Celia Haddon - Cat Expert

Understanding animals through their behaviour


Cats tend to develop food allergies to a familiar food and these can be part of multiple allergies. Food intolerances tend to be to new foods and are usually present from birth, but can occur later in the cat’s development. Cats can be intolerant to a wide number of food ingredients (Zoran 2002). As far as an owner is concerned, the symptoms, diagnosis and treatment are similar.

Common symptoms of food allergy or food intolerance include chronic vomiting, colitis, diarrhoea, failure to gain weight or weight loss, poor or dull coat, lack of energy. Food allergies may also express themselves in a cat’s skin resulting in overgrooming (Wolberg & Blanco 2008). Among overgrooming cats or cats with skin problems, 12-17% may be suffering from food allergy or hypersensitivity (Bryan & Frank 2010).  If overgrooming occurs in the head or neck area, it is likely to be a sign of food intolerance or allergy, according to some authorities (Gaschen, 2011).  A common mistake is to assume overgrooming is a compulsive habit when it is due to food reactions (Waisglass, 2006). Consult the page on Overgrooming in Cats for more details.

Your vet will want to rule out other possibilities like dietary upsets, internal parasites, infections, idiopathic bowel disease, metabolic diseases of the kidney, liver and pancreas, and, in older cats, various cancers. Sometimes cats with food allergies are also suffering concurrently with other allergies.

Your vet will recommend a trial diet using foods new to your cat. Food allergy tests are not reliable (Mueller 7 Olivry 2017). Special veterinary diets are available from your vet and are easier than home diets. Only feed a home diet if this is recommended, and details given, by your vet since a cat’s digestive system is not very flexible (Zoran 2002). Over the counter organic diets or diets with no additives – good though they may be for some cats – are not going to be much use as a test for food intolerance. Nor will changing brand do the trick (Bryan & Frank 2010). Ordinary cat-foods contain a variety of ingredients that vary from batch to batch.

Trial diets should either be exclusion diets (ingredients cats have never eaten before) 0r be hydrolised protein – among good ones are Hills ZD and Purina HA. Trial diets should be fed for eight weeks (Bryan & Frank 2010). Cats should not be fed anything else during the trial. Cats that hunt or are fed elsewhere may need to be kept indoors.

Allergic diseases will wax and wane, so an improvement after eight weeks does not necessarily mean the cat has food allergy. You have to test by going back to the original diet. A relapse within 1-2 weeks on the original diet confirms a food allergy. Once the cat is stable again on the trial diet, introduce ingredients such as beef, lamb, dairy products etc. one at a time to discover which the cat reacts to. These can then be avoided.

Sometimes this process is short circuited, and after feeding the exclusion diet, the owner is helped to try out different commercial diets with varying ingredients to see if one can be fed without causing the allergy. Blood tests are available which detect antibodies in the blood but do not replace the need for a proper food trial. Antibodies only appear if there is a definite allergy and cannot detect a food intolerance.

Alternatively, just feed the commercial trial diet long term (Leistra & Willemse 2002).

If the food trials identify the food ingredients, which are making your cat ill, then your vet will help you choose a diet which excludes these ingredients. You will need to keep your cat on this diet for the rest of its life. If your cat is a dustbin scrounger, you will have to decide whether it is necessary to make it into an indoor cat.

If the symptoms do not clear up after food trials, it is usually a good idea to ask your vet to refer you to a veterinary specialist. This is the same principle as a GP referring a patient to a consultant. Most vets will be happy to do so and indeed cannot refuse to do so. There are inflammatory and other bowel conditions which can trigger a food allergy. These can be diagnosed by endoscopic investigations and biopsies. A vet who specialises in gastro-enterology or internal medicine will have the equipment and expertise to do these investigations.

A very good review of a cat’s digestive system is available on Google scholar. Put in Zoran 2002 JAVMA.


Bryan, J.,  & Frank, L., (2010) ‘Food allergy in the cat. A diagnosis by elimination,’ Journal of Feline Medicine and Surgery, 12, 861-866.

Gaschen, F. P. (2011), ‘Adverse Food Reactions in Dogs and Cats,’ International Congress of
the Italian Association of Companion Animal Veterinarians, 198-200

Leistra, M., & Willemse, T., (2002), ‘Double blind evaluation of two hypoallergenic diets in cats with adverse food reactions,’ Journal of Feline Medicine and Surgery, 4, 185-188.

Mueller, R.S. & Olivry, T., (2017), ‘Critically appraised topic on adverse food reactions of companion animals (4): can we diagnose adverse food reactions in dogs and cats with in vivo or in vitro tests?’ BMC Vet Res.;13(1):275.

Waisglass, S. E., Landsberg, G. M., Yager, J. A. & Hall, J. A., (2006), ‘Underlying medical conditions in cats with presumptive psychogenic alopeci’, JAVMA, 228, 1705-1709.

Wolberg, A. C. & Blanco, A., (2008) ‘Pruritis in the cat’, Veterinary Focus, 18, 4-11

Zoran, D.L., (2002), ‘The carnivore connection to nutrition in cats,’ JAVMA, 221, 1559-1567.

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