Food hypersensitivity in dogs and cats: Elimination veterinary diet trial pitfalls


Diet trials are key to diagnosis, but common complications must be avoided.

The only method to accurately identify patients with food hypersensitivities is to perform an elimination diet trial for a sufficient time while controlling all concurrent allergies and secondary infections. Last month I outlined how to conduct a successful diet trial. Now let's look at some common complications to avoid or to be ready to handle.

Beware over-the-counter wares

A plethora of over-the-counter novel protein diets claim to be restricted in their protein sources. You and your clients need to read labels closely to ensure they are consistent with the goals of the food trial or management of the food-allergic patient. Because of price and convenience, clients often prefer these over-the-counter foods. Unfortunately, close scrutiny has revealed that many of the over-the-counter "novel protein diets" contain several ingredients not listed on the label.

One study evaluated four popular over-the-counter venison diets, which were tested for soy, beef and chicken.1 Three of the four diets contained soy, beef and/or chicken, and the fourth contained rice protein. For this reason, using therapeutic diets from reputable companies with stringent quality control remains important in determining whether a patient has a food allergy. Once the patient is stable, you can always "work backward" and challenge the patient with an over-the-counter novel protein diet and monitor for a flare. Whereas improvement on a diet may require weeks, most dogs flare within days if not hours.

Home-cooked diets

At times, a client will desire to use a diet cooked at home. In these cases, the challenge is to find a novel protein that fits the previously discussed criteria and is available and not cost-prohibitive. I typically will use white or sweet potato as the carbohydrate. If the patient has not had exposure to fish, I might recommend tilapia as the protein source. We recommend a ratio of one part protein and two parts carbohydrate.

Since this diet is intended to be used as a test diet and not long-term maintenance, we do not attempt to balance the diet with various micronutrients. If the patient is to be fed a home-cooked diet long-term, then we will suggest a resource such as for advice regarding a proper balance of nutrients. There are several new companies providing frozen or freeze-dried novel exotic proteins for feeding dogs or cats, which may provide alternative options for clients.

Sneaking in snacks

One pitfall for successfully implementing an effective food trial is the "unbelievers" at home who cannot comprehend the detriment a little snack can have. Small children who drop food and other dogs at home eating different diets can also provide challenges the owner will have to overcome.


The cost of the therapeutic diets can also be an obstacle in performing a food trial. Supplementing the diet with home-cooked ingredients that are already allowed (such as potato) can help buffer the cost of the food trial and is preferable to over-the-counter foods.

Flavored medications

Flavored medications have become an increasingly common challenge to overcome when enforcing a food trial. Many flavored medications contain beef and pork protein. I have observed patients flare from their once-monthly flavored heartworm preventive. Glucosamine chondroitin is another potential allergen commonly administered.

When it's not just food

It is not uncommon for an atopic dog or cat to have multiple triggers for their disease, with both food and environmental allergens playing a role. A clinician trying to sort out these multiple triggers will also sometimes have to make compromises when developing a comprehensive treatment plan for the pruritic patient. Feeding a large dog such as a Labrador retriever a novel therapeutic diet long-term may leave nothing else in the budget for control of the environmental triggers.

In such cases, I will frequently recommend some of the over-the-counter fish-based diets in an attempt to find an over-the-counter food that will not trigger the food allergy and possibly provide some supportive care for the atopic dermatitis because of the omega-three fatty acids. This, of course, assumes the patient is not allergic to fish and that there are not other protein contaminants in the food but not listed on the label.

Client communication

In our practice, even though we use handouts to help educate clients on the principles of the food trial, we do not rely on the handouts alone. It requires time to properly educate a client on how to perform the food trial. We schedule a follow-up appointment with one of our office staff a few days after initiating the trial, and we schedule another follow-up four to six weeks after starting the trial so that progress, or lack thereof, can be assessed.

Dr. Lewis sees dermatology patients in California, Arizona, Nebraska, New Mexico and Washington. In 1991 he established Dermatology for Animals, PC.


1. Raditic DM, Remillard RL, Tater KC. ELISA testing for common food antigens in four dry dog foods used in dietary elimination trials. J Anim Physiol Anim Nutr (Berl) 2011;95(1):90-97.

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