Understanding Food Allergies

By: Dr. Golden

Bert is a really cute, 2 year-year-old Cavalier King Charles Spaniel who began having intermittent diarrhea and problems with itching and recurrent skin infections when he was about 5 months old. Bert’s human “mom” was advised that his symptoms could be due to a food allergy, and she embarked on an effort to find a better food for him. Early on it appeared that Bert could be allergic to wheat, and she would purchase foods that were wheat-free. These included diets that were specifically formulated for dogs with “intestinal disease” and others that were “hypoallergenic”. Bert’s skin condition improved, but the diarrhea would initially improve and then reoccur. During this time, Bert also continued to receive various dog treats and his monthly heartworm and flea prevention. Convinced that Bert’s problems might still be associated with a food allergy, his “mom” initiated a true food allergy elimination trial.  Food elimination trials are done because there is no specific symptom or test that can confirm a food allergy. Within weeks, Bert’s symptoms resolved and his energy level improved. More about Bert later….

Food allergies occur when there is an abnormal response by your pet’s immune system to a food or food additive that he or she eats. Most commonly, this response develops when your pet eats a specific protein or carbohydrate that he or she happens to be uniquely allergic to. However, food allergies are not limited to proteins and carbohydrates because in some dogs other dietary ingredients can occasionally cause an allergic response. In addition, the adverse effects can cause many different symptoms associated with a number of body systems, so it is often difficult to be sure that your pet has a food allergy. Food allergies should not be confused with food sensitivities, which occur when a certain food may upset your pet’s stomach but the problem is not caused by your pet’s immune system.  Diets too high or too low in certain ingredients can also create disease not related to the immune system in dogs or cats.

Food allergies frequently begin to develop in dogs and cats at less than 1 year of age, but can occur at any age. Very commonly, the pet’s family will dismiss the possibility of a food allergy based on the fact that the pet has “always eaten this food” and has not ever had a problem before. In reality, this is common with food allergies as they frequently take many months to develop. It is also possible that the dietary constituents used to produce a certain brand of dog or cat food may have been changed and the food is now being formulated with very different ingredients.

Common causes of food allergies in dogs include beef, dairy products, wheat, egg, chicken, lamb, and soy. Beef, dairy products, and fish are common causes in cats. However, the increased incidence of reactions to these specific dietary ingredients is more likely to be a reflection of their frequent use in pet foods as compared to other, less common, protein or carbohydrate sources.  No individual food ingredient should be thought to be any more or less likely to cause an adverse reaction than any other. A simple rule to remember is that any food ingredient could induce a food allergy in any individual at any age. For an individual dog or cat, beef is no more or less likely to cause a food allergy than chicken, or lamb, or duck, or any other protein or carbohydrate source no matter how expensive or unique. As such, many dog foods that are marketed as “hypoallergenic” simply contain a protein and/or carbohydrate source that is used less commonly in animal foods but these ingredients may or may not be any more or less hypoallergenic in any individual dog or cat. In fact, when you arbitrarily switch between diets looking for one you hope is hypoallergenic, you may actually be complicating future efforts at determining the best diet if your pet does have food allergies.

Common signs of food allergies include non-seasonal itching (itching that does not occur at the same time every year), recurrent skin infections, a “greasy” skin coat, recurrent ear infections, diarrhea, vomiting, and coughing, among others. Many other diseases can induce similar signs and must also be considered when trying to determine the cause for these medical problems. The only way to accurately assess for a food allergy is to perform a true food allergy elimination trial. The basis of this trial is to restrict your pet to a minimum number of food ingredients, which they are unlikely to have previously consumed, for 6-8 weeks.  During this time, your dog or cat cannot receive any other foods or treats. Even monthly heartworm and flea prevention products that contain flavorings to entice consumption by the pet must be replaced with non-food based pills or topically applied alternatives (such as topical Revolution). A positive response is identified if the symptoms of concern become reduced or eliminated. Because any protein or carbohydrate source can cause an allergic response in any individual, the selection of the ingredients for a food allergy elimination trial is partly scientific and partly a guess. Unfortunately, random trials with many different commercial diets that claim to be “hypoallergenic” only serve to increase the difficulty of selecting a protein or carbohydrate source to be used if a true food allergy elimination trial is to be attempted. The basis for selecting a diet is not just that the diet has a novel (one never consumed by the pet) protein and carbohydrate, but that it also contains the least number of other ingredients. The best type of allergy elimination trial diet is one that is home prepared and limited to a single protein and a single carbohydrate that is unique for that particular dog or cat. Alternatively, some companies produce specific prescription diets that are prepared from single unique protein and carbohydrate sources and, equally important, have very limited other ingredients.

Bert’s amazing improvement while on the strict chicken and sweet potato diet, strongly supported a diagnosis of food allergy. It is interesting to note that his diet consisted of chicken, a food ingredient often accused of being a cause for food allergies. It was fortunate that Bert tolerated chicken because it allowed the use of a readily available and inexpensive protein. Unfortunately, this is not true in all cases and many require diets made with very unusual protein sources, or diets that have protein sources that are broken down into smaller proteins (hydrolyzed diets), and thus are less likely to create a food allergy.

While Bert’s mom was very pleased with Bert’s response, she was also aware that a diet consisting of a single protein and carbohydrate source (in this case chicken and sweet potato) was unlikely to be nutritionally complete.  She will need to add other ingredients and vitamin/mineral supplements to make the diet complete for long-term feeding. Such diets are best formulated in consultation with a veterinary nutritionist, and each ingredient should be added individually to the diet and judged to determine if it induces any adverse effects.

Food allergies can cause a variety of abnormal responses within your pet’s body and must be considered as a possible cause of many illnesses or problems. Unfortunately, there is no easy way to assess for a food allergy without performing a food allergy elimination trial. The time delay caused by the 6-8 weeks it takes to determine if your pet is improving on the new diet, further adds to the difficulty and frustration of performing such a trial. Performing a food allergy elimination trial requires you to be very dedicated to improving the life of your pet and very, very committed to adhering strictly to the trial diet (absolutely no treats or other foods, at all!) for the entire period.  However, if your pet has a food allergy, the reward to your pet and to you can be great, just like it was for Bert and his mom.