DCM and grain-free diets

Important Update - June 2020

A new study² published on Jun 15, 2020 suggests that Dilated cardiomyopathy (DCM) in dogs is NOT related to grain-free diets (the diets rich in legumes).

This is a huge relief to vegan pet guardians because legumes (soybeans, lentils, peas) are extensively used in plant-based diets for dogs, and many guardians became worried that their choice of a diet for their companion animal could negatively impact their dog's heart function (Canine DCM is a disease of a dog's heart muscle). 

However, now there is a peer-reviewed study where researchers reviewed 150 related research papers, and concluded that there is no link between DCM and legumes. Researchers said that DCM is generally linked with genetics or the breed of the dog, but not with the diet.

But then the question is why did FDA make the link on the first place? Or where did FDA make a mistake? Researchers said that FDA's reports were flawed with sample bias and several confounding factors.

Factors included incomplete diet history, age of the sample population, concurrent diseases, and unreported duration of the diet being fed at the time data were collected (FDA, 2019a).² 

Another confounding variable is the body condition of these dogs and the number of treats and table scraps being given at home).² 

Brief Synopsis of the Canine DCM issue as it pertains to grain-free diets

In 2018 Food and Drug Administration (FDA) issued a statement that could suggest that legumes in dog food cause heart problems. Legumes are extensively used in plant-based diets and so a lot people feeding their dogs vegan diets, as well as grain-free meat-based diets (that also use legumes) got concerned.

FDA issued another statement about a potential association between DCM and grain-free diets that contain legumes. In their statement, they caution dog guardians against feeding these diets to their dogs. Upon careful review of the report and other literature, we can see that the report is biased and contains several 'confounding factors'. These factors include small sample size, environmental factors and sampling bias. Furthermore, the reported DCM cases are connected with specific commercial brands and we should not generalize these findings to all dog foods.

FDA report

U.S. Food and Drug Administration (FDA) released a statement in 2019 about a potential association between certain dog foods and a heart disease called dilated cardiomyopathy (DCM). In their statement, the FDA implicated specific ingredients, particularly peas, lentils and potatoes, as well as grain-free diets as having a potential link with this condition.¹

FDA documented over 500 cases of dogs who have developed DCM and found out that more than 90% of diets these dogs consumed were grain-free, 93% contained peas and/or lentils, and 42% contained potatoes/sweet potatoes. As a result, FDA issued a cautionary statement against these products and currently continues the investigation. The organization also states that DCM in dogs is a complex scientific issue which has not yet been linked to any one cause.¹

Small sample size and problematic brands

The FDA warning is based on a relatively few number of cases (515 dogs with DCM out of over 77 million dogs living in the U.S.). Implicated brands include Acana, Zignature, Taste of the Wild and several others, as below graph shows. With such a small sample size, it could be a production or ingredients sourcing issue with these specific commercial brands, and not an issue with all dog foods. It's worth noting that none of the implicated brands are vegan products made by vegan pet food manufacturers.

Problematic proteins

The reported link between grain-free diets and DCM appears to be an issue with meat-based and fish-based commercial products. This conclusion seems to be in agreement with previous research that found association between fish, poultry, animal fat and LDL cholesterol and heart disease in dogs. It could also be the case that grains have a protective effect on cardiovascular health of dogs fed animal-based diet. According to FDA, certain ‘exotic meats’ could also be a contributor, as well as environmental factors. Chicken and lamb proteins were reported in more than half of DCM cases as the below graph shows.

Environmental factors

It's interesting to note that DCM cases in case have increased just in the last few years. The fact that it’s a recent development points to the possible environmental cause, a there have not been major changes in nutritional formulations of dog formulas (plant- or meat-based) in recent years that could have caused heart issues. Environmental factors include heavy metal exposure during production process, as well as ingredients and packaging sourcing of implicated commercial companies.

Correlation does not imply causation

A golden rule in statistics, the phrase "correlation does not imply causation" refers to the inability to legitimately deduce a cause-and-effect relationship between two variables solely on the basis of an observed association or correlation between them. In other words, the fact that most dogs that developed DCM were on grain-free diet does not mean that grain-free diets cause DCM. An association between grain-free diets and DCM does not mean that one causes the other.There could be many other confounding factors at play, such as inclusion of predisposed breeds in the collected sample, incomplete medical records and sampling bias.²

Sampling bias

Sampling bias could skew the results of the FDA investigation. Independent review into FDA data collection methods revealed that the organization was asking veterinary professionals to report cases of diet-related DCM specifically in dogs eating the types of diets already designated as suspect by the FDA. If we ask guardians and veterinarians of dogs who are fed grain-free diets to report DCM cases, then we will unsurprisingly see an association between grain-free diets and DCM. In order to avoid sampling bias, FDA officials should encourage reporting of all DCM cases, from dogs on all diets.²

Conclusion

It's hard to draw conclusions from a report with such a small sample size and biased data collection. Based on what was reported, it could be a good idea for dog guardians to avoid products from implicated brands and exotic meats, especially for dogs predisposed to DCM. More careful investigation with correct scientific methods is needed to gain deeper understanding of this issue.   

References

1. FDA Investigation into Potential Link between Certain Diets and Canine Dilated Cardiomyopathy. U.S. Food and Drug Administration, June 27, 2019. LINK
2. Sydney R McCauley, Stephanie D Clark, Bradley W Quest, Renee M Streeter, Eva M Oxford, Review of canine dilated cardiomyopathy in the wake of diet-associated concerns, Journal of Animal Science, Volume 98, Issue 6, June 2020, skaa155, https://doi.org/10.1093/jas/skaa155