What's the truth behind the link between peas and heart problems in dogs?
Many owners will already be aware that in 2018/19 a number of grain free pet foods were associated with an increased risk of a heart condition called Dilated Cardiomyopathy (DCM). Investigation is ongoing and recently a new report was released by TUFTS University Researchers.
The Daily Express recently caused concern with an article that warned pet owners against giving pets leftovers, especially those with peas and other legume vegetables in. This was in response to this study which looked at possible dietary causes of DCM.
At VetChef we have reviewed the original research article by TUFTS university researchers in detail and have found that this study actually makes no suggestion that this is the case. There have also been no changes to the FDA recommendations and there have been no suggestions by researchers or the FDA that pet-owners need to remove peas from their pets diet (except in specific cases - kibble foods where they are used as a main ingredient).
So, in brief, the conclusion is that it is safe to continue to use peas as an occasional part of a properly balanced diet and most recently released research does not change this. Peas provide an excellent source of potassium, magnesium, fibre and antioxidants and (as with any vegetable) continue to offer positive benefits on pets (and their humans) when used correctly. For more detail, read on...
What was the new study actually investigating?
The study by TUFTS University researchers was actually just intended to help focus scientists’ investigations. It is also important to remember that the ongoing investigation by the FDA (including this study) is in relation to a specific group of processed kibble pet foods where peas are used as a main ingredient, and there is no implication anywhere that these findings are relevant in other situations.
More about the Diet Related Dilated Cardiomyopathy (DCM) Investigations:
What actually happened in 2018?
In July 2018, the FDA (USA Food and Drug Administration) announced that it had begun investigating reports of DCM in dogs eating certain pet foods. Many of the implicated foods were labelled as ‘grain free’, and most contained high proportions of peas, lentils or other legume seeds (pulses) combined with potatoes in various forms.
DCM is usually seen mostly in large breed dogs (and American cocker spaniels). The new issue was noticed by vets because cases of dilated cardiomyopathy were being reported in breeds of dog who do not usually develop it including some small breeds like Shih-Tzus.
When the information from hundreds of cases was collated it became apparent that these unusual cardiomyopathy cases tended to be linked to a particular group of grain free and ‘boutique’ brands of pet food.
You can read the initial FDA Announcement here:
From the start it was clear that the association between DCM and diet was going to be a complex one. Whilst we could see a link, there were (and still are) all kinds of interacting features and inconsistencies to pick apart.
Early on there were suspicions that a deficiency in the amino acid Taurine might be responsible as some affected dogs had Taurine deficiency on blood tests. However, pretty quickly it became apparent that it was not this simple. As investigation continued it was notable that whilst SOME dogs with diet-related DCM had taurine deficiency (a well known cause of dilated cardiomyopathy), others did not. Interestingly though, they ALL improved when switched to a conventional diet whether or not they had taurine deficiency on their blood work…
Another puzzling feature is that these cases appeared to increase ‘all of a sudden’ in 2018/19. These ‘grain free’ type foods have been around far longer than this so it is odd that so many cases should be reported at the same time. Was there something in the sourcing/processing that has changed?
The vast majority of cases that were reported also involved dry pet food products suggesting that something about the way these foods are produced may be relevant.
(Table from FDA.gov website - FDA Investigation into Potential Link between Certain Diets and Canine Dilated Cardiomyopathy)
In the short term the FDA recommended recall of pet foods that were involved in 2019 and vets were advised to report suspect cases. As a general practice vet, I suggested to my own clients that pet foods whose main ingredients were peas or legumes should be avoided until the link was better understood.
What was the recent study about?
To explain what scientists were really looking for in this study, I thought it might be helpful to first highlight how many different stages there are between the start and finish of a pet food.
Let’s consider the ‘start’ as choosing the type of pea to plant in the ground and grow, and the ‘end’ to be point where a dog has successfully digested/absorbed the nutrients and incorporated them into their body tissues (to build muscle etc). This problem is a complex one and I felt listing the processes helps to show which parts the researchers are currently working on.
Here are all the steps that could be involved between making a pet food and a dog developing a diet-related heart condition…
Food has to be grown and picked - is there anything in the production that has changed? Weather changes? Import/export/parasiticides etc?
Food has to be transported - was anything changed in the way the ingredient was transported that year? Was transport slower/frozen/dried?
Pre-production processing - the ingredient may undergo processing before it is added to a pet food (peas for example are often split up into separate ‘parts’ like pea fibre and pea protein)
Food is made up of lots of different ‘bio-chemicals’ - what does the biological make-up of these peas look like? Is it relevant?
It is added to the food - what amount? What form was it added in? Dried/fresh?
It is processed - what temperature? What was it combined with? What effect did the processing have on the biochemical structure of compounds that are in the food? Has the processing method changed?
What does the final food ‘look’ like is in its final form? What is its signature biochemical make-up -as well at its 26 essential nutrients, hundreds of other natural and synthetic chemicals are present in foods and supplement ingredients. Which (if any) are relevant and where did they come from?
How was the food stored? (does the recipe make-up make it more vulnerable to storage deterioration?)
A dog eats it - what breed is the dog, what else do they eat?
A dog’s digestive system breaks down the food into its nutrients - iIs there anything about the chemical makeup of this food that might stop other nutrients from being broken down correctly?
The dog absorbs the nutrients - is absorption being obstructed or affected by one of the many natural and synthetic biological chemicals? How much of the ‘obstructing’ nutrient does it take to cause a problem? Is it just one chemical or several?
The dog ‘uses’ the nutrient to build muscle/support metabolic processes - even if the dog absorbed plenty, is there something about the final biochemical make up of these foods affecting the ability of a dog to USE the nutrients? - Toxins, anti-nutrients?
We know that it has to be a multi-factorial issue so almost certainly more than one of these stages is affected before dogs get sick. This recent study by TUFTS university aimed to look at just one of the above steps:
“The final food in its final form has a signature biochemical make-up. What is this biochemical make up (hundreds of compounds), which (if any) are relevant and where did they come from?”
From that they hope to work backwards to see what has happened and to determine how we can make sure that it doesn’t happen again.
So, what did they find? The researchers found that there were just over 100 chemical compounds that differed significantly between the two groups of foods (DCM-Linked and non-DCM linked). Some were higher and some were lower.
Of these compounds, a significant number were also found in peas (and to a lesser extent lentils).
What does this tell them?
This suggests that scientists’ suspicions back in 2019 that peas and lentils were a significant ‘piece of the puzzle’ were correct. It means that researchers can now progress in investigating the rest of the ‘pea-puzzle’. What is it about the biochemical makeup of a pea that causes the problem? What antinutrients might they need to consider? Why is it only a problem when we use too much?
Researchers do discuss some of the areas of interest that this study has highlighted for them:
B vitamins 1,2,5,6,9 and 12 were all found to be significantly lower in the affected diets. Vitamins B6 and B12 are co-factors for carnitine and taurine synthesis. This means that without enough B6 and B12, dogs may not be able to produce sufficient amounts of these two nutrients that are so critical for healthy cardiac function.
Dietary Fibre tends to be significantly higher in the grain free/legume based diets. It is a known digestive complication that absorption of nutrients can be hindered by excessive fibre
Whilst carnitine itself was not different between the two diets, there were differences in other protein (amino acid) compounds. These could theoretically interfere with carnitine metabolism AFTER it is absorbed by the dog, and studies over 2 decades ago identified several compounds that interfere with carnitine transporters in the heart muscle. This can result in heart muscle being unable to take-up and use carnitine even if there is plenty there
Peas are usually split into their components ‘pea fibre’ and ‘pea protein’ before being added to pet food. It’s possible that only one of these components is implicated (or a specific combination of them) as the study did not differentiate between them. This also needs further investigation.
Quite rightly, University researcher Dr Lisa Freeman has described the recent findings as just one “piece of the puzzle”.
There is a lot more work to do before we will understand what happened, and we should most certainly retain our sense of proportionality when looking at this study. We do not need to stop feeding all legumes in response to this study, we must only consider the common factors and be sensible about those.
Most of the implicated foods were kibble foods that contained peas or lentils as a main ingredient. If you are feeding kibble foods, look for ones that do not contain peas or lentils as a main ingredient. You do not need to avoid all peas and legumes and small amounts are likely to be safe even in kibble foods
If you are feeding other types of foods (e.g. home-cooked) it is fine to feed small amounts peas and lentils. It’s quite possible that the existing concerns about DCM do not apply to home-cooked foods but, until researchers have fully understood what is going on, we at VetChef are recommending that home-cooked recipes containing larger amounts of peas or lentils should be fed no more than once a week. We’d also recommend using veterinary/nutritionist formulated recipes (like those at VetChef) wherever possible as other internet sources of home-cooked recipes are often poorly balanced and are likely to pose more risk of nutrient imbalance. The other nutritionists and I at VetChef take great care to ensure that all our recipes contain sufficient levels of B vitamins, appropriate levels of fibre (not too high!) and optimal amino acid (protein) profiles. If you are concerned that a home-cooked recipe that you are currently using might not be balanced, you can create a pet profile here and obtain hundreds of recipes for free (all adjusted to meet the specific needs of your own pet)
Keep an eye out for ongoing research from reliable sources. I’ll be keeping an eye out too and will make sure that we comment on new research as it appears. Remember that tabloid newspapers and social media may not always be an accurate source of information.