Grain-free Diets and Heart Disease in Dogs: Two New Studies

I have to admit, I didn’t think I would again be addressing the topic of diet-associated dilated cardiomyopathy (DCM) so soon after my recent podcast and post summarizing the debate. But the science around this topic is racing ahead, and there are two new studies to talk about.

Adin, D. et al. (2021) Effect of type of diet on blood and plasma taurine concentrations, cardiac biomarkers, and echocardiograms in 4 dog breeds. Journal of Veterinary Internal Medicine. John Wiley & Sons, Ltd, p. jvim.16075. doi: 10.1111/jvim.16075.

The first study compared heart ultrasound findings and blood tests associated with heart function in dogs from breeds with and without a known predisposition to DCM and eating a variety of types of diet. Here is the breakdown of these categories:

Breeds
At risk for genetic DCM- Doberman Pincers
Suspected risk for dietary DCM- Golden Retrievers
No known DCM risk- Whippets and Schnauzers

Diets
Grain-free (GF)
Grain-inclusive (GI)Diets the FDA has indicated may be a risk factor for DMC because they contain pulses, legumes or potatoes in the top 10 ingredients (FDA PLP)
Diets not containing these ingredients (FDA non-PLP)

Because the study specifically targeted healthy dogs, the goal was not to identify DCM or to show a relationship between this disease and diet. The goal was to see if any changes in the heart could be detected that might suggest some negative effects of diet below the level of clinical disease. 

Of the numerous factors evaluated, most showed no difference between the different groups. One significant difference was a higher level of the blood marker high-sensitivity cardiac troponin (hs-cTnl) in dogs on GF and FDA PLP diets than on the GI and FDA non-PLP diets. This biomarker is associated with damaged heart muscle, so the difference could suggest that there is some damage occurring in dogs on these diets that has not risen to the level of clinical disease yet. This would fit with findings of other studies that indicate the length of time a dog is on a grain-free diet is associated with the development and severity of changes to the heart, so the effect of diet may be a slowly progressive or cumulative one.

Another finding was that taurine levels were higher in dogs on GF diets than on GI diets. This is different from the finding of a previous study in Golden retrievers which found low taurine levels in dogs with DCM on GF diets. 

Overall, the research is showing rather consistently that taurine is probably only a factor in diet-associated heart disease in some breeds (especially Goldens), and it doesn’t seem to be related to any effect of GF diets in most other breeds.

In general, this study provide weak support for the hypothesis that GF and FDA PLP diets might have negative effects on the heart, but in these healthy dogs most measurements were normal in both groups, so no strong conclusions can be drawn.

Walker, A. L. et al. (2021) Association of diet with clinical outcomes in dogs with dilated cardiomyopathy and congestive heart failure. Journal of Veterinary Cardiology. Elsevier. doi: 10.1016/J.JVC.2021.02.001.

The other study took a different approach. This was a retrospective study, meaning the investigators looked back at medical records to compare dogs with DCM and with congestive heart failure (CHF) for whom the diet fed at the time of diagnosis and treatment was known. They compared dogs who were eating a GF diet when diagnosed and were then switched to a GI diet with those who were already on a GI diet when they developed DCM. 

The hypothesis was that dogs on a GF diet who changed foods would have a better outcome than dogs on a GI diet when both were treated with the same standard medical therapies. This may not seem to make sense at first if GF diets are supposed to damage the heart. However, in dogs that develop DCM and heart failure at least partly due to something in their diet, there is a chance that changing the diet could actually help make the heart work better. These dogs could benefit from both the usual treatments and a diet change. However, in dogs who develop DCM without any contribution from the diet, there isn’t anything to add to standard medical treatment to help them, so they wouldn’t do as well as dogs who could benefit from changing foods. 

The results supported this hypothesis pretty well. While overall the difference in survival time was not statistically significant (344 days go dogs initially on GF diets compared to 253 days for dogs on GI diets), this difference became both larger and statistically significant when the dogs the sickest dogs who died within a week of diagnosis were excluded. In this group, the dogs changed from GF to a GI diet lived an average of 465 days compared with only 263 days for dogs already on a GI diet at diagnosis). This makes sense since the dogs who died right after being diagnosed were probably too sick already for the potential benefits of diet change to have time to be felt.

The study also found that dogs on GF diets developed DCM earlier (average of 6 years old) than dogs on GI diets (average of 9.3 years old). The longer a dog has been fed a GF diet before diagnosis, the less time they lived after developing DCM. Dogs changed from a GF diet to a GI diet also were more likely to be able to reduce or discontinue the use of the main medications used to treat their heart disease (furosemide and pimobendan), suggesting again that the GF diet was harmful and that diet change provided an added benefit to standard medical treatment.

The ultrasound findings for the two groups did not differ in most respects. However, a couple of values did improve more in the GF dogs than in the GI dogs.

Overall, this study provides moderate evidence to support the hypothesis that GF diets have negative effects on the heart which can be partially or fully reversed with diet change. While this kind of study can’t prove GF diets cause heart disease in dogs, it does add to a growing body of information that implicates these diets as at least a risk factor. If patients improve more with changing from a GF diet to a GI diet and medical therapy together than with medical therapy alone, that looks pretty suspicious for some negative effect of these diets on heart function. More definitive studies will need to be done, but since these are complex and time-consuming to conduct, it is worthwhile to consider this kind of evidence in the meantime when making choices about what to feed our dogs and what to recommend to clients.