Hydrolysed protein

Hydrolysed protein is protein that has been deliberately broken down into very small peptides by hydrolysis, in order to reduce its potential to trigger an allergic reaction. The principle rests on how food allergy works: the immune system reacts to whole proteins or large protein fragments, so if a protein is chopped into pieces small enough that the immune system no longer recognises them, the allergenic potential falls sharply. This is why hydrolysed-protein diets are a mainstay of the dietary investigation of suspected food allergy and adverse food reactions in both dogs and cats, used as part of a strict elimination trial under veterinary guidance. They are an alternative strategy to the [novel protein](/glossary/novel-protein) approach, which avoids reactivity by using a protein the animal has never met, rather than by dismantling a familiar one. Hydrolysed diets have practical advantages: the source protein is one the manufacturer can control tightly, and the small peptides are typically very [digestible](/glossary/digestibility). The trade-off is that hydrolysis can give the food a distinctive taste and smell that some animals find less palatable. On a label you will see ingredients such as hydrolysed poultry or hydrolysed soya protein. These are therapeutic diets, best used on veterinary advice. See the [Petipedia glossary](/glossary).

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