Many people confuse food allergies and food intolerances, which may sometimes appear to be the same, but are actually very different. A food intolerance will often cause a digestive 'upset' of some sort, such as vomiting or diarrhea. A food allergy, on the other hand, causes an immune system reaction when the offending protein/substance is introduced. This reaction produces severe itching, chewing (especially on the feet and rear legs), loss of hair which produces a moth eaten appearance, and sores. There are also secondary problems which arise, including staph infections on the skin from the sores.

It is interesting to know that food allergies develop over a period of time. A dog is never allergic to a food the first time it eats it. As it eats the food several times, its immune system "learns" to be allergic to it. That is, the system mistakenly identifies it as a foreign substance in the body, and launches an attack against it. Each subsequent attack becomes worse, and that is why the symptoms seem to get worse and worse.

The food allergy is one of the itchiest conditions known to dogs. Animals eat a variety of processed food proteins, fillers, and colorings which are further processed inside their bodies. Proteins may be combined or changed into substances recognized by the immune system as foreign invaders to be attacked. The resulting inflammation may target the GI tract or other organ systems but, in dogs and cats, it is the skin that most often suffers from this immunologic activity.

To determine whether or not a food allergy or intolerance is causing the skin problem, a "hypoallergenic diet" is fed for a set period of time. If the pet recovers, food allergy/intolerance has been diagnosed and the pet may return to an appropriate commercial food.

There is no universal "hypoallergenic diet" that is of use for all pets; the creation of a hypoallergenic diet is made on an individual basis. The owner must provide a protein and carbohydrate source with which the pet has had no prior experience. In the past, lamb has been the protein source of choice as American pet food companies had traditionally failed to produce lamb-based pet foods. Unfortunately, recent production of lamb and rice- based foods have removed lamb from the "acceptable hypoallergenic diet" list.

In the past, home cooking of the hypoallergenic diet was felt to be the only way to insure that the pet is not exposed to fillers or additives during the period of the test. Fortunately, many pet food companies have discerned the need for diets using unusual protein & carbohydrate sources with a minimum of additives. Foods can be obtained based on venision and rice, fish and potatoes, egg and rice, duck and oat, and more. Our hospital generally recommends duck and potato based foods for dogs and venison and potato based foods for cats. We have chosen these products because they are available both as canned as well as dry formulas. (Most pet owners prefer to feed a combination of dry and canned food.)

It is important that during the diet trial no unnecessary medications be given. No edible chew toys (such as rawhides or bones) should be given. Treats must be based on the same food sources as the test diet. (Beware of Rice cakes, though, as wheat is commonly used as a filler.) Chewable heartworm preventives should be replaced with tablets.Recently a new approach has been introduced using diets made from “hydrolyzed proteins.” This means that a conventional protein source is used but the protein is broken down into molecules too small to excite the immune system. There are two such diets currently marketed:

CNM HA (“HA” stands for “hypoallergenic”) - from the prescription diet division of Purina.

EXclude - made by DVM dermatologics. This product is purchased in powder form to be mixed with water to achieve the desired consistency.

HOW LONG TO FEED THE TRIAL DIET
 

Work has shown that some food allergic animals require eight to ten weeks to respond. This may be an extremely inconvenient period of time for home cooking. Our current recommendation calls for a recheck appointment after four weeks of diet trial and then again after eight weeks of trial. Eighty percent of food allergic dogs will have responded to diet trial at least partially by six weeks. The Labrador retriever and cocker spaniel appear to require up 10 weeks of trial diet before showing a response. Some animals may even require a longer period.
If a commercial food was used for the test, simply keep using it. If you wish extra proof of the diet's effectiveness, return to the original food; itching resumes within 14 days generally if food allergy was truly the reason for the itchy skin.

Generally, an unsuccessful food trial is strongly suggestive that an inhalant allergy is really the primary problem but there are some other considerations that should at least be mentioned: .Are you certain that the dog received no other food or substances orally during the trial? Was sarcoptic mange ruled out? Your pet may require a longer diet trial. Are you certain regarding the factor which pointed us toward the food allergy? If your pet has not been biopsied, now may be a good time. If an inhalant allergy has risen to the top of the list, symptomatic relief either via medication, special baths, or allergy shots will likely be necessary. Chronic itchiness can be extremely uncomfortable and prompt relief is our goal as well as yours.