Why is grain-free bad for dogs? What the latest research actually shows

If you’ve been worrying about grain-free dog food and dilated cardiomyopathy, here’s the unsettling-but-important update: the science has moved forward since the FDA’s last public report, and the answer today is more specific than “grain-free is bad.” It’s also more concerning.

In December 2025, a Tufts veterinary nutrition team won the inaugural AKC Canine Health Foundation Discovery of the Year award for identifying a likely mechanism behind diet-associated DCM — the first biologically plausible explanation for what those pea-and-lentil-heavy diets may actually be doing to dogs’ hearts. The implications change how we’d read a dog food label today, and they don’t fit neatly on the page-one Google results that were written in 2019 or 2022.

The short answer has changed since 2018

The original 2018 FDA notice that kicked off this whole conversation flagged “grain-free” diets as a potential risk for non-hereditary dilated cardiomyopathy in dogs. Reports of DCM in breeds without a known genetic predisposition — Golden Retrievers, Labs, mixed breeds — started piling up at the agency. By 2019, the FDA had identified 16 dog food companies with ten or more associated DCM cases, and the AKC’s review of that data found more than 90% of the implicated diets were grain-free and 93% contained peas or lentils.

That second statistic turned out to matter more than the first. Researchers spent the next several years digging into what actually distinguished the DCM-associated diets from regular dog food, and the consistent finding wasn’t the absence of grains. It was the presence of pulses: the dried seeds of plants like peas, lentils, chickpeas, and dry beans, used in grain-free formulas as protein and carbohydrate replacements for things like rice or corn.

The Tufts University team, led by veterinary nutritionist Dr. Lisa Freeman, has published more than 30 peer-reviewed studies on diet-associated DCM, and the picture they’ve built is consistent. Pulse-rich diets are the common thread. Some grain-INCLUSIVE diets also contain heavy doses of pulses and have been associated with DCM cases. The “grain-free” framing was a marketing category that happened to correlate with the actual nutritional risk factor, but it was never the precise description.

The FDA stopped publishing routine updates on its investigation in December 2022, which a lot of pet owners read as “case closed, never mind.” That’s the wrong read. The FDA paused updates because they don’t have the resources to keep investigating every report, not because the link was disproven. Academic research kept going — and accelerated, actually.

The mechanism discovery that changed the science

On December 16, 2025, the AKC Canine Health Foundation announced Dr. Freeman as the winner of its inaugural Canine Health Discovery of the Year Award. The recognition was for her team’s 2025 paper in the American Journal of Veterinary Research, which did something the field had been missing for seven years: it proposed a plausible biological mechanism for how pulse-rich diets damage the heart.

Here’s what the study found, in plain English. Freeman’s team measured urine samples from dogs with diet-associated DCM and compared them to healthy controls. They were looking for a specific compound: di-22:6-BMP, a known biomarker for drug-induced phospholipidosis in humans and other animals. Dogs with DCM eating high-pulse diets had significantly elevated concentrations of this biomarker compared to dogs with DCM on low-pulse diets and compared to healthy dogs on either type of diet.

Phospholipidosis sounds like a Scrabble word, but the idea is straightforward: certain substances cause abnormal accumulation of phospholipids inside cells, particularly inside the cellular structures called lysosomes. That buildup damages tissue. In humans, drug-induced phospholipidosis is a known toxicity pattern for certain medications. The Tufts team’s hypothesis is that something in pulse-rich diets — they’re still working on identifying what — triggers a similar process in dogs, with the heart being one of the affected tissues.

What this doesn’t mean: the case isn’t closed. The FDA still hasn’t formally concluded a causal link. Phospholipidosis is a strong lead, not a verdict. But Freeman’s team is now investigating which compounds in pulses are responsible and how they trigger the process, which is the actual question that needed answering.

It’s not grain-free — it’s pulse-rich

The practical implication is that “grain-free” is the wrong filter to apply when reading a dog food label. The actual question is: does this diet rely heavily on pulses as protein and carb sources?

Pulses are the edible seeds of legume plants. The ones most strongly associated with DCM cases are:

• Peas — and their derivatives: pea protein, pea flour, pea fiber, pea starch (these often appear as multiple separate ingredients in the same bag, which is a label-splitting tactic that hides total pea content)
• Lentils — green, red, yellow
• Chickpeas (also labeled as garbanzo beans or chickpea flour)
• Dry beans — navy, kidney, pinto, black, white
• Some research also implicates potatoes and sweet potatoes, but the evidence here is weaker than for pulses

What’s interesting is that soy — which is technically also a legume — has NOT shown up as a DCM signal. Tufts’ Petfoodology team notes the association is specifically with non-soy pulses. That’s a clue researchers are still working with.

The label test is simple: read the first 10 ingredients on your dog’s food. If you see one or more pulses listed there, especially as multiple variants (pea protein + peas + pea flour), the diet is pulse-rich regardless of whether the bag says “grain-free” or not. Some grain-inclusive diets — yes, the kind with brown rice or oatmeal in the formula — also load up on peas and lentils to hit protein targets cheaply. The grain-free label is neither necessary nor sufficient to identify the risk.

Which dogs are most at risk

The FDA data through November 2022 showed 1,382 reported DCM cases from 2014 onward, with the vast majority concentrated between 2018 and 2020 — the peak of the grain-free trend. The breeds with the most reports weren’t the ones traditionally prone to genetic DCM (Doberman Pinschers, Boxers, Great Danes for the genetic form). Instead, the top breeds in the FDA data were:

The breed distribution tells you something important: this isn’t a “your dog’s breed is or isn’t at risk” question. Any dog eating a pulse-rich diet for a long enough time can develop diet-associated DCM. Dogs from breeds with a separate genetic predisposition to taurine sensitivity — Cocker Spaniels, Newfoundlands, Goldens, English Setters — may be at heightened risk because their bodies are less efficient at managing taurine on a marginal diet, but they’re not the only ones affected.

Time on the diet is the other variable that matters. Most cases reported to the FDA were dogs that had been on the implicated diet for more than a year, often several years. DCM is a slow disease; the heart can be showing sub-clinical changes — early enlargement, irregular rhythms — long before obvious symptoms appear. A 2024 study of Irish Wolfhounds found that even apparently healthy dogs on high-pulse diets had significantly more ventricular premature contractions (a type of irregular heartbeat) than those on low-pulse diets. The heart starts to notice well before the owner does.

This is also a quiet argument for periodic cardiac screening if your large or giant breed has been on a pulse-rich diet for years. We covered large and giant breed feeding considerations more broadly in our piece on elevated dog bowls, which also bears on the bloat-prone breeds where any cardiac stress matters more.

Symptoms to watch for

DCM presents differently in different dogs, but the common signs reflect a heart that can’t pump efficiently:

• Coughing, especially when lying down or at rest (fluid buildup in or around the lungs)
• Exercise intolerance — your dog tires faster than usual, doesn’t want to walk as far, slows down mid-play
• Labored or rapid breathing, especially at rest
• Fainting or collapse, often during or right after exertion
• Abdominal distension from fluid retention
• Pale or bluish gums, especially with exertion
• Weight loss or visible muscle loss, particularly along the topline

The frustrating thing about early DCM is that it often shows up first as “my dog seems a little slower lately” or “she’s coughing a bit when she sleeps.” Both are easy to write off as aging. If your dog has been on a pulse-rich diet for over a year and you’re noticing any of these patterns, an echocardiogram with a board-certified veterinary cardiologist is the diagnostic standard. The procedure itself typically runs $300 to $600 at a general practice and $600 to $1,000+ as part of a full workup at a board-certified cardiologist, depending on market — which is one of the reasons people start to take a hard look at what a comprehensive vet workup actually costs when the cardiology referrals start.

What to do today: the label check and brand selection

The actionable side of all this isn’t complicated, but it does involve actually reading the bag.

One thing worth flagging: don’t panic-switch. Sudden diet changes cause GI upset, and if your dog is on a grain-free or pulse-heavy diet for a real medical reason — diagnosed protein allergies, a prescribed therapeutic diet — talk to your vet before switching. For dogs whose owners picked a pulse-rich diet because the marketing sounded good or the bag had a wolf on it, transitioning over 7-10 days to a manufacturer-vetted, low-pulse formula is the standard play.

This is also where the food allergy picture gets nuanced. We’ve written about French Bulldog food allergies and the elimination diet protocol, which is one of the few legitimate medical reasons to be feeding a novel or limited-ingredient diet. The grain-free movement scooped up a lot of dogs whose actual problem was a chicken allergy, not anything to do with grains, and the pulse-replacement carbs created a different problem entirely.

The good news: diet-associated DCM can improve

One important distinction between hereditary DCM and diet-associated DCM is that the diet-associated form is partially reversible. Hereditary DCM tends to be a one-way street — medications manage symptoms but don’t restore lost heart function. Diet-associated DCM, by contrast, often shows measurable echocardiographic improvement after a diet change, sometimes within months.

The Animal Medical Center summarized a 2025 study showing that dogs eating non-traditional diets diagnosed with DCM or early heart muscle changes showed improvement in heart function when their diet was changed to a traditional diet. Veterinary cardiologists have been observing this pattern clinically for several years — it’s part of why they were confident enough to keep recommending diet changes even while the FDA’s mechanism investigation was still open.

That reversibility window is also why early detection matters so much. Catching sub-clinical heart enlargement before it progresses to symptomatic congestive heart failure is the difference between “we changed her diet and her echo normalized over six months” and “we’re managing her CHF for whatever time she has left.” Cardiac medication regimens for DCM dogs aren’t cheap or simple — pimobendan, ACE inhibitors, diuretics, often more — and the lifetime cost of managing late-stage CHF can run into the thousands per year, which is part of what makes long-term pet insurance for senior dogs a real conversation worth having before you need it.

The honest caveats

A few things worth saying directly, because the dog-food internet tends to split into two camps and neither one is fully right.

First: the FDA has not formally established causation. They have a strong correlation, a growing body of mechanism research, and clinical reversal patterns when dogs are switched off implicated diets. That’s not the same as a controlled randomized trial proving causation, which would be unethical to run. The veterinary research community thinks the weight of evidence supports caution, but they say “associated with” rather than “caused by” for a reason.

Second: the funding picture in this research is real and worth knowing. Several of the lead researchers — including Dr. Freeman — have received research funding, sponsored lectures, or professional services payments from major grain-inclusive pet food manufacturers like Hill’s, Purina, and Royal Canin. A 2022 journalist investigation flagged these ties as a potential source of bias. The researchers have been transparent about disclosing funding in their published papers, and the actual data they’ve collected is what it is, but pretending the financial picture doesn’t exist is naive.

Third: the boutique grain-free industry has not been a neutral party either. Many of the implicated brands changed their formulations during the investigation period — quietly reducing pulse content or adding taurine supplementation — which makes retrospective analysis harder and arguably suggests the brands themselves took the signal seriously, regardless of what their marketing was saying publicly.

The honest synthesis: it’s a “where there’s smoke” situation. Over 30 peer-reviewed studies, a 2025 mechanistic discovery, consistent clinical reversal patterns, FDA case data biased but not invented, and a research community that’s gotten more confident about the pulse-DCM link, not less, since 2018. That doesn’t add up to a clean verdict. It adds up to “the smart move is to read labels and pick a manufacturer with veterinary nutritionists on staff.” Which is a less satisfying answer than “grain-free bad, problem solved,” but it’s the one the science actually supports.

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