dog breed would have a greater impact on the overall number.

The authors make assumptions about why the Raw-fed dogs were spayed and neutered less than the other groups. Spaying and Neutering is not a clear-cut decision as it relates to the dog’s health, and it hasn’t been for quite some time. It’s possible that more of the raw-fed group were breeders or the owners intended to show the dog. It’s possible that more conventional and vegan dogs were acquired from rescues and were already fixed when acquired. For the Large and Giant Breeds, it isn’t uncommon to wait longer to spay or neuter. The Survey and much of the period covered was during Covid-19. So before any assumptions are made about raw feeders, we would have to compare the spay and neuter rate to dogs of the same age, not dogs that were a year or two older on average.

COVID-19- Risk Perception and Tolerance

Speaking of Covid-19, we cannot ignore the potential effects of Covid-19. Covid-19 presents unique challenges with interpreting and drawing conclusions from the results.

The Survey was available from May to December of 2020. This covered the beginning when there were many lockdowns. Most of the survey results also came from the UK, not the United States.

The abundantly clear issue is the lockdowns, but besides that, there is the issue of risk tolerance. While some people may have been undeterred to visit a vet, assuming it was open, others were probably less inclined to do so unless it was truly dire. Everyone has a different risk tolerance, and there were and are likely differences among those different feeding ideologies. (Conventional, Raw, Vegan)

While individual risk perception has shifted drastically, it’s important to consider people’s perceptions of the risk during the period covered by the Survey. Not what people’s risk perception is now or how they would perceive the risk based on what they know now. As we all know, some people were in a state of panic and now claim that they never thought covid-19 was something to be worked up about

One other possible impact of Covid-19 was that Due to the various lockdowns, more people were at home with their pets. This could have led more people to notice issues that they didn’t notice before.

Given the Risk perception and Tolerance, this may have led different groups to go to the vet more or less often.

Interpreting Health Results

The number of Vet visits is not an indicator of health. The owner’s interpretation or memory of what the vet said isn’t an indicator of health, nor is the owner’s perception of health.

As discussed above, some health disorders are not associated with diet at all. Many Breeds are at heightened risk for many health disorders, and many disorders are multifactorial, and diet could be just one small factor.

However, one area of concern is the apparent increased risk of internal parasites. The authors explain that this might be due to some guardians’ belief in minimizing harm to living organisms, including internal parasites, and thus don’t give worming products.

The problem with this argument is that the raw feeding group didn’t have the same increased risk even though many in the raw feeding and holistic community (Most often the same thing) avoid giving these products, albeit for other reasons.

So, the apparent increased risk might be from the diet itself.

Therapeutic Diets

The next concern is that those feeding a vegan diet ended up switching to a therapeutic diet more often than the raw group and slightly less than the conventional group.  

While the authors note several times that those feeding a raw meat diet were less likely to make a switch for various reasons, they state it only once for those providing a vegan diet.

While the authors repeatedly make claims about the biases of Raw feeders, it is likely that those feeding a vegan diet are subject to the very same biases. In fact, I looked through several Vegan Dog and cat groups/ pages and found many of the same thought processes as those seen in Raw Feeding groups, with the only exception being a preference for Vegan Food instead of raw food.

So the fact that more of the vegans switched despite the same biases is slightly concerning.

I have also read a case report where the owner switched, and the issue was resolved just for the problem to recur after switching back to the vegan food; this was repeated several times.

So if the raw group number is low, as a result of owners not following the vet’s advice regarding a therapeutic diet, it’s possible that the vegan group is also low.

Switching Diet Types and Owner Biases

One thing that is not evaluated is the fact that while switching diets is not exactly common, it does occur.

Owners will switch either because of a health issue or the dog or cat not doing “well on a diet”. This has two possible effects. This could either increase or decrease some of the health measurements used.

This would likely have a more significant impact on the conventional or raw diet groups; because research suggests that when switching to vegan diets, it is heavily influenced by the owner’s morals and ethical concerns with meat consumption. Therefore, it is possible, if not probable, that the owners who stop feeding vegan diets are a result of the dog or cat not doing well on the vegan diet.

So, the question is, what percentage of owners have stopped feeding a vegan diet due to real or perceived health or wellness issues. What percentage of owners stopped feeding a conventional or raw diet and switched to one of the other diet types for real or perceived health or wellness issues?

The Survey treats the results of Vegan and Raw Diets Vastly Different

While Both the Vegan and Raw groups had better health based on their metrics, the study’s authors treat the groups very differently. They discuss the issues with Raw Diets while barely addressing the same issues within Vegan Diets.

Case in Point

The authors make a note of the fact several times throughout the paper that some of the issues related to raw feeding stem from nutritional inadequacy and the risk of pathogens. While they only pay lip service (Once), for Vegan Pet Foods. Several studies have shown that Vegan Foods are just at much a risk of being nutritionally inadequate.

Regarding pathogens, yes, vegan diets would be a lower risk for most food pathogens. We shouldn’t forget that several foods have been recalled over the last several years for mycotoxins which come from the same ingredients used in many vegan foods.

Study Conclusions

Reading the conclusions from the papers, and let’s be clear that most only read the study’s conclusion, not the whole study, explains why the first study received almost no media attention, 2 News articles, 2 blog posts, and 71 tweets. One of the News Articles is a blog post we wrote last year about anthropomorphism. In contrast, the second received considerable traction with 344 news articles, 3 Blogs, and 131 Tweets in the short time since its publication, per Altmetric.

The fact that the second study was on dogs while the first study was on cats probably also slightly influenced the amount of attention.

Ultimately the Frist study is much more reserved, and the section on study limitations was only 671 words. They also make it repeatedly clear several times that you shouldn’t read too much into the results.

The Second study makes very bold proclamations (Great way to get attention), and if you have made it this far, you know that the data they have so far doesn’t truly support their claims. The authors of the second study made these claims despite the section on the study limitations being 1091 words. Or around 30% of the words in this entire post, and that includes both study’s conclusions in full below.

When the section on study limitations is that long, you should never place much value on the results.

Study 1: Conclusion

“Owners who fed their cats PB diets had a positive perception of their cats’ health and reported a belief of better general health, better body condition, and fewer health disorders as compared to owners who fed their cats MB diets. Furthermore, the reported lifespan of cats did not differ based on diet type. While these data are owner reported and thus warrant follow-up research involving more objective evaluations, the hypothesis that owners of cats fed a PB diet would report higher prevalence of negative health outcomes was not supported by these findings.” (Dodd, 2021)

Study 2: Conclusion

“Vegan diets are among a range of alternative diets being formulated to address increasing concerns of consumers about traditional pet foods, such as their ecological ‘pawprint’, perceived lack of ‘naturalness’, health concerns, or impacts on ‘food’ animals used to formulate such diets [8935]. Critics have asserted, albeit without evidence, that biological and practical challenges in formulating nutritionally adequate canine vegan diets mean their use should not be recommended [1358].

By 2021, no large-scale study of dogs had been published, describing how health outcomes vary between dogs maintained on vegan or meat-based diets. Our study of 2,639 dogs and their guardians is among the first such studies. Among 2,596 respondents who played some role in pet diet decision-making, pet health was one of the most important factors considered.

In total, 2,536 respondents provided information, each relating to a single dog who had been fed a primarily conventional meat (1,370 = 54%), raw meat (830 = 33%) or vegan (336 = 13%) diet for at least one year. Information was provided about seven general health indicators, and 22 specific disorders. Considering all seven general indicators of health, dogs fed conventional Meat appeared less healthy than either of the other two dietary groups. They had poorer health indicators in nearly all cases. Considering dogs fed raw Meat or vegan diets, the former group had marginally better health indicators overall. However, there was a statistically significant, medium-sized difference in ages, with dogs fed raw meat diets being younger on average. This can provide health protective effects. Other non-health related factors may also have improved the apparent health outcomes of dogs fed raw Meat, for three of seven general health indicators.

Additionally, a significant body of studies have indicated that raw meat diets commonly include significant dietary hazards, particularly nutritional deficiencies or imbalances, and pathogens. When considering these 22 specific disorders individually, different prevalence levels were apparent between the dietary groups. However, very small numbers of affected dogs fed vegan diets, may have prevented the detection of statistically significant differences in some cases. (Knight, 2022)

Accordingly, when considering health outcomes in conjunction with dietary hazards, the pooled evidence to date from our study, and others in this field, indicates that the healthiest and least hazardous dietary choices for dogs, among conventional, raw Meat and vegan diets, are nutritionally sound vegan diets. Regardless of ingredients used, diets should always be formulated to be nutritionally complete and balanced, without which adverse health effects may eventually be expected to occur.”

Conclusion

Contrary to media reporting, the large surveys/studies do not demonstrate that vegan foods are safe and healthier than conventional or raw food.

The studies/Surveys have multiple moderate to severe limitations. Between the two studies, we have information on 336 dogs and 256 cats. This is vastly different from the raw food bacterial survey, which had over 16,000 responses. While individual biases may have lowered their number similar to here, the large data set means it would have a smaller effect.  

When it comes to long-term safety and evaluating the health claims surrounding Vegan Foods for our dogs and cats, there probably won’t be any answers until VCA and Banfield collate what data they have on Dogs and Cats Fed Vegan Foods. The other options are Vetcompass or possibly the Golden Retriever Lifetime Study. The VCA and Banfield might be more likely as their parent company, Mars, has its own Vegan Pet Food brand. 

We are not going to lie; we are biased against vegan pet foods, as we don’t believe they are necessarily the best thing for our dogs and cats for multiple reasons. However, if they produce evidence showing that it is safe long-term and has actual benefits, we are more than prepared to change our opinion on the matter. However, currently, they do not have the data, and a 6-month feeding trial ultimately isn’t proof that they are safe or beneficial long term.

Works Cited

Dodd, S.A.S., Dewey, C., Khosa, D. et al. A cross-sectional study of owner-reported health in Canadian and American cats fed meat- and plant-based diets. BMC Vet Res 17, 53 (2021). https://doi.org/10.1186/s12917-021-02754-8

Knight, A., Huang, E., Rai, N., & Brown, H. (2022). Vegan versus meat-based dog food: Guardian-reported indicators of health. PloS one17(4), e0265662. https://doi.org/10.1371/journal.pone.0265662

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