While the majority of patients presenting for skin and/or ear disease have environmental allergies such as atopic dermatitis and feline atopic skin syndrome, which is a diagnosis of exclusion, flea bite hypersensitivity and cutaneous adverse food reactions should be ruled out first. It’s paramount to perform a strict elimination diet trial to ensure overall success in allergic skin disease management.
The following are key points to optimize the value of an elimination diet trial:
1. Choose a limited antigen diet containing a novel or hydrolyzed protein that is different from a patient’s previously fed protein. This means that if a patient has been fed poultry, it is more ideal to select a diet not containing poultry derivatives. Clinically, it is commonly the case that patients fed a hydrolyzed poultry-based diet fail to respond as well if they are poultry-sensitive as those patients fed a novel non-poultry meat or hydrolyzed soy or amino acid-derived diet. Similarly, a hydrolyzed fish diet may not help if a pet is intolerant or allergic to fish.
Food allergens are usually proteins rather than carbohydrates, though carbohydrates have been reported to be allergenic.1 Grain-free diets do not generally offer significant benefit if the protein source is not different from what was previously fed. Optimal diet selection often requires detailed review of the patient’s dietary history.
Prescription or home cooked diets are often preferred over diets that do not require a prescription for purchase. Many over-the-counter diets have been shown to be contaminated with other proteins not listed on the ingredient list and this can make interpretation of a diet trial challenging.2
2. Ensure the elimination diet trial is performed long enough. A period of 6-10 weeks on a new diet should suffice as a “washout” period from the previously fed offending protein.
3. Serology is generally not very clinically relevant and unreliable. Food allergen-specific immunoglobulin E (IgE) can be measured, though serology has been unreliable both in elimination diet trial protein selection and the ultimate diagnosis of food allergy.1 The best case is to confirm that a flare occurs upon provocative diet challenge at the end of the diet trial.
4. The absence of gastrointestinal (GI) signs does not rule out cutaneous adverse food reactions. Not all pets with skin/ear disease resulting from a food allergy also have GI signs. If they do, a diet trial should absolutely be investigated.
5. Be strict – no other treats, bones, flavored medications, supplements, or parasiticides should be offered. Control what can be controlled – flavored joint supports should be discontinued or replaced with a hypoallergenic version if available. Long-acting oral or topical parasiticides are often preferred to be flavored, monthly chewables (though some options exist now with hydrolyzed or synthetic flavoring). Treats or foods to aid in pill administration can provide small albeit significant amounts of a potentially offending protein that can deem the diet trial ineffective. Flavoring in oral suspensions should be synthetic or those that do not contain meats such as vanilla, maple, or carrot. Pills can instead be administered in the canned/wet formulation of the diet used for a trial, vegan marshmallows, non-dairy ice cream/coffee creamer, or pill wrap powders containing limited protein ingredients. If the pet is using flavored toothpaste, it should be discontinued.
If young children are in the home, be mindful and understanding that a strict elimination diet trial may not be successful given a higher chance for more frequent dietary indiscretions as a toddler may drop food off a highchair.
6. Ensure secondary infections, if applicable, have been resolved. Confirmation of a food allergy is best made upon documenting a relapse of clinical signs upon re-exposure to the originally fed and offending protein/diet. It is important that patients are directed to perform a diet challenge only after infections have been confirmed to be resolved. A diet challenge should not be directed while on medications that could mask the flare that you’re monitoring for as a sign to confirm a food allergy. If infection is present at the time that a diet challenge is performed, the patient may mistakenly be diagnosed with a food allergy when instead they merely have an infection.
7. Confirm via provocative diet challenge. If after re-exposure to an originally fed and allergenic diet a patient flares (this can occur within a few hours and as late as 2 weeks), they are confirmed to have food allergies.
If you have a client who is interested in a referral to a board-certified veterinary dermatologist, feel free to reach out to the veterinary dermatologist to determine if they have specific preferences about how and when a diet trial should be performed. There can be a multi-month wait before the patient may be evaluated by a specialist. Ruling out a food allergy can actually be very helpful in setting up a patient for additional diagnostics and therapies such as allergen-specific immunotherapy.
Yamazaki received her bachelor’s degree from the University of California, San Diego and Doctor of Veterinary Medicine from Atlantic Veterinary College at the University of Prince Edward Island in Canada. She returned to California, completing a rotating internship and dermatology specialty internship in San Diego before accepting dermatology residency positions at Animal Dermatology Clinic in Tustin and Ontario, California. Yamazaki obtained Diplomate status with the American College of Veterinary Dermatology in 2019. She briefly relocated to Marietta, Georgia, before returning to California to practice dermatology in Oakland at Dermatology For Animals, a Thrive Pet Healthcare partner.
- Jackson HA. Food allergy in dogs and cats; current perspectives on etiology, diagnosis, and management. J Am Vet Med Assoc. 2023;261(S1):S23-S29. Published 2023 Mar 18. doi:10.2460/javma.22.12.0548
- Horvath-Ungerboeck C, Widmann K, Handl S. Detection of DNA from undeclared animal species in commercial elimination diets for dogs using PCR. Vet Dermatol. 2017;28(4):373-e86. doi:10.1111/vde.12431