Cats And Dogs Can Digest Plant-Based Food Just Fine
For years, one of the quickest ways to start an argument about veganism has been to mention feeding a dog or cat without animal flesh. Dogs need meat. Cats are carnivores. Plants cannot provide what they need. It is cruel.
End of discussion.
Except science has an inconvenient habit of carrying on after internet arguments have declared a subject settled. A new review of 31 studies has found that nutritionally sound vegan and vegetarian plantbased foods are generally well digested by both dogs and cats, with digestibility broadly comparable to conventional meat-based foods. That does not mean every homemade bowl of lentils is suddenly appropriate for every cat. It does mean one of the most confidently repeated objections to plant-based companion animal food is looking increasingly shaky.
Dogs And Cats Can Digest Plant Proteins
Andrew Knight, a veterinary professor affiliated with several universities, reviewed research examining complete meat-free diets as well as individual plant and fermentation-derived ingredients. Of the 31 studies included, 22 were specific to dogs, two to cats and seven applicable to both species.
Across the 5 studies measuring apparent total tract digestibility of complete vegan or vegetarian diets, digestibility exceeded 80% for dry matter, 85% for organic matter, 80% for crude protein, 89% for fat, 88% for nitrogen-free extract and 86% for energy. Researchers also found dogs and cats could digest proteins derived from soy, other legumes, pulses, grains and microbial fermentation. Were plant ingredients always more digestible than animal ingredients? No.
Sometimes they performed better. Sometimes animal ingredients did. Sometimes there was no significant difference at all. But that is rather different from the claim that dogs and cats cannot properly digest plant protein. Even where individual plant proteins showed lower digestibility for particular nutrients, overall digestibility generally remained high.
One study comparing two vegan dog foods with a chicken-based food found all three highly digestible. Fat digestibility was actually slightly higher in both plant-based foods, while organic matter digestibility was slightly higher in the chicken food. There were no significant differences in dry matter, crude protein or energy digestibility.
Another real-world trial involved 61 companion dogs eating either a plant-based kibble or chicken-based kibble for 12 weeks. Digestibility exceeded 80% for dry matter, 85% for protein and 97% for fat in both groups, with no significant differences between them.
Not exactly the digestive catastrophe we are frequently warned about.
Nutrients Matter More Than Marketing Categories
There is an important distinction. Digestibility is not nutritional completeness. The review itself stresses this. Vitamins, minerals and other nutrients have to be considered separately, and the research focused largely on macronutrients rather than micronutrients. That is why the conclusion is not “feed your cat whatever plants happen to be in the fridge”. It is that nutritionally sound, properly formulated plant-based foods can be well digested. But notice how strangely one-sided this conversation often becomes. Plant-based companion animal foods are expected to prove themselves nutrient by nutrient before some people will even entertain the possibility that they can work. Conventional foods, meanwhile, frequently receive the benefit of the doubt simply because they contain animal flesh. The scientific question is not whether an ingredient sounds suitably carnivorous to us. It is whether the finished food supplies what the animal requires in a form they can use. And the evidence reviewed here challenges the assumption that plant ingredients inherently fail that test.
There are still gaps. Most of the research concerns adult dogs, not puppies, kittens, senior animals or individuals with impaired digestive function. Cat-specific evidence is particularly limited, and more in-home research would be valuable. The review was also not systematic, something the author explicitly acknowledges. Those are reasons for more research. They are not evidence that the existing research says the opposite of what it actually says.
Then There Are The Animals Being Fed To Them
This conversation becomes much bigger once we stop looking only at the animal standing beside the food bowl.
Dogs and cats are estimated to consume around 9% of farmed animals used for food globally, rising to around 20% in the United States. And the environmental cost is substantial.
A separate study examined 31 commercially available dry dog foods in the UK, comparing plant-based, poultry-based, red-meat-based and veterinary renal foods. Plant-based foods had the lowest environmental impact across every category assessed. For every 1,000 calories of food, beef-based diets were estimated to require 102.15 square metres of land. Plant-based diets required 2.73. Beef-based foods produced an estimated 31.47 kilograms of CO₂ equivalent per 1,000 calories. Plant-based foods produced 2.82.
Another review found that ingredients themselves account for around 70% of companion animal food’s carbon impact. Packaging and transport are not the main story here. What goes into the food is. And then there is the comforting idea that conventional companion animal foods merely make use of slaughterhouse “waste”. The environmental review challenges that too. Animal byproducts are commodities with economic value. Other industries buy them. In the figures cited by the researchers, such materials generate around 11% of beef revenue and 7.5% of pork revenue. Calling them waste makes their economic role disappear.
Some lower-quality animal ingredients may also require more animal bodies to provide equivalent nutrition. Estimates cited in the review suggest around 1.4 times more carcasses may be required for dogs and 1.9 times more for cats compared with higher-quality animal flesh. So the ethical question cannot simply be: Is my dog okay?
What about the chickens?
The cows?
The pigs?
The fishes?
Their interests do not disappear because their bodies arrive ground up inside a bag with a smiling Labrador printed on it.
The Debate Has Moved On
None of this proves that every plant-based product is nutritionally sound. It certainly does not prove that every plant-based food is suitable for every dog or cat. But that was never the serious claim. The relevant question is whether appropriately formulated plant-based foods certified by veterinarians can meet companion animals’ needs.
The evidence increasingly suggests they can, particularly for dogs, while the research base for cats continues to develop. At the same time, the environmental advantage appears enormous. We can keep repeating that dogs and cats “need meat” as though saying it confidently enough settles the issue. Or we can ask the more useful question. What nutrients do they actually need, and can we provide those nutrients without breeding and killing billions of other animals to do it?
Increasingly, science is giving us an answer worth listening to.