by Roger Ross, DVM
Food, whether high quality or cheap, whether a typical national brand or a special "natural" brand, whether commercial or home made ... can cause allergies in some pets.
About 20% of pets with skin allergies can be greatly improved by getting on the right hypoallergenic diet.
And about 75% of pets with frequent or chronic GI or digestive problems are greatly improved with hypo-allergenic diets or diets designed for "sensitive stomachs"
Food sensitivity or "intolerance" is a little different from food allergies. When we talk about food sensitivity, we're not talking about a true allergic reaction but rather simply a food group such as fat, dairy, or soy that your pet doesn't digest well. We usually figure out which food group is causing the problem by trial and error.
At our clinic, if your pet has frequent gastro intestinal problems, we'll often put your pet on one of the prescription "intestinal diets" made by Purina, Hills, or Royal Canin . If the GI problem is greatly improved, then we'll challange your dog by giving it different foods groups to see what foods cause problems and which seem to be safe.
If your cat or dog doesn't have a food allergy but simply doesn't digest fats or starches well, we can often solve the problem by supplementing your pet's diet with pancreatic enzymes and probiotics.
And, of course, sometimes what's needed is not the purchase of any special digestive aid, but rather a serious change in habits.... some pets simply can't tolerate human junk food, potatoe chips, pop corn, table scraps and so forth without paying the consequences.
Gastrointestinal Food Allergies
TEXTBOOK OF VETERINARY INTERNAL MEDICINE
Client Information Series
Michael D. Willard
An allergy is an immune-mediated reaction that harms the body instead of protecting it.
Examples of such reactions include fatal human reactions to a single bee sting or eating a single strawberry. These are called "hypersensitivity" reactions. Certain types of reactions by the body (depending on the type of hypersensitivity reaction, of which there are four) cause an exaggerated response that produces excessive irritation (inflammation) or decreases the size (constriction) of vessels or airways.
The substances that mediate these reactions (antibodies and lymphocytes) are programmed to respond to specific substances called antigens. Antigens that cause hypersensitivity reactions are usually proteins or carbohydrates, and they may be found in almost anything, including food.
Depending on where the hypersensitivity reaction takes place and how many antibodies or lymphocytes are involved, the consequences may vary from sudden, life-threatening episodes to delayed ones that cause inflammation in just one part of the body.
In dogs and cats, most hypersensitivity reactions that result from eating foods cause either skin disease (characterized by scratching) or various gastrointestinal (GI) signs such as diarrhea and/or vomiting. Sometimes both the skin and the GI tract are affected in animals that have a food allergy, but many animals with food hypersensitivity have either skin or GI signs but not both.
The GI signs of food allergy sometimes occur immediately after eating (i.e., immediate-type hypersensitivity reactions). However, food allergy in pets is more commonly a . 'delayed" hypersensitivity reaction, meaning that the consequences arise hours or days after eating the food and then persist for hours or days after each exposure. Because most pets eat the offending antigens every day, GI signs tend to be more or less constant.
There is seldom a clear-cut association between eating and the onset of signs, making it hard to determine that eating a particular food is causing the disease. To help diagnose this problem, we can look for microscopic changes on small pieces of intestine obtained by doing surgery or by passing a long instrument from the outside into the stomach. However, changes that suggest allergy (i.e., eosinophilic inflammation) are usually a form of inflammation. Inflammation caused by food allergies usually resembles that caused by other diseases.
The best way to diagnose a food allergy is to feed the pet a hypoallergenic diet (i.e., a therapeutic dietary trial) and see if the problems disappear.
When performing a therapeutic trial for a food allergy, the diet must be carefully chosen. Because there is no one diet that is hypoallergenic for all pets, one must design or find a diet that is appropriate for each animal.
The pet may be allergic to almost any component of its current diet; therefore, we want foodstuffs that the pet has not eaten before. We usually choose a diet that
(1) contains as few ingredients as possible,
(2) contains foodstuffs that we know the pet has not eaten in the past (and hence is unlikely to be allergic to), and
(3) contains foodstuffs that we know hardly ever cause allergic reactions (e.g., potato, rice).
Because some patients that are allergic to multiple antigens require a strict hypoallergenic diet, homemade diets are sometimes needed.
Although inconvenient and restrictive, they are often the most successful in treating the allergy. Most homemade diets are not balanced but are adequate for use in mature animals for the 2 to 4 months when the animal is having the trial. We have to make many assumptions when we choose these diets, and it is possible that the pet is allergic to something unexpected.
When such a dietary trial is begun, it is imperative that absolutely nothing else be fed. Even flavored pills or toys can contain enough antigens to cause signs of food allergy to persist. The dietary trial must be performed long enough to allow the clinical signs of delayed-type hypersensitivity to disappear.
Some patients evidence improvement within a day of dietary change, whereas others require 4 to 8 weeks before improvement is seen. If a patient has a dietary allergy, it may have a genetic predisposition to allergy and may eventually become allergic to the ingredients of the hypoallergenic diet that it responded to well at first.
Other tests have been tried in order to determine what dietary components a pet is sensitive to. As of this writing, these tests have not always correlated well with the results of dietary trials.
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