One of the most common issues seen today in dogs and cats is allergies, which can be divided into 3 categories: flea allergies, seasonal/environmental allergies, and food allergies. Food allergies are the least common but often the most frustrating type of allergy to diagnose and control.

Food allergy or more appropriately named adverse food reaction is a hypersensitivity reaction to one or more components of the diet. This abnormal reaction is caused by an immune response to a food component the animal has previously been exposed to which then causes an allergic reaction throughout the body.  Food allergies can occur at any time during a pet’s life however signs most commonly start presenting themselves when the animal is between 1.5 -5 years of age.

Food allergy signs can be very subtle and often include dermatologic and gastrointestinal signs. Dermatologic signs include non-seasonal pruritus and otitis externa (ear infections).  Pruritus can present as face rubbing, scratching, licking, head shaking, ear scratching, skin redness, hair loss, poor skin/coat condition, and perianal pruritus (itching around the rectum).  Gastrointestinal signs also accompany the dermatologic signs and include soft stools, intermittent diarrhea, flatulence, or frequent defecation.

Diagnosing food allergies can be difficult as there is not a definitive test and is usually diagnosed with consistent clinical findings, a thorough diet history, and an elimination food trial with resolution of signs.  The different components of the food the animal can be allergic to are the protein source, grain source, different preservatives present or a combination of these, therefore a thorough diet history is critically important to determine what the animal’s previous exposure has been.  Owners may be asked about all food sources the animal has had which includes current and past diets, other individuals, such as dog walkers, pet sitters, grandparents and toddlers, who may feed the animal food. A complete history will allow the veterinarian to determine whether a single novel therapeutic diet or a therapeutic hydrolyzed diet would be best for the animal. Elimination food trials typically last a minimum of 8 weeks and strict adherence to the trial diet is essential and will provide invaluable information to help identify the underlying cause and possible management of the animal’s clinical signs. Minimal exposure to other foods, such as the occasional kibble from a housemate or treats from visitors, during this 8 week period could potentially cause results of the food trial to be misinterpreted. Also during the food trial, veterinarians may recommend substitutions for flavored medications, supplements, or preventatives that could affect the outcome of the food trial.

There are many different commercial therapeutic (prescription) diets available for food trials. One option for an elimination food trial is starting the animal on a novel protein diet. “Novel” simply means that the animal has no previous exposure to the ingredients therefore the animal should not have any immune response already present. These therapeutic diets usually contain one intact novel protein and a limited number of ingredients therefore decreasing the possible allergic response that could occur. A hydrolyzed therapeutic diet is another option for an elimination food trial. Hydrolyzed diets contain one protein source that has been broken down in size until it is unrecognizable by the immune system therefore an allergic response does not occur. This diet is often helpful in animals that were rescued or recently adopted where a thorough diet history is difficult or impossible to know. Both of these diets are highly digestible which can also help with gastrointestinal signs associated with food allergies.

Confirmation of food allergies requires a re-challenge of ingredients, treats, and flavored medications once the food trial is complete. A re-challenge involves reintroducing each potential allergen one at a time in order to determine which is causing the allergic response. In many cases the client (and animal) are satisfied with the improvement seen during the food trial therefore the decision is often made to leave the animal on the elimination diet long term.

Food allergies can often be very frustrating for the animal and client, however with the appropriate history combined with clinical signs and an appropriate elimination diet, a satisfactory outcome is possible. It is worth mentioning that changing an animal with a suspected food allergy from one brand of over the counter available food to another is NOT an elimination food trial. Often commercial diets contain more than one protein source therefore they are not ideal for the initial diagnostic food trial. Therapeutic (or prescription) diets are best for food trials as the ingredients are strictly regulated and a veterinarian can help choose the best diet for both the animal and the client.