A healthy heart equals a happy dog. With cardiac health being so important, pet owners were understandably concerned when in July 2018, a statement from the FDA surfaced about a possible link between a cardiac disorder and grain-free diets. The purpose of this blog is to help summarize and understand the FDA investigation into grain free diets and dilated cardiomyopathy.
Suggestions for Pet Owners
It is important to remember that all pet food, even grain-free food, is not created equal. The issue of DCM and grain-free is much more complex than the FDA presents and it is much too early to make any concrete claims. Certain elements such as nutrient inclusion, processing and quality of ingredients can greatly influence the cardiac health of a dog. Pet owners should still be aware of the ingredients in their dog’s food and opt for diets with quality ingredients from a brand they trust. Lastly, if you have any concerns about your pet’s cardiovascular health, consult your veterinarian.
Dilated Cardiomyopathy (DCM)
The heart is one of the most important organs in the body, responsible for pumping blood to the muscles and other organs. The heart is a four chambered pump, comprised of two atria and two ventricles.
The heart receives oxygenated blood from the lungs, where it moves through the left atria and left ventricle. The muscular left ventricle forces oxygenated blood out into the major artery, the aorta and is subsequently distributed to all of the tissues in the body. Once the blood arrives at the tissues, there is a gas exchange, whereby oxygen is exchanged for carbon dioxide produced by the tissue cells. The blood containing carbon dioxide then travels back to the right side of the heart, where it is pumped through the right atria and right ventricle and redistributed back to the lungs. The carbon dioxide is expelled, and the cycle continues.
Overtime, the constant pumping of the heart can result in wear and tear on the heart muscles. One such condition, called dilated cardiomyopathy, causes a decrease in the heart’s ability to pump blood to the tissues and eventually leads too heart failure. DCM is a result of the left ventricle, the chamber of the heart responsible for generating the most force, becoming enlarged and ventricular walls weakening. This means that while more blood is filling the ventricle chamber, the muscles are not strong enough to force the blood out of the heart. Poor ventricular function leads to inadequate blood flow and heart failure.
Certain large and giant breeds are more prone to developing DCM. Golden Retrievers, Labradors, Dobermans, Great Danes, Boxers, Newfoundlands, Irish Wolfhounds, and Saint Bernards are some of the breeds genetically predisposed to developing the disease. While typically not as common in small and medium breeds, Cocker Spaniels, Miniature Poodles and Schnauzers can also be predisposed. Some symptoms of DCM are coughing, weakness, pale gums, increased heart rate, difficulty breathing and fainting. DCM is usually diagnosed through a combination of an echocardiogram (ultrasound of the heart), electrocardiogram and x-rays of the chest area.
Ultrasound of a healthy dog heart
Traditionally canine diets have been formulated using grains such as corn, wheat, rice and barley as the primary source of fibre. In the last decade, there has been a boom in “grain-free diets” in the pet food market.5 These diets substitute grain sources for other fibre sources like pulses and legumes, in order to avoid some of the negative health effects associated with the use of grains in pet food.
Pulses and legumes are ingredients like peas, beans and lentils. They contain more complex carbohydrate sources than grains and are more slowly digested. This means that sugars like glucose and fructose, which cause diabetes, aren’t as readily available. There have been multiple scientific studies showing that grain-free diets help improve glucose handling in dogs. Lower circulating glucose helps to reduce the incidence of diabetes. A 2014 study from the University of Saskatchewan compared the effects of pea and rice diets on canine cardiovascular and insulin responses. The researchers fed seven beagles either a pea-based diet or a rice-based diet for 12 weeks. At the end of the feeding period, cardiovascular and glycemic index measurements were examined. The researchers found that the pea diet resulted in a lower glucose response than the rice-based diet, indicating an insulin protecting effect. Meanwhile, no differences in cardiovascular function was observed.
Pulses and legumes also provide a higher protein content than traditional grains do. This allows for pet food manufactures to substitute a portion of animal protein for plant protein. With a higher percentage of plant protein, the fat and calorie content of the diet is reduced. A lower fat content may help to reduce obesity-related illnesses in dogs. In addition, since both protein and carbohydrates in grain-free diets are more slowly digested, dogs stay fuller for longer.
Now that we understand the scientific background behind the investigation, let’s delve more into what the FDA has to say on the subject. In the summer of 2018, the FDA began an investigation into a potential connection between grain-free diets and several cases of canine DCM. Several reports of DCM in breeds not typically associated with the disease had been reported to the FDA. It was observed that some of the dogs diagnosed with early heart disease were fed grain-free diets. In the animals tested, several of the dogs presented with low blood taurine levels.
Taurine is a free amino acid in the body. While most amino acids are used as the building blocks of protein, Taurine is a major constituent of bile. Previously it was thought that dogs required only 18% crude protein, comprised of 10 essential amino acids; Arginine, Histidine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan and Valine. Historically, it was thought that dogs could synthesize their own Taurine from Methionine and Cysteine. The 2018 FDA report may suggest otherwise.
An updated report was released in June of 2019, with more current results on the FDA’s investigation. The FDA reported that there had been a total of 515 cases of canine DCM between 2014 and 2019. The majority of these cases were reported in 2018 and 2019, suggesting that these cases are not solely the result of genetic disposition to the disease. However, most of these cases were in breeds most commonly associated with predisposition to DCM, with the Golden Retriever having the highest number of cases. The majority of cases were also reported in male animals that were middle aged to senior, which is typical of the disease. Of the 515 reported cases, 452 dogs were being fed dry-food diets.
Since 2018, the FDA has launched product testing of grain-free and grain-containing products. The product testing examined the following factors; protein, fat, moisture, crude fiber, total dietary fiber, soluble fiber, insoluble fiber, total starch, resistant starch, cystine, methionine, and taurine. Once all moisture was removed, it was found that the grain-free and grain-containing diets were very similar in all tested areas. Furthermore, nearly all grain-free diets met and exceeded the 0.65% methionine-cystine AAFCO nutritional requirement for adult dogs.
As of April 2019, the FDA has issued veterinary diagnostic testing and necropsies on cases with confirmed DCM. Necropsies will examine histology of the heart, in combination with whole blood, urine and feces analysis.
What does this mean?
The statement from the FDA suggests that Taurine may actually be an essential nutrient in dogs, particularly in predisposed breeds like Golden Retrievers. Pulses and legumes do contain lower levels of Methionine and Cysteine, the building blocks of Taurine. Grain-free diets can still incorporate other ingredients like eggs, fish, chicken and beef to account for the low Methionine-Cysteine content. Amino acids like Methionine, Cysteine and Taurine can also be added as an individual supplement to pet food. This means that if formulated properly, grain-free diets are not deficient according to the current nutrient standards for dogs. However, if new research reveals the need to increase Taurine requirements for canines, both grain-free diets and grain-containing diets will need to make a change.
It is also important to remember that while the FDA states that there is a correlation between grain-free diets and DCM, this does not mean that the grain-free diets are the causation of DCM.10 The FDA statement only refers to individual cases and product testing, the latter of which produced no evidence of grain-free deficiencies. In order to come to a concrete conclusion on the topic, multiple scientific, research studies will need to be conducted. These studies should include multiple feeding trials by a non-biased source, in order to better understand Taurine production, absorption, and metabolism in dogs.