There are several motivations for producing plant-based foods for pets.

• More than half of pet owners say they are more likely to purchase food that is sustainably produced.
• Vegans and vegetarians make up about 2-3% of the general population in NZ and Australia, but 10-16% of pet owners. There is increasing interest from owners to feed plant-based diets.
• Pet food production is a significant source of CO2 emissions and water usage, and meat-based products are far worse than plant-based ones.
• There is increasing competition for the same basic ingredients, for their use in pet foods, and human foods.
• Most pet owners are strongly interested in animal welfare, although few recognise the moral inconsistency in their concern for cuddly furry animals, and those that are farmed to produce the by-product that goes into their food. However, the concern for the welfare of food-producing animals is growing.

Making a complete and balanced diet for a cat without using animal products is possible, but difficult, and requires special care. Cats cannot obtain all the essential nutrients they require from plants. As one example, they need pre-formed vitamin A, as they cannot synthesise it from beta-carotene found in carrots, unlike dogs and humans. Thus, for a plant-based diet to contain all the essential nutrients, it needs to be supplemented with some essential nutrients not found in plants (e.g. vitamin A, taurine, and the fatty acid arachidonic acid). However, there are sound and growing reasons to make plant-based pet foods, but it is difficult, and will result in serious deficiency if not done properly.

The introduction of the study by Knight et al, makes the case reasonably well for vegan pet foods. They also make the point that the ultimate, and perhaps only way to judge a food as being good, is by seeing whether animals remain healthy when eating it. The proof of the pudding literally is in its eating. However, it is very thin evidence of adequacy of a commercial diet to simply ask owners whether they believe their pet’s diet is leading to health or disease.

The study analysed the answers of cat owners using an online survey. Respondents knew the purpose of the study before answering the survey, and therefore there is very likely to be a selection bias towards vegan pet owners. The proportion of pet owners that responded that were vegan is far greater (26%) than has been found in other studies of pet owners (6%, Dodd et al 2019), and that suggests a selection bias within pet owners.

The authors aimed to look for associations between the diet the cats were fed, and how healthy they were. Their method for establishing health was to ask owners to report the presence of disease based on their recall of their veterinarian’s assessment, or their own assessment. This is an invalid and highly unreliable way of establishing the presence or absence of disease. In addition, it is likely that owners who believe that their cat’s health is attributable to their diet are more likely to report health, and discount disease. That is likely to be the case for vegan pet owners.

Despite the invalid, unreliable, and biased method of defining cats as healthy or diseased, the authors found no meaningful evidence of an association between diet and health status of cats in this study. The authors’ conclusion that there was a trend towards improved health and the feeding of vegan diets is true, but is likely to be a) the result of respondent bias, and b) not biologically meaningful.

In summary – there are important and growing reasons for considering vegan food for cats (and dogs). However, because cats require nutrients not supplied by plants, vegan pet foods need to be very carefully supplemented, and manufactured, otherwise serious disease can result. The study by Knight et al did not, and could not, detect any meaningful relationship between feeding vegan diets and cats.

As our environment and food ability changes, it is important to investigate alternative options for ourselves and our animals. Currently there is limited information on the safety of alternative diets for cats, who struggle to meet their nutritional needs without a high percentage of meat in their diet. While some studies show support for a supplemented alternative diet, more research is needed to truly evaluate safety. Without adequate supplementation of nutrients such as taurine, cats may suffer from serious health conditions such as liver and heart problems.

Cat studies are prone to methodology issues due to a cat's ability to come and go as they please. It is likely that some of the 'vegan' cats included in this study may actually be supplementing their diet outside the home. And, as the authors themselves acknowledge, this particular study is survey based and, because of this, it is likely to be prone to participant bias and highly limited in its ability to evaluate health outcomes for cats. I would caution that just as you would not base your own diet on a survey of other people, it's best not to base your cat's diet on the results of this survey. As always, it's best to consult a veterinarian if you are concerned about your cat's diet.

This study delves into the controversial topic of cats being fed vegan diets, a subject that has long raised eyebrows among veterinarians. Traditionally, it's been believed that cats require meat in their diets due to their unique digestive systems. Early research supported this notion, highlighting serious health issues in cats fed plant-based diets.

This latest study challenges these preconceived notions. It found no greater evidence of poor health in cats following a vegan diet, and even suggests some potential benefits; reduced visits to the vet, and fewer medications. It's worth noting that these positive trends didn't always reach statistical significance, so larger studies might be necessary for conclusive results.

But, the study relied on surveys, which are subjective and can be prone to bias. For instance, vegetarian or vegan cat guardians were over-represented. This group may view these diets more favourably for their pets. Additionally, the duration of time the cats had been on these diets remains unclear, and it is known that deficiencies do take several months to develop. In an ideal world, scientists would conduct clinical trials involving a large cat population, directly measuring health through veterinary exams and lab tests.

Nevertheless, this study adds to a growing body of evidence suggesting that vegan diets for cats might not be as harmful as once believed. It challenges conventional wisdom and prompts further research into the matter.