Are cats on vegan food less likely to be overweight? What an Australian survey of 1,305 owners really showed and what vets say

What was published

On 23 October 2026 the scientific journal Frontiers in Animal Science published a paper on how a vegan diet affects cats' weight. Its lead author is Andrew Knight, adjunct professor at Griffith University and associate professor at Murdoch University's veterinary school in Australia. The researchers analysed responses from the owners of 1,305 cats: 127 were fed a vegan diet and 1,178 a conventional meat-based diet. Knight is known as an advocate of plant-based diets for animals and has previously published similar surveys on the health of dogs and cats on vegan diets. This work is widely debated, and many vets criticise it for relying on owners' opinions rather than examinations.

According to the owners, a vet had recorded overweight in 4 of the 127 cats on vegan food (3.1%) and in 48 of the 1,178 cats on meat-based food (4.1%). After adjusting for age, sex, neutering, activity and feeding method, the odds of being overweight were 34% lower for cats on a vegan diet.

What the survey actually showed

"34% lower" sounds impressive, but what matters is what lies behind it. The difference between the groups was not statistically significant. The confidence interval — the range in which the true value most likely lies — was very wide: it is consistent with both lower and higher odds of being overweight for cats on vegan food. Put simply, with this number of cats the difference could be down to chance.

The researchers also wanted to compare four other weight-related conditions, but not a single owner in the vegan group reported them, so the effect of diet on them could not be assessed.

This study doesn't allow us to conclude that a vegan diet definitely protects cats from becoming overweight, but we did see a consistent pattern that is worth investigating further.

Andrew Knight, lead author of the study

Why the findings should be read with caution

The study has serious limitations, which the authors themselves point out:

• owner-reported data. The scientists did not examine the cats or check what they were actually being fed;
• a small vegan group. 127 cats and only 4 cases of overweight are too few for reliable conclusions;
• diet composition wasn't analysed. It is not known how balanced the food the cats ate was;
• it doesn't prove cause. Owners who choose vegan food may approach their pet's diet and weight differently in general;
• no data on long-term health. The survey doesn't answer whether such a diet is adequate for a cat over its whole life.

Interestingly, most of the cats on vegan food ate mainly dry food that was available to them all day — a feeding method that is usually linked to a higher risk of obesity, not a lower one.

The authors believe the next step should be a large study in which scientists themselves measure what and how much cats eat and what condition they are in.

Cats are obligate carnivores

Vets point out that cats are obligate carnivores. Their bodies are adapted to a diet of animal-based food, and there are some substances a cat cannot make in sufficient amounts itself. The main example is taurine: without it, cats develop heart muscle disease and retinal degeneration that leads to blindness. Cats also need preformed vitamin A, which is found only in animal-based foods, and particular fatty acids. Another important substance is the amino acid arginine: if it is lacking, a cat can develop dangerous ammonia poisoning after just one meal. That is why a cat's diet cannot be put together "the human way", however healthy it may seem.

Modern plant-based cat foods are supplemented with these substances synthetically. But how well such foods suit a cat over many years has been little studied so far.

What veterinary organisations say

The British Veterinary Association does not currently recommend feeding cats vegetarian or vegan diets. Vets advise discussing any change to a cat's diet with your vet and making sure the food is complete and suited to the animal's life stage. Knight himself also advises owners who do choose vegan food to use only commercial diets with the right supplements that provide all the necessary nutrients.

Overweight in cats is a real problem

Although the study did not prove that vegan food is beneficial, the issue it raises is genuinely important. According to veterinary studies, between 30% and 60% of cats are overweight or obese. Extra weight is not a cosmetic problem: it is linked to arthritis, diabetes and urinary tract disease and reduces a cat's quality of life. An obese cat moves less, grooms less well, copes less well with anaesthesia and on average lives a shorter life.

Why cats put on weight

Most often the reason is simple — the cat takes in more energy than it uses. Contributing factors include:

• food left in the bowl all day, especially dry food;
• an indoor-only life with no chance to run and hunt;
• neutering — afterwards metabolism slows and appetite often increases;
• treats and food from the table "because they asked so nicely";
• boredom — for many cats food becomes their main entertainment.

Age often plays a part too: in middle age, roughly from 5 to 10 years, cats are especially prone to gaining weight, while older cats, by contrast, often lose weight because of illness. So both a sharp gain and sudden weight loss are worth showing to your vet.

How to tell if your cat is too heavy

Vets look not only at the number on the scales but also at body condition, using a special scoring scale. At home you can check like this: in a cat in good shape, the ribs can be felt easily under a thin layer of fat but cannot be seen; from above there is a visible waist behind the ribs; the belly doesn't sag. If you have to search for the ribs and there's no waist, it's time to talk to your vet. It helps to weigh your cat once a month: a change of 200–300 grams is a lot for a cat.

What this means for Europe

Plant-based cat foods are also sold in the UK and Europe. Commercial pet foods are subject to labelling rules: if a food is described as complete, it must meet all of the animal's needs, and manufacturers are guided by the nutritional guidelines of FEDIAF, the European pet food industry federation. Veterinary organisations in Europe, as in the UK, do not recommend switching cats to a meat-free diet without veterinary supervision.

For owners in the UK and Europe, the lesson of the Australian survey is rather this: overweight in cats needs tackling, not by changing the "ideology" of the food, but with the right amount of food, exercise and weight monitoring.

How to help your cat stay a healthy weight

• Measure food. Weigh out the daily ration as your vet recommends rather than guessing.
• Feed in portions several times a day instead of a full bowl for the whole day.
• Add wet food — it is more filling for the same number of calories.
• Play for at least 10–15 minutes twice a day: fishing-rod toys, balls, chasing toys.
• Use puzzle feeders so your cat has to "hunt" for its food.
• Count treats — they are part of the daily allowance.
• Lose weight slowly. Crash dieting is dangerous for cats: it can cause serious liver disease. A weight-loss plan should be drawn up by your vet.

If you are still considering plant-based food

If you are considering plant-based food for your cat for ethical reasons, be sure to discuss it with your vet. Choose only complete commercial foods from manufacturers who can back up their composition and research; never put such a diet together yourself. Take your cat for regular check-ups and blood tests, and keep an eye on its heart, eyesight and coat. At the slightest change in your cat's wellbeing, it's worth going back to a proven diet. Be especially careful with kittens, pregnant and nursing cats, and cats with kidney, heart or urinary tract disease: for them, dietary mistakes are most dangerous.

What happens next

The authors themselves admit that their survey is only a starting point for further research. To understand how plant-based foods affect cats' health, large studies are needed in which the animals are examined and their diet precisely recorded. Until then the veterinary consensus remains the same: a cat needs a complete, balanced food in the right amount — and it is usually the amount, not the "type" of food, that solves a weight problem. If your cat needs to lose weight, start with a visit to your vet: they will assess body condition, rule out disease, choose a food and draw up a plan so your cat loses weight safely — usually no more than 1–2% of body weight a week.