Best Dog Food for Allergies: Hydrolysed vs Novel Protein

Most articles answering this question hand you a list of brands. The more useful answer is that there are two different jobs a food can do here, and the food that does one badly does the other well. Which you need depends on whether you are trying to find the allergen or trying to live with a known one.

The Problem With Supermarket “Limited Ingredient” Food

The obvious move, if your dog reacts to something, is a limited-ingredient food from the pet shop with one protein on the label. The difficulty is that the label is frequently wrong.

A 2019 study in Veterinary Medicine and Science tested 21 over-the-counter limited-ingredient diets and found DNA from undeclared animal species in every single one, with a median of three undeclared protein sources per food. Separate work has found undeclared animal DNA in more than 80% of limited-antigen and single-protein diets, and one analysis found undeclared chicken DNA in 65% of the commercial foods it examined. The cause is usually cross-contamination on shared production lines rather than anything deliberate.

For a dog that is merely a bit itchy, this may not matter much. For a diagnostic elimination trial it matters completely: if the “duck and potato” food contains traces of chicken and beef, a dog that fails to improve has told you nothing, and you have spent ten weeks finding it out.

If You Are Still Diagnosing: Hydrolysed Diets

Hydrolysed diets take an ordinary protein and break it into fragments small enough that the immune system no longer recognises them as the original food. The advantage over a novel protein is that it does not depend on you correctly remembering everything your dog has ever eaten, including whatever it found on a pavement two years ago.

These are veterinary diets and need a prescription, which is the point rather than an inconvenience: the manufacturing controls that make them useful diagnostically are the same controls that put them behind a vet.

Once You Know the Trigger: Novel Protein Diets

After a trial has identified the culprit, the requirements loosen considerably. You no longer need a food that is diagnostically airtight; you need one that reliably avoids one specific protein and that your dog will eat for years. That is where a novel-protein or limited-ingredient diet becomes reasonable, and where the contamination risk above shifts from fatal to tolerable — trace cross-contact is a different problem from an unidentified trigger.

Look for a named single protein the dog has not reacted to, a short ingredient list you can actually read, and a manufacturer that publishes its sourcing.

The Part That Actually Fails Most Trials

It is rarely the main food. Trials are usually undone by everything around it: a dental chew, a flavoured heartworm tablet, the crust of toast from a child, a neighbour who gives biscuits. A food trial means the prescribed diet and water, and nothing else, for the whole period.

On duration, a literature review found a minimum of around 10 weeks may be needed to identify 95% of food-allergic dogs, although trials are sometimes shortened to roughly 4 weeks when run alongside a short course of anti-inflammatory steroids. For the full protocol, including the re-challenge step that actually confirms the diagnosis, see our guide to the food allergy elimination diet.

Before You Change Food At All

Food allergy is a less common cause of itching than owners expect. Environmental allergy and fleas account for far more cases, and they look similar from the outside. Changing diet for a dog with atopic dermatitis costs months and changes nothing. Our page on telling food, environmental and flea allergy apart covers how vets separate them, and why blood and saliva allergy tests do not answer the food question.

Frequently Asked Questions

Sources

• Fossati et al. (2019), Veterinary Medicine and Science — mammalian DNA in limited-ingredient canine diets
• Merck Veterinary Manual — Cutaneous Food Allergy in Animals