The controversy began in earnest during the 2010s, when grain-free formulations exploded across the American pet food market. Sales at one boutique retail chain tripled between 2011 and 2015, and by 2019 grain-free products accounted for 43 percent of all extruded diets sold there. By 2017, diets built on peas, chickpeas, lentils, sweet potatoes and tapioca made up more than half of the dog food market. When the FDA announced its investigation the following year, it triggered a wave of research across academia and industry, spanning randomized controlled trials and observational studies in both client-owned and research colony dogs. Yet although that body of work focused narrowly on dilated cardiomyopathy, many individual veterinarians began broadly advising owners to avoid grain-free diets for any cardiac concern, including murmurs and mitral valve disease, and even for breeds predisposed to heart disease, purely out of caution.

A central weakness in this literature has long been its reliance on owner-reported diet histories. Previous studies repeatedly identified owner recall of primary diet type, treats, supplements and other food items as a substantial methodological limitation, with reports of grain-free status frequently overestimated, misattributed or incomplete. The new analysis, led by researchers affiliated with the Dog Aging Project, set out to quantify exactly how inaccurate owner reporting of grain-free status actually is, and then to determine whether that inaccuracy could distort the apparent relationship between diet and heart disease in a large longitudinal cohort. The DAP follows more than 50,000 companion dogs of all breeds and ages, collecting annual data on health, lifestyle and environmental factors that influence canine longevity.

To validate owner reports, the team took advantage of a natural experiment within the survey structure. From January 2020 to June 2023, the DAP’s original diet survey asked owners a simple yes-or-no question about whether their dog’s primary diet was grain-free. In July 2023, a far more comprehensive questionnaire was introduced, asking for the full brand name and formula of the diet, along with how long it had been fed. Owners who reported feeding the same diet for at least twelve months could therefore be assessed twice: once by their own grain-free label, and once by independent verification. A coder individually checked 13,049 such responses against online ingredient lists, classifying any diet containing rice, corn, wheat, barley or oats as grain-inclusive.

The validation revealed striking misclassification. Thirty-five percent of owners reported feeding grain-free diets, yet when a grain-free claim was made, it was correct only 49 percent of the time, essentially a coin flip. By contrast, owners who reported grain-inclusive diets were far more reliable, with a negative predictive value of 92 percent, and overall accuracy across all reports was 77 percent. The researchers suspect naming conventions drive much of the error: diets with titles such as a meat-and-potato recipe, which carry no grain in the name but contain grains in the ingredient list, were frequently mislabeled as grain-free by owners who judged by packaging rather than ingredients.

Crucially, the team did not stop at documenting the error. They ran simulation studies with synthetic populations of 10,000 dogs, introducing reporting inaccuracy rates of 25, 50 and 75 percent across a range of hypothetical true effect sizes, from protective to severely harmful. The simulations demonstrated that this particular pattern of misclassification, in which grain-free diets are inconsistently reported while grain-inclusive diets are reliably reported, would attenuate true associations, pulling observed odds ratios toward 1, but would not create false associations or reverse their direction. In other words, if grain-free diets truly caused heart disease, the analysis should still have detected a harmful trend, merely a weakened one. Based on the degree of attenuation observed, the researchers estimated that their measured odds ratio of 1.05 corresponds to a true odds ratio of roughly 1.07, a negligible effect.

The longitudinal analysis itself drew on the first three years of DAP diet data, covering 47,444 dogs enrolled before the end of 2023, including 7,786 dogs whose owners completed an end-of-life survey capturing diagnoses reported after the last annual follow-up. Confounders were identified using a directed acyclic graph, a formal causal inference tool, rather than ad hoc selection. The unadjusted odds ratio for grain-free diet on new cardiac diagnoses was 0.98, with a p value of 0.56. After adjusting for breed status, sex, neuter status, body size and survey year, the adjusted odds ratio was 1.05, with a confidence interval spanning 0.91 to 1.21 and a p value of 0.52. Mixed-effects models and a diet-switching analysis produced consistent results. Across every modelling approach, grain-free diet status showed no effect on the risk of incident cardiac disease.

What did matter were other factors. Single-breed dogs were more likely than mixed-breed dogs to receive new cardiac diagnoses, with an odds ratio of 1.23, and neutered animals were diagnosed substantially more often than intact ones, with an odds ratio of 1.68, the strongest association in the model. Larger dogs showed smaller odds ratios, and diagnoses became more common in later survey years. The researchers argue that neuter status, which may reflect biological protection from sex hormones or simply longer lifespans and greater time at risk, deserves far more attention in future diet and cardiac research, noting that previous studies may have been affected by failing to account for it.

The most common diagnoses in the cohort were murmurs, accounting for 57 percent of reported cardiac conditions, followed by congestive heart failure, valve disease and arrhythmia, each around 8 to 9 percent. Because murmurs and valve disease dominate the cardiac burden in companion dogs, the findings are particularly relevant to practitioners who have been advising owners to transition dogs with valve disease away from grain-free diets as a precaution. The authors caution, however, that the study was not designed to detect effects on individual cardiac diseases, nor does it examine whether diet influences survival after a diagnosis, questions that ongoing work aims to address.

Important limitations remain. The original DAP diet survey did not capture individual ingredients, so the analysis cannot speak to specific components such as peas, lentils or potatoes, which prior research has flagged as potential concerns when fed in high proportions, possibly through impaired amino acid digestibility and taurine status. Moreover, the data collection period of 2020 to 2023 coincides with years of intense public scrutiny, during which many manufacturers may have reformulated grain-free products to remove suspect ingredients. If industry reformulation has already addressed the problem, the absence of an association in this cohort may reflect safer formulations rather than proof that all grain-free diets were always harmless. The team also notes possible recall bias regarding diet duration and the possibility that diets were reformulated between the time they were fed and the time their ingredients were verified in 2025.

Even with those caveats, the study’s strengths are considerable: prospective data collection, three years of dietary exposure, inclusion of dogs that died during the study window, confounder selection guided by formal causal tools, and consistency across multiple analytical methods. The conclusion is preliminarily reassuring for the millions of dog owners who have worried, or been warned, that grain-free kibble might be silently damaging their pet’s heart. At the population level, grain-free status appears to have no effect on new cardiac diagnoses, and the imperfections in owner reporting, while real, were of a kind that could only have masked a true effect, not invented a clean bill of health. As the researchers emphasize, considerably more research is needed to determine whether specific ingredients affect specific cardiac diseases, but the blanket avoidance of all grain-free diets now lacks support from the largest longitudinal dataset yet brought to bear on the question.

Subject of Research: The relationship between grain-free diets and new cardiac diagnoses in companion dogs, and the accuracy of owner-reported diet data, in the Dog Aging Project cohort.

Article Title: Multiple Modelling Methods Suggest That Grain‐Free Diets Are Not Predictive of New Owner‐Reported Cardiac Diagnoses Over Two Years in the Dog Aging Project, Despite Owner Misclassification of Diet

Article References: O'Brien, J., Bishop, M., Dog Aging Project Consortium, Tolbert, M. K., & Ruple, A. (2026). Multiple Modelling Methods Suggest That Grain‐Free Diets Are Not Predictive of New Owner‐Reported Cardiac Diagnoses Over Two Years in the Dog Aging Project, Despite Owner Misclassification of Diet. Veterinary Medicine and Science, 12(5), Article e71213. https://doi.org/10.1002/vms3.71213

Image Credits: AI Generated

DOI: 10.1002/vms3.71213

Keywords: grain-free diets, canine cardiac disease, Dog Aging Project, dilated cardiomyopathy, diet misclassification, owner-reported data, veterinary nutrition, longitudinal study, logistic regression, causal inference, dog health, FDA investigation

The clinical story began long before the emergency that defined it. The boy was born at full term with a normal birth weight of 2608 grams, but by two months of age he was hospitalized for poor weight gain and declining cardiac function. Oral medications stabilized him enough for discharge after a two-month stay. Genetic testing eventually revealed a nonsense mutation, designated c.153C > G, in the TAZ gene, the molecular signature of Barth syndrome. This X-linked recessive condition arises from defects in an enzyme that remodels cardiolipin, a phospholipid essential to the structure and function of mitochondria, the energy-producing structures inside cells. The result is a constellation of problems: dilated cardiomyopathy in which the heart muscle stretches and weakens, generalized muscular hypotonia, and cyclical neutropenia that leaves patients vulnerable to infection. When the child was readmitted at one year of age with severe cardiac dysfunction and a brain natriuretic peptide level of 2096 pg/mL, a marker of profound heart strain, inotropic drugs failed to rescue him and he was transferred to Osaka for transplant registration and placement of a Berlin Heart EXCOR, the only durable ventricular assist device approved for small children in Japan.

His condition deteriorated faster than the transplant system could move. On admission he weighed just 6.1 kilograms and measured 67.5 centimeters. Echocardiography showed a left ventricle dilated to 38 millimeters, a z-score of +5.7 relative to normal body size, an ejection fraction of only 15 percent, and severe mitral regurgitation; his BNP had surged to 7667 pg/mL. Soon after arrival he developed runs of non-sustained ventricular tachycardia, a dangerous rhythm disturbance, and amiodarone therapy dropped his blood pressure. The team established venoarterial extracorporeal membrane oxygenation through neck vessels as an emergency salvage measure, but acute pulmonary congestion followed, forcing the decision to implant a biventricular assist device using centrifugal pumps. For the left side, surgeons used a 6-mm apical inflow cannula and a 6-mm arterial outflow cannula; for the right side, they placed a 14-Fr inflow cannula into the inferior vena cava via the right atrium and an 8-Fr outflow cannula into the distal pulmonary artery trunk, all secured with purse-string sutures.

What happened next is the technical heart of the report. The right ventricular assist device pumped roughly 900 mL/min, yet the left-sided pump could not function efficiently. The culprits were severe pulmonary hypertension and pulmonary regurgitation, which together prevented blood pushed into the pulmonary circulation from returning effectively to the left heart. In a decisive maneuver, the surgeons relocated the right-sided outflow cannula from the pulmonary artery into the left atrium, temporarily routing oxygenated blood directly to the left side of the heart and bypassing the obstructed pulmonary circuit. Left ventricular assist device flow stabilized at approximately 600 mL/min. The strategy bought time, but it carried trade-offs: left atrial cannulation raises the risk of systemic thromboembolism, and the circuit could not be disconnected from the artificial lung that oxygenates blood outside the body. The team therefore treated the configuration as a bridge within a bridge, to be dismantled as soon as the pulmonary vasculature could tolerate normal routing.

That evaluation came quickly. Cardiac catheterization on postoperative day 5, performed during temporary interruption of right-sided pumping, recorded a pulmonary artery pressure of 21/15 mmHg with a mean of 18 mmHg and a pulmonary vascular resistance index of 3.5 Wood units times meters squared, values indicating acceptable pulmonary vascular physiology. On postoperative day 13 the outflow cannula was moved back to the pulmonary artery trunk and the artificial lung was removed from the circuit. Bedside echocardiography then showed improving right ventricular contraction, but chest X-rays revealed progressing pulmonary congestion, which the surgeons attributed to excessive pulmonary blood flow generated by full right-sided support. Their response was a careful titration: right pump flow was gradually reduced to low-flow assistance. Throughout this period the left pump maintained a stable 900 mL/min flow and central venous pressure held near 12 mmHg even when right-sided support fell to 400 mL/min or was interrupted entirely, evidence that the native right ventricle and pulmonary circulation had recovered enough to fill the left pump on their own. Concerned about circuit thrombosis during prolonged low flow, the team removed the right ventricular assist device on postoperative day 20.

The recovery of other organs lagged behind the heart but eventually followed. Acute kidney and liver failure complicated the early postoperative course, requiring continuous hemodiafiltration from postoperative day 7. Bilirubin climbed as high as 15.1 mg/dL and renal dysfunction persisted for more than a month, but hemofiltration was discontinued on day 44, total bilirubin normalized on day 61, and the child was extubated on day 55. Only after these markers of end-organ recovery did the team secure in-house approval for heart transplant registration, the prerequisite under Japanese rules for implanting the Berlin Heart EXCOR, which was converted from the temporary centrifugal left ventricular assist device 76 days after the original biventricular implantation. The boy then remained stable on the pulsatile device for 374 days before undergoing successful heart transplantation, a total mechanical support journey of roughly 450 days from the first emergency pump to the donor heart.

The Osaka team frames the case within a strategy known as bridge to candidacy, an approach better documented in adults. In Japan, pediatric candidates face an average wait of 686 days for a donor heart, even though ten-year survival after pediatric transplantation reaches 96.2 percent, and by 2022 only 68 patients under 18 had ever been transplanted in the country. The Berlin Heart EXCOR has been approved there only since 2015 and only for patients already registered for transplantation, which creates a chicken-and-egg problem for infants whose comorbidities disqualify them from listing. Adult data show the workaround can succeed: large series report that short-term mechanical support can reverse refractory cardiogenic shock long enough for conversion to durable devices, with survival comparable to direct bridge-to-transplant pathways, though right ventricular support during the conversion emerges as a mortality risk factor. Pediatric evidence is thinner, but a Berlin group’s ten-year experience with 56 children and a multicenter United States study both suggest that prior extracorporeal support does not necessarily doom Berlin Heart outcomes, while low body weight, kidney and liver dysfunction, and biventricular support do worsen survival.

The case also contributes to a re-evaluation of Barth syndrome itself as a transplant indication. Because the condition combines heart failure with skeletal myopathy and immune compromise, patients were once considered unsuitable candidates, but after the first successful transplant in 1997, London investigators reported four successful cases, and a registry analysis of 43 transplanted Barth patients found outcomes for survival, infection, malignancy, and graft vasculopathy essentially equivalent to those of other recipients. The Osaka authors add an important caveat drawn from recent metabolic studies: transplantation does not fully normalize exercise tolerance, muscle mass, or substrate metabolism, because the underlying cardiolipin defect persists in skeletal muscle and other tissues. Their patient was not systematically assessed for these parameters after transplantation, a limitation the team acknowledges, and long-term multidisciplinary follow-up of neurodevelopment and metabolic status continues.

Beyond the individual rescue, the report is a detailed argument for staged, physiology-driven management of the failing right heart in small children. When pulmonary hypertension and valve regurgitation sabotage the left-sided pump, temporarily diverting right-sided outflow to the left atrium can stabilize the circulation; once catheterization confirms that pulmonary vascular resistance has fallen, rerouting to the pulmonary artery removes the thrombotic risk of left atrial cannulation and permits artificial lung removal, and stepwise flow reduction then tests whether the native right ventricle can carry the load. In this case that sequence converted a child in refractory cardiogenic shock with failing kidneys and liver into a registered transplant candidate with a durable device. The authors suggest the approach may extend the bridge-to-candidacy strategy to other high-risk pediatric patients with biventricular failure complicated by pulmonary hypertension, a population for whom waiting lists are long and options have historically been few.

Subject of Research: Bridge-to-candidacy mechanical circulatory support and heart transplantation in a pediatric patient with Barth syndrome-associated biventricular heart failure

Article Title: Successful bridge to heart transplantation in a pediatric patient with biventricular heart failure associated with Barth syndrome: a case report

Article References: Arita, K., Kido, T., Taira, M., Watanabe, T., Narita, J., Ishida, H., Ishii, R., Ueno, T., & Miyagawa, S. (2026). Successful bridge to heart transplantation in a pediatric patient with biventricular heart failure associated with Barth syndrome: a case report. Journal of Artificial Organs, 29(4), Article 60. https://doi.org/10.1007/s10047-026-01587-2

Image Credits: AI Generated

DOI: 10.1007/s10047-026-01587-2

Keywords: Barth syndrome, heart transplantation, ventricular assist device, Berlin Heart EXCOR, biventricular heart failure, pediatric cardiology, pulmonary hypertension, cardiogenic shock, mechanical circulatory support, TAZ gene, dilated cardiomyopathy, bridge to candidacy