Food Intolerance or Food Allergy?

By Jennifer Coates, DVM on Jul. 6, 2012

Feline food allergies and food intolerances are similar but not identical conditions. An allergy involves the immune system. Basically, the body is responding to an ingredient (or ingredients) in the cat’s food as if it was an invading microorganism, and then mounts an immune reaction to fight it off. Food intolerance revolves around the digestive system’s inability to handle a particular ingredient in a normal way.

I like to use a human example when explaining the difference between food allergy and food intolerance to clients. Many people know of someone who is allergic to peanuts, shellfish, or something else they might run across in a meal. Yes, these unfortunate folks may experience gastrointestinal symptoms as a result of their allergies, but other, more serious symptoms frequently develop too. These may include hives, rashes, itchiness, facial swelling, and even a potentially life-threatening allergic reaction called anaphylaxis.

Lactose intolerance is a classic example of food intolerance. Clinical signs are generally limited to the gastrointestinal tract (e.g., nausea, diarrhea, abdominal pain, and flatulence). Some people also report headaches and irritability, but this is hard to assess in cats. Symptoms may be manageable enough that people will put up with them from time to time to indulge in a favorite food.

The differences between food allergy and food intolerance are similar for cats. When an owner brings a cat with a food allergy in to the veterinary clinic, itchiness and skin lesions, not gastrointestinal problems, are usually the primary concerns (although with continued questioning we often learn that the cat does also vomit excessively and/or have loose stools ). On the other hand, a cat with a true food intolerance will typically have chronic or intermittent vomiting, diarrhea, and/or excess gas production without dermatologic or other issues, unless the individual also has an unrelated disease that is responsible for those symptoms.

The cornerstone of therapy for both conditions is avoiding the offending ingredient(s) (although this is sometimes easier said than done). If you and your veterinarian perform a food trial with a novel ingredient or hydrolyzed diet and your cat’s symptoms disappear, you can simply continue feeding that food or slowly reintroduce traditional ingredients to determine which one(s) your cat reacts to so you can pick foods without them in the future.

If your cat’s response to a rigorous food trial (i.e., 8-12 weeks of eating NOTHING but a novel ingredient or hydrolyzed diet) is less than ideal, additional diagnostic testing becomes necessary. In some cases, a second dietary trial with a different type of hypoallergenic food is the best option, but sometimes gastrointestinal biopsies are needed to definitively distinguish between food allergies, food intolerances, and other conditions with similar clinical presentations.

If the final diagnosis is a food allergy, and hypoallergenic diets alone are not adequately controlling a cat’s symptoms, instituting immunosuppressive drug therapy is generally the next step. These medications are not without significant side effects, and are ineffective against food intolerances, so I don’t reach for them willy-nilly. When a cat does not respond satisfactorily to several dietary trials and I am convinced that food intolerance is to blame, the search for a diet without the ingredient(s) that trigger the adverse reaction must go on.