Pet Factsheets

Food allergy

We probably all know people who are unable to eat strawberries or nuts due to an allergy but it isn't only people who can react to their food. Whilst food allergies are not common in cats they can be affected too. Food allergies can produce many different symptoms, some of which can be quite distressing for your pet. No allergy is pleasant but at least with a food allergy it is usually possible to avoid the cause of the symptoms so that your pet can lead a normal life.

What is a food allergy?

A food allergy is an adverse reaction to the ingestion of a food or a food additive. Most cats will have a reaction to their food at some time in their life. Usually this is a sensitivity to a particular food type (not a true allergy) and only causes a mild tummy upset. Once you recognised the reaction, and had avoided that food in future, the problem probably went away. An allergy is a different matter altogether. If your cat is allergic to their diet, they produce antibodies against some part of their food. Antibodies are the body's natural defence mechanism against unwanted invaders and are usually produced to fight off bugs which may cause disease. In an allergic animal the immune system is over-reactive and produces antibodies against things which should be found in the body. The most common dietary allergens in cats include dairy products, beef and fish (all proteins). Each time that food is eaten the antibodies in your pet's body react with the food and this reaction causes the symptoms. Once antibodies have developed, the immune system is able to remember that particular food for many years and if your cat eats it again the same reaction will occur.

Cats appear to have a higher incidence of dietary intolerance than dogs. Food allergies can occur in conjunction with other allergic conditions and so it can be difficult to diagnose and document in patients with multiple allergies.

How do I know if my cat has an allergy to food?

Food allergies can produce many symptoms and so it can be difficult for your vet to make a diagnosis without doing further tests. The most common signs of an allergy to food are itchy skin or tummy upsets. Other changes that can occur are hyperactivity, weight loss, lack of energy or even aggression.

Eliminating the offending part of the diet should resolve the symptoms but it takes a long time for the old food to be completely eliminated from your cat's body and a new diet may have to be fed for many months before any improvement is noticed. An elimination diet trial is a very long process during which strict dietary control is essential - even one stolen treat may set the investigation back to day one! 

There are currently no reliable, sensitive nor specific blood or salivary tests. The best available blood tests may help to predict the most suitable diet to use for an exclusion diet. In cats, the accuracy of testing for food-specific immunoglobulin is low. Currently, the best diagnostic procedure to identify adverse food reactions in cats remains an elimination diet with subsequent provocation trials.

What is an elimination diet?

An elimination diet is a diet containing one type of protein and one type of carbohydrate, eg chicken and rice. This diet is fed for a number of weeks as the sole food (all titbits and additional food must be avoided). During this time all the old diet is removed from the body. The symptoms of allergy should improve as long as the new diet is being fed. The problem with a home-made exclusion diet is that it is unlikely to contain everything that your pet needs for a healthy life. Having identified what diets resolve the problems in your pet your vet will try to identify a commercially produced diet that you can feed your pet for the rest of its life. 

Can allergies be treated?

Unfortunately, it is not possible to cure a cat with an allergy to food. The simplest solution is to avoid the particular protein(s) in the diet which is causing the problem. Many pet foods contain a mixture of different proteins and so choosing a new diet for your allergic pet is not easy and you should discuss it with your vet. They will be able to recommend a diet that does not contain the offending food. The part of the diet causing the problem must be avoided for the rest of your pet’s life. It is not uncommon for animals which have been allergic to one part of their diet to go on to develop other allergies so be watchful for the symptoms recurring. In rare cases there may not be a suitable commercial diet available and you may be forced to prepare home-cooked diets for your pet.