What is a food elimination trial diet?
Also known as a hypoallergenic diet trial, a food trial is a diagnostic test to determine if a cat has a food allergy. A food allergy is an abnormal immunologic response to one or several food components (allergens) and is the third most common type of allergies in cats. Food allergies require time to develop, and a cat may have consumed a diet for an extended period of time before developing an allergy to an ingredient.
Cats of any age can develop food allergies, the mean age is 4-5 years and there is a higher incidence in Siamese and Siamese type cats.
During the 8 to 12 week trial, the cat will be fed a novel source of protein while monitoring for a reduction in clinical signs. The cat must not consume anything else including treats, chews, dental sticks, toothpaste, flavoured oral medications, supplements, table scraps, scavenging or hunting.
Diligent flea control is also vital as it is not uncommon for cats to have concurrent allergies.
What are the potential allergens in cat food?
Cats can develop an allergic response to any ingredient in a food, common triggers include:
Protein sources: Chicken, beef, turkey, lamb, dairy, fish, pork, horse, soy and eggs.
Carbohydrate sources: Wheat, corn, rice and barley.
What are the symptoms of food allergies in cats?
It can take weeks or months for clinical signs to develop within a few minutes to a few hours of exposure to the allergen(s). Most symptoms of food allergies relate to the skin, however, some cats can also develop gastrointestinal disturbances.
Common signs include:
- Non-seasonal itching of the head, face, pinnae and neck
- Pale fluid-filled lumps on the skin
- Areas of hair loss, especially around the face and neck
- Secondary bacterial or fungal infection can develop due to trauma
- Vomiting and diarrhea
Starting the cat on a food elimination diet
An elimination-challenge diet trial (ECDT) is a four-step process, eliminate, challenge, confirm and identify and is a long but necessary process. The diet will consist of a novel protein that the cat has not been exposed to before, contain one or two protein sources, be nutritionally balanced and contain no additives.
Veterinary therapeutic limited-ingredient diet: This prescription diet consists of limited ingredients and one novel protein source such as rabbit, salmon, venison, goat, alligator or kangaroo as well as novel carbohydrates such as potato, sweet potato, rice, oatmeal, or pea. It will be necessary to know which protein and carbohydrate sources the cat has previously been exposed to. Prescription limited-ingredient diets are preferred to over the counter limited-ingredient diets as they are manufactured in a way that reduces cross-contamination.
Veterinary therapeutic hydrolysed-protein diets: Conventional proteins are used, but they are broken down by enzymes to be so small the immune system no longer reacts to them.
Complete and balanced home-cooked diets: The final option is a home-prepared diet, however, this can be time-consuming. It will be necessary to seek the advice of a veterinary nutritionist who can work with you to create a suitable homemade hypoallergenic diet.
Over the counter hypoallergenic diets are not recommended as they are often manufactured within the same plant as other pets foods and there is the risk of contaminants invalidating the diet.
- The new diet should be introduced gradually, over a few days to avoid gastrointestinal upset or fussiness. Gradually mix in the new food while decreasing the old food.
- All members of the family must be compliant, and absolutely no other sources of food can be fed during the trial. It is advised that all cats in the household commence the diet unless there is a medical reason a cat cannot safely do so.
- Keep the cat indoors to prevent hunting or scavenging which will invalidate the diet.
- If the cat is on a flavoured medication, he or she will have to switch to a non-flavoured form.
- Do not hide medications in any type of food unless there is a canned form of the hypoallergenic diet.
Confirm (the diet challenge)
After 8-12 weeks, the original diet or components of the former diet are re-introduced to see if the cat has a reaction.
Pet owners may then try to identify the allergen in the previous diet. Obviously, commercial diets contain several ingredients which makes it hard to pinpoint the problem ingredient. The cat remains on the test diet, and the pet owner reintroduces a single component of the previous diet for two weeks to see if symptoms return. Return to the test diet only until symptoms resolve and then introduce a second protein source to evaluate.
Possible reasons the trial fails
There are a number of reasons a food elimination trial may fail.
- Poor owner compliance
- Flea allergy dermatitis
- Non-allergic pruritis
- Cross-contamination during the food production process
- Improper choice of novel protein (ie; one the cat has consumed in the past)
- Other allergy (non-food related)
Long term management
There is no cure for food allergies, the goal is to identify the protein or carbohydrate and avoid it. It may not always be possible to pinpoint the exact trigger and the cat will remain on the hypoallergenic diet. In some cases, the cat will develop allergies to the new food source, at which point it will be necessary to try a different hypoallergenic diet.