Cats are carnivores. Every cat owner knows the look a cat gives you when the bowl isn't what it expected. So a headline saying vegan cats might be slimmer was always going to start a fight. Let's look at what the study actually found.
The study
It was published on 8 October 2026 in the journal Frontiers in Animal Science, by Andrew Knight and Jenny Mace. It's based on an online survey of owners, about 1,305 cats that had been on their diet for at least a year. 1,178 ate normal meat-based food. 127 ate vegan food.
Owners reported what their vets had said about their cat's weight and health. The researchers adjusted for age, sex, neutering, activity and feeding habits.
The headline number
Vegan-fed cats had 34% lower odds of being assessed as overweight. Some weight-related problems, like arthritis, showed up only in meat-fed cats: 15 cases there, none among the vegan cats.
Now the small print
And there's a lot of it. Only four vegan-fed cats were overweight. With numbers that small, the real effect could be anything from 82% lower odds to 142% higher. In plain words: the difference was not statistically significant. It might be real. It might be luck.
The raw numbers are also tiny on both sides. Vets called 4.1% of meat-fed cats overweight and 3.1% of vegan-fed ones. Vet studies usually estimate that 30% to 60% of cats are overweight or obese, so this group of owners may not be typical.
The data came from owners, not from medical records. The survey ran in 2020 and recruited through pet groups on social media and Facebook ads; 90% of owners were women and most lived in the UK or Europe. The vegan cats were also younger on average, about 6 years old against 8. And nobody checked what was actually in the food.
Owners and vets didn't always agree, either. Vets rated 94% of meat-fed and 96% of vegan-fed cats as an ideal weight, while owners said 70% and 76%.
One more thing worth knowing: the authors are linked to the Sustainable Pet Food Foundation, and no outside funding was declared.
To their credit, they say all this themselves. "We can't conclude from this study that vegan diets definitely protect cats against becoming overweight," Knight said. The small number of vegan cats means "these results cannot be considered conclusive". They're calling for a bigger study that measures diet and body condition directly.
A twist about feeding
Funny detail: the vegan cats were more likely to eat mostly dry food (79%) and to have food available all day (53% against 36%). Those are habits usually linked to more weight, not less. So either the food made a difference, or these particular cats are just very good at self-control. We've met cats. We have doubts.
What it means for you
Don't change your cat's diet because of a headline. Cats need specific nutrients that come naturally in meat, and any diet change, vegan or not, should be planned with your vet.
If your cat is getting round, the boring fixes come first: measured portions instead of a bowl that's always full, more play, fewer treats. Your cat will complain. Cats complain about everything. It's fine.