Dog owners care deeply about their pets; and providing them a healthy diet is of utmost importance to millions of Americans. Indeed, a trip down the pet food aisle reveals an overwhelming display of dog foods—a far cry from the limited offerings I remember feeding my childhood dogs. Over the past 20 years, many dog owners switched to grain-free diets; by 2019, grain-free dry dog food comprised approximately 40 percent of all kibble sales.
Which is why I was surprised to hear of the suspicion that grain-free dog foods might cause some cases of dilated cardiomyopathy (DCM), a disease of the heart muscle resulting in decreased pumping, arrhythmias, and heart failure. As a veterinary cardiologist, DCM is one of the worst diagnoses you can give a dog, as there is usually no cure, and progression occurs rapidly. But, nutritional DCM—in which the dog eats a diet that is not complete and balanced and lacks important nutrients—can be partially reversed with proper diet change and nutritional supplementation. The thought that complete and balanced grain-free diets might cause DCM made me hopeful that I might sometimes reverse the death sentence that I diagnosed in about 5 percent of patients annually.
Over time, however, I did not appreciate improvements in patients with idiopathic DCM, despite diet changes and nutritional supplementation. Turning to the literature for answers, I found that while many articles discuss the link between DCM and grain-free diets, most, like this editorial, are opinion pieces—meaning that they did not undergo the stringent peer-review process necessary to ensure that the study is scientifically sound. Other articles that are peer-reviewed still lack sufficient data to conclude that grain-free diets cause DCM.
While numerous anecdotal reports of dogs eating grain-free diets developing DCM were circulating, my colleagues and I at BSM Partners asked a critical question: How many dogs are actually diagnosed with DCM annually, and is this number increasing, considering the huge rise in popularity of grain-free dog foods?
In collaboration with Dr. Stacey Leach, chief cardiologist at the University of Missouri Veterinary Health Center, and with the assistance of a group of veterinary cardiologists across the US, we collected data on 68,000 dogs from 14 cardiology services across the past 20 years. We also assembled historical sales data regarding grain-free dog food. This retrospective study was submitted for peer review, and the current manuscript can be found here.
We hypothesized that if grain-free diets were a significant cause of canine DCM, an increasing trend in DCM would follow the rising sales of grain-free products over time. However, nationally, our analysis did not support a significant change in DCM incidence over time, nor a correlation with grain-free pet food sales. Specifically, the average overall incidence rate of DCM among cardiologists from 2000 to 2019 hovered around 3.83 percent; while grain-free pet food sales increased by 500 percent from 2011 to 2019.
While these data do not support a national epidemic of grain-free diets inducing DCM, surveys of this sort do not always identify smaller cohorts of animals affected by the variables investigated. Cardiologists reporting dogs with partial or complete recovery from DCM after diet change and taurine/carnitine supplementation are compelling; as I mentioned, spontaneous recovery from DCM is uncommon. These reports may represent individuals within the population with specific nutritional requirements not met in certain diets. Dogs, like humans, are individuals with sometimes very particular nutritional needs.
There is more than one explanation for why some dogs recover after such a devastating diagnosis. Importantly, recovery from DCM does not only occur in cases of nutritional deficiency reversed with diet change; but also, in dogs with myocarditis (infection or inflammation of the heart muscle). Indeed, cardiac troponin I (cTnI)—a measurement of cardiac cell death, and acute myocarditis—was severely elevated in some dogs with DCM that recovered after diet change. Since cTnI is not normally severely elevated in dogs with nutritional DCM, myocarditis must be considered as a differential etiology in dogs with DCM that improve over time.
With many questions remaining, we at BSM Partners are excited for the discoveries we will glean through further research efforts. Our largest study, focusing on the effects of different diets and amino acid metabolism, is underway and will conclude in early 2021. Further research considering neonatal metabolism and breed-specific nutritional requirements were also initiated this fall. We encourage others—pet owners, researchers, veterinarians and those in the pet food industry—to aid us in our goal of improving canine cardiac health through nutrition.