I have been following with great interest the emerging evidence about grain-free and exotic protein diets as a possible risk factor for heart disease in dogs. I first raised the subject in response to several cases of dilated cardiomyopathy (DCM) I saw in my practice, and which became part of a study which has recently been published looking at the issue in this breed. There have been several other papers recently published touching on the relationship between diet and DCM in dogs, and I want to quickly discuss each of them

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 Dec 1;253(11):1390-1394. doi: 10.2460/javma.253.11.1390.

This is an excellent summary of what we know and don’t know about this issue so far. The bottom line is that a suspicious number of cases of DCM have been appearing in dogs eating what have been called BEG diets- boutique, exotic protein, grain-free. What this means is that diets without grains, diets with a high proportion of legumes, and diets with animal proteins that have not been traditionally used in dog food, and which consequently have not been studied as thoroughly in terms of their nutrient content and other factors, have been associated with DCM in a variety of breeds. This is not proof that the diets, or any particular characteristic of them, is causing this disease. Such proof will require different kinds of research studies. However, this is a potential warning sign that deserves to be acknowledged and followed up with appropriate research.

In some cases, the diets and disease has also been associated with a deficiency in the amino acid taurine. This is an amino acid that dogs do not normally require in the diet since they can make as much as they need. However, in some breeds there appear to be genetic factors that make individuals more susceptible to taurine deficiency, and associated heart disease. These may include reduced production of taurine, increased loss of taurine, or increased need for taurine. Certain diets that have low levels of the ingredients from which taurine is made or that contain substances, such as legumes and some types of. Fiber that make reduce absorption or synthesis of taurine and its precursors or that encourage taurine loss make act in con cert with these genetic factors to lead to deficiency and disease in some dogs. Many of the details in this hypothetical series of steps remain to be understood.

An example of how this problem may work comes from another recent paper looking at golden retrievers with DCM, including several of my patients.

Kaplan JL, Stern JA, Fascetti AJ, Larsen JA, Skolnik H, et al. (2018) Taurine deficiency and dilated cardiomyopathy in golden retrievers fed commercial diets. PLOS ONE 13(12): e0209112.

In this study, the dogs with DCM had taurine deficiency, and most were eating BEG diets. Changing the diet and supplementing taurine, along with other treatments, seemed to improve or cure the disease in most, but not all of the dogs. Again, this was not a study designed to determine if the diets caused the taurine deficiency or the DCM, but the fact that all the dogs were on the diets that we are concerned about, and the fact that changing the diet and adding taurine, among other interventions, seemed to help most of these dogs, does make looking more closely at these diets worthwhile. It also makes it reasonable to consider avoiding these diets in golden retrievers, and perhaps other breeds known to have a higher-than-average risk of taurine deficient DCM even if we are not certain if the diets are the cause or, if so, how exactly that works.

It is important, however, not to get too fixated on taurine. Many of the dogs seen with DCM and eating BEG diets are not taurine deficient, so golden retrievers appear to be experiencing a different problem than these other breeds. It is possible that other aspects of these diets besides their effects on taurine levels could be a risk factor for DCM, and we know even less about how this might work.

This is illustrated by the third new study, which looked at dogs with DCM and evaluated the differences between those on grain-free diets and those on grain-based diets.

DarcyAdin, Teresa C.De Francesco, BruceKeene, SandraTou, KathrynMeurs, ClarkeAtkins, BrentAona, KariKurtz, LaraBarron, KorinnSaker. Echocardiographic phenotype of canine dilated cardiomyopathy differs based on diet type.J Vet Cardiol. 2019;21:1-9.

In this group of dogs, grain-free diets were associated with some signs of more severe heart disease than that exhibited by dogs on diets containing grains, though the differences did not appear in all measures of heart disease severity. None of the dogs in this group were taurine deficient, so whatever the relationship between diet and DCM here, it had nothing to do with taurine.

The great deal we don’t know about DCM and diet is frustrating to all of us. We have to try and resist the temptation, however, to substitute our own beliefs and theories for the missing facts. Proponents of grain-free and other unconventional diets will point to the gaps in our knowledge as evidence that we can’t really blame these diets and that there is no need to change what they feed. While it is true that we can’t be certain what role, if any, such diets are playing in causing heart disease, the fact that they are consistently associated with DCM in several different groups of dogs is, at the least, reason for concern and further research. What is more, none of the claims for the health benefits of grain-free and other unconventional diets have any compelling scientific support, so there is no good reason to choose such diets even if the evidence for their potential risks are still very preliminary.

Bottom Line

We cannot say with certainty that BEG diets cause heart disease. We can only say that they have been associated with DCM in both golden retrievers with taurine deficiency and in other breeds without taurine deficiency. We can also say that changing diets appears to have benefitted some of these dogs, though many other treatments were employed at the same time, which limits out ability to know how important a factor this diet change was in the dogs’ recovery.

We can also say that none of the claims for health risks from grains in pet foods, or for health benefits from grain-free or other BEG diets, are supported by any reasonable scientific evidence. Certainly, the evidence for such diets is weaker than even the very limited evidence against them.

As pet owners and veterinarians, we need to proportion our confidence in any conclusions to the strength of the available evidence and be willing to change our minds as new evidence emerges. We also need to make our decisions now, even before we have perfect evidence. Right now, there is no solid reason to think grain-free diets have any health advantages, and there is weak evidence to suggest they might have health risks for some dogs. If you have a golden retriever, it seems reasonable to avoid the diets that have been associated with taurine deficiency and DCM in this breed. Even if you don’t have a golden, you should at least give some thought to why you might want to feed or avoid BEG diets. The evidence can’t make the decision for you, but it should certainly be considered.