Almost 4 years ago, in July of 2018, the U.S. Food and Drug Administration released a public alert stating that they had reports of an apparent increase in the national incidence of Dilated Cardiomyopathy (DCM) in dogs. At the time, it was speculated (without evidence) that the perceived increase in cases was related to the consumption by dogs of a large and diverse group of commercial dog foods that were marketed as being grain-free.

What followed was a fair bit of panic, a whole lot of hyperbole, and of course, a social media feeding frenzy. Dog owners and pet professionals lined up on sides, joined FB groups that aligned with their respective beliefs, and created catchy but pejorative acronyms that targeted the suspect products. (Some may BEG to differ on this last point….).

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Some Science

Lucky for us all, what also followed was a great deal of science. (Never underestimate the dedication of nutrition researchers who are presented with a challenging question). Although it lacks the pizazz and emotional turmoil of social media, the scientific method, conducted in this case as controlled feeding studies with dogs, has actually provided us with helpful information and answers.

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I first wrote about this science – specifically about the role of taurine in DCM shortly after the FDA letter first appeared (see “The Heart of the Matter“). The “Heart” article includes information about the history of taurine nutrition in dogs and cats, plus identifies diet and non-diet-related risk factors for DCM. I wrote again about this issue when one of the first controlled feeding studies with dogs was published in 2020 (see “It’s Not Rocket Science“) and also provide a summary of this issue in my newest book.

Since 2020, additional feeding studies with dogs, conducted by independent research groups, have been published. These have examined the nutritional value and health effects of feeding dogs foods without grains. They have also studied a variety of the pet food ingredients that have frequently replaced grains in commercial foods. These include pulses such as peas and lentils and tubers such as potatoes. It has been hypothesized that these relatively new ingredients might have an influence on dogs’ taurine status and ultimately, upon heart health. Here is a quick summary of the questions that have been asked and what we have learned so far from this research (Note: Only controlled feeding studies are included in this review) :

• Is it Grains vs. No Grains? A controlled, 4-week feeding study with dogs found that taurine status was not affected by the presence or absence of grains in the diet (1). Although total fecal bile acid excretion was not affected, they did find that a higher proportion of excreted bile acids was made up of primary bile acids in dogs fed the grain-free food. This type of shift is suggestive of increased microbial fermentation due to the presence of a type of fiber called oligosaccharides (see “Rocket” for details). However, the impact of this change on taurine status in dogs over time is not known – but does require further study.
• Is it Carbohydrate Source? In this study, dogs were fed one of three commercially available dog foods that were marketed as grain-free, but contained different carbohydrate and protein sources (2). The foods were compared with a traditional dog food containing grains that was produced by the same company. Feeding the grain-free products for 50 days did not influence blood and plasma taurine levels.
• Is it Plant-based Food? Dogs were fed either a plant-based food containing pea protein or an animal-protein based traditional food (control diet) for 12 weeks (3). Dogs fed the plant-based dog food had higher plasma/blood taurine concentrations than at baseline and when compared with dogs fed the traditional food at 4 weeks. In this study, parameters of heart health were also measured. Dogs fed the diet containing pea protein had no evidence of clinically-relevant blood or heart-related changes after 3 months of consuming the plant-based food.
• Is it the Plant Fibers? This study examined the hypothesis that foods containing peas or lentils would also provide higher levels of dietary fiber, which in turn might influence taurine status via the path of altering bile acid excretion (see above; 4). Dogs were fed foods containing a variety of pea/lentil sources for 7 days. Digestibility and blood taurine values decreased but taurine values remained within normal range. However, because the pulse-based diets influenced nutrient digestibility (and had higher levels of fiber), it was again noted that the effects of long-term feeding may have the potential to influence taurine status.
• Is it Green Lentils?: In this RCT (randomized, controlled trial) a group of female beagles was fed a food containing 45% green lentils (this is quite high) or a food containing poultry byproduct meal, for 3 months (5). No differences were found in plasma/blood taurine levels, either over time or between the two diet groups. Dogs fed the lentil diet had higher fecal bile acid excretion when compared with dogs fed the control diet.
• Is it Taurine Synthesis? This study is a bit more complicated, but provides some important information (6). The researchers asked whether or not feeding a grain-free dog food influenced dogs’ ability to produce taurine in the body from precursors such as the amino acid, methionine, among others. In a balanced and controlled feeding study, healthy dogs were fed either a grain-free food (the control) or the control food supplemented with various compounds that may influence the availability of methionine for conversion to taurine in the body. They found that adding taurine and/or these other compounds (choline, carnitine, and creatine) to the grain-free food might spare methionine so that it can be used for other purposes in the body (such as taurine production).

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The Question of Correlation

Another approach to understanding a possible relationship between DCM cases in dogs and feeding grain-free foods is to examine changes in each of these factors over time. In other words, if grain-free foods are a causative agent of DCM in dogs, we would expect these two things to vary together. The research question is: Does the diagnosis of DCM in dogs correlate with changes in the popularity and feeding of grain-free foods? This is highly relevant because, prior to 12 years ago, the grain-free pet food market was almost non-existent. Starting around 2010, foods formulated to contain little or no grain ingredients increased in availability. This increase was in response primarily to consumer demand, rather than to a demonstrated nutritional or health-related need for these foods. By the year 2019, it was estimated that grain-free pet foods comprised at least 25 percent of the U.S. market! By the estimate of Dr. Greg Aldrich, this would mean that about 22 million dogs were eating some brand of grain-free dog food in the year 2019. Not to put too fine a point on this, but if these foods were directly the cause of DCM in dogs, we would have expected to see a dramatic increase in DCM cases nationwide over the last 12 years.

Did this happen?

Recently, a team of researchers with the consulting group BSM Partners, published a paper that specifically examined this relationship (7).

The Study

The researchers contacted accredited veterinary colleges in the United States plus a group of private referral specialty clinics. They requested retrospective data for diagnosed cases of DCM in dogs spanning the period of the year 2010 to the year 2019. The researchers also acquired annual sales data for grain-free pet food sales sold in the United States during roughly the same period. Data were analyzed using statistical tests for correlation.

Results:

• DCM Cases: Participating hospitals provided over 68,000 confirmed cases of DCM. Over the 10-year period of 2011 to 2019, DCM incidence among dogs did not increase significantly.
• Grain-Free Food Sales: Conversely, during the same period of time, the sale of grain-free brands of pet food increased by more than 500 percent.
• No Correlation: Given these two trends – a relatively flat incidence rate for DCM and an exponential increase in grain-free food sales, it was not a surprise to find a lack of correlation between the number of cases of DCM in dogs and grain-free pet food sales.
• Breeds: Only a portion of the reported cases included age and breed data. This subset of data showed a slight but significant increase in DCM among mixed-breed dogs. However, this change was still not correlated with grain-free pet food sales.

Conclusions

The authors conclude that the data collected in this study, while having limitations, revealed no significant increase in DCM cases in dogs overall accompanied at the same time by a five-fold increase in the sale of grain-free pet foods. Although certain dietary factors may play a role in diet-related DCM, additional research is needed to understand what influence, if any, various select nutrients may have upon the incidence of DCM in dogs.

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Where are We Now with This Issue?

We know a number of things:

• Dilated Cardiomyopathy is Multifaceted: First, DCM is a complex disease that is most likely influenced by multiple factors. One of the most important and well-studied of these is genetics – a number of dog breeds are known to be genetically predisposed to developing DCM. Other risk factors for DCM include adult size, metabolic rate, age, presence of overweight conditions, and, as we have learned, dietary factors that may influence a dog’s taurine status over time. All of these factors, taken together, may affect an individual dog’s lifetime risk of developing DCM.
• Dietary Factors: Plant-based ingredients such as peas, lentils and potatoes are frequent replacements for grains in grain-free dog foods. Most of the current studies have shown that feeding foods with these ingredients does not directly influence the taurine status (or heart health) of dogs. However, shifts in bile acid excretion have been reported by several groups and this type of change may (over time) contribute to an alteration in gut microbial populations, fermentation processes, and possibly taurine homeostasis. Still, this information is a far reach from concluding that these ingredients directly compromise a dog’s taurine status – there is no evidence of that. There is also no evidence to date that these ingredients negatively affect a dog’s heart health or contribute to the development of DCM. We need long-term studies to determine if shifts in fecal bile excretion actually lead to these outcomes and present a risk to dog health.
• It is NOT Grain-Free Foods: Grain-free products are a large and diverse group of foods that include multiple brands, a range of formulations, and a wide variety of ingredients. To date, there is no evidence that feeding grain-free foods are a direct cause of DCM in dogs. This recent study provides one more piece of important evidence as it found that the dramatic rise in feeding of grain-free foods over the last 12 years was not associated with an accompanying rise in DCM cases in dogs.

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Follow the Science.

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Cited Studies

1. Pezzali JG, Acuff HL, Henry W, Alexander C, Swanson KS, Aldrich CG. Effects of different carbohydrate sources on taurine status in healthy Beagle dogs. Journal of Animal Science 2020; 1-9, doi:101093/jas/skaa010.
2. Gizzarelli M, Calabrò S Vastolo A., et al. Clinical findings in healthy dogs fed with diets characterized by different carbohydrates sources. Frontiers in Veterinary Science 2021; 8; doi.10.3389/fvets.2021.667318.
3. Cavanaugh SM, Cavanaugh RP, Gilbert GE, Leavitt EL, Ketzis JK, 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.
4. Quilliam C, Ren Y, Morris T, et al. The effects of 7 days of feeding pulse-based diets on digestibility, glycemic response and taurine levels in domestic dogs. Frontiers in Veterinary Science, 2021; 8;doi.10.3389/fvets.2021.654223}.
5. Reilly LM, He F, Clark L, de Godoy M. Longitudinal assessment of taurine and amino acid concentrations in dogs fed a green lentil diet, Journal of Animal Science, 2021;99;skab315.
6. Banton S, Pezzali J, Verbrugghe J, 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, Journal of Animal Science, 2021;99, skab223.
7. Quest BW, Leach SB, Garimella S, et al. Incidence of canine dilated cardiomyopathy diagnosed at referral institutes and grain-free pet food store sales: A retrospective survey. Frontiers in Animal Science, 2022; 3:846227.

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