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Thiamine deficiency & fish

Is feeding a fish based food going to make my cat sick? Let’s dive into this – feeding fish to your cat has long been associated with thiamine deficiency, but does the same risk extend to fish based commercial products? While some products have been recalled over concerns of a lack of thiamine, is this something we need to be concerned abut when selecting a pet food? All these questions and more have been popping up all over the internet as of late, so let’s see if we can answer some of them.

First, we need to look at how thiamine deficiency occurs and where fish fits into this picture.

Thiamine deficiency has three main causes:
1) inability to absorb thiamine due to gastro-intestinal disease
2) inability to process thiamine due to liver disease
3) decreased level of thiamine in food

Symptoms of thiamine deficiency
Most cats show anorexia and vomiting before neurological signs set in. These signs include fairly rapid onset of impaired vision, dilated pupils, ataxia, vestibular signs, tremors and seizures.

How can a diet be deficient in thiamine?
Thiamine is destroyed by heat, so the heating process of cooking food can cause a deficiency if not added back in after cooking. Thiamine can also be inactivated through the addition of sulphur dioxide or sulphite preservatives to meat. Feeding food that is rich in thiaminase activity such as some raw fish blocks the absorption of thiamine in the diet, which is why an all-raw fish diet in cats can be a cause of thiamine deficiency.

What about commercial products?
Commercial products that are labelled as fish, fish flavoured or some other descriptor does not necessarily mean the diet is entirely made of fish. Particularly cheaper products will use a combination of meat proteins, combining fish with other meats such as chicken, beef or lamb; this may be characterised on the label as ‘fish, meat or meat derivatives/by-products, etc’. This means while the main protein source is fish, it doesn’t mean it’s the only protein source unlike feeding a homemade diet of only fish. It’s also a good idea to familiarise yourself with the ‘rules’ of pet food labelling and how this translates to the amount of labelled meat is in the product.

Photo by NastyaSensei on

Another factor to consider is commercial pet food is complete and balanced, meaning anything lost in the cooking process is added back in as a supplement and the activity of enzymes like thiaminase are accounted for in the formulation process. Thiaminase is also deactivated through heat and cooking, so a commercial product that is fish flavoured or contains fish is unlikely to cause a deficiency.

What about recalls?

Recently there have been a few recalls that have occurred as a result of pet foods not reaching the required levels of thiamine. This is unfortunately as a result of a lack of testing – pet foods are not required to undergo final formulation testing and many will simply be formulated to the AAFCO standards, without having a real-world test to check they meet these levels after cooking and processing. For your pet, this again stresses the importance of choosing a diet that conducts routine testing on their products and feeding trials rather than just hoping for the best.

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So, should you avoid feeding your cat fish, or a fish based food?

The short answer is no. Many pet owners query the concern about heavy metal contamination aswell, but you would need to eat alot of fish all the time to get an excessive dose – with cats and dogs, it’s always a good idea to avoid feeding diets that are only consisting of one ingredient all the time, as we discussed above. As long as fish is not the sole diet of your pet, it’s unlikely they will either be exposed to excessive levels of heavy metals or thiaminase.

Still worried about thiamine deficiency? Leave a question below!


Kritikos, G., Parr, J.M. and Verbrugghe, A., 2017. The role of thiamine and effects of deficiency in dogs and cats. Veterinary Sciences4(4), p.59.

Smith, D.C. and Proutt, L.M., 1944. Development of thiamine deficiency in the cat on a diet of raw fish. Proceedings of the Society for Experimental Biology and Medicine, 56(1), pp.1-3.

Luippold, A. and Gustin, M.S., 2016. Mercury concentrations in wet and dry cat and dog food. Animal Feed Science and Technology, 222, pp.190-193.

Markovich, J. E., Heinze, C. R., and Freeman, L. M. (2013). Thiamine deficiency in dogs and cats. Journal of the American Veterinary Medical Association 243, 5, 649-656, available from: <; [Accessed 29 March 2022]

Odom, G. and McEachern, D., 1942. Subarachnoid injection of thiamine in cats; unmasking of brain lesions by induced thiamine deficiency. Proceedings of the Society for Experimental Biology and Medicine, 50(1), pp.28-31.

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