When I left vet school in 1999 there was no such thing as grain-free pet food. But over the past few decades, it has become one of the most influential trends in the pet food industry.
Over the years new pet food brands, needing a point of difference in a competitive market, have convinced pet owners that grains are “fillers” – cheap, unnecessary padding that had no place in their dog’s diet. Instead, they should be eating a high protein, high meat diet like their wolf ancestors.
There was just one problem.
Animal-derived protein is expensive.
When grains were removed from many pet foods, they often weren’t replaced with more meat. Instead, they were replaced with legumes.
Ingredients such as peas, lentils, chickpeas and faba beans contain protein too, allowing manufacturers to achieve the high protein percentages they had convinced consumers their dogs needed, but at a much lower cost than using equivalent amounts of animal-derived protein.
For a few years this seemed to work out fine.
Then something unexpected happened.
The Connection Between Grain-Free Dog Food and Heart Disease in Dogs
Veterinary cardiologists in the United States noticed an unusual increase in dogs developing dilated cardiomyopathy (DCM), a serious heart disease where the heart muscle becomes enlarged and weak, eventually leading to heart failure and death.
DCM itself was not new. Veterinarians had seen it for years, particularly in breeds with a known genetic predisposition to the disease. Dobermans and Great Danes being the classic examples.
What was unusual was the type of dogs developing it.
Suddenly, cardiologists were diagnosing DCM in breeds not normally considered high-risk, including Golden Retrievers, Whippets, Miniature Schnauzers, and pit bull-type breeds. Many of these dogs had one striking thing in common: they were eating grain-free diets that were very high in legumes.
The other unusual aspect was that many affected dogs improved following dietary change, something that doesn’t happen with inherited DCM.²
In July 2018, the US Food and Drug Administration (FDA) launched a formal investigation. By the time the FDA published its last major update in late 2022, over 1,380 dogs and 20 cats had been reported with possible diet-associated DCM. More than 90% of implicated diets were grain-free, and 93% contained peas and/or lentils as prominent ingredients.¹
Some grain-free brands have pointed to the FDA’s decision to pause public updates in late 2022 as evidence that the issue has been resolved. It hasn’t.
The FDA paused updates specifically because the science was not yet conclusive, not because the concern had abated. Research has continued to accumulate since then.
What Does the Current Research Actually Say About Grain-Free Diets and Heart Disease in Dogs?
After more than 30 peer-reviewed studies, including controlled feeding trials, metabolomic analyses, cardiac imaging studies, and long-term echocardiographic monitoring across multiple universities, a more coherent picture is emerging.³
Unfortunately there is no simple answer. But, the evidence increasingly suggests that diet-associated DCM is a multifactorial condition, where several nutritional and biological factors interact in genetically susceptible dogs.
Does Taurine Deficiency Cause Diet-Associated DCM in Dogs?
In the 1980s veterinarians discovered that many cats developing DCM were deficient in taurine, an amino acid found almost exclusively in animal tissues. When taurine was added back into their diets, many of these cats recovered, transforming what had once been considered an untreatable heart disease into a preventable nutritional condition.⁴
So, when veterinary cardiologists began seeing unusual cases of diet-associated DCM in dogs decades later, it was entirely logical to ask whether the same thing might be happening again.
Dogs, however, are different.
Unlike cats, dogs do not have a dietary requirement for taurine. Healthy dogs synthesise taurine from two sulphur-containing amino acids, methionine and cysteine, provided these amino acids are available in sufficient quantities.
Early investigations found that some affected dogs, particularly Golden Retrievers, had low blood taurine concentrations, and many improved after a change in diet, often alongside taurine supplementation and standard cardiac treatment.⁵
At first, taurine deficiency seemed to explain the problem.
However, as more dogs were studied, researchers discovered that many affected dogs had normal taurine concentrations despite developing DCM.⁶ ⁷
This was a turning point.
It suggested that taurine deficiency could explain some cases, but not all of them. Researchers therefore began looking more broadly at how certain diets might influence taurine metabolism, nutrient availability and heart function.
Can Legume-Heavy Diets Affect a Dog’s Ability to Make Taurine?
As we’ve established, dogs synthesise taurine from the sulphur-containing amino acids methionine and cysteine. But this process depends entirely on those precursor amino acids being present in the diet in sufficient, bioavailable amounts.
This is important because nutrition is not simply about the total percentage of protein in a food. What ultimately matters is the amino acids that protein provides. Different protein sources provide different amino acid profiles, and not all proteins are nutritionally equivalent.⁸
Compared with animal proteins and grains such as rice and oats, legumes are significantly lower in the sulphur-containing amino acids methionine and cysteine - meaning fewer of the precursors dogs need to synthesise taurine are present in the diet.
Legumes also contain naturally occurring compounds known as anti-nutritional factors, including phytates, tannins and trypsin inhibitors, which can reduce the digestibility and bioavailability of nutrients. Although cooking and processing reduce many of these effects, they do not eliminate them entirely.
Replacing grains with large amounts of legumes may therefore inadvertently reduce the bioavailability of the amino acid precursors needed for taurine synthesis, with downstream consequences for taurine metabolism and heart health.⁹
Do Genetics Make Some Dogs More Vulnerable to Diet-Associated DCM?
Some breeds may naturally have higher taurine requirements than others or have a metabolic difference that affects how efficiently they synthesise or utilise taurine.
Golden Retrievers have been the most extensively studied breed, and research has shown that breed-specific taurine reference intervals are higher than those reported for the general dog population, suggesting these dogs may have greater metabolic demands for taurine than most other breeds.¹⁰
A predisposition to taurine deficiency has also been identified in several other breeds, including Newfoundlands, American and English Cocker Spaniels, English Setters, and Labrador Retrievers. Body size may also play a role - there is evidence that large adult size combined with a relatively slow metabolic rate can influence the rate at which dogs produce taurine.¹¹
This may help explain why some dogs develop diet-associated DCM while others eating identical food remain unaffected.
How Do Legumes Deplete Taurine? The Bile Acid–Fibre Connection Explained
Legumes are high in fermentable soluble fibre, significantly higher than traditional grains like rice or oats. In the gut, this fibre binds to bile acids - compounds the liver produces to aid digestion that are chemically linked to taurine before being released into the intestine.
Normally these bile acids are reabsorbed and recycled back to the liver. But when large amounts of soluble fibre are present, they are carried out in the faeces along with their attached taurine. The gut microbiome accelerates this further by breaking down bile acids before they can be recycled. Because no two dogs share the same gut microbiome, the extent to which this happens varies significantly between individuals, although the precise mechanisms involved are still being investigated.
The body must now synthesise new bile acids to replace those lost, continually drawing on its taurine reserves. In most dogs this drain can be managed. But in dogs with a genetic limitation in taurine synthesis, a microbiome that breaks down bile acids particularly rapidly, or insufficient methionine and cysteine in the diet, taurine can eventually be depleted within cardiac tissue - even when blood levels still appear normal.
This mechanism helps explain:
• Why legumes show up so consistently in the diets of affected dogs
• Why taurine supplementation often helps even when blood taurine isn’t low
• Why diet change allows some dogs to recover cardiac function
• Why two dogs eating identical food can have completely different outcomes
• Why certain breeds are far more vulnerable than others ⁷ ¹²
Could Legumes Damage the Heart Through a Mechanism Beyond Taurine?
A 2025 study from Tufts University found evidence that certain compounds in high-legume diets may directly cause damage to heart muscle cells. The researchers identified a urinary biomarker suggesting that the internal recycling machinery within cardiac cells was being disrupted.¹³
It is early evidence and not yet fully understood, but it may help explain why some dogs fail to improve even when taurine is supplemented, and raises the possibility that legume-rich diets may affect heart health through more than one pathway simultaneously.
When Does Legume Inclusion in Dog Food Become a Problem?
The short answer is: when legumes stop being supplementary ingredients and start being significant contributors to both the protein and carbohydrate in the formulation.
One of the clearest messages to emerge from the diet-associated DCM investigations is that formulation quality matters. Replacing grains with large amounts of legumes fundamentally changes the nutritional profile of a diet and formulating a genuinely complete and balanced food is far more complicated than simply meeting minimum nutrient requirements on paper.
Historically, legumes were used in small amounts alongside grains. The concern is not that they are inherently dangerous, but that some modern formulations rely on them to a degree that was rarely seen before the grain-free trend emerged.
A review of pulse ingredients in pet foods concluded that legumes can make valuable nutritional contributions when used appropriately, while also highlighting the importance of understanding how high inclusion rates may influence nutrient digestibility, amino acid availability and overall diet formulation.¹⁴
The most useful question to ask when evaluating a dog food is simply this:
“What role are legumes playing in this formulation?”
Because, based on what the research currently shows, the risk concentrates in a specific set of circumstances: high legume inclusion rates, in diets without careful attention to amino acid bioavailability, in genetically susceptible dogs, fed over a prolonged period.
How Has Diet-Associated DCM Shaped How I Developed Our Ocean Fish Recipe?
At the time I was developing our Ocean Fish recipe, one of the veterinary cardiologists at the forefront of the diet-associated DCM investigations was clear in his guidance: until we understood more, he would avoid feeding heavily legume-based grain-free diets.
That advice aligned with my own interpretation of the emerging evidence and is reflected in our final formulation.
It’s worth noting that many of the brands most heavily associated with grain-free nutrition during the FDA investigation have since quietly introduced grain-inclusive recipes into their ranges, without explanation. For me, that shift validates a formulation decision I made years earlier, when the evidence was still emerging.
Our Ocean Fish recipe contains 9% peas, considered a low level of legume inclusion, and well below the levels that have flagged concerns in the research. Alongside that sits 12% rice. That combination is not accidental.
Peas are relatively rich in lysine but low in the sulphur-containing amino acids methionine and cysteine - the very precursors needed for taurine synthesis, and the exact nutrients implicated in the bile acid drain mechanism described above. Rice provides the inverse profile: lower in lysine but higher in methionine and cysteine. Used together in appropriate proportions, they complement each other in a way that neither ingredient achieves alone.
Independent laboratory testing of our Ocean Fish recipe at Massey University’s accredited Nutrition Laboratory confirms that our combined methionine-cystine level sits at 1.18% on a dry matter basis - well above the AAFCO minimum requirement of 0.65%. These are the amino acids that matter most in the context of taurine synthesis and DCM risk.
Although AAFCO sets no minimum levels for taurine in dog food, we do test for taurine and our food contains taurine at 0.19 mg/100mg dry matter. This comes naturally from our ocean fish protein source and we also supplement taurine directly in our vitamin and mineral premix.
This means our food supports taurine through three independent pathways simultaneously: naturally occurring taurine from our ocean fish protein source; direct taurine supplementation in the premix and robust methionine and cystine levels that support the dog’s own endogenous taurine synthesis. No single pathway is relied upon alone.
Unlike heavily legume-based formulations, our recipe doesn’t rely on high-fibre plant ingredients as bulk, which means less interference with the bile acid recycling process described earlier.
You'll also never see us engage in the practice of ingredient splitting. This is where manufacturers list the same ingredient in multiple forms, such as peas, pea protein and pea fibre as separate entries, making each appear lower on the ingredient list than the combined legume proportion actually warrants. If you look at our ingredient list, what you see is what you get.
So, Should You Feed Your Dog a Grain-Free Diet?
My honest answer as a veterinarian: not if there’s a well-formulated alternative available. The evidence doesn’t prove grain-free diets cause DCM in every dog, but it does suggest that heavily legume-based formulations carry a risk that simply isn’t worth taking when good alternatives exist.
We still don’t have every answer, and I will continue to follow this research closely. My thinking and how we formulate our products will evolve as the evidence does.
One thing is clear: pet nutrition is rarely as simple as marketing makes it seem.
Good nutrition shouldn’t follow trends. A complete and balanced diet is far more than a list of ingredients - it’s the result of understanding how those ingredients interact to deliver the right nutrients in forms the body can actually digest, absorb and use over a lifetime.
I take the trust you place in me when choosing to feed Genius very seriously. And I feed this food to my own dog.
Every formulation decision was made with the evidence in mind, working alongside a specialist pet nutritionist. At the end of the day, I need to be able to sleep at night.
And I do.
— Dr Paula Short, Veterinarian and Founder, Genius Pet Food
Frequently Asked Questions
Is grain-free dog food bad for dogs?
Not necessarily. Current evidence does not suggest that all grain-free diets are harmful. However, grain-free diets that rely heavily on legumes such as peas, lentils and chickpeas have been consistently overrepresented in reported cases of diet-associated DCM.
What is diet-associated DCM?
Diet-associated dilated cardiomyopathy (diet-associated DCM) is a form of heart disease that appears to be influenced by diet rather than inherited genetics. Unlike inherited DCM, many affected dogs have shown improvement following dietary change, often alongside taurine supplementation and standard cardiac treatment.
Does grain-free dog food cause heart disease?
A direct causal relationship has not yet been proven. However, an association between certain grain-free, legume-rich diets and diet-associated DCM has been observed repeatedly in reported cases and scientific investigations. Researchers are continuing to investigate the underlying mechanisms.
Are peas bad for dogs?
No. Peas are nutritious ingredients that have been used safely in pet foods for many years. The concern is not the presence of peas themselves, but formulations that rely heavily on legumes as major sources of both protein and carbohydrate.
Why does the amount of legumes in a food matter?
Current research suggests that the role legumes play within a formulation may be more important than simply whether they are present. Historically, legumes were used in relatively small amounts alongside grains. The concern raised by recent research is that some modern grain-free diets rely on legumes as major sources of both protein and carbohydrate, fundamentally changing the nutritional profile of the diet.
Should I avoid grain-free dog food?
Every dog is different, and dietary decisions should always be made in consultation with your veterinarian. Personally, based on the current evidence, I would be cautious about feeding a heavily legume-based grain-free diet unless there were compelling medical reasons to do so.
Is grain-free dog food better for allergies?
Not usually. Most food allergies in dogs are caused by proteins rather than grains. Unless a dog has a confirmed allergy to a specific named grain, which is uncommon, there is generally no evidence that a grain-free diet is healthier or less likely to trigger allergic disease. Many dogs that improve on a grain-free diet may actually be responding to a change in protein source rather than the removal of grains.
References
¹ FDA Investigation into Potential Link between Certain Diets and Canine Dilated Cardiomyopathy - US Food & Drug Administration
² Association of diet with clinical outcomes in dogs with DCM and congestive heart failure - Walker et al., 2022. Journal of Veterinary Cardiology
³ Diet-associated DCM: systematic review - Mansfield et al., 2024. Journal of Small Animal Practice
⁴ Myocardial failure in cats associated with low plasma taurine - Pion et al., 1987. PubMed
⁵ Prospective study of DCM in dogs eating non-traditional or traditional diets - Freeman et al., 2022. PubMed
⁶ Effect of type of diet on blood and plasma taurine concentrations, cardiac biomarkers, and echocardiograms in 4 dog breeds - Adin et al., 2021. Journal of Veterinary Internal Medicine
⁷ Effects of a 28-day feeding trial of grain-containing versus pulse-based diets - Quilliam et al., 2023. PubMed / PLOS ONE
⁸ Investigation of diets associated with DCM using foodomics analysis - Smith, Freeman et al., 2021. Scientific Reports / PMC
⁹ Taurine-Deficiency versus Diet-Associated DCM in Dogs: Mechanistic Review. WJARR
¹⁰ Development of plasma and whole blood taurine reference ranges in Golden Retrievers - Ontiveros, Stern et al., 2020. PubMed / PLOS ONE
¹¹ Role of Diet as a Predisposing Factor for DCM in Dogs: A Narrative Review - Pezzali et al., 2025. Veterinary Sciences / MDPI
¹² Retrospective study of DCM in dogs eating non-traditional diets. PMC
¹³ Dogs with diet-associated DCM have higher urinary phospholipidosis biomarker - Freeman et al., 2025. PubMed
¹⁴ Pulse ingredients in pet food — Mansilla WD et al., 2019. Journal of Animal Science
