Is it safe to feed cats and dogs a vegetarian diet?

After quitting meat for ethical, health or environmental reasons, some pet owners want their pets to join them in a plant-only diet. But is it safe to make our carnivorous felines and omnivorous pups give up meat or animal protein altogether? 

The short answer is, it's a gray area: It's a possibility for some pets, but not all of them. And it's never recommended to switch your pet to a plant-based diet on your own. Plant-based diets are newer to market and the science is still developing. To make sure your pet gets enough of all the essential nutrients you'll likely need a little help. 

Many people who visit Dr. Lindsey Bullen, a North Carolina-based veterinarian and board-certified animal nutritionist, one of about only 100 in the U.S., make this mistake, even though they're often acting with the best intentions. "I think some clients just feel they can do it better," Bullen told Live Science. "But they don't actually know what goes into formulating a diet for their pet." 

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Revamping an animal's diet without expert help is often detrimental to the pet's health. Animal proteins that cats and dogs typically eat have a lot of amino acids in a form that's easy for your pet's body to use — more than what's usually in plant protein. Pets that don't get enough protein can experience weight loss, muscle loss, weakness, poor digestion and even fluid buildup in their chest or abdomen, according to the Cummings Veterinary Medical Center at Tufts University in Massachusetts. 

Cats, in particular, need taurine, an amino acid found in meat protein. In fact, they can't live without it; if taurine is not supplemented properly in a plant-based diet, cats can experience poor neural function, reproductive problems and heart disease, Bullen said. Even the wrong mineral balances in a DIY plant-based pet diet can be a problem. The wrong calcium-to-phosphorus ratio, for instance, can increase the risk of fractures in dogs and cats and also stunt puppy or kitten growth, Bullen said. 

But plant-based pet diets can be done. "Vegetarian [diets] can be done safely in both [cats and dogs]," Bullen said. "Vegan can be done safely in dogs but is very difficult in cats." Felines are obligate carnivores, so a lot of their nutritional needs are tied to meat-specific ingredients. As a result, cats need a lot more additives to make a vegan diet complete and balanced. 

Bullen even prescribes plant-based diets in certain cases, including for pets that have skin or gastrointestinal food allergies to meat products. (Her own dog has both types of allergies and is on a hydrolyzed soy-based diet.)

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If you're planning to switch to a plant-based wet or dry food for your pet, Bullen encouraged consumers to buy from brands that have done digestibility studies, ingredient interaction studies, and feeding trials on their plant-based options. But before you make the leap, it's important to make sure a plant-based diet is a good fit for your animal. An expert, such as a vet or a nutritionist they consult, will first consider the pet's overall well-being, including age, environment and other health issues. If the pet is otherwise healthy, it's likely that a well-formulated plant-based diet could work for them.

If a vegetarian or vegan diet is a safe option, the next step is for a vet or nutritionist to put together a very specific plan. For instance, when Bullen formulates a homemade vegetarian pet diet for a client, she provides a complete list of ingredients, including proportions, explicit cooking guidelines, feeding instructions and monitoring guidelines. She gets specific about every ingredient, including the brand of tofu or the percentage of fat in the cottage cheese. 

Bullen encourages owners to take an active role in their pets' nutrition, but she also warns against anthropomorphizing, or giving human traits to animals. "Dogs and cats are vastly different from the human species," she said. "Your goals [for yourself] are great, but we need to keep the pet happy and healthy." Working with an expert is the safest way to meet your goals and your pets' needs.

Originally published on Live Science.