Posted on 06-11-2014
Food Allergies: Using Hypoallergenic Diets to Eliminate Symptoms
Food allergies can be complex and often confusing. In light of a recent conversation with a client, here is a brief explanation about specialty diets and why we recommend certain foods to help alleviate allergies.
We see a lot of dogs and cats who have food allergies. Symptoms of food allergies can include itchy skin or ears and/or digestive tract problems like frequent vomiting or chronic diarrhea. We often have to treat the symptoms of food allergies with medication but the most effective long term treatment is to find a food that doesn’t cause any reactions.
Unfortunately, there are no reliable tests for food allergies. The only thing we can do is to try a new diet and see how well it works. This sounds simple, except when you consider the bewildering variety of pet foods and food ingredients that are available these days.
Where do you begin, and how do you go about it?
First of all, you need to know that almost all food allergy reactions are caused by proteins. Proteins are large molecules that do many important things in the body. The body’s immune system recognizes its own proteins and leaves them alone. But if a foreign protein gets into the body, the immune system will react and produce antibodies to try to get rid of it. In the case of food allergies, undigested proteins from the food can sometimes get through the protective barriers of the intestines. This triggers an immune response against those proteins. If this happens repeatedly, inflammation builds up in the walls of the intestines and can also lead to more generalized inflammation that can cause the itchy skin problems we so often see in our patients.
It is important to understand that proteins are found in every meat, grain, or vegetable, so any of these ingredients have the potential to trigger an allergic reaction. For years, the most effective way to address food allergies has been to switch to a completely new diet that contains none of the ingredients in the old food. For example, if the original diet contained lamb and rice, we might try fish and potatoes (Remember that snacks and treats count in a diet as well, be cautious not to give something that may cause a reaction). Overall, switching diets like this works a little over half the time. The main reason for continued allergic reactions is the fact that the new food has proteins too. Some of these proteins may be similar enough to the ones the body is already allergic to trigger an immediate reaction. Others may be okay at first but as they leak out of the intestines they begin to trigger a new allergic reaction of their own, leading to a recurrence of the symptoms.
It is also important to know it can take over 4 weeks after the diet change for symptoms of food allergy reactions to calm down. Although most dogs and cats respond within one to two weeks, veterinary dermatologists feel it takes 2 full months before a new diet can be considered to be ineffective.
The current best answer to the question of which diet is least likely to trigger a food allergy reaction is one where the proteins have been broken up into pieces too small for the immune system to notice. These are known as Hydrolyzed Protein Diets and there are several on the market that have been used with great success. Royal Canin makes two (HP and Anallergenic), Hills makes one (Z/D) and Purina makes one (HA). Of the four diets we use Royal Canin HP the most often because we get consistently good results and the diets are highly palatable. HP, Z/D, and HA are all 90 to 95% effective for eliminating food allergies (compared to 50 to 60% for the select protein diets mentioned above). Royal Canin Anallergenic is considered to be 100% effective.
This brings us to a client with a dog who has ongoing skin irritation due to food allergies. He said the ingredients in the food he had most recently been feeding his dog to try to control her allergies were normal-sounding food ingredients like lamb, pumpkin, potatoes, and other things you would find on the shelf at the grocery store. The dog was still itching. Unfortunately, that diet had been making his dog itch because something in it was causing an allergic reaction. We switched him to Royal Canin HP and his dog has done wonderfully.
His problem was with the HP ingredient label, which had a bunch of complex and hard-to-pronounce words that sounded nothing like wholesome food. He worried that he might be giving his dog harmful chemicals. We understood his concern and went through the ingredient label with him, ingredient by ingredient. The main ingredients were hydrolyzed soy protein, hydrolyzed chicken liver, and powdered cellulose. Sound yummy? Hardly. However, a common source of soy protein for people is tofu, so when you read “hydrolyzed soy protein”, think of tofu with the proteins broken into little digestible bits. Likewise, “hydrolyzed chicken liver” is liver where the proteins have been broken up as to not cause an inflammatory reaction. Since there are no regular vegetables or bones to provide fiber, cellulose (the main component of plant cell walls) is necessary to provide this in the diet. The rest of the ingredients on the label were the vitamins and minerals needed to make the diet complete. One needs an education in biochemistry to recognize many of them, which is why we have nutritionists to formulate the diets to provide everything your dog needs to stay healthy.
We all like it when a simple natural diet works well for our pets’ needs. With all the news about harmful food ingredients (both for us and our pets), it is comforting to see familiar ingredients on a label. But when those diets let us down, as is often the case with food allergies, it is wonderful to have very effective high-quality diets available to help improve our pets’ lives.
--Dr. Gregg Bennett
Tumwater Veterinary Hospital
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