Why a Diet Change Won't Fix Food Your Cat's Allergies

By Jennifer Coates, DVM on Oct. 31, 2014

When I discuss the possibility that a cat might be suffering from a food allergy, owners will often say “that’s not possible, I changed his food and he didn’t get any better.” This has no effect on my tentative diagnosis for a couple of reasons:

The chance that the food change removed the ingredients most commonly associated with food allergies is slim.

Even if the ingredient list looks appropriate, over the counter foods are often mislabeled.

The most common ingredients associated with food allergies in cats are, in descending order:

beef

dairy products

fish

lamb

wheat

chicken

corn gluten/corn

Cats can be allergic to one or more of these ingredients.

I took a look at the label of a typical, dry cat food and found five of these ingredients — salmon, corn gluten meal, poultry by-product meal, whole grain corn, and tuna meal. The only way to know which of these might be to blame for a cat’s clinical signs is to eliminate them ALL from his diet and reintroduce them one by one. If the cat is truly food allergic, his symptoms should disappear while eating the elimination diet and then return when he is once again exposed to the offending allergen.

Now that you have a list of the most common food allergens for cats, you might be tempted to simply find a food that does not contain any of them. Theoretically that should work, but in practice it may not because over the counter foods often contain ingredients that are not included on their labels.

A study recently published in the journal Food Control revealed that 20 of 52 commercially available dog and cat foods were potentially mislabeled, and one food contained a “non-specific meat ingredient that could not be identified.” Researchers examined DNA taken from the pet foods looking for the presence of beef, goat, lamb, chicken, goose, turkey, pork, and horse.

A press release about the study stated:

Of the 20 potentially mislabeled products, 13 were dog food and 7 were cat food. Of these 20, 16 contained meat species that were not included on the product label, with pork being the most common undeclared meat species. In three of the cases of potential mislabeling, one or two meat species were substituted for other meat species.

While a seemingly high percentage of pet foods were found to be potentially mislabeled in this study, the manner in which mislabeling occurred is not clear; nor is it clear as to whether the mislabeling was accidental or intentional and at which points in the production chain it took place.

For these reasons, I prefer to use prescription, hydrolyzed diets (e.g., Purina HA, Hill’s z/d Ultra, Royal Canin Hypoallergenic) when I want to diagnose or rule out food allergies in cats. The hydrolyzation process breaks down proteins into such tiny pieces that the cat’s immune system no longer mounts an allergic reaction to them. Hydrolyzed diets are also manufactured under the strictest of quality control measures so the chances that something not identified on the label will be included is exceptionally low.

As long as a cat eats nothing but a hydrolyzed diet for 6-8 weeks, veterinarians and owners can have confidence in the results of the food trial. The same cannot be said when a cat is switched from one over the counter food to another.