There has been a lot of buzz about a recent US Food and Drug Administration (FDA) statement alerting pet owners about a possible link between dilated cardiomyopathy (DCM), a type of heart disease, in dogs eating diets containing peas, lentils, potatoes and other legume seeds as main ingredients. These ingredients are commonly found in diets that are advertised as “grain-free”.1
The statement suggests a potential relationship between the amino acid taurine and DCM in dogs. It is thought that foods with high levels of peas, potatoes, and lentils may cause low taurine levels in dogs and contribute to heart disease. However, some dogs with DCM on grain-free diets showed normal blood taurine levels. DCM is also reported to occur in dogs eating diets that are not grain-free.1 Millions of healthy dogs around the world eat grain-free diets their entire lives; this is the first time that grain-free diets have been implicated as a potential cause of heart disease. Complicating the matter further is that genetics may also play a role in the development of DCM.2 So, what is going on? To dive deeper into this issue, we must look at what is currently known about the relationship between diet and the development of heart disease in dogs.
What is Taurine?
Taurine is a unique amino acid. Most amino acids are used to make protein, but taurine is a free amino acid in the body.3 Though the exact function of taurine is not entirely understood, it is known to be involved in heart health. In dogs and cats, taurine also plays an important role in activating bile acids in the liver, enabling them to break down fats.3 Cats must get taurine from their diet, but dogs can make taurine using two other amino acids, methionine and cysteine. Therefore, taurine is not considered necessary in dogs’ diets if enough methionine and cysteine are present.3 Although the methionine content in pulses is lower compared to animal-based proteins, this can easily be accounted for by using ingredients rich in this amino acid or using supplementation.4
This Issue is Not New…
This is not the first time that diet has been linked to heart disease in dogs. In the early 2000’s, before grain-free diets became mainstream, lamb and rice diets were identified as being correlated with low taurine and heart disease in dogs.5 It was suggested that the lamb meal in these diets did not provide enough methionine and cysteine.5 However, it could not be confirmed that lamb meal was a direct cause of heart disease in dogs. Instead, it was realized that the diet as a whole must be considered to make sure it provides all the nutrients dogs need. This causes one to ask, “why are peas, lentils, and grain-free diets being blamed for causing heart disease in dogs, when we know that ingredients themselves are not the issue?” The challenge is that pointing a finger at ingredients without more in-depth information causes panic and uncertainty for pet parents without providing any fact-based answers or solutions.
Not All Protein is Created Equal
In terms of protein, the type is just as important as the amount in the diet. Taurine is naturally found in animal-based proteins. Therefore, diets that contain an adequate level of high-quality animal protein should provide sufficient levels of taurine.6 However, lower quality animal-based proteins (i.e. those that provide low levels of one or more essential amino acid) may not provide adequate methionine and cysteine for dogs to produce enough taurine. Knowing this, it’s critical to consider ingredients’ protein quality when formulating foods for both dogs and cats. Pet foods are also often supplemented with single amino acids, particularly methionine, lysine, and taurine, to ensure they contain sufficient amounts.3
How Does Cooking Affect Amino Acids?
Cooking can also affect protein and amino acids in food. Different formats of pet food (e.g. canned versus kibble) require different cooking temperatures. Cooking pet food is also required for food safety. However, cooking protein at excessive temperatures can potentially lead to the destruction of amino acids which can decrease the amount of amino acids available for an animal to use.7 On the flip side, not cooking ingredients enough can also be an issue. For example, some ingredients in their raw form may contain factors that can affect the absorption of other nutrients.7 Because of this, it is important that the effects of cooking on amino acid availability are accounted for when formulating pet foods.
What About Fibre?
The amount and type of dietary fibre in a food may also affect taurine status. In the body, bile acids joined with taurine support fat digestion. Bile acids are then reabsorbed in the small intestine to be used again. However, certain types of fibre are thought to bind with bile acids causing the bile acids to be excreted in the feces rather than reabsorbed.8 When this happens, the body must use more of its taurine to make bile acids, and this can decrease blood taurine levels. Furthermore, the types of bacteria in the gut may also impact taurine status. More research is needed to investigate the effects of dietary fibre and gut bacteria on taurine status.
Since the FDA report was released, two research papers and one review paper have been published on this issue. The results of both studies showed that dietary-associated DCM occurs with some grain-free diets,9 but suggests that the cause is likely multifactorial, resulting from a combination of dietary, metabolic, and genetic factors.10 Even with the publication of this research, a cause-and-effect relationship between DCM and grain-free diets has not been proven.11
What Can We Conclude?
Overall, it is important to remember that “correlation does not equal causation”. Not all grain-free diets are nutritionally equal, and it is likely misguided to point fingers at single ingredients or the “grain-free” aspect of diets as the cause of heart disease in dogs. The evidence shows that the issue is much more complex than suggested by the FDA statement, and that protein quality and quantity, processing techniques, fibre content and other characteristics of a diet can all contribute to taurine status. While FDA researchers work to uncover science-based facts and compile a comprehensive report, we recommend contacting your veterinarian with any concerns about your pet’s health.
1. CVM Updates – FDA Investigating Potential Connection Between Diet and Cases of Canine Heart Disease. July 12, 2018. Retrieved September 15, 2018, from https://www.fda.gov/animalveterinary/newsevents/cvmupdates/ucm613305.htm
2. Backus, R. C., et al., Taurine deficiency in Newfoundlands fed commercially available complete and balanced diets. J. Am. Vet. Med. Assoc. 2003. 223(8): 1130-1136.
3. National Research Council. Nutrient Requirements of Dogs and Cats. 2006. Washington, D.C.: The National Academies Press.
4. Boye, J., Zare, F., and A. Pletch. Pulse proteins: Processing, characterization, functional properties and applications in food and feed. Food Res. Int., 2010. 43(2): 414-431.
5. Torres, C. L., et al., Taurine status in normal dogs fed a commercial diet associated with taurine deficiency and dilated cardiomyopathy. J. Anim. Physiol. Anim. Nutr. 2003. 87(9-10): 359-372.
6. Thompson, A. Ingredients: Where Pet Food Starts. Top. Companion Anim. Med. 2008. 23(3): 127-132.
7. Tran, Q. D., Hendricks, W .H., and A.F.B van der Pol. Effects of extrusion processing on nutrients in dry pet food. J. Sci. Food Agric. 2008. 88(9): 1487-1493.
8. Stratton-Phelps, M., et al., Dietary Rice Bran Decreases Plasma and Whole-Blood Taurine in Cats. J. Nutr. 2002. 132(6): 1745-1747.
9. Adin, D., et al., Echocardiographic phenotype of canine dilated cardiomyopathy differs based on diet type. Vet. Card. 2019. 21: 1-9.
10. Kaplan, J.L., et al., Taurine deficiency and dilated cardiomyopathy in golden retrievers fed commercial diets. PLOS ONE, 2018. 13(12): e0209112.
11. Freeman, L. M., et al., Diet-associated dilated cardiomyopathy in dogs: what do we know? J. Am. Vet. Med. Assoc. 2018. 253(11): 1390-1394.
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