Bramble Heritage, of Somerset, England, lived to the age of 175. According to her biographer, at the time of her death she was recognized by Guinness World Records as “the world’s oldest bitch.” Bramble, to clarify, was a dog—a collie. The average collie life span (in human years) is 14; Bramble outlasted that estimate by over a decade. The secret to her longevity? Her human caretaker, Anne Heritage, credits Bramble’s vegan diet. For 25 years, Bramble dined on brown rice, lentils, textured vegetable protein, herbs, and yeast extract.

Since her death in the early aughts, more and more pets have followed in Bramble’s pawprints. Their humans are almost always, like Anne Heritage, vegans themselves. Unlike Heritage, they have an industry that’s sprung up to support them. Heritage made Bramble’s meals at home; these days, dog owners have their pick of vegan dog food: Wild Earth, V-dog, Natural Balance, Nature’s Recipe, Evolution, Halo. It’s not just dogs. From cats and ferrets to birds and snakes, traditionally meat-eating animals of every stripe are being made to go vegan, too.

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For their owners, Bramble is proof of their rightness, a folk hero of the movement, invoked whenever they’re accused of mistreating their canine (and otherwise) companions. This happens, as you might imagine, quite a lot. For every Bramble, there’s a story of a vegan kitty wasting away on a diet of rice milk, potatoes, and pasta. When the ethos of eating meets the pathos of puppies, so many tears flow. What there’s considerably less of, though, is science.

Vets will often recommend meat-free diets for dogs and cats with digestive issues, but beyond that, it's unclear how healthy—or unhealthy—veganism is for animals. “There really isn’t a lot of research on this,” says Sarah Dodd, a veterinarian who studies plant-based pet diets. The majority of commercial vegan pet foods don’t meet the Association of American Feed Control Officials' (low) minimum standards for being labeled as nutritionally adequate.

Dodd knows how confusing this can be for the generally well meaning pet-owning public, beset as it’s lately been by pet-care fake news. “I joined a lot of groups about pet nutrition and could spend all day, every day, correcting the misinformation,” she says. “Being a Facebook vet is a full-time job.” And no, she adds, by way of example: Coconut oil and turmeric won’t fix your dog’s broken leg.

The trend of food-conscious humans extending their morality to animals who don’t know the difference seems to date back to the early 2000s, when dog- and cat-care bloggers began raising concerns about feeding pets conventional kibble, often citing the research of a Belgian pet acupuncturist who found that dogs fed processed food didn’t live as long as those fed homemade diets. Indeed, pet food has been found to sometimes contain contaminants, such as trace amounts of heavy metals. Flocking to social media, such as the Facebook groups Dodd mentioned, pet owners debate such things as whether premium pet food is healthier (it’s not) and whether carbs are OK for cats (debatable).

But vegan-pet parents aren’t simply concerned about feeding their animals gluten-free organic. They’re often environmentalists, and producing food for meat-eating pets accounts for between 25 and 30 percent of the environmental impacts associated with meat production. One in four of those climate-changing cows, in other words, is farting for Fido. When Dodd surveyed over 3,600 dog and cat owners online about their pets’ diets, around 2 percent said their pets are vegan—but 35 percent said they’d be open to it.

The line between person and pet blurs. “I’ve been vegan for 16 years,” says Kathryn, whose senior chihuahua, Hobbes, is an “aspiring vegan” Instagram star who eats a blend of vet-prescribed non-vegan diet food and Natural Balance vegan wet food. “That’s the main motivation. Ultimately I just want to give Hobbes the best care and nutrition possible. If that aligns with my ethics, that would be ideal.”