Christopher Lea, a veterinary-medicine professor and a director of the Auburn University Veterinary Clinic, says that once people think they’re doing right by their pets, even a veterinarian can have a hard time persuading them to use a type of food they’re confident is unhealthy. “One thing you’ll learn is that people are very passionate about their pets’ diets,” Lea says. Sometimes, controlling a dog’s diet can turn into an opportunity to exercise a person’s own food anxieties: You may crave white bread or soda made with corn syrup, but it’s relatively easy to enforce a strict diet on a dog that can’t go buy its own kibble.

Just as it does with human diets, misinformation can turn into popular belief with disconcerting ease. People with the resources to buy specialized food and health products, both for their pets and themselves, create a demand that brands fill with expensive specialty goods. That high-end market positioning tends to be self-reinforcing in America, where expense and rarity are seen as signifiers of high quality.

After a while, most consumers won’t know the origin of the belief that’s motivating their purchases—in this case, that dogs shouldn’t eat any grains. Instead, they see that all the fanciest dog food is grain-free, and that the people they know who are really into their pets buy that food, and the righteous choice feels clear, if they can afford it. Before I heard about the FDA warning, I had never thought much about why I feel like I have to feed my 12-pound Chihuahua $100-a-month grain-free food, other than that it seems fancy, and Midge is my fancy girl.

The FDA stopped short of recommending that consumers switch their pets off the grain-free foods. “Because we have not yet determined the nature of this potential link [between grain-free dog food and DCM], we continue to encourage consumers to work closely with their veterinarians, who may consult a board-certified veterinary nutritionist, to select the best diet for their pets’ needs,” said a spokesperson for the FDA in an emailed statement.

Lippman agrees that the FDA findings are still early and inconclusive. “We don’t know if it’s the fact that the diets are grain free, or if it’s the fact that in these grain-free diets, they seem to substitute for the grains with a lot of legumes, like lentils and peas” that might be causing the heart problems, she explains. Still, she thinks it’s better to be safe. “Even though I think it’s uncommon and unlikely to happen to your dog, it’s so unnecessary to be feeding grain-free,” she cautions. “DCM is just not a disease you want to mess with, and as a pet parent, to think that you could have caused it, even inadvertently, is really devastating.”

Lea also sees no reason to stick with grain-free food. “I don’t feed grain-free diets to my pets, and I’d certainly be cautious after what I’ve read and what I’ve seen from our cardiologist,” he says. But he worries that even scientifically demonstrated risk may not be enough to sway some people. “I’ve been doing this for 20 years, and some people just have very passionate feelings about grains.”

* This article previously mischaracterized how the body responds to gluten in celiac disease.