Diet trials: The true test of food allergies

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In the past, it was commonly believed that food allergies were rare among dogs and cats. However, with advancements in veterinary medicine and more accurate dermatologic protocols and methods, there has been a notable rise in the diagnosis of food allergies. Therefore, Julia E. Miller, DVM, DACVD, a dermatologist with Animal Dermatology Group in Louisville, Kentucky, and an assistant clinical professor of dermatology at Cornell University College of Veterinary Medicine in Ithaca, New York, stressed that it is crucial for veterinary professionals to continue their ability to identify these cases. She helped attendees at the Fetch dvm360 conference in Nashville, Tennessee address food allergy cases during her session sponsored by Blue Buffalo.¹

According to Miller, 10% to 25% of atopy dermatitis cases are caused by a food allergy.^1,2 Food allergy, more formally referred to as cutaneous adverse food reaction, is an adverse immunologic reaction to an allergen in the diet. Diagnosing a food allergy can be quite frustrating since it presents very similarly to environmentally-caused allergies. The same signs of skin pruritus, scratching, licking, and scooting can be present. “Could this be a food allergic dog? 100%. Could this be an atopic dog? 100%. It’s so difficult to identify the difference, especially on sight alone,” Miller explained.

Age at onset could give a clue for food allergy as it can happen at any age, while atopy usually occurs at 1 to 3 years of age (with exceptions). Symptoms occurring in a dog aged less than 6 months or older than 4 years could be a clearer sign pointing to food allergy rather than atopy. Seasonality can also help point to identification because atopy can occur relative to the season, but the season has no impact on food allergy. Miller stated, “So if you have a dog starting with itch at 6 years of age, and it is non-seasonally pruritic, you better do a diet trial on that dog. That's very important.”

And finally, previous methods of using medications and the patient’s response can help with identification. If a patient is not responding to any treatments, it could possibly be food allergy rather than atopy.

To accurately diagnose, a diet trial could be the ideal approach for specific cases. Although this is the ideal method, diet trials are extremely difficult to get right and not all clients will be able to comply to the strict requirements necessary for it to be successful. It is also important to note that other conditions should also be taken care of before starting a diet trial. Miller said as an example, “If [the patient] is covered in bacteria, your diet trial is never going to work. It's never going to be accurate if you don't actually clear the other stuff. So clean the slate. That is super important.”

Miller also explained that serum, saliva, and hair tests are not effective diagnostic methods for food allergy and are not recommended by specialists.^1,3

“So, now we have our patients selected, who sounds like a food allergic dog. Now you need to have a conversation with a client about if a diet trial is possible. And you have to have this conversation. If you're a veterinarian that sends dog food out the door without this conversation, shame on you, right? Because you are wasting your client’s money unless they know how to properly do a diet trial,” Miller said.

Thorough client handouts can be a tremendous help with this communication, she noted. Printing out a copy of the complete plan, including necessary recheck appointments, can be helpful for clients.

For a diet trail to be successful, the patient must only eat the selected diet by the veterinary professional. This means none of the following add-ons¹:

• Over the counter (OTC) treats
• Meal toppers
• Flavored pills/capsules
• Flavored toys
• Flavored parasite preventions
• Human/table food
• Another pet’s food

Miller also advised attendees to be cautious of shared water bowls for patients on a diet trial for risks of cross-contamination.

When the client is on board, what diet do you select? There are 3 options:

1. Home cooked novel protein
2. Prescription novel protein
3. Prescription hydrolyzed protein

Food selection should also consider the patient’s diet history (what’s not working?), the pet’s palate, and if dry or wet food is the best approach. OTC diets are never considered a diet trial because there is a high chance of cross-contamination. Miller reminded attendees that no one size fits all and diet trials must be specifically tailored for the patient.

“Here are our most common allergens: chicken, and I have egg and duck in there. I do believe, and I've seen this be the case, that the feathered friends cross react and I do believe egg cross reacts with chicken and the reason I believe it is my own dog is my little chicken allergic gal. Beef is maybe surpassing chicken these days is one of our No. 1 allergens. We used to think beef was kind of a novel protein, [but] it's really not anymore. And then also dairy and lamb are in there. Now we can sometimes see wheat allergies. I hate to admit it, because I don't like to blame a grain. But occasionally you can get wheat, soy, corn, pork, and fish, these are much lower.”

According to Miller, after 3 weeks on a diet trial, more than 50% of dogs will show improvement. After 5 weeks, more than 85% of dogs show improvement, and after 8 weeks, this jumps up to more than 95% of dogs showing improvement. “So the way that I feed diets is I have the client check back in with me at 4 to 6 weeks. If there is zero change in 4 to 6 weeks, I am done. I do not feed that diet for another 2 months. If there is some change in that 4-to-6-week plan, I continue the diet a little bit longer and see how good I can get it,” Miller said.

Finally, at the end of the trial, if the patient has not improved then it might not be a food allergy, or the client did not correctly complete the trial. This would require a pivot in treatment methods moving forward. If the patient does show improvement, then a long-term diet change should be discussed.

References

1. Miller JE. Don’t Dread the Diet Trial! Demystifying Food Allergies and How to Accurately Diagnose Them. Presented at: Fetch dvm360 conference; Nashville, TN. May 17, 2024.
2. Miller JE. The itchy and scratchy show: How to confidently diagnose canine allergies (part 1). Presented at: Fetch dvm360 conference; Charlotte, North Carolina; March 15-17, 2024.
3. Favrot C, Steffan J, Seewald W, Picco F. A prospective study on the clinical features of chronic canine atopic dermatitis and its diagnosis. Vet Dermatol. 2010;21(1):23‐31.