Food Allergy, Canine

Food Allergy

By Dr. Karen Burgess

What causes a food allergy?
Food allergy is responsible for 10% of allergic skin disease in dogs and cats. It occurs when a pet’s body identifies a component of their diet as foreign or “bad” causing the immune system to respond. Antibodies to the offending nutrient are produced which leads to inflammation in particular with the re-exposure that occurs with every meal. The most common food allergens in dogs are beef, dairy, wheat, egg, and chicken. In cats beef, dairy and fish are most problematic. 50% of food allergic cats and dogs are allergic to multiple components in the food. Owners often think that a recent switch in food “caused” a food allergy when in actuality it takes time for these allergies to develop.

What is the difference between food allergy and food sensitivity?
Some pets have food sensitivity instead of a true food allergy. This is a situation where pets do not tolerate a particular food component but are not having a systemic allergic response. An example of a food sensitivity would be eating spoiled food or someone that was lactose intolerant.

What are common signs of food allergy?
The most common symptom associated with dog and cat food allergy is a non-seasonal itchiness that is not due to another cause such as parasites (i.e. fleas, mange). Typically these signs develop prior to one year of age and are non-responsive to steroid therapy. Common signs include recurrent ear infections, facial itching, and peri-anal itching. Repeated skin infections and hair loss may also be noted. Some pets will display gastrointestinal signs (vomiting, diarrhea, weight loss, flatulence) in addition to or instead of skin signs with food allergy.

How is food allergy tested for?
Clinical signs and history (in particular symptoms prior to a year of age) may be highly suggestive of a food allergy. The only true way to diagnose a food allergy is to perform an eight to twelve week food trial using a veterinary approved prescription hypoallergenic diet (see additional information below on Food Trials). If symptoms resolve this is a strong indicator that the pet is allergic to some component in their previous diet. After completion of the food trial, pets are challenged with individual proteins or carbohydrates to see when they again become symptomatic (typically within two weeks of re-exposure). The goal is to determine whether there is an over-the-counter diet that may be acceptable for long-term use. Owners may continue the hypoallergenic diet indefinitely as it can often be difficult to transition successfully to a commercial product. Some companies do offer blood testing for food allergies. These tests are notoriously unreliable with numerous studies showing both false negative and false positive results. An appropriately performed food trial is the only valid way of testing for a food allergy.