Denise Cummins Ph.D.

Good Thinking

Why Dogs and Humans, But Not Cats, Can Be Vegans

Dogs and humans can digest starches. Cats and wolves can't.

Posted Jun 10, 2014

They wanted to do what was best for their kitten, and so they fed him the same diet that kept them healthy: A vegan diet.

There was only one problem: Cats are strict carnivores that can get vital nutrients only from animal tissue. That is their place in the food chain: They are predators that live on fresh kill. In the wild, their diet consists primarily of protein and fat, with minimal carbohydrate. Commercial cat food is heavy on carbohydrate, leading to an increase in obesity and diabetes in domestic cats.

But things were much worse for this kitten. After being fed a steady diet of pasta, rice, and potatoes, the kitten became extremely weak and almost unresponsive. The concerned owners rushed him to a veterinary clinic where he received fluids and meat for three days in order to recover.

The veterinarian who treated the cat admonished vegan pet owners to feed their kitten lots of meat or to adopt pets more suited to a vegan diet, such as rabbits and guinea pigs. But she failed to mention another appropriate companion animal for vegans: Dogs.

Dogs Aren't Wolves—And Shouldn't Be Fed That Way

Robert Wayne, a geneticist at the University of California, Los Angeles recently commented, “Every day I get an email from a dog owner who asks, should they feed their dog like a wolf. I think this paper answers that question: no.”

He was referring to a paper recently published in the science journal Nature. A careful analysis of wolf and dog DNA revealed surprising and not so surprising differences. 

The surprising difference was that dogs possess genes for digesting starches while wolves do not.

The research team led by Kerstin Lindblad-Toh, a geneticist at Uppsala University in Sweden, found 36 regions of the genome that set dogs apart from wolves — but are common among dogs of different breeds. Ten of those genes help dogs to digest starches, splitting them into sugars so that they are readily absorbed. Most humans have also have genes that allow starches to be easily digested. According to Lindblad-Toh, this suggests that the rise of farming, beginning around 10,000 years ago, led to the adaptations in both species that allowed both humans and dogs to eat starches.

In fact, in 2002, Bramble, a 25 year old border collie fed a vegan diet, won the Guinness Book of World Records for oldest dog.

What foods will hurt a dog? Some of your favorites: Chocolate, grapes, raisins, avocadoes, bread dough, alcohol, hops (think beer), macadamia nuts, onions, garlic, and the sweetener xylitol (think chewing gum).

The bottom line: Dogs are omnivores who co-evolved with humans to be able to digest carbs. But cats are carnivores. Keep that in mind when feeding your pets.