How to do an elimination diet food trial for dogs

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How to do an elimination diet food trial for dogs

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

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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 dogs 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 something they are eating and second, to identify which food ingredients trigger the symptoms and which do not and are safe to feed.

There’s a great variety of ingredients used in dog 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 dog 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 dog 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, people you meet in the park, etc not to feed anything else to your pet - no other foods, table left-overs or treats,

  • avoid all treats, chews, 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,

  • do not allow any scavenging or hunting - use a short lead, constant supervision and, occasionally, a muzzle if needed; if your dog accidentally eats something other than the new diet, make a note of what, when and how much, and monitor for any symptoms,

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

  • if you have several dogs, you can either use strict feeding times to make sure the dog doing the food trial does not get any other dog food or feed all of them the new diet (if complete and age-appropriate); if you have cats, place cat feeding bowls high enough that they are accessible only to the cat(s),

  • 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.

What dog food to use for a food trial?

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

Novel protein diets

The idea with this commercial dog 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 dog’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 dog 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 puppies 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 dog anything else other than this food and water. Keep a diary to record your dog’s symptoms each day, for example, any vomiting or diarrhoea or itchiness levels, rashes, etc.

Take 5-7 days to gradually introduce the new food mixed with the old. Count the 6-8 weeks from the moment the dog had only the new food.

If your dog 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 (which is not the same as when you finished giving the medication, your vet can advise you on that). Otherwise the effects of the new food cannot be told apart from the improvements due to medication.

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, chews, 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 a dog 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, you need to discuss with your vet investigating other types of allergies..

If your dog 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 dog 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 dog 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 dog’s symptoms.

Phase 4 - repeated challenges with individual ingredients

In this phase, while continuing to feed the new diet, offer your dog 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 dog 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. After this you can try the carbs - rice, potato, sweet potato, etc.

Use the listed ingredients on your dog’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 dog likes and that do not trigger any gastrointestinal or skin symptoms.

Reasons for an inconclusive food trial

One reason for the new food not to make a difference is if the dog has other uncontrolled allergies - FAD, atopy, or, less commonly, 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 one of our experienced vets will gladly help you!

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