Q: Can My Cat Go Vegetarian Or Vegan?

Answer: No. (At least not yet, anyway)

In 2005, responding to a study that found two popular vegan cat foods to be nutritionally deficient, federal veterinary nutrition consultant David Dzanis wrote, "a vegan diet for cats is at least theoretically possible." The real problem with vegetarian cat food is not that it can't be done, it's that it is not natural. Unnatural doesn't mean bad, but it does mean tremendously difficult. And given the state of scientific testing of vegan and vegetarian cat food, none of the experts we spoke to would recommend shifting away from meat.

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.

You might ask: dogs can go vegetarian without much of a problem. Why not cats?

Cats are among the pickiest eaters on the planet; they require certain proteins and compounds found in animal flesh to survive. Their digestion systems are not like ours (or dogs', for that matter); ours are fairly flexible, enabling our livers to synthesize essential nutrients from plant proteins. "Cats can't do that with vegetable sources," says Colleran. Kornreich concurs: "Certainly cats have problems producing essential amino acids" from non-animal materials, he told me.

The one proper study on this topic, from 2006, appeared in the Journal of the American Veterinary Medical Association, and measured the health (mostly via questionnaire) of 34 cats fed a vegan or vegetarian diet for at least one year, and 52 cats fed a conventional diet for at least one year. Seventeen of the vegetarian or vegan cats were given a physical. Three of those were found to have low taurine levels. (Taurine deficiencies, according to that study, can cause a weak heart that has trouble pumping blood, and weak eyesight.) Makers of vegetarian cat food usually include taurine supplements, but these cats tested low anyway. Another problem: 35 percent of the cats surveyed were outdoor cats, and could have been supplementing their vegetarian home diet by hunting outside. (The three cats that tested low were exclusively indoor cats, fed only vegetarian food.) And, note the authors of the study, no research has been done into the long-term effects of a vegetarian feline diet.

Many cats have gone vegetarian and survived. Evolution Diet, which makes vegetarian cat food, claims cats fed its food live longer and healthier lives than those fed conventional food. That's possible -- but the quality of conventional food is a pretty low bar. Most conventional dry cat food has a large percentage of carbohydrates, which are also not ideal for a feline digestive system. (Meanwhile, vegetarian and vegan cat foods often insist they meet the requirements set by the Association of American Feed Control Officials, but the AAFCO is a voluntary organization with no regulatory powers.)

Can dogs go vegetarian or vegan? Read our answer here.

Photo by Suzi Jane