Diagnosing food allergies often frustrating
By: Dr. Daniel Eubanks
Last month, we introduced the concept of allergies in our pets.
We discussed allergic individuals as those who produce an abnormal antibody in response to exposure to certain antigens, usually foreign proteins. We listed three types of allergies in our pets flea, food and inhalant.
Having discussed flea allergy last month, let’s now consider food allergy.
First of all, food allergy should be distinguished from food intolerance.
Food intolerance is a non-systemic, local reaction to some particular ingredient in the food. The offensive component is frequently an additive a preservative, coloring agent, etc. It usually causes only gastrointestinal disturbance with no systemic manifestation. This does not involve the immune system.
Food allergy involves the production of the abnormal antibody IgE by the immune system in response to something in the diet, usually a protein or carbohydrate. The allergy is manifested not as a GI disturbance, but rather as a profound itch dermatitis. The face, feet, ears and abdomen are primarily affected. Unlike flea and pollen allergies, this is a non-seasonal affliction.
Making the diagnosis of food allergy can be frustrating and elusive. One must remember allergic individuals are seldom sensitive to only one antigen. They might be allergic to more than one dietary ingredient and also might be allergic to fleas and pollens.
Non-seasonal, chronic itching involving the face, feet, ears and belly, with the absence of external parasites like fleas and skin mites, should prompt suspicion of food allergy.
Blood tests are available to screen for food allergy. Skin testing might be a somewhat more reliable screening test. But the patient’s response (or lack of response) to a dietary restriction trial is the only truly definitive diagnostic test.
Simply put, if we suspect the animal is allergic to something in his diet, then we don’t feed that "something" to him for a while and see if he gets better.
Simply put, but not simply done.
The problem is we don’t have a clue as to which "something" in his diet is causing the problem.
Frequently, clients are on the right tract about food allergy but make the following mistakes. They substitute brand B for brand A for one week, don’t see an obvious improvement and then conclude it must not be an allergy to the food.
Ingredients in most commercially available pet foods are pretty much the same variations of poultry, beef, or fish by-products, wheat, corn and soy. Not that there is anything wrong with these ingredients. The 90 percent "normal" pet population process these staples just fine.
But if the pet is allergic to corn glutton or wheat or chicken or beef, there is no difference between brand A and brand B. Other than the color of the bag, we haven’t changed a thing. Even if you by random chance select the appropriate ration, if the item to which he is allergic is a component of his dog biscuits or even his chewable vitamin or monthly heartworm preventative, the pet is still consuming his allergen and will show no response.
The avoidance test diet must be totally exclusive of any flesh protein or carbohydrate, which was a component of his previous diet.
That’s where the familiar lamb and rice diet came from. Prior to the 1980s, pet foods never included lamb or rice so that combo made an ideal avoidance test diet. However, lamb and rice have since been used so extensively and indiscriminately added to poultry and beef containing foods that both ingredients are now potentially the offending allergens.
Appropriate test diets now include such exotic flesh meats as rabbit or venison and novel carbohydrates such as potato.
The ration may be home cooked, commercially available from high-end specialty stores or a prepared prescription diet.
A typical avoidance diet trial should be used for at least three months with absolutely no treats or chewables, which might invalidate the results. Positive response, as indicated by resolution of the itchy rash, would support the suspicion of food allergy.
Definitive diagnosis of food allergy can be difficult to confirm, yet rewarding to discover. A patient with genuine food allergy, once properly diagnosed, can be successfully treated with an appropriate diet and thus remain drug free.
Next time we discuss inhalant allergy.

