How to do an elimination diet food trial for cats

Estimated Reading Time 8 minutes
How to do an elimination diet food trial for cats

Elimination diet food trials are done in cats both to diagnose and treat various food intolerances or allergies. Read our article to learn how to do one successfully!

Are you concerned about your pet? Meet a vet online!
  • Included free as part of many pet insurance policies
  • Help, treatment and if you need it, a referral to your local vet
  • Open 24/7, 365 days a year

What is an elimination diet food trial and when do you need to do one?

An elimination diet food trial, or shortly a ‘food trial’, is a procedure used in cats suspected of having food allergies or intolerances.

The goal of such a food trial is two-fold. First, to confirm that the symptoms are indeed (completely or partially) due to the food they are eating and second, to identify which ingredients in the food trigger the symptoms and which do not and are safe to feed.

There’s a great variety of ingredients used in cat foods and treats nowadays. This sometimes makes a food trial a rather lengthy process. Arm yourself with patience though, it is well worth it - once you know which foods your cat can’t have, managing their food allergy or intolerance becomes much easier.

Preparatory work before the food trial

Once you start the food trial, for a set period of time, your cat should not be allowed to eat anything else apart from the chosen food. This strictness is very important because the smallest amounts of uncontrolled foods can trigger a reaction and mess up the food trial.

So there are some precautions to take before starting:

  • make sure you speak with all the family members, friends, visitors, etc not to feed anything else to your pet - no other foods, table left-overs or treats,

  • avoid all treats, supplements, probiotics, toothpastes, etc, even some flavoured medications as they may contain animal protein in the formulation, ask your vet about this if you are unsure,

  • offer your cat only plain water to drink during the food trial without anything added to it, no milk or rehydration drinks,

  • if you have several cats, you can either use strict feeding times or microchip-controlled feeders to make sure the cat doing the food trial does not get any other cat food or feed all of them the new diet (if complete and age-appropriate),

  • stock sufficient amounts of the new food so you wouldn’t run out of it during the trial, otherwise you’d have to restart it.

Food trials are recommended even for cats with outdoor access, where a 100% control over their diet is impossible. Speak to your neighbours not to feed your cat anything or use a ‘do not feed me’ collar. Keeping them indoors during the food trial is a possibility, but it is not recommended by feline specialists because the stress from the ‘house arrest’ outweighs the benefits of a non-allergenic diet. The idea is to find a diet that improves the cat’s symptoms in the normal life circumstances of that cat.

What cat food to use for a food trial?

There are several types of diets that can be used as a new food in an elimination diet food trial:

Novel protein diets

The idea with this commercial cat food is to provide a type of protein that your pet never had before (venison, rabbit, kangaroo, ostrich) because they can’t be allergic to something they never ate. Sometimes the source of carbohydrates is new as well, for example, potato instead of rice.

Limited ingredients diets

This type of food is very similar to a novel protein diet, but the ingredients are less exotic (duck, salmon, pork). Instead, the focus here is to have only one type of animal protein in the food.

This can be either a commercially formulated food or a home-cooked diet. We strongly recommend the commercial diets because the home-cooked ones are often time-consuming to make and nutritionally unbalanced.

Novel protein and limited ingredients diets are often called hypoallergenic diets.

Hydrolysed protein diets

This type of food is categorically different from the hypoallergenic foods described above or any regular pet food you buy in the shops or cook at home.

The difference is that the proteins in it are subjected to a process (hydrolysis) that breaks them down into fragments so small, the immune cells cannot detect them, therefore can’t react to them. The proteins can be of any origin, chicken, fish, lamb, it makes no difference, because hydrolysis makes them all unrecognisable for the immune cells of the gut.

The hydrolysis is done enzymatically under very special conditions that you cannot replicate at home, therefore these foods are always commercial. Various brands have them on offer and you can recognise them by the ‘hydrolysed’ description on the package.

So which one to choose?

Speak to your vet or the nutritionist vet nurse at your practice and they will help you choose a new diet for the food trial based on your cat’s medical history and symptoms, but also your own preferences and possibilities.

Most vets will recommend using a hydrolysed protein diet as a new diet and consider a hypoallergenic food only if your cat absolutely refuses to eat the hydrolysed protein diet. Hydrolysed protein diets are often less tasty than normal food (the protein fragments are not easily recognised by the taste buds either) and some pets don’t like them that much. But the hydrolysed protein diet by default can’t trigger any allergic reactions while the other diets may still contain ingredients that your pet is allergic to. Be advised that, because of the special way of manufacturing them, hydrolysed protein diets are a bit pricier than regular food.

For kittens that are not fully grown yet, care must be taken that any chosen diet is age-appropriate, a home-cooked diet is absolutely contra-indicated for them.

The food trial proper

A food trial usually consists of 3 or 4 phases.

Phase 1 - the new diet (6-8 weeks)

During this phase, feed strictly only the new chosen diet for 6-8 weeks. As mentioned above, do not give your cat anything else other than this food and water. Keep a diary to record your cat’s symptoms each day, for example, any vomiting or diarrhoea or itchiness levels, rashes, etc.

Cats can be very peculiar about their food, so take time to gradually introduce the new food mixed in with the old. Count the 6-8 weeks from the moment the cat had only the new food.

If your cat had very bad symptoms that needed urgent treatment with anti-itchiness, anti-inflammatory or antibiotic medication, you can start the new diet asap, but the 6-8 weeks should again be counted only from the moment the medication effects have passed (your vet can advise on that). Otherwise the effects of the new food cannot be told apart from the improvements due to medication. Steroids especially have long wash-out times.

Phase 2 - the challenge (2 weeks)

After the 6-8 weeks of phase 1, re-introduce small amounts of the old food, along with any usual treats, supplements, etc. and monitor if the symptoms return. If the symptoms were due to an intolerance or allergy to a food ingredient, they usually reappear within 2-3 days to 2 weeks. It is important only to give very small amounts of the old foods or treats, sudden changes can cause an upset tummy regardless of whether they have an intolerance or allergy.

Phase 3 - the new diet again (2-4 weeks)

Once symptoms have recurred, return to feeding strictly only the new diet until they are gone again (this usually takes 2 to 4 weeks).


As mentioned above, the food trial has 2 goals and phases 1-3 are a test for the 1st one, to confirm a food intolerance or allergy and its contribution to the itchiness threshold.

If there’s no change in symptoms, despite a correctly done food trial, investigating atopy or other allergies is recommended.

If your cat improved considerably during phases 1 and 3, you have two choices.

Option 1 is to skip any further food challenges and, should the new diet be a complete and balanced food that the cat happily eats, simply continue to feed them that for life. This is a perfectly acceptable way to deal with a food intolerance or allergy, though you still don’t know what exactly your cat is allergic to.

Option 2 is to proceed to Phase 4, which corresponds to the second goal of a food trial, to identify the specific ingredients that cause the cat’s symptoms.

Phase 4 - repeated challenges with individual ingredients

In this phase, while continuing to feed the new diet, offer your cat ingredients from their previous food or treats on their own.

For example, if their old food was beef-based, feed them small bits of plainly cooked beef. If their favourite treat was salmon-based, offer small flakes of cooked salmon and so on.

Only offer one new ingredient at a time, for up to 2 weeks, and watch for the return of the symptoms.

If there is no return of the previous symptoms, this ingredient can be added to the ‘safe foods’ list. However, if there is a flare up, this ingredient should be avoided and the cat not fed anything else but the new food again until the symptoms are gone.

Do not start another challenge with a new ingredient until the flare-up has disappeared completely.

Trial various proteins first (chicken, beef, lamb, turkey, duck, egg, fish) as these are the most common triggers.

Use the listed ingredients on your cat’s old foods, treats, supplements, etc for indications about which ingredients might trigger their symptoms.

After you have a good idea which ingredients are safe and which not, you can use complete foods containing them as challenges.

The point is to find several complete diets for long-term use that your cat likes and that do not trigger any gastrointestinal or skin symptoms.

Reasons for an inconclusive food trial

As previously mentioned, one reason for the new food not to make a difference is if the cat has other uncontrolled allergies - FAD, atopy, contact allergy or some other rare allergy form.

A few other reasons could be:

  • not treating secondary skin infections and/or skin parasites completely before the food trial,

  • not keeping strictly to the new food and water only regime during the food trial.

These are, in a (big) nutshell, the most important principles of an elimination diet food trial. If you have any questions about it, feel free to book a call with us and our experienced vets will gladly help you!

Contact a UK vet online right now!

What can we do for your furry friend?

  • Assess how they are in that exact moment
  • Answer your questions, offer advice, and make a plan about your concerns
  • Recommend easily available, over-the-counter pet health products when sufficient
  • Make a referral to a local vet when necessary
Book an appointment
  • Included free as part of many pet insurance policies Included free as part of many pet insurance policies
  • Help, treatment and if you need it, a referral to your local vet Help, treatment and if you need it, a referral to your local vet
  • Open 24/7, 365 days a year Open 24/7, 365 days a year
Low cost consultations, 24 hours a day.Low cost consultations, 24 hours a day.

With FirstVet, the vet clinic and pet shop are only one tap away. Get fast advice, trusted care and the right pet supplies – every day, all year round.


25 Horsell Road


N5 1XL