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Why Diets for Pets with Food Allergies Fail

You have a pet that is so itchy that it has constant hair loss and skin infections due to scratching. Your veterinarian suggests a dietary elimination trial by trying a hypoallergenic diet. Six weeks into the trial, nothing has changed.

Does this sound familiar? It happens all the time in veterinary practice. Why?

First of all most allergies, especially those characterized by generalized body itching, are seldom caused by food alone. Second is that other common allergies like fleas were not adequately controlled. A recent study published in the Journal of Animal Physiology and Animal Nutrition suggests another reason that is more alarming.

How the Allergic Response is Instigated

Antigens are large protein molecules in food, on pollen surfaces, in insect saliva, on bacteria or viral surfaces, etc., that bind with host antibodies. In all cases the antibody response is the start of an elaborate immune response to eliminate danger from the invader. For antigens that are attacked by allergic antibodies this means the release of histamines. Normally this is a good thing.

But for animals with an over-active allergic immune response, this causes the release of massive amounts of histamines. Histamines are responsible for the allergy associated inflammation and itching of the skin, ears, rectum, and eyes. Histamine release in the intestines due to food antigens interferes with normal digestion and may cause excess gas production, vomiting, soft stool, or diarrhea. Veterinarians often recommend hypoallergenic food trials to see if food may a major contributing factor for the immune response.  

Hypoallergenic Pet Diets May Not Be What They Seem

A team from the University of Padua in Italy examined twelve commercial, dry canine diets advertised as limited antigen. Eleven of the diets featured novel protein sources (proteins other than beef, poultry, etc.) and one that featured hydrolyzed proteins. Hydrolyzed proteins are broken down to their component amino acids, which are small and don’t act as antigens.

The researchers then examined the food microscopically to identify bone fragments that were classified as mammal, avian (bird), or fish. They also performed a sensitive chemical test that identified the type of DNA based on animal type.

The researchers found that only two of the diets contained the animal class that was identified by label ingredients. The other ten had animal fragments and DNA of animal classes not listed on the label. Avian contamination was found in six of the ten diets, fish contamination in five and mammalian in four.

The tests were not sensitive enough to identify the species of animal class, so it is unclear if avian contamination meant poultry, if fish contamination meant the fish proteins that are commonly found in pet food, or if the mammalian contamination was beef or lamb or some other common protein antigen.

The main finding is these diets were not as antigen limited as their claims declared. The researchers concluded that dogs may fail to respond to such diets because they contained potential allergens.

False Diagnosis of Food Allergy

Because of potential allergenic contamination in commercial antigen limited diets, the researchers point out that failure to prove a food allergy in such a trial may be misleading. Their recommendation is to consider a homemade diet before ruling out food as a potential allergen, since homemade diets have limited ingredients that can be carefully controlled.

Dr. Ken Tudor

Image: ra2studio / Shutterstock

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