Food trials for allergies and sensitivities
The food trial is a diagnostic test, just like a blood test or skin scraping. The difference between a food trial and other tests is that it is carried out over a longer period of time, and in your own home. You, the owner, are responsible for making sure that the test is carried out properly so that the results are as useful as possible.
In a nutshell, we will put your pet on a new diet, which must be strictly adhered to for a period of 10-12 weeks. During the trial he is to get NO other food. (More about this later.)
We are doing this food trial because food allergy or food intolerance is a possible diagnosis. The goal of the food trial is to "clean up" the system, stop the input of any possible food allergens, and allow antibodies made to previous allergens to wane. Ultimately we hope that this also clears up the dermatitis and itching or gastroenteritis.
The key to this process is to stop feeding any ingredients that the pet has had before, and put them on something truly novel. And when I say any ingredients, I mean any. If a pet has had chicken, beef, wheat, corn, lamb, rice, venison, fish, potatoes, turkey or whatever, at any time in its life, we have to eliminate those ingredients. With some pets this can be quite difficult, especially dogs who have been fed a laundry list of foods previously.
The food selected for a food trial may contain novel ingredients (commercial or home made) or may be made of hydrolyzed proteins.
In the novel ingredients category there are specific dry (kibble) and a few canned diets that are:
- formulated by a qualified veterinary nutritionist (DACVN or PhD in nutrition) so that we know the diets are complete and balanced, and have...
- unusual protein sources ("novel" to the pet in question) and are...
- of a single protein type...
- that is not commonly available in store-brand pet foods, minimizing the risk that the pet has had it before and...
- have a very limited ingredient list, and...
- are manufactured in strictly controlled environments that minimize or eliminate the risk of cross-contamination with other proteins
Unfortunately, most limited ingredient diets available in the pet stores fail on the last point. Many have been shown to contain proteins from sources other than is listed on the label. In other words, a pet store "limited ingredient" diet that should contain only lamb might have traces of chicken or beef or other unwanted proteins that could cause the pet to "fail" a food trial if they are allergic to that ingredient from previous exposure. Also note that these diets are only useful if the animal has never had those ingredients before.
Some novel ingredient commercial foods that we have had good success with are diets made by Rayne Clinical Nutrition. Rayne started out as a local company and developed some of these diets for our local veterinary dermatologists. They are formulated by veterinary nutritionists, so we know that they are properly balanced. They consisted of a novel meat source (vegetarian, rabbit, kangaroo or alligator). They are very palatable and most come in both dry and canned (subject, as always, to availability as of 2021 and COVID and flood related supply issues). Another line of novel protein diets are the Hill's Prescription Diet d/d varieties, which come in venison, duck, and salmon, and Royal Canin's duck-based diet. Again, these diets are made in extremely well controlled environments to minimize or eliminate cross contamination of proteins.
Home made diets are appropriate for short term food trials. Giving a pet a 2-ingredient diet with a novel protein and a single carbohydrate source will result in short term nutrient deficiencies but these will correct once on a fully balanced diet again. We do not recommend feeding a very restricted diet like this for longer than 6-8 weeks. In other words, this is fed ONLY for the duration of the actual food trial and should never be fed long term. Longer term feeding of a home made diet with more ingredients should only be done with input from a veterinary nutritionist. In recent published studies most home made diets, even those made from recipes provided by veterinarians and published in books, fail to provide complete and balanced nutrition, no matter how lovingly prepared. (If you really want to make a home made diet for your pet we encourage you to consult with a veterinarian at petdiets.com to ensure that what you are feeding is nutritious and complete.)
In the hydrolyzed protein category are prescription dry foods. These diets are made from proteins that have been broken down (hydrolyzed) into small segments that the body cannot recognize as being allergens. The base protein is usually chicken or soy, but because the protein is hydrolyzed they should (in theory) be hypoallergenic even to pets with chicken or soy allergies. However… one study fed dogs with known chicken allergies a diet made from hydrolyzed chicken and found that 40% of them “relapsed” when fed this diet, so we now try to use hydrolyzed soy for initial food trials (if we are using a hydrolyzed food).
The choice of diet depends on your pet's previous diet history, including maintenance diet, snacks, chews, and people food. In some animals, especially dogs who are fed table scraps, it is easiest to go right to a hypoallergenic food or a two-ingredient fresh food rather than trying to determine which obscure ingredient might be safe to feed.
Cats might do better on a home-cooked trial with controlled ingredients, or on one of the Rayne Clinical Nutrition diets. They are more finicky eaters than dogs, in general, and are much easier to prepare homemade food for simply because they don't eat as much.
If a commercial hypoallergenic diet is fed, keep in mind that most cats do better on the canned formulations than dry. We don't know why this is, but it is a phenomenon noted by many veterinary dermatologists.
A vegetarian diet is never, ever a good idea for cats; they are obligate carnivores.
The important thing in an elimination food trial is to do it once, do it right so that there is no question as to whether it was helpful, and then to return to an appropriate commercial diet. This commercial diet may or may not be what your pet was eating before we started the food trial.
In order to maximize the information that the food trial gives us, and to make all of the effort worthwhile, you will need to follow a few simple rules.
1. Introduce the diet gradually over a 7 day period to avoid an abrupt food change that might cause diarrhea. Mix in the new diet ¼ new to ¾ old for two days, then ½ and ½ for a few days, then mostly new, then completely on to the new diet.
2. Nothing is to pass your pet's lips except the recommended food. Nothing.
3. All treats, flavored medications or vitamin supplements must be withheld.
4. The feeding dish should be glass, ceramic or stainless steel (not plastic).
5. Do not feed restricted homemade diets long term (see above).
6. Make a note of the amount of itching and skin lesions that you see at the beginning. Assess how often you are seeing scratching, how red the ears are, how many spots there are on the abdomen, how much the pet wants to lick and chew the feet, etc. Every two weeks reassess the skin and the amount of itching.
7. Stay on the diet at least 8 weeks. We usually recommend a 10 week trial before deciding that it is not working. If it is helping, you may see improvement earlier. Keep in mind that it will take at least 5-6 weeks for the body to be cleared of previous allergens and for antibody levels to start to decrease, so don't give up if you have been feeding for a month and don't see improvement. Tough it out.
8. Outdoor pets should be confined during the course of the trial to prevent them from getting other foods. This is particularly important for those dogs and cats that tend to roam the neighborhood begging from neighbors or raiding garbage cans.
9. Glucocorticoids (Vanectyl-P or prednisone) may be needed for humane reasons early in the dietary trial to control intense itching and skin lesions. The food trial must be continued 2-3 weeks beyond the effects of the drugs.
10. Secondary infections with yeast or bacteria should be treated while the food trial is being started. This includes ear infections.