Conducting a Food Trial for Food Allergies in a Pet

Diagnosing food allergy has nothing to do with a better quality of food or a grain-free diet. It means finding food sources that your pet hasn’t had before.

Pets may scratch because of a food allergy.
Food allergies are rare — they account for only about 10% of allergies overall. By: hyakushiki_thebest

A lot of people with pets totally misunderstand food allergies and food trials.

They want to “change the food” and believe their pet’s itching and scratching might go away.

However, changing the food does not constitute a helpful solution for your itchy dog or cat. So don’t waste time and money on buying different bags of food every week if your goal is to diagnose true food allergy.

Diagnosing true food allergy has nothing to do with a better quality of food, a grain-free diet, a different brand, a food “that promotes a healthy coat” and so on. It means finding food sources that are novel — meaning your pet has never eaten them before.

To determine whether or not your pet has a food allergy, you must conduct a food trial.

That means choosing a limited-ingredient, novel diet — one that consists of a protein and carbohydrate that your pet has never eaten before. You need to feed this diet exclusively for 8–12 weeks.

First, let’s talk about some basics — which, again, are often misunderstood.

What Is Food Allergy?

Food allergy is an immune-mediated adverse reaction to a food antigen.

Certain foods trigger an allergic response in your dog, which causes her to itch.

How Common Is It?

Food allergy is grouped under allergic diseases that cause your pet to itch and scratch.

Pets suffer from:

  • Inhalant allergies (atopy)
  • Flea bite allergy
  • Food allergy

For lots more allergies, see our Expert Guide on Allergies in Pets.

  • Experts believe that food allergy accounts for only about 10% of allergies overall.
  • Food allergy and atopy probably account for 20% of itchy pets.

Based on the above evidence, many of my clients still express 2 big misconceptions:

  1. They believe food allergy is more common than it actually is.
  2. They believe a simple food switch can fix the problem.

Don’t Confuse Food Allergy With Food Intolerance

  • Food intolerance means your pet can’t handle certain foods and has gastrointestinal symptoms such as vomiting or diarrhea. This would be similar to a human who needs to avoid certain spices, certain foods, certain taquerías or hot chicken with peanuts.
  • Food allergy manifests itself as scratching and skin conditions.


The gold standard for diagnosing food allergy is to put your pet on a limited-ingredient diet for somewhere between 8 and 12 weeks.

After that time, if there has been significant improvement in the itching, we begin to add back regular foods into the mix and see if the pet begins to scratch again. This is a challenge.

If there is no improvement in the animal’s itching after 12 weeks on a limited diet, your vet may choose a second diet trial or may assume your pet is not food allergic.

Conducting a Food Trial

It may be difficult to come up with a limited-ingredient diet.

That’s because the pet food industry is now an insane market of high-quality, low-quality, middle-quality, natural and not-so-natural, grain-free, preservative-free, everything-free, “buy it because we tell you to” bandwagon of food choices.

Long ago, veterinarians recommended lamb and rice for dogs and sometimes lamb baby food for cats to conduct a food trial.

Why? Well, it wasn’t because this was a particularly great diet for dogs or cats. It was because most dogs and cats had not been exposed to lamb or rice.

Today your pet has probably been exposed to lamb, rice, quinoa, fish, potatoes, duck, salmon, buffalo and, well, almost everything that ever walked or grew in a field. This means finding a novel diet is difficult.

A food trial means feeding new foods to your pet, then later adding in others. By: Jacob Davies
A food trial means feeding new-to-your-pet foods, then later adding in others and monitoring for symptoms. By: Jacob Davies

Choosing a Diet

It’s important to consult with your vet or a veterinary dermatologist when conducting a food trial.

There are 3 basic ways to formulate a diet:

1. Hydrolized Protein Diets

Veterinary diet companies have created these diets to find as non-allergenic a diet as possible.

Examples include:

  • Hills z/d
  • Purina HA
  • Royal Canin HP

2. Novel Protein Diets

Based on your pet’s prior dietary exposure, you may be able to find a commercial diet made up of foods your pet has never eaten before.

These might include:

  • Venison and potato
  • Whitefish
  • Rabbit and green pea

3. Home-Cooked Diets

The actual mechanics of home-cooking a novel diet are complicated.

Ingredients may be difficult to find or you may not enjoy cooking duck, venison, whitefish, rabbit, etc.

Back when we used to ask our clients to boil lamb and rice, many of them said their homes smelled so gross they couldn’t continue to feed it.

Your veterinary team and/or veterinary dermatologist are great sources for determining how to go about diagnosing food allergy.

Seek dietary guidance — do it systematically and scientifically, and you may be rewarded with a pet who ditched the itch.


This pet health content was written by a veterinarian, Dr. Debora Lichtenberg, VMD. It was reviewed for accuracy by Dr. Pippa Elliott, BVMS, MRCVS, and was last updated Dec. 17, 2018.