Food Allergy or Intolerance

Pet Tales
by  Barry B. Burtis D.V.M.

Food allergy or intolerance

Despite our best efforts to choose the right food for our pet, sometimes a pet may have problems caused by what they are being fed. Food allergies or a food intolerance are two such problems that can develop. It can be very difficult to differentiate between the two.

True food allergies are the result of an immune reaction to an ingested protein while adverse reactions or food intolerance can be a response to anything ingested: fats, carbohydrates or proteins.

Symptoms for either problem are similar and can range from gastrointestinal signs to skin disorders. The most common skin conditions that can result are itchiness anywhere on the body's skin surface, recurring ear problems or repeated skin infections. Allergies and food intolerances can both cause vomiting, diarrhea and increased frequency of passing stools. Of course it is always important to remember all these clinical signs could easily have other non-related causes such as an under active thyroid gland, inflammatory bowel disease or pancreatitis.

The actual incidence of food allergies in dogs and cats is unknown. There is a lack of reliable diagnostic tests available to determine whether an animal has an allergy or intolerance to certain foods. A study put out by a task force for the American College of Veterinary Dermatology agrees that the tests traditionally used to assist in the diagnosis of skin allergies, including intradermal skin testing, are unable to accurately diagnose food allergy.

The only widely accepted, tried and true method is elimination diet testing.  This means that for 8-12 weeks the dog or cat being tested is fed either a novel protein source or a hydrolyzed diet. If this trial results in the patient improving, it is followed by a provocation test with the old food. Only by finding improvement on the new diet, followed by a recurrence of trouble on the old, can food allergy truly be proven. 
Feeding a novel protein means the dog or cat must be fed a protein source that it has never been exposed to previously. It does not mean you can switch to a new brand of food because the same protein sources - usually beef, chicken, fish, lamb and so on - are used by all pet food manufacturers in the production of commercially available foods. Venison, duck, rabbit and other unusual protein sources must be fed. It should be noted that although thirty years ago lamb could be considered one of these unusual protein sources, it no longer can be. Contrary to many people's understanding, therefore, lamb and rice diets cannot be thought of as diets to rule out food allergies or food intolerance problems.

Hydrolyzed diets are available from most veterinarians. These diets have had the proteins they contain broken down into small pieces by hydrolyzation. They are so small they
escape detection by the body's immune system and therefore cause no allergic reaction but still have all the nutrition the pet needs. So for a minimum of 8 weeks, the animal's diet must be limited to a food to which it is unaccustomed.  All other treats, heartworm preventives and anything else the pet might normally eat must be avoided. It may not be easy to convince the pet of the importance of such a trial. It may not like its new food, it may miss its usual treats. Special diets may be expensive and unique protein sources are becoming ever more difficult to find. As a result, gaining an owner's compliance with such a feeding trial may be difficult.

For these reasons it is hoped that perhaps a test used for food-allergy diagnosis in humans, may be able to be used successfully in animals.  The colonscopic allergen provocation test is currently being evaluated in dogs. In the future it may also be possible to measure levels of specific immune system indicators in fecal samples from pets thought to be affected by food allergy or intolerance problems.