Visiting Vet: Food allergy

Use elimination diets to test for pet allergies and rule out other causes.

A pet can be checked for food allergies using an elimination diet. — Christian Bowen

Hey, parents. Remember when your kids were little, and the pediatrician had you introduce foods slowly, one at a time, giving the new food for a week or two before trying the next one? According to the Centers for Disease Control and Prevention, an estimated 4 to 6 percent of children and 4 percent of adults are affected by food allergies. Symptoms can range from rashes and diarrhea to anaphylaxis — a potentially life-threatening reaction. Dogs get food allergies, too. So when Jada, a young goldendoodle, experienced an episode of hives, rapid breathing, swollen eyes, and severe itchiness after being fed a treat, the veterinarian who spoke with the owner advised this was likely a food allergy and prescribed diphenhydramine — an antihistamine commonly known by the brand name Benadryl.

Food allergies in dogs and cats are rarely this severe. In dogs, the most common signs include itching around the face, legs, feet, and anal area, and recurrent ear infections. Some dogs will get vomiting and/or diarrhea. Cats with food allergies typically scratch around the head and neck. Both dogs and cats may develop secondary bacterial infections, scabs, oozing sores, and hair loss. Now before you go off the deep end and decide your itchy pup has a food allergy, let’s look deeper.

If Jada is scratching madly but has no other symptoms, the first thing to rule out is ectoparasites. That means creepy-crawlies on the skin. Fleas. Lice. Mites. OK. Once we are sure these are not the problem, the next most likely culprit is called atopy. That’s an inhalant allergy. It can be a reaction to pollen, molds, dust mites, and so on. I always tell owners, “Dogs get itchy the way people get hay fever.” Statistically, Jada is far more likely to have canine atopy, but specialists now say about one in five dogs do have real food allergies. Unfortunately, neither blood tests nor skin tests appear to be accurate for diagnosing food allergy in dogs. So how do we make the diagnosis?

The first thing to remember is that an allergy requires exposure. It takes time for the immune system to start to react to any particular food item. That’s why your pediatrician had you feed eggs for two weeks to see if your kid was going to react. That’s why peanut butter allergies don’t manifest the very first time your child has a Reese’s. The first information we need is a very thorough and accurate dietary history of exactly what Jada has been fed. Not just now. Ever. Including treats, table scraps, and so on. The reality is that with thousands of commercial diets out there, it is hard to fully assess every potential allergen Jada has eaten. Then we start looking for other clues.

If Jada’s itchiness is seasonal, we would be more suspicious of atopy. Age of onset may also be a clue. Most food allergies manifest by the age of 3 years in dogs, or even younger, though about 15 percent of cases occur later in life. Some food allergies may come on quickly, after just a few exposures. Others may take years to develop. About a third of food-allergic dogs show concurrent gastrointestinal signs, like vomiting or diarrhea. If your veterinarian suspects food allergies, the next step is an “elimination diet trial.”

The cool thing about an elimination diet trial is that it is a food, a diagnostic tool, and a treatment. Please do not just switch brands or flavors, or buy a bag at the grocery store that says “for sensitive skin.” That is not a true diagnostic challenge. What Jada needs is an eight- to 12-week trial on a very specific prescription diet that eliminates virtually all possibility of allergic reaction. During those eight to 12 weeks, it is essential she gets absolutely nothing else to eat. No flavored heartworm preventive pills. No treats. No table scraps. If truly food-allergic, 90 percent of dogs will show marked improvement by eight weeks. That last 10 percent may take another month, so it’s worth it to do the whole course. If at the end, Jada is still scratching madly, we have ruled out food allergy. Period. You can now move on to looking for other causes with your veterinarian.

If Jada is all better on the elimination diet, veterinary dermatologists usually recommend a careful challenge with the dog’s previous food, by adding one-third of her old diet to two-thirds of the prescription food for up to 10 days. If Jada is food-allergic, her symptoms should recur. One reason to do this is that during that three-month trial period, seasons change. Is Jada better because of the diet, or because the oak pollen is gone? Let’s find out. Carefully. This is usually a safe approach to confirm our diagnosis, but not a technique advised in those rare cases when a dog has had severe reactions, like Jada had. Beef, dairy, chicken, and wheat are the most common culprits, but other foods may also cause allergies.

The main reason elimination diet trials fail to make a diagnosis is poor compliance by owners. After recently attending a virtual continuing education series about food allergies, I realized I need to advise owners to take more stringent measures. A single dose of flavored heartworm preventive can apparently make some allergic dogs itchy for three to four weeks, obscuring the benefit of the elimination diet. Are your kids dropping food on the floor? Is Jada sharing a water bowl with another dog that eats other foods, then slobbers in the shared bowl? Are you running out of the special diet because you didn’t order in time, or because of supply-chain issues? If you think Jada has a food allergy, sit down for a heart-to-heart with your veterinarian, make a comprehensive plan, and follow it precisely. If we do it right, food allergy is a “can’t miss” diagnosis, and we can spare Jada a lifetime of misery by simply choosing the right diet.