Food Elimination Trials in Dogs: The Best Way to Diagnose a Food Allergy

Cocker spaniel eating birthday cake at home

If your dog has itchy skin, recurring ear infections, tummy troubles e.g. soft stools or regularly passes more than 3 motions a day, you may be wondering if food is to blame. While diagnostic tests are widely advertised, the gold standard for diagnosing a food allergy in dogs is a properly conducted food elimination trial.

At Tribe Vets, we know that food trials require commitment, but they are often the quickest route to getting long-term answers and helping your dog feel more comfortable.

What Is a Food Elimination Trial?

A food elimination trial involves feeding your dog a carefully selected diet, and nothing else, for several weeks. During this time, any ingredients that may be triggering an allergic reaction are removed from the diet, allowing the immune system, gastro-intestinal tract and skin to settle.

If your dog's symptoms improve and then return when their previous food is reintroduced, a food allergy is very likely.

Which Food Should I Feed?

There are two main options:

A Hydrolysed Diet

This is our preferred option for most dogs.

Hydrolysed diets contain proteins that have been broken down into such tiny pieces that the immune system is unlikely to recognise them as allergens. They are complete, balanced diets and are designed specifically for diagnosing and managing food allergies. These are different to hypoallergenic diets, they specifically need to be hydrolysed. Brands include Purina HA Hydrolysed, or Hills Z/d.

A Novel Protein Diet

Alternatively, we may recommend a diet containing a protein your dog has genuinely never eaten before, such as venison or rabbit.

Choosing a novel protein can be more difficult than it sounds. Many dogs have been exposed to a surprising variety of ingredients through treats, chews and previous foods. Even insect-based diets may not be suitable, as most dogs have encountered insects during their lives.

We'll help you decide which diet is most appropriate for your dog.

How Long Does the Trial Last?

A food trial should usually last 6–8 weeks. Some dogs improve within a few weeks, while others take longer for their skin and digestive system to recover.

It's important not to stop early, even if you don't see immediate improvement.

The Golden Rule: No Cheating!

This is the most important part of the trial.

For the results to be meaningful, your dog must eat only the prescribed trial diet.

That means no:

Treats
Dental chews
Human food
Leftovers
Pig's ears or other chews
Flavoured medications (unless we've confirmed they're suitable)
Food stolen from other pets
Training treats made from anything other than the trial food

Even one small treat can trigger the immune system and effectively restart the trial, making it difficult to know whether the diet is working.

What About Treats?

The good news is that your dog can still enjoy rewards.

Some hydrolysed diets are available as matching treats, or you can simply use a portion of your dog's daily food allowance as training treats throughout the day.

Many dogs are just as happy eating their normal kibble when it's given as a reward.

Feeding More Than One Pet?

If you have multiple pets, mealtimes may need a little more planning.

Feed pets separately where possible, remove uneaten food promptly, and make sure your dog cannot help themselves to another pet's dinner. Even stealing a few mouthfuls can interfere with the trial.

What Happens Next?

If your dog's symptoms improve significantly during the trial, the next step is usually a food challenge. This involves gradually reintroducing the previous diet to see whether the symptoms return.

Although it can feel frustrating if your dog starts itching again, this step is important because it confirms whether food really is the cause. Without it, we can't be certain that the improvement wasn't due to seasonal changes or another factor.

Once a food allergy has been confirmed, we can help you choose a long-term diet that keeps your dog comfortable while providing complete nutrition.

Remember: Food Isn't Always the Culprit

Many itchy dogs actually suffer from environmental allergies, such as pollen, grasses or house dust mites. It's also possible for dogs to have both food and environmental allergies at the same time.

If your dog doesn't improve during a carefully conducted food trial, don't lose heart. It gives us valuable information and helps us focus on other causes so we can find the best treatment plan.