• A food allergy is an immune response to something in the pet’s diet that did not cause problems in the past.
  • Food allergies commonly cause itchiness and/or vomiting and diarrhea in dogs and cats.
  • Food allergies are diagnosed with an elimination diet trial.
  • Long-term treatment can be very successful if the offending ingredient is avoided.

What Is a Food Allergy?

Food allergy (also called food hypersensitivity) refers to a type of physical reaction to food. Food reactions are classified into two categories: those that are the result of immune system stimulation and those that are not. Food allergy occurs when the immune system begins to overreact to ingredients that the pet has eaten with no problems in the past. Food intolerance occurs when what is eaten has a direct, negative effect on the stomach and/or intestines, such as spoiled meat, chewed up toys, food additives, and abrupt changes in diet. Food intolerance is not an immune reaction.

The list of known food allergens (substances that pets can be allergic to) is extensive and includes beef, eggs, poultry, dairy, lamb, pork, fish, corn, wheat, soybeans, preservatives, and dyes.

Overall, the immune system’s job is to find threats to the body and destroy them by sending signals to activate special cells. An allergy results when this system misjudges a safe substance, and the cells cause damage to the surrounding tissues. This is why animals with food allergies often have vomiting and diarrhea. Food allergies can also cause skin problems because the signals released may act in other parts of the body, too.

Signs of a Food Allergy

  • Skin
    • Itchiness (all over or even just in a few areas)
    • Skin infections
    • Ear infections
    • Hair loss
  • Stomach and intestines
    • Vomiting
    • Diarrhea
    • Abdominal pain
    • Weight loss

Diagnosis and Treatment

Many diseases can cause either gastrointestinal signs or itchiness, so your veterinarian will want to rule them out to diagnose a food allergy. Food allergies tend not to be seasonal, and signs are usually seen year round. The most obvious indicator of food allergy is that the signs clear up when the responsible ingredient is removed from the diet.

An elimination diet is the only proven way to determine which food is affecting your pet. Elimination diets consist of ingredients that haven’t been offered to the pet in the past, called novel ingredients.  Your veterinarian will prescribe a diet that contains only novel ingredients. The elimination diet can be thought of as a diagnostic test that may last up to 10 weeks. This test takes so long because the allergen may continue to stimulate your pet’s immune system for weeks after it is eliminated from the diet. The elimination diet will be the only food that your pet is allowed to eat during the trial period. During this time period, no other food, treats, or bones may be fed to your pet. Even regular medications, such as heartworm preventives, must be given in a nonflavored form. It may be difficult, but this is very important to help your veterinarian determine the food that is affecting your pet. If you want to give your pet a treat during this period, you can offer him or her a small amount of the same food that is being used in the trial. Talk with your veterinarian about this option.

Your veterinarian will probably also need to treat your pet for concurrent skin infections or diarrhea at the beginning of the diet trial because these problems may not resolve without medication.

If the skin and gastrointestinal problems resolve during the trial, your veterinarian may then “challenge” your pet’s immune system by feeding the previous diet to see if the signs come back. Sometimes, the diet used for the elimination trial may continue to be fed after the trial is over, if it is balanced and formulated to provide complete nutrition for your pet.