Two years ago, a study was published that claimed nutritionally sound vegan diets are "the healthiest and least hazardous dietary choice for dogs".
Authors
Alexander German
Professor of Small Animal Medicine, University of Liverpool
Richard Barrett-Jolley
Senior Lecturer covering Veterinary Neuroscience and Neuropharmacology, University of Liverpool
We recently published a study challenging those findings. Based on our analysis of the data the original study used, we argue the association between diet and dog health (or more accurately, the owner's opinion of their dog's health) is minimal at best.
To understand why we came to a different conclusion, you need to understand how previous research on vegan dog food has been conducted and why scientists have different views on the subject.
To date, there are several published studies about the health effects of vegan dog food. Some are experimental cohort studies, where various health metrics are monitored while dogs are fed a vegan diet.
The longest was a 12-month study published in 2024, where 15 dogs ate dry dog food made from plant-based ingredients. All dogs remained healthy and there were no obvious adverse effects. However, since there was no control diet group, we cannot assume that means a plant-based diet is superior to a conventional one.
Some published studies do claim superior health for dogs fed vegan food versus other food types. However, these studies based their findings on information from owner surveys. The results from such studies rely on owner recollections and perceptions. You are studying owners' beliefs about how healthy their dog is rather than their actual health.
The largest of these surveys, published in 2022, gathered data from over 2,000 dog owners. It included information both about the owners and their dogs, including of course the type of food the dogs were fed.
Owners were asked to recall details of their dogs' veterinary care (such as number of veterinary visits and medication) and to report how healthy they believed their dog to be. The results of this study suggested that dogs fed a vegan diet appeared to fare better than those fed a conventional diet.
However, the statistical analyses did not explore the effect of confounding factors such as the age or breed of the dog or characteristics of the owners.
What does the new study contribute?
We conducted further analysis on the data from the original study, using different statistical techniques, effectively creating models to explain the data. We tested the effects of other owner and dog variables, as well as dog and owner diet.
For example, we looked at the owner's age, sex and education status, and the dog's sex, breed, age and whether they were neutered. Some statistical models also included veterinary care variables.
We found owner opinions of dog health were most strongly associated with the age of the dog: owners of younger dogs reported them to be in better health. Other variables (such as owner age, owner education and breed size) also featured in our analysis. For example, we found younger owners reported their dogs to be in better health.
Models that explained the data best of all included veterinary care variables. For example, visiting the vet more was associated with poorer owner-reported health. However, the association between vegan dog food and owner-reported health was minimal in all our models, whether or not we included the veterinary care variables. Once you take other variables into account, the effect of vegan dog food disappears.
So, why did the original study suggest a positive effect for vegan diets?
We can't be sure but it was something we looked into. One possibility is that the survey population was unusual with many more vegan dogs than expected - 13% compared with about 1% in the general population. We also found almost all the owners that fed their dog vegan food consumed either a vegan or a vegetarian diet themselves.
This is concerning given the study findings relied on owner reports of dog health. Such recollections and responses might be influenced consciously or unconsciously by owner beliefs. If you believe that a vegan diet is best it might have an unconscious effect on perception of your dog's health.
What does this mean?
You cannot draw a firm conclusion about what diet type is actually best for dogs from our findings. However, notwithstanding the limitations of using owner reports, there is no meaningful association between feeding vegan food and dog health. Instead, other variables are likely to be far more important.
Plus, most commercial vegan dog foods are formulated in the same way as conventional diets. Apart from only using plant-based raw materials, such vegan dog food is made by the same manufacturing processes. Many ingredients are also the same. Given such similarities, it would be surprising for one diet to give a markedly superior health on effect.
Ultimately, the most important thing for dog health is for the diet to be formulated correctly so that it meets all essential nutrient needs, according to evidence-based guidelines.
From the data published so far, no major health concerns have been identified for feeding vegan diets to dogs. However, the evidence does not suggest that there is any meaningful health benefit either.
Alexander German's academic position at the University of Liverpool is financially-supported by Royal Canin. He has also received research funding from the same company for projects unrelated to the current study. Finally, he has received financial remuneration and gifts for providing educational material, lecturing and consultancy work, again unrelated to the current study.
Richard Barrett-Jolley has received funding from UKRI and PetPlan. He is also currently Chair of the BBSRC funding panel "Committee A".
