In a recent article in Nature Medicine, the author wrote that “Allergic diseases have reached pandemic levels.” I cannot cover the entire spectrum of allergic conditions in this article, but I do want to discuss how foods can contribute, or even be the primary cause, of allergic skin disease in dogs and cats.

Foods can cause many adverse reactions in dogs and cats, but the terms food allergy or food hypersensitivity only refer to those reactions that cause an immune response by the body. Food allergy is thought to make up 10 to 20 percent of allergic skin disease in dogs and cats and is the third most common skin disease after flea sensitivity and inhalant allergies. As with the other cause of allergic skin disease, the signs in dogs are pretty non-specific and can involve the ears, feet, and the body in general. Cats with food allergies can actually have severe itching without any obvious skin lesions, but they can also show signs around the ears and head.

The exact mechanisms of how foods cause an allergic reaction are still poorly understood, but we do know that there are some common risk factors:

• Certain foods: In dogs these include beef, chicken, dairy products, and wheat. In cats they are beef, dairy products, and fish. Celiac disease in people is a chronic inflammatory disease caused by gluten, a protein found in wheat, barley and rye. Gluten intolerance has been identified in the Irish setter, and other breeds may also be affected.

• Any disease that affects the function of the GI tract: This can include parvovirus in puppies, inflammatory bowel disease (IBD) of cats and dogs, and irritable bowel syndrome in dogs.

Besides food reactions that are related to the body’s immune system, there can be reactions to food that occur due to an individual’s intolerance to something. The difference between food allergy and food intolerance is that a food allergy requires prolonged exposure to a food for the immune reaction to develop, whereas food intolerance occurs on the first exposure to a substance.

So how are food allergies diagnosed? This is not a simple question since a food allergy may be only one part of your pet’s overall allergy problem. Several companies advertise diagnostic tests for food allergies, including a recent test discussed in a national dog magazine that claims to diagnose allergies using a saliva sample collected by the owner. Unfortunately, in a study to evaluate that test’s claims, even a sample of tap water was determined as needing a special hypo allergenic diet. Other companies use blood tests, and these also have been shown to be very non-specific. The gold standard for diagnosing food allergy has always been a dietary elimination trial. You feed a specific diet that includes a novel protein and you see if your pet’s skin condition improves. For an elimination trial to be successful, it needs to be fed for at least eight weeks and you need to avoid commercial snacks and treats, human foods, and other supplements that may contain allergic proteins.

You can purchase an elimination diet, but you will need to select a product with the guidance of your veterinarian, as many of the diets on the market claiming to be hypo allergenic have not actually been tested in dogs and cats with known adverse food reactions. You can also use a homemade elimination diet, but you have to be very careful and use a recipe that is nutritionally adequate. Nutritional disease can be seen in as little as three weeks in young dogs fed an improperly prepared homemade diet, and just because the diet came from Dr. Google does not mean that it is adequate.

Food allergies, just like allergies in general, can be a very complex issue. In any case of a pet with signs of skin allergies it is always worthwhile to do a formal elimination trial to see what part food may play in the overall problem.

Examples of food intolerance include:

• Food poisoning due to microorganism such as Salmonella or E. coli

• Excess Vitamin A or D toxicity

• Specific foods, such as onions or chocolate in dogs or the food preservatives benzoic acid or propylene glycol in cats

• Lactose intolerance — similar to the problem some people have, it can also be seen in dogs and cats, especially since cow’s milk contains more lactose than milk from either dogs or cats.

Dr. J.M. Kiel is the U.S. Army veterinarian currently supporting NAS Whidbey Island and Naval Station Everett. Please send questions or comments to Dr. Kiel at
joseph.kiel@navy.mil.