Hypoallergenic Diets

In the last few years, commercially-formulated hypoallergenic diets have become increasingly popular and readily available to pet owners and veterinarians. This growth in the “special-diet” segment of the petfood market reflects a growing awareness of, if not necessarily an increased incidence in, the occurrence of adverse reactions by dogs and cats to commercial petfoods, including food allergy (hypersensitivity) and dietary intolerance.

Food hypersensitivity is defined as an itchy skin disorder of dogs and cats that occurs when a pet eats a diet that contains an ingredient to which it is allergic. The major complaint and primary consistent finding is itchiness.

Food allergies in dogs and cats are thought to account for approximately 5% of all skin diseases and 15% of allergic skin diseases seen in veterinary practices. The term “food allergy” is often mistakenly used to describe adverse reactions to food in general and should only be used to describe food sensitivities that involve the immune system.

How and why animals get hypersensitive to foods remains poorly understood. In most cases, the offending allergen is a protein found in the diet called a “glycoprotein”. It is not know whether sensitization occurs in the lining of the intestines or after the allergen is absorbed. In fact, it may be that glycoproteins become allergenic only after digestion or as a result of food processing (e.g. heating).

In dogs, the most common allergens are beef, dairy products, chicken, wheat, eggs, corn and soy. In the cat, the most common ones are fish, beef and dairy products. However, pets can be allergic to foods other than these and to more than one kind of food.

The most reliable and accurate method of diagnosing food allergies is by means of an elimination diet which incorporates “novel” protein and carbohydrate sources which the pet is not normally exposed to. Blood tests are considered worthless.

The test diet must be free of additives (preservatives, food colouring, flavouring). For this reason, when trying to determine if a pet is allergic or not, commercial “hypoallergenic” diets are unreliable as elimination diets and should not be relied upon. Instead, the test diet must be homemade. In dogs, commonly used ingredients include tuna fish (canned in water), rabbit, venison, turkey, duck, and lamb/mutton. In cats, frequently used ingredients include rabbit, venison, or strained lamb or ham baby food. These can be mixed with potatoes, rice, or tapioca in both canine and feline diets.

Since these diets are not adequately balanced nutritionally, vitamin, mineral and essential fatty acid supplementation is necessary if a prolonged testing period is anticipated. For most dogs and cats, a test diet consisting of 1/3 protein, 2/3 carbohydrate, 2% corn oil (on dry matter basis), supplemented with a vitamin and mineral mixture, will meet the animal’s nutritional and essential fatty acid requirements for the short term.

In the past, veterinarians used a feeding trial of only 3 weeks duration to rule out food allergy but this has proven to be inadequate. A home-made elimination diet must be fed for up to 10 weeks in both dogs and cats, and in some cases, as long as 13 weeks, in order to truly rule out allergies. During this time period, nothing else must be fed to the pet, including snacks, treats, rawhide chew toys, etc.

If itchiness is reduced significantly or ceases completely while on the trial diet, the offending diet should be fed again. Itchiness should recur within 48 hours, although it may recur as late as 10-14 days post-feeding. A return of itchiness after feeding the “old” diet again confirms the diagnosis of food hypersensitivity. A search for the offending ingredient(s) can then be instituted.

Once the diagnosis of food allergy has been made, a commercially available “‘hypoallergenic” diet can be chosen.

Note: This section of the Canada’s Guide to Dogs website is intended as a source of information only. It is not intended as a substitute for professional care. Always consult with your Veterinarian about health related matters.