Going against the grain: grain free diets

Update: This post has been updated to include the latest research on grain free diets and dilated cardiomyopathy

You may have heard the lastest buzzword in pet food is “grain free”. However, grain free pet foods came into the market with little to no scientific evidence to support the trend that was largely led by consumer demand following an increase in the popularity of gluten free diets for humans and an incorrect assumption that this is a “healthier” option. Unfortunately, human healthcare trends cannot and should not be extrapolated to cats and dogs, as they are vastly different to us and do not always share the same diseases or disease processes that we do; in fact, coeliac disease (for which the gluten free diet is designed to treat) has only been noted in one breeding line of the Irish Setter dog, that has since had it bred out – no other dogs or cats show diseases directly related to or caused by the presence of grains. However, the absence of grain from the pet’s diet is currently being investigated due to a suspected link to a form of heart disease called Dilated Cardiomyopathy.

Grain free diets are not necessarily a healthier choice

So why does grain free continue to be a popular choice for pet owners? The answer lies in client education. Clients by and large don’t read scientific reports, recall lists, statistics or have the background to wade through the misinformation and discern what is marketing and what is the truth. That’s our responsibility as veterinary professionals; to explain, interpret and educate pet owners to be able to sort the fact from fiction. So let’s go through some of the common questions and beliefs owners have about grains and grain free diets and how we can help them understand the science:

What are the benefits of grains in pet food?

– A fantastic source of carbohydrates; providing an easy to digest form of energy

– Each grain source has its own nutrient profile, and have unique benefits that can be used to provide many different nutrients to the food

– Provides prebiotic fibres, feeding the intestinal microbiome for healthy gut bacteria, immune system function and good stool consistency

– Good source of essential fatty acids; corn for example is a potent source of linoleic acid and amino acids

– By using grain as a carbohydrate energy source, it allows fats and proteins to be freed up so they can be better utilised for skin and coat health, supporting the immune system and body/muscle condition

What we know so far

The latest research we have on grain free diets points to the inclusion of suspect ingredients such as peas, legumes and lentils. These are used to replace the grain and offer a carb source in the diet. Groundbreaking research comparing the top DCM implicated diets showed a correlation between high pea and lentil content appears to impact the bioavailability of certain nutrients that are vital to heart health. B group vitamins were significantly lower in diets high in peas, which act as cofactors in the chemical pathways that make taurine and l-carnitine. A deficiency in B1, also known as thiamine, is known to directly cause dilated cardiomyopathy so this is also being explored as a potential trigger. This study also found that the diets high in peas and lentils contained cardiotoxic compounds that directly damage the heart muscle such as cyanide. It’s no longer believed that anti-nutrient factors play a role in the condition as these are largely inactivated by cooking and processing. For more on this research and analysis, read the full study here.

But my pet has grain allergies!

One of the most common reasons cited by pet owners for changing to a grain-free diet was allergies; when treating a food allergy, you may be recommended to try a ‘novel protein source’ meaning a type of meat protein your pet has never had before. Majority of food allergies in dogs and cats are caused by meat based proteins, not grains. The most common allergens are chicken, beef and lamb therefore a dietary change to a different meat source (such as venison, duck, crocodile, or kangaroo, etc) owners typically will notice their pet has improved. Where grain-free diets come into play, is they often also contain a novel protein source, thus causing a resolution of symptoms – which leads owners to assume that grain was the problem, despite the fact that the absence of grain in the diet is actually not having any effect on the patient’s condition.

But pets don’t need carbs!

A grain free diet isn’t a carb free diet. When grains are removed from the diet, a carb source still needs to be added to provide the benefits as mentioned above. In the case of grain free diets, other carb sources such as legumes, soybeans, potato or peas may be utilised – and it’s these carb sources that are believed to be the culprit between grain free diets and DCM as diets with lots of peas or soybean seemed to have more DCM cases reported so far.

Despite pets not having any absolute requirement for carbohydrates, it doesn’t mean that a carb-free diet is a good idea, or even possible to achieve in most cases. A carb-free diet would lack in fibre – despite also not being an essential nutrient itself, fibre is vitally important and incredibly beneficial to the gut microbiome and a lack of fibre can cause a range of issues such as diarrhea, constipation, or anal gland impaction. Carbohydrates have not, as some may claim, been linked to obesity or weight gain, in fact they can help regulate body weight; increased fibre diets allow for the formulation of moderate to low fat weight loss diets by increasing bulking and enhance fullness of the patient to reduce begging. In addition, carbs are an easy to digest, readily available source of glucose and are often utilised in some performance diets for racing dogs.

Carbohydrates are readily available sources of energy for working dogs

But…what about carnivores?

Cats are obligate carnivores, so require meat to be present in their diet. It does not mean, however, that they must eat only meat to survive (in fact this is not a balanced diet and will likely cause many other issues in the long run). It also does not mean that cats do not (or cannot) eat or digest carbohydrates. In the wild, cats (and dogs) will eat the internal organs of their prey first as this is the most nutritious part of the body. Held within the stomach and intestinal contents of their (typically herbivorous) prey is plant matter, which the carnivore also ingests. Cats and dogs have the necessary enzymes to digest carbohydrates for this reason and can break it down into simple sugars for absorption in the small intestine as an energy source.

So what should I do now?

If you’re feeding your pet a grain-free diet, have a think about why you’ve chosen this diet:

Was it allergies? Speak to your vet about starting a food elimination trial to determine the true cause of their allergies – if they improved on the grain free diet, what is the meat protein source being used? Was it different from their previous diet? If this is the case, you’ve probably already determined a few problem proteins for your pet and may need to find a diet that avoids those protein sources, or potentially use a therapeutic hydrolysed diet where the protein is broken down and no longer recognised as an allergen.

If you are concerned about feeding carbohydrates to your pet, or are concerned about weight gain, ask about your options for weight loss diets, or lower carb options such as wet diets.

The FDA investigation into the potential link between DCM and grain free diets is ongoing, however if you are concerned about heart disease, your pet is an at risk breed or your pet is displaying symptoms such as exercise intolerance, coughing or difficulty/rapid breathing and is on a grain free diet, please seek the advice of your vet who may refer your pet to a veterinary cardiologist for evaluation, and submit a report to the FDA.

As these diets are typically not well researched or science based, I’d recommend transitioning to a diet that includes grains and is heavily researched and quality controlled, as there’s just too many unknowns with grain free diets and I’d rather be safe than sorry. The current evidence from the FDA investigation suggests any potential damage to the heart from eating a grain free diet can be either fully or partially reversed with a diet change to a grain inclusive formula, so it’s never too late to switch.

If you still insist on feeding grain free, ask your veterinarian or nutritionist for a recommendation on a science-based, feeding trialled and researched formula that is grain free.

So do you feed grain free? What made you choose to feed grain free to your pet?


Food and Drug Administration. (2019) Investigation of Potential Link Between Certain Diets and Canine Dilated Cardiomyopathy. [website] Available at: https://www.fda.gov/animal-veterinary/outbreaks-and-advisories/fda-investigation-potential-link-between-certain-diets-and-canine-dilated-cardiomyopathy [Accessed on 3/11/2020]

Richard C. Hill, The Nutritional Requirements of Exercising Dogs, The Journal of Nutrition, Volume 128, Issue 12, December 1998, Pages 2686S–2690S, https://doi.org/10.1093/jn/128.12.2686S

Smith, C.E., Parnell, L.D., Lai, CQ. et al. Investigation of diets associated with dilated cardiomyopathy in dogs using foodomics analysis. Sci Rep 11, 15881 (2021). https://doi.org/10.1038/s41598-021-94464-2

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