Hydrolyzed Protein and Elimination Diets for Cats With Allergies

By Tailwisp Editorial TeamUpdated October 20, 20264 min read

An itchy cat that over-grooms, scabs around the neck and ears, or has chronic vomiting or loose stool may have a food allergy. The only reliable way to find out is with a carefully run diet trial. Understanding hydrolyzed and limited ingredient diets helps you work with your vet and get answers.

What is a food allergy?

A food allergy is an immune reaction to a protein in food. In cats, common triggers are beef, fish, chicken and dairy. Signs include itching, especially of the head and neck, scabs, hair loss from overgrooming, ear problems, vomiting, diarrhea, and sometimes sneezing. It can start at any age. See cat food allergies and sensitive stomachs and cat skin allergies.

Food allergy versus other problems

Fleas, environmental allergens such as pollen and dust mites, skin infections and mites cause similar itch, and are more common than food allergy. Your vet will rule these out first. See fleas on cats and ringworm in cats. Because food allergy cannot be reliably diagnosed with blood, saliva or hair tests, a diet trial is needed.

Hydrolyzed protein diets

In these foods, proteins are broken down by enzymes into very small pieces, called peptides. They are too small to trigger the immune system in most cats. Hydrolyzed diets can be fed to cats whose triggers are unknown, since they work whatever the original protein. Most are prescription foods, available from vets. Some cats find them less tasty, so introduce slowly.

Novel protein diets

A novel protein is one the cat has not eaten before, such as duck, venison, rabbit or kangaroo. The immune system has not been sensitized to it. The challenge is knowing what your cat has eaten in the past, since many foods contain hidden ingredients. Novel protein diets are also available as veterinary formulas. Over time, a cat may become allergic to the new protein as well.

Over-the-counter limited ingredient foods

These foods contain fewer ingredients, and are marketed for sensitive cats. They can be useful for mild sensitivities, but studies show that some contain proteins not listed on the label, due to shared equipment or ingredient contamination. For an elimination trial, vets generally prefer prescription diets made with controls. See limited ingredient cat food.

How to run an elimination trial

1. Rule out parasites and infections first, and treat them.
2. Choose the diet with your vet.
3. Feed it exclusively for eight to twelve weeks. Some cats improve in a few weeks, but eight to twelve is needed to be sure.
4. Control everything. No treats, table scraps, flavored toothpaste, flavored medicines, supplements or other foods unless approved. In multi-cat homes, keep the cat separate, or feed all cats the same diet. See feeding cats in a multi-cat home.
5. Keep outdoor hunting in check, since prey counts as food.
6. Track signs. Keep a diary of itch, vomiting and stool.
7. Challenge. If signs improve, your vet may ask you to reintroduce old foods one at a time, to identify the trigger, or you may continue the diet.

Tips to improve success

• Introduce the new food gradually, over a week or two, unless your vet says otherwise. See how to switch cat foods.
• Offer wet and dry versions if both exist.
• Warm wet food to improve appeal.
• Use pieces of the same diet as treats.
• Clean bowls thoroughly. See how to clean cat food bowls.

Why strictness matters

Even a tiny amount of the trigger can cause signs. A single cheat can restart the cycle, and spoil weeks of work. Tell everyone who feeds your cat.

Medication during the trial

Your vet may prescribe medication for severe itch or infection while the diet works. Never give human medicines. See cat poisoning: what to do.

What if there is no improvement?

If signs persist after a proper trial, the problem may be environmental allergies, or another condition, such as inflammatory bowel disease. Your vet may suggest additional tests. See inflammatory bowel disease in cats.

Long-term feeding

Once a trigger is found, avoid it for life. Many cats stay on a hydrolyzed or novel protein diet permanently. Check complete and balanced labeling. See cat food aafco statement explained.

Costs and practicalities

Hydrolyzed diets are more costly than ordinary food, but a good trial can save months of itching, medication and vet visits. Ask your vet about sample sizes, and buy a small bag first. Write down the dates, and set reminders for rechecks.

When to see a vet

See a vet if your cat is itchy, has chronic vomiting or diarrhea, or has skin sores. Use the US vet directory to find a clinic.

This article is general educational information, not veterinary advice. Every cat is different. If your cat is unwell, or you are unsure about a symptom, diet change or medication, contact your veterinarian.