When your veterinarian tells you that your cat or dog could have food allergies, the next thing they’ll probably recommend is a diet trial.
This kind of restrictive diet can be difficult for you and your pet, but elimination diets are very important for figuring out which food (usually a protein) is the cause of the allergy.
We promise, a diet trial is worth it, and we’re here to help you complete a diet trial right the first time.
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Why Does Your Pet Need a Diet Trial?
Diet trials are something that your veterinarian will recommend if your pet’s symptoms and history suggest they could have a food allergy.
Food allergies often develop in young animals (less than 1 year old) or older adult animals (usually 5 years or over). Most of the time, pets are allergic to the meat proteins in the foods they eat.
Gluten, grains, or fruits and vegetables are much less common allergies in dogs and cats. Additionally, many meat proteins can look like each other, so, for example, if your pet is allergic to chicken, they are usually allergic to other poultry, including turkey or duck.
Food allergies can cause your dog or cat to start showing signs of skin problems (itching, ear and skin infections), or digestive issues (vomiting, diarrhea, gassiness), or both.
While you can find tests for food allergies in pet stores, they unfortunately aren’t reliable. A diet trial is the only way to diagnose or rule out food allergies, and it is often the first step in your veterinarian’s process to find out why your pet is sick and how to help them.
Why Is a Prescription Diet Necessary?
Prescription diets are often more expensive, but they are guaranteed to contain ONLY what is on the label. Commercial diets that are available from pet stores do not have the same guarantee, and several scientific studies have shown that they often contain small amounts of allergy-triggering foods not listed on their labels.
Even a tiny amount of an allergen can be enough to trigger reactions in some food-allergic pets. You want to use a prescription diet for the trial to make sure you have the best test possible to diagnose or rule out a food allergy.
The same issue holds true for people on restrictive diets, like in this example:
Imagine a person with celiac disease orders a "gluten-free" salad at a restaurant. The kitchen staff uses the same cutting board and knife they just used to prepare a wheat-based sandwich without thoroughly cleaning them first.
When the knife touches the salad, it transfers gluten — a microscopic amount equivalent to the weight of a single grain of rice.
For someone with celiac disease, this small amount is enough to trigger an autoimmune response. Even the most minute cross-contamination can cause significant health issues, making food preparation an exercise in extreme precision and care.
After a diet trial, many pets are able to transition back to a commercial diet, or at least add some commercial treats back into their foods, so prescription diets often aren’t necessary forever, just for a few months.
How Does an Elimination Diet Trial Work?
A diet trial is a period of time where you will remove everything that your pet is currently putting in their mouth (flavored treats, medications, supplements, foods, etc.) and replace it with something that your pet won’t be allergic to. Your veterinarian will give you recommendation on what types of food to feed. See the section below for more details.
You’ll want to transition your pet to their new diet over 7 days, mixing their old and new foods together to avoid stomach upset.
Transition Your Pet's Food Over 1 to 2 Weeks
Days 1 and 2 (or 1–4): Mix 25% new food with 75% old food
Days 3, 4, and 5 (or 5–10): Mix 50% new food with 50% old food
Days 6 and 7 (or 11–14): Mix 75% new food with 25% old food
After that, your pet should be ready to go with their new diet.
How Long Does an Elimination Diet Last?
The diet trial period lasts for 8 weeks in dogs and 12 weeks in cats.
At the end of the trial, your pet will be evaluated for improvement.
If your pet has not improved and your trial has been strict (meaning your pet ate only what they were supposed to), then your veterinarian will conclude that food allergies are not the cause of your pet’s symptoms. This could mean they have environmental allergies, also known as atopic dermatitis.
If your dog or cat has improved, your veterinarian will talk to you about food options for the future.
Your vet may recommend feeding your pet's old diet for a short time (usually 1 – 2 weeks). This short period on their old diet is called a rechallenge. If your pet’s old symptoms return with their diet rechallenge, that will confirm that they have a food allergy.
Not all pets should be rechallenged, depending on their symptoms, so your veterinarian will decide with you if this is appropriate.
What Kind of Pet Food Do You Use?
There are two types of diets that are used in trials, but both of them are prescription, meaning that they require a veterinarian’s approval to purchase.
First, your veterinarian can prescribe a hydrolyzed diet, meaning that the proteins in the food are broken down too small to trigger an allergic reaction.
Second, your veterinarian can prescribe a diet made from a protein that your pet hasn’t eaten before, such as rabbit or kangaroo, because pets are less likely to be allergic to food they’ve never eaten. That is called a novel protein diet.
Because it’s often impossible to know a complete diet history for your pet (especially if they are adopted), hydrolyzed diets are usually the safer choice. However, some pets, especially cats, are very picky and prefer the taste of novel protein diets.
Some diet trial options are only dry foods, while others come in canned and dry forms. Your veterinarian will give you a list of suggestions and work with you to find out what option works best for your pet.
Homecooked diets are often not recommended for diet trials in dogs or cats, because it is difficult to balance a homecooked diet with all the nutrients a pet needs to keep them healthy lifelong.
Why Restrictive Diets Often Don't Work
One of the main reasons diet trials fail is that, without realizing it, many pet owners give their pets other things that trigger their allergy while feeding them the prescription diet.
So what do you need to stop giving your pet during a diet trial?
Unfortunately, this is a pretty long list.
If you think about it, there are a lot of items that your dog or cat interacts with that could contain meat proteins or could be contaminated with meat proteins in the manufacturing process.
This includes the obvious items to avoid:
- Treats
- Pet food
- Human food – table scraps
The list of things to avoid also includes:
- Pet toothpaste
- Pill pockets
- Most pet vitamins
- Joint supplements
- Most fish oils
- Oral flea and heartworm preventatives
- Flavored rubber toys or dental chews
- Rawhides, antlers, and Himalayan cheese chews
You should also avoid peanut butter during diet trials because some pets are allergic to peanuts.
Make sure to wash your pet’s food and water bowls and all their rubber toys at the start of a diet trial to remove any particles from their old food that were carried over in saliva. Ideally, wash and sanitize them in the dishwasher if they are dishwasher-safe. Wash fabric toys as well. We have tips for safe cleaning in this article.
Supplements, Treats, and Toys You Can Give During a Diet Trial
It is important to consult your veterinarian about any supplements or vitamins that you want to give during a diet trial, but here are some suggestions.
Parasiticides
First, if your pet takes an oral flea or heartworm preventative, you should find an alternative option with your veterinarian (often a topical spot-on).
Probiotics
If your pet benefits from a regular probiotic, Proviable-DC from Nutramax® is a safe option to continue during diet trials.
Joint Supplements and Fish Oil
If your pet takes joint supplements or fish oil, Nutramax® also makes several of these products that are safe for your pet to take during diet trials.
Welactin fish oil for dogs or cats or Dasuquin or Cosequin joint supplements are generally good options for diet trials — please speak to your veterinarian to make sure this is right for your pet.
Joint supplements for dogs:
Joint supplements for cats:
Toothpaste
If you brush your pet’s teeth, you can switch to the vanilla mint enzymatic toothpaste flavor during a diet trial.
Warning: Only use pet toothpaste. Human toothpaste is dangerous because it can be high in sodium or contain xylitol, among other potential hazards.
Dental and Other Chews
Unfortunately, there aren’t great options for dental chews, rawhides, or any other chews during a diet trial.
For big chewers, you can try filling unflavored rubber toys, like Kongs or Toppls, with frozen prescription canned food, canned pumpkin puree, or sunflower seed butter instead.
V-dog is a vegan pet food company that makes vegan dental chews that are safe for diet trials.
Treats
For treats during diet trials, your best option is fresh fruits and veggies.
You should never give grapes, raisins, garlic, or onions because they are toxic to pets.
You should also avoid apples during diet trials for skin allergies because apples can look like birch tree pollen to your immune system. If you eat an apple, it can make you itchy if you’re allergic to birch trees.
Melons, berries, pears, peaches, and other fruits are often pretty popular with a lot of dogs, and you can also try cucumbers, celery, cooked sweet potatoes, red or green peppers, and carrots. See our safe fruit and vegetable lists for the appropriate amount to give your pet, as too much of a good thing can be bad.
There are a few companies that make great treat options that are safe for pets during diet trials, and some prescription pet foods also come with their own treat option.
Unfortunately, even if a bag of pet store treats says it’s meat-free, it could still be contaminated by meat proteins if the factory isn’t 100% vegetarian.
It’s always better to check with your veterinarian before you buy anything over the counter during a diet trial. That said, here are a couple of treat options to try.
Sam’s Yams sweet potato rawhides from Front Porch Pets are an alternative to rawhide chews.
Serenegy, a company started by a veterinary dermatologist, makes Potato Pleasers, Oat Delights, and Pumpkin Oat Harvest biscuits.
How to Give Medications During a Diet Trial
If your pet still needs to take medications during their diet trial, there are several options.
1. Vegan marshmallows make great pill pockets and they don’t contain gelatin, an animal protein that is present in regular marshmallows.
2. You can try making meatballs of canned food if there is a canned version of the prescription food you're feeding your pet.
3. Raspberries (aka nature’s pill pocket),
4. Pushing pills into pieces of cooked sweet potato, bananas, or soft melon.
5. If your pet hates all the other options, you can try vegan cheese (like cashew or almond) or sunflower seed butter.
Lastly, you can try hydrolyzed chicken pill pockets, which are often a popular choice for cats, even though the packaging states they are for dogs.
The most common flavors of pill pockets for dogs and cats often contain chicken, even if they’re peanut butter flavored, so those aren’t a good idea.
Make sure to speak to your veterinarian about whether any of your pet’s regular medications are flavored as well. Most chewable medications for dogs are flavored, as are compounded liquid medications for cats.
There are ways to adjust your pet’s medications to remove or substitute these flavors during diet trials, and it is important to make these changes so that your pet’s diet trial is as strict as possible.
Signs that Your Pet Isn’t Reacting Well to Their New Diet
Not all diets will work for all pets. Some pets, especially cats, are very picky about their food flavors, textures, and shapes, and it can take some trial and error to find a diet that they’ll eat.
Sometimes, mixing the new food with a little warm (not hot!) water, adding some of an approved prescription canned food, or adding a teaspoon of canned pureed pumpkin on top of new kibble can help entice your pet to try a new diet.
If your dog or cat has not eaten any of their food for 24 hours, please call your veterinarian to find out if they have recommendations for what else to try.
Additionally, call your vet immediately if your pet starts to vomit or have diarrhea, if they don’t have any bowel movements for 2 days, or if they appear to be straining when they try to defecate!
If your pet starts to lose weight, seems to be constantly hungry, or is less energetic than usual, these are also signs that their new food isn’t working for them right now. Your veterinarian may make some tweaks to their food plan to help, or change their diet entirely. It’s very important to let them know as soon as possible if your pet is not feeling like themselves. The goal of a diet trial is to help your pet feel better, so you never want them to feel worse first!
This Is a Lot of Work. Is a Diet Trial Really Worth It?
Yes! Food allergies can make your pet itchy, prone to getting skin and ear infections, or nauseated and gassy. Those are pretty awful things to feel all of the time.
If you can find a diet that works for your dog or cat, they will be much happier and healthier in the long term. Additionally, it is always safer (and cheaper) to manage your pet’s health issues through diet changes, if possible, rather than needing to give them medication forever.
A diet trial is not the answer for every patient’s problems, but if your veterinarian recommends one, it is certainly worth a few months trial to find out if it can help your pet.
