Glossary

Hydrolyzed protein diet

A veterinary diet whose proteins are chopped into pieces too small for the immune system to recognize, used to diagnose and manage food allergy.

Also called: hydrolysed diet, hydrolyzed diet, HA diet, hypoallergenic diet, hydrolyzed protein dog food

In a hydrolyzed protein diet, the proteins are broken by water and enzymes into very small fragments, which an allergic dog's immune system is far less likely to recognize and react to. The source can be chicken, soy, salmon or another protein, and the food is made in a way that reduces cross-contamination.

It is a main tool for an elimination diet trial to diagnose food allergy, in which a dog eats only the diet, with no treats, for several weeks. It is also used for some dogs with chronic digestive disease.

Most of these diets are sold through vets, and cost more than ordinary food. Hypoallergenic on a pet food label has no legal meaning, so the term should not be trusted on its own. Use one under veterinary supervision, and follow the trial exactly, since a single treat can undo the result.

Last reviewed November 8, 2026

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Related terms

Food allergy An immune reaction to a protein in the diet that usually causes itchy skin and ear problems, and sometimes digestive upset. Prescription diet A food formulated to help manage a medical condition such as kidney disease or food allergy, fed under veterinary supervision. Novel protein A protein source a dog has never eaten before, used in elimination diets because the immune system has not learned to react to it. Limited-ingredient diet A food built around one protein and one carbohydrate source to reduce exposure, often used to look for a food allergy.