When we asked Elizabeth Colleran, former president of the American Association of Feline Practitioners and the owner of two West coast veterinary clinics focused on cats, whether cats can be fed vegetarian cat food, before even finishing the question she let loose with a disdainful sigh. "No," she answered flatly. Bruce Kornreich, of Cornell University's Feline Health Center, was a little more measured. "It is...controversial," he told me.
The impulse to feed our cats vegetarian or vegan diets is one to which Colleran is sympathetic. When you want to eat carefully -- whether it involves becoming a vegan or maybe just a good mindful locavore -- it's frustrating to then have to change approaches just for your cat. But making your cat go vegetarian, says Colleran, is not the answer. "I understand why people want to be vegetarians or vegans but to impose that on an obligate carnivore is just asking for nutritional problems," says Colleran.
Meat contains complete proteins that evolution has primed cats to digest. When shifting to a vegetarian or vegan diet, you'll have to supplement that with synthetics: synthetic taurine, methionine, cysteine, omega fatty acids, the list goes on. Some of those will be chemically identical to non-synthetic versions; synthetic taurine, for example, is usually added to meat-based cat foods and has been proven to serve its required purpose. But some may differ. Does methionene and cysteine have to be absorbed in tandem? Does a cat's liver metabolize an omega-3 fatty acid from an avocado the same way it does one from fish oil? We don't know. No conclusive independent long-term studies on vegetarian cat food have been completed. And when we're dealing with something as potentially dangerous as removing meat from an obligate carnivore's diet, we'd prefer to look at some numbers to make sure this won't cause diabetes or heart defects or cancer in five years.