A study published in 2015 in the Journal of the American Veterinary Medical Association that looked at vegetarian commercial pet foods found that of the 24 foods tested, most were not compliant with the minimum labeling standards set by the feed producers’ group. Because some foods aren’t always formulated correctly, Dr. Freeman said, a meat-based diet from a reputable company is the best way to ensure that nutritional gaps are filled.

“If people are doing this because they are under the impression that it’s healthier, that’s just not true,” Dr. Freeman said.

While plant-based diets are known to have health benefits for humans such as reducing the risk of chronic illnesses like heart disease or Type 2 diabetes, pets will not necessarily get the same benefits.

“While dogs and cats get some of the same heart diseases that people do, they are very resistant to coronary artery disease, the main heart disease affecting humans,” Dr. Freeman said. “So the nutritional strategies that are beneficial for preventing heart disease in humans are not useful in dogs and cats.” Since obesity is the main risk factor for diabetes in cats and dogs, she said, maintaining a pet’s ideal body weight with a consistent diet is the key to successful treatment of that disease.

Dr. Michael Roth, a veterinarian in Richmond, Mass., and himself a vegan, said that some dogs have an allergy to common dog food ingredients like beef or dairy and that some may benefit from a vegetarian or vegan formula to help ease skin rashes and other allergy symptoms. He recommends that his clients try a vegetarian formula for 12 weeks to see if it relieves itching and improves the skin and coat. Many owners who see an improvement in their dogs, he said, are reluctant to move their dogs back to a meat-based diet.

“Is the vegan diet the best diet for all dogs out there? I don’t think anyone would say that, just like nobody would claim there was one best diet for all the people on the planet,” Dr. Roth said.

Dogs, like humans, have varying degrees of tolerance for certain foods, he said. He fed his most recent dog, Dawn, a golden retriever, a vegan diet. She lived to age 11 before developing a fatal cancer, about the same age that her brother, Sam, raised on a diet that included raw meats, also died of cancer.