Ettinger & Feldman — Textbook of Veterinary Internal Medicine
Client Information Sheet
Catherine A. Outerbridge
|What is food hypersensitivity?Food hypersensitivity, or food allergy dermatitis, is a chronic skin disorder that occurs in dogs and cats. Food hypersensitivity is caused by a persisting allergic reaction to a food product. The most likely food allergens are those that your pet is fed frequently. No correlation exists between the quality of the diet and an allergic reaction. Food allergy reactions are most commonly to a protein source (chicken, beef, soy, egg, milk products) in the diet but could also represent a reaction to a carbohydrate or rarely, to a preservative or food additive.
What are the symptoms of food hypersensitivity?
Dogs and cats with food hypersensitivity may exhibit some or all of the following symptoms:
The onset of food hypersensitivity can be sudden and it will continue as long as the offending food source is ingested. Once a pet is allergic to a food product, it may take weeks to months for the symptoms to resolve once the allergenic food item is removed from the pet’s diet.
What testing is needed and what is the treatment?
Unfortunately, no reliable skin or blood test is currently available to diagnose food hypersensitivity. The diagnosis of food hypersensitivity requires that your pet undergo an elimination diet trial. An elimination diet trial is a challenging exercise for most owners and if it is not done correctly it will fail to provide the needed information to answer whether or not your pet has food hypersensitivity. An elimination is either homemade or a commercial prescription diet that contains a protein and a carbohydrate source that your pet has never been exposed to previously.
Alternatively, newer, hydrolyzed or low molecular weight diets contain more common ingredients that have been molecularly altered to be below the allergenic threshold. These and other diets used to diagnose food allergy are “veterinary prescription only” diets and must be used under the supervision of a veterinarian.
A home-cooked elimination diet in a ratio of one cooked pound of protein (fish, pork, tofu, pinto beans, rabbit, and venison) to 6 cups carbohydrate (potato, oatmeal, rice, tapioca grain, but not the packaged pudding mix) can be considered if owners are able to cook for their pet. Most pets can be fed daily about a cup of this diet for every 10 pounds of body weight. A home-cooked diet allows preservatives and other food additives to also be avoided during the elimination trial. A home-cooked diet is not usually nutritionally balanced for long-term use.
The elimination diet trial must be completely strict. Potential pitfalls to avoid during the diet elimination trial include the following:
Switching to a new diet should happen gradually over several days by feeding more of the new diet and less of the old diet each day. Cats can be particularly challenging to get to accept a trial diet. It is important to not allow your cat to go more than 48 hours without eating. It may be necessary to try several different diets before your pet finally accepts a trial diet. Once your pet has transitioned onto the trial diet your pet should only be allowed to eat the prescribed diet and to drink water. NOTHING ELSE SHOULD PASS YOUR PET’S LIPS.
It is useful to keep a diary of any changes you may note during the diet trial. These changes may include changes in the following:
In addition, record any instances when the pet may have cheated by consuming food items not permitted during the food trial. The diet trials usually continue for 8 to 12 weeks, at which point you should have your pet re-examined and discuss any observations you have made during the elimination diet trial with your veterinarian. Your pet may not have 100% resolution of clinical signs during the elimination diet trial yet still have food hypersensitivity. Animals with food hypersensitivity may continue to exhibit some degree of itchiness during an elimination diet trial if they have still had access to the offending food item, if they have concurrent secondary skin infections, or if they have concurrent other skin allergies.
To confirm the presence of food hypersensitivity, a re-challenge with the original diet is performed. You will be instructed to begin feeding your pet the original diet plus any treats or food items that were routinely fed to your pet prior to starting the elimination diet trial. If your pet is food allergic, the clinical signs, specifically itching, should worsen within hours to days of beginning the previous diet. Most animals with food hypersensitivity will experience an exacerbation of their clinical signs within 2 weeks of being fed their previous diet. Should this occur, your pet would need to be fed the elimination diet again. Once the clinical signs have again resolved (usually very rapidly), your veterinarian will instruct you as to the next step in discovering the offending allergen. The good news is that if your pet has food hypersensitivity, so long as the offending substance is eliminated from your pet’s life this will decrease or control the clinical signs.
Many pets with food hypersensitivity may have an “allergic personality.” This means that they may also be predisposed to other allergies, such as flea allergy dermatitis or atopic dermatitis (environmental allergens, i.e., pollens, molds, house dust). It is strongly recommended that all pets with suspected or confirmed food hypersensitivity be kept on strict flea control and be monitored closely for the development of secondary skin infections, increased itching or other evidence of a concurrent allergic dermatitis. However, with food hypersensitivity controlled, your pet’s itch threshold will be substantially reduced, allowing your pet a more comfortable and higher quality of life.