The cause is not yet known but it hasn’t gone away – Clinical Nutrition Service at Cummings School

Recently, the United States Food and Drug Administration (FDA) issued their fourth update on diet-associated dilated cardiomyopathy (DCM) – this time, in the form of frequently-asked questions about this serious heart disease.  To make sure pet owners have the most accurate and up-to-date information, I thought this would be a good opportunity to write an update on diet-associated DCM since my last update was over a year ago.  While the specific cause is not yet known, we’ve learned a lot since then!

Diet-associated DCM has been devastating both for the affected dogs and their owners. Veterinarians working closely with these patients have been impacted by the distress the diagnosis has caused owners because of the severity of the disease, cost of treatment, and sadness when a beloved dog is sick or dies.  But, in addition, most owners I’ve worked with thought they were feeding their dogs the best food possible, only to find out that the diet may have contributed to their dogs’ heart disease.  While the number of cases may have decreased, it hasn’t gone away.  Cardiologists and other veterinarians dealing directly with these dogs and owners who have lost dogs to this disease know it’s all too real.

The FDA’s latest update

The most recent update from the FDA provided good background information on this ongoing issue, addressing many of the common questions that veterinarians have been getting.  Of most interest to those of us actively engaged in researching or following this issue was the update on the number of reports the FDA has received.  As of July, 2020, more than 1100 dogs with DCM  have been reported to the FDA (and over 20 cats).  In the latest update (with numbers as of November 1, 2022), another 255 dogs with DCM had been reported to the FDA, bringing the total number of dogs with DCM reported to the FDA to 1382.

Some may see the lower number of recent reports as an indication that diet-associated DCM is disappearing, which could be happening due to changing diet formulations or the decreasing popularity of grain-free diets.  However, I see this as another 255 dogs being reported to the FDA (that’s still about one dog every three days).  Not all cases of diet-associated DCM get reported to the FDA.  Diagnosing DCM requires an echocardiogram (ultrasound of the heart) which is not always performed. Reporting a case to the FDA is time-consuming. Veterinarians have become busier since the pandemic and may not always report cases (and, while owners can submit reports, they may not be aware of the importance of doing so).  So, while the lower rate of reports to the FDA might mean that fewer cases are occurring, it might just reflect fewer veterinarians and pet owners reporting DCM cases.

What is clear about diet-associated DCM is the amount of supporting scientific evidence published on this disease since the FDA’s first alert in July 2018. In the 4 ½ years since that alert, 16 peer-reviewed research articles on the topic have been published (see compiled list below).  As a result of the work by many veterinarians and other scientists, more pieces of the puzzle have been added, and we are getting closer to an answer.  This disease provides an excellent opportunity for scientists, industry, and trade organizations to collaborate to understand this current problem and to optimize our pets’ nutrition and health.

DCM has more than one cause (and more than one outcome)

DCM is a serious disease of the heart muscle which causes the heart to beat more weakly and to enlarge.  DCM is the second most common heart disease in dogs but, until recently, when veterinarians referred to DCM, they were usually talking about primary (hereditary) DCM, which is common in certain large- and giant-breed dogs, such as Doberman Pinschers, Great Danes, Irish Wolfhounds, and Boxers.  Primary DCM is presumed to be a hereditary disease although only a few genes associated with DCM in different breeds have been identified so far. Primary DCM is progressive, commonly resulting in congestive heart failure (fluid buildup in the lungs or belly) or irregular heartbeat that can cause dogs to faint or even die suddenly.

However, in addition to primary DCM, dogs can also develop secondary DCM as the result of certain medications, infections, or nutritional causes.  The nutritional causes of secondary DCM can be nutrient deficiencies (such as taurine or vitamin B1 deficiency), but also can be levels of nutrients or other dietary compounds that are too high (such as heavy metal toxicity).  We sometimes see secondary DCM in dogs or cats eating home-prepared diets (unless the recipe was formulated by a Board-Certified Veterinary Nutritionist^® and strictly followed, home-prepared diets are nearly always nutritionally unbalanced and can put animals at risk for secondary DCM).  A unique feature of these secondary forms of DCM is that they can affect any dog breed and are not limited just to those breeds affected by hereditary DCM.  In addition, the hearts of dogs with secondary DCM due to nutritional causes can improve with diet change, something we don’t see in dogs with primary DCM.

The improvement in dogs’ hearts after diet change was one of the features that alerted cardiologists to the current diet-associated DCM problem.  The other was the increase in DCM cases being diagnosed in dog breeds that don’t usually develop DCM.  Multiple studies have now shown improvement in heart size and function in dogs with diet-associated DCM after diet change (and medical treatment to control symptoms), something not seen in dogs with primary DCM.  In addition, dogs with diet-associated DCM can live much longer after diet change than dogs with primary DCM.  However, improvement of the hearts of dogs with diet-associated DCM can take months to years and often is not complete, especially in dogs with severely affected hearts.  And sometimes dogs with this potentially reversible disease die suddenly due to an irregular heartbeat before their hearts have time to improve.

Associated diets – not just grain-free

In addition to these clinical differences in dogs with diet-associated DCM, it was identified early on that these dogs were eating diets with similar properties.  Research has now shown that these diets (often termed “non-traditional diets”) are commonly grain-free commercial dry diets that contain pulses and, to a lesser extent, potatoes or sweet potatoes.  Pulses are peas, lentils, chickpeas, and dry beans.  While pulses are part of the legume family, soy (another legume) has not been associated with this problem.  Some research suggests that peas may be most associated with this form of DCM, but this may just reflect the fact that peas are used more commonly in dog foods compared to other pulses. In 2017, 51% of dry dog foods contained peas, while 23% contained chickpeas, and 14% contained lentils.  So, while pulses – and especially peas – seem to be the most likely culprits, we have a lot more to learn about their effects on dogs eating diets high in these ingredients (for example, concentration in the diet, effects of processing, and effects of different fractions of peas such as whole peas, pea protein, pea fiber, etc).

Many have linked diet-associated DCM with grain-free diets.  In fact, it appears to be more closely associated with diets containing pulses, rather than with the presence or absence of grains in a diet.  In the past, it was primarily grain-free diets that included high levels of pulses and potatoes as ingredients to replace grains, but now some grain-inclusive diets contain pulses and can be associated with DCM as well.  Most dogs with diet-associated DCM have been eating non-traditional diets for over one year (sometimes many years), so DCM does not seem to develop immediately after eating these diets and not every dog that eats these diets develops heart problems.

Spectrum of disease

DCM represents an advanced stage of heart disease, but it appears that the heart starts to get sick long before obvious DCM has developed. In fact, it’s important to note that the FDA’s numbers refer only to dogs with DCM, and not less severe forms of the disease.  In its 2019 update, they stated: “We did not include in these numbers the many general cardiac reports submitted to the FDA that did not have a DCM diagnosis. However, this case information is still valuable, as it may show heart changes that occur before a dog develops symptomatic DCM.”  Studies now suggest that dogs with less severe forms of the disease appear to represent the same disease process – just an earlier stage.  Dogs with less severe stages of the disease have similar improvements in heart size and function after diet change.  In fact, when detected early, dogs with less severe forms appear to have a better response to diet change than dogs with DCM that are having symptoms.

Even in dogs thought to be healthy, researchers have now identified negative effects of non-traditional diets on the heart, including a larger left ventricle (the main pumping chamber of the heart), weaker contraction of the heart, higher levels of a blood marker reflecting damage to the heart muscle, and more dogs with irregular heartbeats.  And while studies of DCM suggest worse effects the longer dogs have been eating non-traditional diets, one study showed that in dogs eating a high pea, plant-based diet, the left ventricle increased in size after only three months.  Therefore, the number of DCM cases reported to the FDA might be just the “tip of the iceberg,” representing only the most severely affected dogs.

Mechanisms

The FDA’s data and the research evidence published thus far supports an association between non-traditional diets and DCM, but the specific cause is not yet known.  A number of nutritional deficiencies can cause DCM, such as thiamine, carnitine, or vitamin E, but deficiencies have not been identified in the published studies.  Taurine deficiency can cause secondary DCM and was one of the first suspected causes of this current problem, but it has not been found in most dogs with diet-associated DCM (except in one study of Golden Retrievers).  However, blood levels of taurine may not be the best indicator of taurine status so more research is needed.

Common toxins and excessive levels of nutrients that can be associated with DCM also have been investigated and have not been identified thus far in the dogs with DCM or in the associated diets.  More unique, high-tech approaches to identifying the cause of this problem are beginning to be published (for example, our recent foodomics and metabolomics studies), and additional research is underway by many researchers.  Thus far, studies suggest that high levels of peas and lentils in the diet seem to be the strongest predictor for development of diet-associated DCM, and numerous compounds are being investigated to help identify the specific cause and mechanism. While the specific cause has been challenging to identify, our current hypothesis is that compounds in these ingredients may have toxic effects on the heart.

Cats

While the majority of cases reported to the FDA have been dogs, more than 20 cats with suspected diet-associated DCM were also reported as of July 2020.  DCM used to be one of the most common heart diseases affecting cats until 1987 when the landmark discovery of the link between taurine deficiency and DCM was made.  However, taurine deficiency as a cause of DCM in cats has become very uncommon since taurine levels in commercial diets were increased.  Just as in dogs, grain-free cat foods and cat foods containing peas and other pulses have become common (in 2017, 46% of dry cat foods contained peas).  Recently, we published a small study of cats with DCM that showed that cats eating high-pulse diets that changed diet lived longer than cats eating high-pulse diets that did not change diet.  Research is ongoing but it is possible that some cats, particularly those eating high-pulse diets for long periods of time, might also develop a secondary diet-associated DCM, similar to what is being seen in dogs.

Diet-associated DCM: Where are we now?

1. The ingredients most likely at the heart of diet-associated DCM are peas and other pulses, although more research is needed on other ingredients. The presence or absence of pulses cannot be predicted based only on the diet’s name or whether the diet contains grains, so the full ingredient list of the product must be reviewed.  If the diet contains pulses (for example, peas, pea protein, lentils, chickpeas, etc) in the top ten ingredients (or multiple pulses anywhere in the ingredient list), it might put some dogs at risk for heart problems.
2. When we diagnose dogs and cats with DCM (or earlier changes, such as reduced contraction of the heart, enlarged heart chambers, or irregular heartbeats), we recommend changing their diet to a reduced sodium diet that does not contain pulses or potatoes/sweet potatoes in conjunction with appropriate medical treatment. However, it is important to work with your veterinarian to determine the best medical and nutritional treatment for each individual pet.
3. If your dog develops DCM, please report it to the FDA to help the ongoing investigation.

Cardiologists continue to diagnose dogs with diet-associated DCM, especially in regions where non-traditional diets are common.  My colleagues and I (and many others) are working hard to solve this challenging and deadly disease affecting dogs which, unfortunately, has not gone away.

Peer-Reviewed Research Studies on Diet-Associated DCM

1. Kaplan JL, Stern JA, Fascetti AJ, et al. Taurine deficiency and dilated cardiomyopathy in golden retrievers fed commercial diets.  PLoS One 2018;13(12): doi: 10.1371/journal.pone. 0209112.
2. Adin D, DeFrancesco TC, Keene B, et al. Echocardiographic phenotype of canine dilated cardiomyopathy differs based on diet type.  J Vet Cardiol 2019;21:1-9.
3. Ontiveros ES, Whelchel BD, Yu J, et al. Development of plasma and whole blood taurine reference ranges and identification of dietary features associated with taurine deficiency and dilated cardiomyopathy in golden retrievers: a prospective, observational study.  PLoS One 2020;15(5): doi: 10.1371/journal.pone.0233206.eCollection 2020.
4. Adin D, Freeman LM, Stepien R, et al. Effect of diet type on circulating taurine concentrations, cardiac biomarkers, and echocardiograms in four dog breeds.  J Vet Intern Med 2021;35:771-779.
5. Freid KJ, Freeman LM, Rush JE, et al. Retrospective study of dilated cardiomyopathy in dogs. J Vet Intern Med 2021;35:58-67.
6. Smith CE, Parnell LD, Lai C-Q, Rush JE, Freeman LM. Investigation of diets associated with dilated cardiomyopathy in dogs using foodomics analysis.  Sci Reports 2021; 11, 15881.
7. Bakke AM, Wood J, Salt C, et al. Responses in randomized groups of healthy, adult Labrador retrievers fed grain-free diets with high legume inclusion for 30 days display commonalities with dogs with suspected dilated cardiomyopathy.  BMC Vet Res 2022;18:157.
8. Cavanaugh SM, Cavanaugh RP, Gilbert GE, et al. Short-term amino acid, clinicopathologic, and echocardiographic findings in healthy dogs fed a commercial plant-based diet.  PLoS One 2021;16(10):e0258044.
9. Freeman L, Rush J, Adin D, et al. Prospective study of dilated cardiomyopathy in dogs eating non-traditional or traditional diets and in dogs with subclinical cardiac abnormalities. J Vet Intern Med 2022;36:451-463.
10. Haimovitz D, Vereb M, Freeman L, et al. Effect of diet change in healthy dogs with subclinical cardiac biomarkers or echocardiographic abnormalities. J Vet Intern Med 2022;36:1057-1065.
11. Karp KI, Freeman LM, Rush JE, et al. Dilated cardiomyopathy in cats: Survey of veterinary cardiologists and retrospective evaluation of a possible association with diet.  J Vet Cardiol 2022; 39: 22-34
12. Quest BW, Leach SB, Garimella S, Konie A, Clark SD. Incidence of canine dilated cardiomyopathy diagnosed at referral institutes and grain-free pet food store sales: A retrospective survey. Front Anim Sci 2022.
13. Walker AL, DeFrancesco TC, Bonagura JD, et al. Association of diet with clinical outcomes in dogs with dilated cardiomyopathy and congestive heart failure. J Vet Cardiol 2022;40:99-109.
14. Adin DB, Haimovitz D, Freeman LM, Rush JE. Untargeted global metabolomic profiling of healthy dogs based on grain-inclusivity of diet and reevaluation after diet change in dogs with subclinical cardiac abnormalities. Am J Vet Res 2022;25: 2460/ajvr.22.03.0054.
15. Owens EJ, LeBlanc LL, Freeman LM, Scollan KF. Comparison of echocardiographic measurements and cardiac biomarkers in healthy dog eating non-traditional or traditional diets. J Vet Intern Med 2022 Dec 8. doi: 10.1111/jvim.16606. Online ahead of print.
16. Smith CE, Parnell LD, Lai C-Q, et al. Metabolomic profiling in dogs with dilated cardiomyopathy eating non-traditional or traditional diets and in healthy controls.  Sci Rep 2022: https://doi.org/10.1038/s41598-022-26322-8.

FDA Alerts/Updates

1. United States Food and Drug Administration. FDA investigating potential connections between diet and cases of canine heart disease. July 12, 2018.
2. United States Food and Drug Administration. FDA investigation into potential link between certain diets and canine dilated cardiomyopathy – February 2019 update.
3. United States Food and Drug Administration. FDA investigation into potential link between certain diets and canine dilated cardiomyopathy. June 27, 2019.
4. United States Food and Drug Administration. Questions & Answers: FDA’s Work on Potential Causes of Non-Hereditary DCM in Dogs. December 23, 2022.

Conferences

1. Scientific Forum Exploring Causes of Dilated Cardiomyopathy in Dogs, Kansas State Veterinary Diagnostic Laboratory, Manhattan, KS. September 29, 2020.

Commentaries and Review Articles

1. Freeman LM, Stern JA, Fries R, Adin DB, Rush JE. Diet-associated dilated cardiomyopathy in dogs: what do we know?  J Am Vet Med Assoc 2018;253:1390-1394.
2. Mansilla WD, Marinangeli CPF, Ekenstedt KJ, et al. The association between pulse ingredients and canine dilated cardiomyopathy: Addressing the knowledge gaps before establishing causation. J Anim Sci 2019;97:983-997.
3. McCauley SR, Clark SD, Quest BW, Streeter RM, Oxford EM. Review of canine dilated cardiomyopathy in the wake of diet-associated concerns. J Anim Sci 2020;98:1-20.

Related Peer-Reviewed Publications on Nutritional Effects of Grain-Free Diets

1. Pezzali JG, Aldrich CG. Effect of ancient grains and grain-free carbohydrate sources on extrusion parameters and nutrient utilization by dogs. J Anim Sci 2019;97:3758-3767.
2. Alvarenga IC, Aldrich CG. Starch characterization of commercial extruded dry pet foods. Transl Anim Sci 2020;4:1017-1022.
3. Donadelli RA, Pezzali JG, Oba PM, et al. A commercial grain-free diet does not decrease plasma amino acids and taurine status but increases bile acid excretion when fed to Labrador Retrievers.  Transl Anim Sci 2020;4:1-12.
4. Pezzali JG, Acuff HL, Henry W, et al. Effects of different carbohydrate sources on taurine status in healthy Beagle dogs.  J Anim Sci 2020;98:1-9.
5. Banton S, Pezzali JG, Verbrugghe A, et al. Addition of dietary methionine but not dietary taurine or methyl donors/receivers to a grain-free diet increases postprandial homocysteine concentrations in adult dogs.  J Anim Sci 2021;99:1-12.
6. Reis LG, Morris T, Quilliam C, et al. The effect of fermentation of high- or low-tannin fava bean on glucose tolerance, body weight, cardiovascular function, and blood parameters in dogs after 7 days of feeding: comparison with commercial diets with normal vs. high protein.  Front Vet Sci 2021;8:653771.
7. Quilliam C, Ren Y, Morris T, Ai Y, Weber LP. The effect of 7 days of feeding pulse-based diets on digestibility, glycemic response, and taurine levels in domestic dogs.  Front Vet Sci 2021;8:654223.
8. Reilly LM, He F, Clark L, de Godoy MRC. Longitudinal assessment of taurine and amino acid concentrations in dogs fed a green lentil diet.  J Anim Sci 2021;99:1-16.
9. Reilly LM, He F, Rodriguez-Zas SL, Southey BR, et al. Use of legumes and yeast as novel dietary protein sources in extruded canine diets.  Front Vet Sci 2021;8:667642.
10. Tôrres CL, Biourge VC, Backus RC. Plasma and whole blood taurine concentrations in dogs may not be sensitive indicators of taurine deficiency when dietary sulfur amino acid content is reduced.  Front Vet Sci 2022;9:873460.

Disclosure Statement: Dr. Freeman has received research or residency funding from, given sponsored lectures for, or provided professional services to Aratana Therapeutics, Elanco, Guiding Stars Licensing Co LLC, Hill’s Pet Nutrition, Nestlé Purina PetCare, P&G Petcare (now Mars), and Royal Canin.

Lisa M. Freeman, DVM, PhD, DACVIM (Nutrition)

Dr. Freeman is a veterinary nutritionist and a professor at Cummings School of Veterinary Medicine at Tufts University. She is on the cutting-edge of science, with hundreds of articles in prestigious journals, speaking engagements at national and international conferences, and awards for her scientific achievements. However, she also is passionate about providing objective and accurate information on pet nutrition to veterinarians, pet owners, and other animal enthusiasts.