What is Food Hypersensitivity?
It is an adverse food reaction (AFR) that may result in a variety of symptoms that are noted on a continuous basis. Makes sense, right? Your pet will have relentless symptoms if they are exposed to an allergen in their food every day. Symptoms are not the same for every pet and may include itch/scratch, relapsing infections, infections that are slow or difficult to resolve, failure of pruritus to respond to a steroid and/or concurrent gastrointestinal upset. The symptoms can be localized to the ears alone, the face and neck, the “hind end” or may be generalized. We think of food allergy more often in very young dogs (less than 6 months of age) or older dogs that have never experienced skin or ear disease before. For cats, we think of food allergy predominantly in cats with severely itchy skin of the head and neck. Ultimately, just like in people, food allergy can start at any age.
How do AFRs develop?
Both pets and people have many layers of protection along the gastrointestintal (GI) tract to help protect from AFRs. Some examples are the enzymes that help digest food, the mucus layer that lines the GI tract to provide a barrier, tight junctions between individual cells and the immune system embedded deeply in the GI tract. All of these help prevent food allergens from crossing boundaries that were not meant to be crossed. An AFR may develop when those protective layers are breached and the immune system is sensitized. Known allergens are typically proteins that weigh between 10,000 and 70,000 daltons. How big is a dalton? It is beyond tiny, on the order of 3.6 x 10 -27 of a pound.
What foods do we recommend?
The latest buzz word in dog food is “grain free” but the top food allergens according to one recent study were beef (60% of dogs), soy (32%), chicken (28%), milk (28%), corn (25%), wheat (24%) and egg (20%). It is important to critically evaluate past diets consumed before changing to a new food. Veterinary dermatologists typically use either a hydrolyzed diet or a novel protein diet.
What is a hydrolyzed diet?
This means the proteins have been modified/reduced to such a small size that the body should not be able to recognize them as an allergen (best if they are hydrolyzed to less than 5000 daltons). Alternatively, changing to a protein that your pet has never eaten may be beneficial also.
All about pet diets
Over-the-counter diets can be deceiving. For example, one popular venison based diet also contains chicken (a top allergen) as its number 3 ingredient. One recent study showed that 3 out of 4 over the counter diets labeled as “soy free” actually contained enough soy to cause an allergic reaction. For this reason we prefer to use veterinary prescription diets that are produced on a dedicated line that won’t be cross contaminated.
Food trials typically last 8-12 weeks
These diets may need to be fed for up to 12 weeks before a response is appreciated. Recently, a new diet that is both novel protein and hydrolyzed protein was released and pets seem to be responding faster, as quickly as 4-6 weeks. No other food, rawhide chews, bones, flavored toys or medications are allowed during a food trial. We even change to a non-flavored heartworm preventive. We consider a food trial a test like any other and it is one of the hardest tests we ask our pet parents to complete. It must be 100% strict in order to prove or disprove a food component. Even occasional transgressions will seriously limit the chances of a diagnosis. If symptoms resolve by the end of the strict food trial then we plan a food challenge to see what the specific food triggers will cause a flare.