Dilated Cardiomyopathy and Grain-Free Diets – The Saga Continues

Over the last five years, I have been writing and talking about the uptick in Dilated
Cardiomyopathy (DCM) in dogs. Some veterinarians, with no scientific studies to back up their claims, asserted that “boutique,” grain-free diets were to blame. The Food and Drug Administration (FDA) became involved, several universities have published studies, and research is still ongoing. This blog provides an update on the research and where the pet food industry and veterinarians stand on the issue.

Dr. Judy's Heart Health Resources

What is Dilated Cardiomyopathy?

Dilated Cardiomyopathy (DCM) is a common heart disease for dogs, second only to valvular heart disease. DCM is a condition in which the heart muscle becomes thin and ineffective at pumping blood, resulting in a very enlarged or dilated heart. Historically, DCM has been considered an inherited disease, found commonly in breeds such as Great Danes, Dobermans, Boxers, Irish Wolfhounds, Cocker Spaniels, and Newfoundlands (and now Golden Retrievers).

Symptoms include panting, lethargy, coughing, lack of appetite, bloated abdomen, and collapse. Unfortunately, all these signs often occur late in the progression of the disease. Diagnosis is made using electrocardiograms, radiographs, and echocardiography. 

Why are grain-free diets thought to be the culprit?

In 2018, veterinarians noticed an increasing number of dogs showing signs of DCM that were not breeds traditionally known to be at risk. In many of these cases, low taurine levels were found. Theories began popping up…is the problem low taurine? Low taurine absorption? Interference with taurine production?

Taurine is an amino acid found in meat that is important for normal functioning of heart muscle. In July 2018, the Food and Drug Administration (FDA) began their investigation. They worked in partnership with the Pet Food Institute, a lobbying group. Its members are people in the pet food industry, representing corporations like Mars, Nestle-Purina, Smucker’s, and Royal Canin. (Can you say, “conflict of interest?”) 

The FDA found 16 dog food manufacturers that had ten or more cases of DCM associated with their food. More than 90% of the diets were “grain-free” and 93% of the diets contained peas or lentils. This supposition was quickly communicated as fact, and veterinarians began advising clients to stop feeding grain-free diets and switch to a product with grains. But why? Since grains do not contain taurine, feeding grain is not the solution to the problem. Unfortunately, the veterinary community has bought into this rhetoric, often recommending a return to poor quality, grain-filled, low-meat diets for dogs.

Other theories….
On June 27, 2019, the FDA released an updated list of dogs affected by DCM. Of the 305 dogs listed, 73% were breeds with known genetic predisposition for DCM. Also, 61% of the dogs had other diseases which may have contributed to cardiac disease, including hypothyroidism, Lyme disease, and mitral valve degeneration. It is impossible to implicate specific types of dog food as being a causative factor when the data is already skewed. Furthermore, when the FDA report is broken down into which pet food manufacturers made the called-out diets, 49% of the brands listed were made by one of the six largest pet food manufacturers in North America. Despite this fact, veterinarians and the FDA incriminated smaller pet food manufacturers, resulting in huge losses in revenue and jobs for many of those companies.

In 2020, a review of the current literature (1) revealed faults within DCM studies in dogs, including sampling bias, inconsistencies in sampling parameters, too many variables, and lack of complete data for case studies on DCM and known genetic predisposition in certain dog breeds. Small sample sizes and overrepresentation of breeds are commonplace in recent DCM studies.

In 2021, Tufts University and fellow researchers published a study (2) comparing diets associated with DCM and diets not associated with DCM. They found that the inclusion of peas represented the greatest difference between the two diets. The results further indicated that peas were also associated with higher and lower concentrations of certain compounds compared to the diets not associated with DCM. Unfortunately, the relationship between these compounds and DCM is unknown, and future research will be required.

In 2023, two studies with contradictory findings were published. The first study (3) concluded that changing from a “nontraditional” diet (one containing legumes and potatoes) to a “traditional” one improved survival time in 91 dogs of breeds that do not have a genetic predisposition to DCM. In another study (4) , funded by Champion Pet Foods, the results stated that legumes and potatoes may not be responsible. This study tracked Siberian Huskies eating 45% of whole “pulse ingredients” (the category of plants that includes peas, lentils, chickpeas, and dry beans) in a grain-free diet showed no indications of DCM-like heart issues over the course of the study. While Siberian Huskies do not have a genetic predisposition to DCM, the study lasted only 20 weeks. In these studies, “traditional” diets are “big pet food kibble,” loaded with “meal” products, GMO grains like corn, synthetic vitamins, preservatives, and other potentially dangerous additives. While this food may prevent DCM, they can create a myriad of other health problems.

…but no conclusions!

From 2021 to 2022 sales of grain-free dog foods fell by $60 million. Meanwhile, grain-inclusive sales spiked in 2019 and rose by $700 million from 2020 to 2021. On February 6th, 2023, a class action lawsuit was filed against Hill's Pet Food, , the Morris Animal Foundation, the Mark Morris Institute, Dr. Lisa Freeman (Tufts University), Dr. Joshua Stern (UC Davis), and Dr. Darcy Adin (Florida) and others claiming all were involved in "an egregious, wide-ranging, and damaging campaign of coordinated, for-profit, faux-scientific misinformation by a large corporation" to make veterinarians and pet owners (falsely - per the lawsuit) believe grain-free pet foods were dangerous, linked to canine heart disease."

Hill's Pet Food has close ties with the veterinary community, due in part to funding of teaching positions at veterinary colleges. The lawsuit provides detail after detail to how the Defendants allegedly fabricated the entire grain-free pet food link to canine heart disease scheme.

“Primary” DCM is the term used to describe the diagnosis in dogs genetically prone to the disease. “Secondary” DCM is the term used to describe diet-related diagnoses in breeds not traditionally prone to DCM. Researchers still don’t know exactly what is causing secondary DCM, but they’ve made progress. At first, grain-free diets were blamed, but further investigation revealed some grain-free diets seem to have no ill effects. More often, the affected dogs have been eating commercial grain-free diets that contain pulses. Peas are the most-implicated pulse, although this could simply be because they are also the most used. Soybeans, a common ingredient in dog food, have not been associated with secondary DCM. It’s possible that potatoes and sweet potatoes may be involved, but they were in fewer of the grain-free diets evaluated. Could the disease be caused because the protein quality is poor or are the legumes and potatoes somehow interfere with the uptake and manufacturing of taurine within the body? The exact mechanism for heart failure and the true relationship to grain-free food is unknown and is all speculation at this point.

In the meantime…
The AKC Canine Health Foundation (CHF) continues to fund research into this perplexing problem, with CHF-funded studies ongoing at several institutions. One CHF-funded study has partnered with investigators at the University of Florida, Tufts University, the University of Wisconsin-Madison, and the University of California, Davis, to screen for DCM in a large population of dogs with no clinical signs of heart disease, focusing specifically on Whippets, Golden Retrievers, Doberman Pinschers, and Miniature Schnauzers. They are comparing ultrasound findings, plus concentrations of blood biomarkers and taurine, and they’re recording each dog’s diet history. The study began in 2019 and will end in March 2024.


Stay tuned…

What is needed are independent labs and scientists studying the problem. In the end, it comes down to funding for research. Studies involving multiple breeds and larger sample groups are warranted to better understand if relationships exist between potential etiologies (such as diet) and the development of DCM for the overall dog population. As of right now, I personally believe the lawsuit will prove that this was a huge hoax perpetrated by a large group of individuals.

Dr. Judy's Heart Health Resources

1 https://academic.oup.com/jas/article/98/6/skaa155/5857674?searchresult=1&login=false
2 https:// https://www.nature.com/articles/s41598-021-94464-2
3 https://avmajournals.avma.org/view/journals/javma/261/7/javma.23.01.0025.xml
4 https://www.sciencedirect.com/science/article/pii/S0022316623355007?via%3Dihub

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