When pieces are better than the whole: Hydrolyzed protein diets (Sponsored by Nestlé Purina)

Part of the 2011 Nestlé Purina Veterinary Symposium publication
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Mar 28, 2011

Clinical signs of food allergy in dogs and cats

Food allergy and food intolerance imply abnormal reactions to a normal food or ingredient. Food allergy is immune-mediated, while food intolerance is considered to be an idiosyncratic reaction. Other forms of adverse reactions to foods can include food intoxication or food poisoning. Unlike food allergy or intolerance, which are abnormal responses to normal foods or ingredients, food poisoning refers to normal, biological reactions to the toxins or infectious agents in foods, rather than to normal foods.


Table 1. Common clinical signs of food allergy in dogs and cats4,7,8,21
Food allergy may manifest with dermatologic or gastrointestinal (GI) signs, or both. Dermatologic signs of food allergy (Table 1) are similar to those of atopic dermatitis, and both food allergy and atopic dermatitis commonly occur together.1 GI signs can include vomiting, diarrhea, and borborygmus.

According to veterinary dermatologists, the majority of dogs and cats with food allergies manifest dermatologic signs, although 15% to 50% are now recognized to also have GI signs.1-4 Moreover, veterinary gastroenterologists recognize that a large percentage of patients with GI signs have some form of food allergy or intolerance.2,5,6 In one study of 70 cats with chronic GI signs, 29% were diagnosed as food allergic based on elimination and challenge testing.5 An additional 20% of cats in the study showed a positive response to diet but did not relapse upon challenge. Similarly, another study demonstrated that 50% of dogs with chronic GI signs were food responsive, although only 20% of these were confirmed by challenge to be food allergic.6

Another study evaluating 128 cats with either pruritus, GI signs, or both, identified 22 (17%) cats that were confirmed food allergic by elimination and subsequent challenge testing.2 Among the cats confirmed to be food allergic, 45% exhibited dermatologic signs, 32% expressed GI signs, and 23% exhibited both signs.

It appears that patients expressing both dermatologic and GI signs are more likely to be diagnosed as food allergic.2-4 In a study of 418,422 dogs in Switzerland, 259 allergic dogs were identified.4 Of these, 65 were identified as food responsive, while 183 were considered atopic. Concurrent GI signs occurred in 31% of the food-responsive dogs, but in only 10% of the atopic dogs. Similarly, cats with both dermatologic and GI signs (42%) were more likely to be food allergic than those with only dermatologic (16%) or GI signs (13%).2

Pathophysiology of food allergy

The exact mechanisms behind food allergy are not fully known, but are thought to involve type I, III, and IV hypersensitivity reactions.7,8 The offending allergens are usually proteins or glycoproteins that can interact with the body's immune system and lead to a hypersensitivity reaction. Interaction between food antigens and the immune system begins in the GI tract, which is the largest immunologic organ in the body.