Debbie Turner remembers the shock when a veterinary specialist said her beloved dog, Kanga Lu, had severe heart damage.
For weeks, Kanga had been experiencing odd symptoms, including fatigue, breathing problems and what her local vet assumed were seizures. But now Turner was being told that the Maltese-Chihuahua mix was in late-stage heart failure. The seizures, it turned out, had been fainting spells.
“So I’m sitting with what I thought was a healthy 6-year-old dog that was having minor seizures, and now I find out she might only have three months to live,” said Turner, 66, of Orlando, Florida. “At that point I felt like I was in a bottomless pit with no way out.”
The first question the specialist had asked Turner when she brought in Kanga — whose blood pressure had skyrocketed — was, “Do you feed her grain-free dog food?” The answer was yes.
Turner is one of a growing list of pet owners whose healthy-sounding dog food may have somehow led to a serious heart problem in their pets called dilated cardiomyopathy (DCM).
The Food and Drug Administration last year announced a possible link between the condition, which can cause heart failure, and grain-free pet foods, which replace grains with ingredients like peas, lentils or potatoes.
By April, the agency said that it had received 524 reports of 560 dogs and 14 cats diagnosed with DCM that appeared to be related to diet. In June, the FDA took the unusual step of listing the 16 brands of dog food under investigation.
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It’s still not known exactly how certain pet foods may be damaging pet hearts, but researchers have found some clues. Possible culprits include deficiencies in certain compounds necessary for heart health, as well as diets with exotic ingredients.
In dogs and cats developing DCM, the “walls of the heart become thin, and its ability to pump blood decreases,” said Dr. Bruce Kornreich, a veterinary cardiologist and director of the feline health center at the Veterinary College of Cornell. “If this continues, your pet can end up with chronic heart failure.”
DCM is a known genetic issue for certain large breeds of dogs, including great Danes, German shepherds and Doberman pincers. But when the FDA and veterinarians around the country started to see dogs of all sizes developing this kind of heart damage several years ago, they grew alarmed.
The number of cases of DCM are likely to rise, experts say.
“We continue to see dogs coming into our hospital affected by this problem,” said Dr. Lisa Freeman, a veterinary nutritionist and professor at the Cummings School of Veterinary Medicine at Tufts University. “It’s not going away.”
Unfortunately, Freeman said, the solution is probably not going to be a simple one, and the suspect foods are not just those described as “grain free.” She and others are now investigating a broader class of foods, dubbed “BEG” foods: ones that are made by boutique companies, contain exotic ingredients, or are grain-free.
The FDA echoes Freeman’s concerns about a complex solution.
“At this time, it is not clear what it is about some diets that may be connected to DCM in dogs, but FDA believes it may be multi-factorial,” said Monique Richards, an FDA spokesperson. “There are multiple possible causes of DCM.”
One known cause is deficiency of taurine, an amino acid essential to dog heart health, Richards said.
A 2018 study found that 24 golden retrievers with DCM that had been fed grain-free dog food were deficient in taurine. When the dogs were switched over to a traditional food, 23 saw significant improvement, and nine out of 11 of the dogs that had congestive heart failure improved so much that they no longer needed medications.
But at Freeman’s clinic in Massachusetts, 90 percent of the dogs with DCM have normal taurine levels. That means there are most likely other pathways to heart damage in dogs consuming BEG diets, she said.
It’s possible that something in BEG foods inhibits how the body uses or absorbs amino acids, said Dr. William Tyrrell, a cardiologist at CVCA Cardiac Care for Pets in Virginia. CVCA is currently working with the FDA on their investigation.
In Tyrrell’s practice, dogs that have been treated for DCM and switched from BEG diets to a traditional dog food have improved.
“We don’t see a 100 percent reversal, but some get out of heart failure and many are able to go off diuretics,” Tyrrell said. “That’s not what happens with dogs that have a genetic cause — those dogs ultimately die of their disease.”
A study published this year in the Journal of Veterinary Cardiology backs that up. The study found that 36 dogs diagnosed with DCM and had normal taurine levels improved when they were switched from a grain-free food to a traditional diet. Most of the dogs also received taurine supplements, which the researchers suspect may have sped up the healing process.
Tyrell believes that ultimately researchers will find that the dogs that develop food-related DCM have a genetic predisposition for the disease that wouldn’t become apparent unless they were fed a certain type of food.
One scary fact: While some dogs may take years to develop DCM, in others, the condition can develop quickly.
“The course seems variable,” said Dr. Jennifer Larsen, a professor of clinical nutrition at the University of California, Davis. “We now know that some take only a couple of months. One of the cases in the FDA database was a pretty young puppy.”
Linda Carroll is a regular health contributor to NBC News and Reuters Health. She is coauthor of "The Concussion Crisis: Anatomy of a Silent Epidemic" and "Out of the Clouds: The Unlikely Horseman and the Unwanted Colt Who Conquered the Sport of Kings."