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 raw feeding movement traces its modern popularity to the 1993 publication of Ian Billinghurst’s book Give Your Dog a Bone, which argued that dogs thrive on bones and raw meat reminiscent of an ancestral canine diet. Today the category encompasses home-prepared BARF recipes, prey-model regimens, commercial frozen and chilled complete diets, freeze-dried products, premixes combined with raw meat, and raw meaty bones. The review stresses that these categories are not interchangeable. They differ in nutrient formulation, ingredient traceability, pathogen-control procedures, storage requirements and owner handling, and studies that lump all raw diets into a single exposure may obscure important variation in risk.

On the nutritional front, the review finds that adequacy is genuinely product-specific. In one analytical study of 33 preprepared raw dog foods labelled as complete, every single product had at least three mineral values outside the FEDIAF reference range. Selenium fell below the minimum recommendation in all 33 products, zinc, manganese and copper were frequently below recommended intakes, 45.5 percent of products exceeded the maximum calcium recommendation, and 57.6 percent exceeded the maximum iodine value. The authors caution that these deviations identify quality-control concerns within the sampled products but do not by themselves establish clinical deficiency or toxicity in the dogs consuming them, and the findings should not be generalized to every commercial raw product on the market.

Home-prepared raw diets fare less well in the literature. Analyses of published recipes, drawn from a broader body of work on home-prepared diets, have identified frequent deficiencies in calcium, zinc, copper, vitamin D, vitamin E and choline. Ingredient rotation, a common owner strategy, does not guarantee nutritional completeness, because adequacy depends on quantitative formulation and nutrient bioavailability rather than variety alone. Puppies are especially vulnerable to inappropriate calcium and phosphorus concentrations, and excessive liver or unbalanced supplementation can produce vitamin and trace-mineral excesses. Professional guidance therefore supports formulation and periodic review by a veterinarian with advanced nutrition training, particularly for growth, disease management or long-term exclusive feeding.

Where raw diets do show consistent short-term effects is in digestibility and faecal characteristics. Controlled studies have repeatedly reported higher apparent total-tract digestibility of protein and fat in raw, mildly cooked or human-grade fresh diets compared with extruded kibble, along with smaller, firmer stools and reproducible changes in faecal microbiota and fermentation products. Yet the review urges technical caution in interpreting these numbers. The diets being compared rarely differ only in processing; they typically vary simultaneously in ingredients, fat, fibre, starch, moisture and energy density, so higher digestibility coefficients cannot be attributed to the absence of heat treatment alone. Human-grade mildly cooked diets can produce similar effects, and no universally accepted healthy canine microbiome signature exists against which these compositional differences could be judged beneficial or harmful. Crucially, long-term clinical superiority of raw feeding over nutritionally complete conventional diets has not been demonstrated.

The microbiological picture is where the evidence is strongest and most troubling. Because raw meat receives no thermal kill step, contamination can persist from slaughter through processing, transport and household handling. Surveillance studies across Europe and the Americas have repeatedly detected Salmonella, Campylobacter, Listeria monocytogenes, Shiga toxin-producing Escherichia coli, Yersinia enterocolitica and other enteric bacteria in commercial raw pet foods. The largest recent United Kingdom retail survey tested 380 frozen raw products collected between March 2023 and February 2024. In the dog-food subset, Salmonella was detected in 24.2 percent of samples, Campylobacter in 14.4 percent, culture-confirmed STEC in 13.4 percent and MRSA in roughly 10 percent, while ESBL- or AmpC-producing E. coli were found in 21.5 percent of the dog-food samples tested for that outcome. Across the full dataset, 28.7 percent of products exceeded statutory microbiological criteria.

The review is equally clear that freezing and freeze-drying are not reliable microbial kill steps. Viable bacteria have been recovered from commercial freeze-dried raw products, and available evidence indicates that drying may reduce rather than eradicate contamination. Parasites add another layer of concern, including Toxoplasma gondii, Sarcocystis species, Neospora caninum and, depending on geographic origin and offal source, Echinococcus. An Italian observational study found that dogs reported to consume raw meat regularly had nearly threefold higher odds of Toxoplasma seropositivity, supporting exposure plausibility even though raw meat cannot be confirmed as the sole source. Domestic freezers may not achieve validated time-temperature combinations uniformly, so parasite control requires source-specific rather than generic assumptions about freezing.

Dogs fed raw diets can shed enteric pathogens without showing any clinical signs, creating a household exposure pathway through food preparation, contaminated bowls and surfaces, faeces and close contact. Multiple observational studies have linked raw feeding to increased faecal carriage of Salmonella and antimicrobial-resistant E. coli, including third-generation cephalosporin-resistant and multidrug-resistant strains in United Kingdom dog populations. Whole-genome sequencing has identified closely related resistant Enterobacterales in companion animals and their household members, supporting recent sharing or a common source, although genomic relatedness alone cannot establish the direction of transmission. Documented human outbreaks underscore that severe outcomes are possible: a cluster of Shiga toxin-producing E. coli O157:H7 infections was linked to raw tripe pet food, and Canadian authorities investigated an outbreak of extensively drug-resistant Salmonella associated with raw pet food and cattle contact. The review notes, however, that outbreak reports establish possibility and severity rather than the population-level burden of raw-pet-food-associated human disease.

On the environmental side, the evidence is the least raw-diet-specific. Life-cycle assessments of pet food generally show that impacts are driven principally by the type and quantity of animal-derived ingredients, with ruminant and human-edible meat dominating land use and greenhouse-gas emissions. A recent United Kingdom analysis of 996 dog foods, including 34 raw products, estimated a greater than 65-fold range in greenhouse-gas intensity across products, with prime-meat content an important driver. Frozen products require cold-chain energy during distribution and home storage, whereas freeze-drying demands substantial manufacturing energy but reduces transport mass and avoids frozen storage, and few matched assessments have quantified these trade-offs. The authors conclude that a poultry or by-product-based raw food may compare favourably with a beef-rich premium kibble, so the raw format itself cannot be assumed intrinsically more impactful.

The review’s overarching message is that raw meat-based diets warrant product-specific and household-specific risk assessment rather than categorical judgement. For owners who choose to continue raw feeding, veterinary counselling should prioritize nutritionally complete formulation appropriate for life stage, manufacturer quality assurance, validated pathogen-reduction processes such as high-pressure processing that reduce but do not eliminate risk, uninterrupted cold chains, strict hygiene including bowl cleaning and handwashing, prompt faeces disposal, and explicit consideration of household vulnerability. Households containing infants, pregnant individuals, older adults or immunocompromised people face a lower margin of safety, and raw feeding may be inappropriate when their exposure cannot be reliably prevented. The authors call for adequately powered prospective cohorts, batch-level surveillance that distinguishes raw diet categories, whole-genome-sequencing source-attribution studies, validation of pathogen-reduction technologies, and matched life-cycle assessments before the long-term benefits and risks of raw feeding can be compared with high certainty.

Subject of Research: Nutritional adequacy, microbiological safety, antimicrobial resistance and environmental sustainability of raw meat-based diets for dogs within a One Health framework

Article Title: Raw meat based diets for dogs and their nutritional and One Health implications

Article References: Tufarelli, V., & Bozzo, G. (2026). Raw meat based diets for dogs and their nutritional and One Health implications. Discover Animals, 3(1), Article 84. https://doi.org/10.1007/s44338-026-00249-0

Image Credits: AI Generated

DOI: 10.1007/s44338-026-00249-0

Keywords: raw meat-based diets, dog nutrition, One Health, Salmonella, antimicrobial resistance, zoonotic pathogens, pet food safety, BARF diet, foodborne illness, life cycle assessment, Toxoplasma gondii, veterinary nutrition