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Feeding an Exclusion Diet Fact Sheet

Dietary allergy or intolerance can underlie a number of diseases. Feeding an exclusion diet is an important part of diagnosis and management.

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What is an exclusion diet?

An exclusion diet is a diet designed to remove ingredients that a patient has previously encountered. Food can trigger clinical disease in a number of ways, including food allergy, toxicity and intolerance (e.g. lactose [milk sugar] intolerance), as well as modulating the gut bacterial flora. Clinical signs of dietary sensitivity are not specific but include vomiting, diarrhoea, itchy skin, ear disease, coughing and wheezing, amongst others.

Why feed an exclusion diet?

We recommend exclusion diet feeding for two reasons: diagnosis and treatment. The diagnosis of food sensitivity requires the demonstration of improvement of signs with the new diet and return of signs when feeding the old food again. If a patient gets better when on an exclusion diet, long-term feeding of an appropriately balanced diet may be a very effective treatment. Of note, in cats, recent studies suggested that increasing the quality of the diet rather changing its composition can be sufficient in a subset of the patients with chronic gastrointestinal signs.

How long do we feed a diet for?

For the purpose of diagnosis, we typically recommend at least 2 weeks of exclusion diet feeding. The new diet is introduced gradually over a period of 3 to 5 days by mixing with the previous diet and increasing the percentage of the new diet each day. When the patient is receiving 100% of the new diet, careful avoidance of any other food elements, including treats, is required.

What foodstuffs can cause dietary sensitivity?

Theoretically, any foodstuff or ingredient (including additives) can trigger a reaction. In pets in the UK, however, we tend to avoid commonly encountered protein ingredients in exclusion diets, such as chicken, turkey, beef, and lamb.

What can we feed?

There are many commercial diets available offering a range of options for both dogs and cats, both in dry or wet form. These are balanced diets often using protein sources which are uncommonly used, reducing the risk of allergic reaction (e.g. soya, duck, salmon). In hydrolysed diets, the proteins have been processed and are split in small fragments which are less likely to induce a reaction of the immune system. Some commercial diets also contain prebiotics (ingredients thought to stimulate the growth of beneficial bacterial population in the gut).

A home-made diet is an alternative to commercial diets and does have the advantage of a better knowledge of its composition. Preparing a home-made diet is, however time-consuming. There have been increasing concerns that some home-made diets may be unbalanced and when home-made diets are recommended, we would strongly suggest to request the opinion of a veterinary nutritionist. If a homemade diet is selected, this can only be recommended when formulated by a veterinary nutritionist.

How much should I feed?

It is impossible to give accurate amounts to feed an individual because there are so many variables, not least the underlying disease. Amounts can be adjusted according to intake and body weight.

What should I give to drink?

Plain water only should be offered. Milk etc. should be avoided as is a common allergen.

But my dog is a scavenger/my cat is hunting!

Dogs, particularly, are scavengers by nature. They will hoover up everything that might be food. This behaviour must be prevented for an effective exclusion diet trial. Times of particular difficulty are when there are young children or visitors in the house, when there are multiple pets, during walks when off the lead and during social events, e.g. parties. Use of a short lead, constant supervision and, occasionally, a muzzle may be necessary.

It is more difficult to restrain a cat from displaying their normal behaviour and doing so can increase their stress levels, reducing the likelihood that they will refuse the new diet. As stated before, studies including cats with outdoor access have revealed a significant advantage of dietary modification, even when only increasing the quality of the diet and not changing the protein source.

What about his treats/vitamins/supplements?

Whilst a balanced diet is very important for long-term health the smallest amount of a triggering food can cause clinical signs, which may often be quite dramatic (think of peanut allergies in children). We, therefore, advise the strictest of exclusions, especially in the diagnostic phase of any exclusion diet trial. All treats, animal-based chews, vitamin supplements etc. should be withdrawn. Note that some medications may contain animal protein in the formulation: ask your clinician about this if you are concerned. Many pets consider any food given outside normal meal times a treat, so normal treats may be substituted with a small morsel of the exclusion diet itself. It is unclear if the diet would retain its nutritional quality if it is mixed with other elements or cooked in the oven to enhance its flavour.

When should I report back?

We typically ask for a telephone report or an email update after 2 weeks, although we may ask you to ring sooner if there are results pending or arrange a repeat consultation if physical examination is warranted. If your pet refuses to eat the new food or is showing worsening signs, or you are worried for any other reason, please call.

If you have any further questions about diets you should speak to your veterinary surgeon who will be able to discuss this with you more fully.


If you are concerned about the health of your pet you should contact your veterinary surgeon.

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