FDA searching for possible links between canine diets, heart disease

Federal investigators continue studying whether dogs eating diets that are high in legumes or free from grain have an increased risk of heart disease.

In August, three Food and Drug Administration officials described the current research into possible links between diet and dilated cardiomyopathy. Much of the presentation reflected updates published by the FDA in late June, when agency officials reported links between canine diets and DCM represent a complex problem that may reflect multiple causes.

"To date, the FDA has not established why certain diets may be associated with the development of DCM in some dogs," one of those updates states. "In the meantime, and before making diet changes, pet owners should work directly with their veterinarians, who may consult with a board-certified veterinary nutritionist, to determine the most appropriate diet for their pet's specific needs."

With DCM, the chambers of the heart progressively dilate and become less able to pump blood through the vascular system. Signs include lethargy and weakness, resulting from decreased delivery of oxygenated blood to the tissues, and coughing, high respiratory rate, and abdominal distention, secondary to increased pressure in the veins that carry blood to the heart and congestive heart failure.

Large- to giant-breed dogs and Cocker Spaniels appear to have a genetic risk of developing DCM, FDA information states. But agency officials issued an alert in July 2018 after receiving reports of DCM in breeds that don't typically have the disease, such as Shetland Sheepdogs, Boston Terriers, and French Bulldogs.

Dr. Lee Anne Palmer, who leads the Adverse Event Review Team in the FDA Center for Veterinary Medicine Division of Veterinary Product Safety, said during the presentation at AVMA Convention 2019 in Washington, D.C., that 93% of the dog foods identified in DCM reports listed peas, lentils, or both among the first 10 ingredients on labels, and about 91% were grain free.

Agency data published in June indicate at least 16 brands had 10 or more DCM reports connected with their products. Dr. Jennifer Jones, a veterinary medical officer in the FDA CVM Veterinary Laboratory Investigation and Response Network program, said during the lecture that the FDA analyzed dog foods from homes and stores and conducted comprehensive nutritional screenings, including analyses of free and total amino acids.

"The bottom line was all except for two products came back normal," Dr. Jones said.

Agency officials also examined medical records of 202 dogs and six cats, conducted more than 90 interviews on diets and environments, and coordinated follow-up echocardiograms or necropsies, she said. Of the animals with medical records, 60% of dogs and all cats had congestive heart failure.

Agency researchers also found that 9% of dogs had hypothyroidism, which can contribute to DCM, and 8% had a history of tick-borne disease. Lyme disease–associated myocarditis can contribute to the disease, Dr. Jones said. Researchers have asked about exposures to contaminants such as heavy metals and narcotics and have collected DNA samples in case a potential genetic link is discovered.

Some dogs have improved with changes in diet, and the FDA has provided examples in updates posted in February and June. Agency officials are studying follow-up echocardiograms to see which dogs improve in response to a diet change.

Dr. Jones said the agency's testing indicated blood taurine concentrations were not predictors of DCM, as dozens of dogs with DCM had normal or high taurine concentrations.

Authors of a commentary published in the Dec. 1, 2018, issue of JAVMA point out that DCM was one of the most common cardiac diseases in cats prior to the 1987 publication of a study that linked the disease to taurine deficiency, leading to a requirement for more taurine in cat foods and a dwindling number of feline cases of DCM. Since 1995, research has found that some dog breeds may have genetic predispositions to taurine deficiency and DCM and that certain diets may be associated with taurine deficiency.

Dr. Jones said during the lecture in August that the potential connection between diet and DCM could be associated with low bioavailability of taurine or the precursor amino acids dogs use in synthesizing taurine or with increased loss of taurine during digestion or decreased ability to synthesize taurine.

Dr. Lisa M. Freeman, a professor of clinical nutrition at the Cummings School of Veterinary Medicine at Tufts University and one of the authors of the Dec. 1 JAVMA commentary, wrote in July on the Petfoodology site of the school's Clinical Nutrition Service that FDA reports on DCM likely underestimate the actual number of dogs affected. She knows veterinarians who do not report cases to the agency.

One of the FDA's June updates indicates the agency also is studying a spectrum of cardiac disease in animals without DCM to understand whether the damage could be related to DCM development or is associated with diet.

Related JAVMA content:

Unusual pet diets may be linked to heart disease (Aug. 1, 2018)