September 2021

Steering the Elimination Diet Trial Toward Success

By Dr. Galia Sheinberg, DVM, DLACVD

In this VETgirl online veterinary continuing education blog sponsored by Purina® Pro Plan® Veterinary Diets, Galia Sheinberg, DVM, DLACVD, discusses getting to the bottom of clinical signs from adverse food reactions (AFRs) through diet trials. Please note the opinions in this blog are the expressed opinion of the author and not directly endorsed by VETgirl.

For a veterinarian, an itchy dog consult can be the start of a long relationship with an owner and a new patient. Being able to steer the diagnostic process successfully is really important. I believe that making the right diagnostic recommendations while understanding what your client is able to do can increase the chances of using the best therapeutic tools. Conducting a diet trial for a canine patient suspected of adverse food reaction (AFR) can be challenging but it’s also highly rewarding when done correctly. It will increase the chances of having good control of allergic skin disease and improving the quality of life of our patients and their owners.

Diagnostic protocol
When we see a patient we suspect has allergic skin disease, it is impossible to tell if that dog is experiencing environmental allergies or an adverse food reaction based on a physical examination and medical history alone. Typical canine atopic dermatitis symptoms like itchy skin, secondary infections, alopecia and ear infections can be quickly identified and managed. Still, clinicians should be on the lookout for dogs with a history of gastrointestinal issues like vomiting and chronic diarrhea, gas or having more than three bowel movements per day because these are more likely to be caused by an adverse food reaction and should go into a diet trial.

We should strive for a very detailed and careful medical history so we are able to identify important markers for canine atopic dermatitis and AFR such as paw licking, gastrointestinal disturbances or head shaking, keeping in mind that for many owners, symptoms might go unnoticed because for them these may seem like normal behaviors.

Our key diagnostic tool to determine if an adverse food reaction is causing our patient’s symptoms is conducting a successful diet trial, where the owner feeds the dog nothing except the recommended diet for a minimum of eight weeks.
Here are some essential points to consider when prescribing a diagnostic diet:

1. Take a thorough diet history. Have a positive and open conversation about what type of food the dog has ever eaten, including treats and flavored supplements or medications.

2. Recommend a prescription hydrolyzed or elemental diet. The food protocol we use at our clinic usually involves feeding a commercial prescription hydrolyzed diet—preferably a vegetarian version—or a prescription elemental diet. These diets are complete and balanced with everything an adult dog needs to meet all nutrient requirements. In the case of the elemental diet, we can use it in growing puppies, which is excellent.

3. Relieve the itch. A mistake we sometimes make as clinicians is to start a diet trial without addressing itch or secondary infections that can increase pruritus. I think it is critical to solve these issues because making the patient comfortable will increase the chances of the owner completing the food trial. Depending on the patient’s needs, we will prescribe either oclacitinib or prednisone for the first two to five weeks. Topical therapy will also be beneficial in helping reduce itching and controlling secondary infections. Once the skin improves, we will stop medications to evaluate the dog’s response to the actual diet trial. Likewise, if a patient has a chronic ear infection, we need to resolve that early on to be able to assess the effect of the diet trial on the ear.

4. Rechallenge the patient. If a dog has responded well to the diet trial, is not itching, and the skin looks great, that’s terrific. The owner will be happy, but it’s not the end of the story. We need to rechallenge the patient with their previous diet or selected ingredients to ensure we’ve accurately made a food allergy diagnosis. Owners may be tempted not to rechallenge. Since their dog has improved, what’s the point of potentially having their misery return? But if we don’t rechallenge with the previous diet, the dog will not have a definitive diagnosis. Improvement might be related to other factors like solving skin infections, inflammation or a seasonal change when it’s an environmental allergy. The first 72 hours can be the most important when challenging the diet, but flaring can occur up to 14 days later.

It is important to know that complete resolution of the itch or skin lesions is not always achieved with a successful diet. Because some dogs will improve partially with the diet but will also have environmental allergies, client education will increase the chances of a correct diagnosis—training the owner to identify flaring skin and know what to look for when challenging the diet.

Clear communication sets owner and patient up for success
We can’t just hand owners a bag of hydrolyzed food for a diet trial and send them on their way with a wish for good luck. We need to explain why we want to do the trial, what we want to achieve and how long the process will last. We also need to set the stage for a potential second diet trial if the first one was unsuccessful but we still suspect an adverse food reaction because of the patient’s history and the need to rechallenge the patient.

We should also stress the importance of doing the diet trial as flawlessly as possible—that the dog must not eat anything except the prescription food we’re using for the trial. This means discussing the elimination of treats (unless approved), human food and, potentially, changes to medications such as flavored flea and tick control products. We need to explain the need to be hyper-vigilant about leaving food out or dropping something on the floor that the dog might eat.

I call owners a week after starting the diet trial to see how they and their dogs are doing. Are patients fully transitioned to the new diet and are they accepting it? Are there any gastrointestinal issues? This communication allows owners to ask questions and identify and solve problems in a timely fashion.

Diet trial options: yes, no or maybe
As I mentioned earlier, therapeutic hydrolyzed or elemental diets are my “go-to” for elimination diet trials. However, there are other options—some better than others.

Over-the-counter limited ingredient diets: Testing has uncovered that some OTC diets contain non-declared ingredients listed on the label. (1,2) For example, a rabbit diet may contain trace amounts of chicken or beef from manufacturing processes. These are not there on purpose, but they’re contaminants. These diets are inappropriate to use in food trials. (NO)

Novel protein diets: These are therapeutic diets based on proteins that the dog probably has not yet eaten. While finding a truly novel protein for the dog can be challenging—especially if the owner can’t provide a complete diet history—these diets can be an option for dogs that do not accept a hydrolyzed diet or an elemental diet. (MAYBE)

Home-cooked diets: I’ve found that many owners want to cook for their pets, and ensuring the diet is nutritionally complete and balanced can be challenging, especially for growing dogs. I only recommend home-cooked diets if a patient doesn’t accept or was unsuccessful on a prescription diet. (MAYBE)

Elemental diets: An amino acid-based diet from Purina is a new tool for veterinarians to diagnose and manage adverse food reactions. It’s a great choice for patients who don’t respond well to other elimination diets and are still suspected of having a food sensitivity. This diet can be especially beneficial for dogs with gastrointestinal issues because of its excellent digestibility and very low allergenicity. (YES)

VETgirl Purina elimination diets blog 92021

If I could leave you with just one piece of advice, it would be this: Be empathetic with owners and give them as much information as they are able to handle to help them through the process. Explaining the steps carefully and the purpose of the effort we are asking them to make is fundamental. Client education can make or break a successful diagnosis. As veterinarians, sometimes we won’t agree with every choice an owner makes. But if we can be flexible, we’re likely to achieve better results. Often, the human side of the elimination diet trial process is just as important as the clinical side—sometimes more so.

1. Raditic DM, Remillard RL, Tater KC. ELISA testing for common food antigens in four dry dog foods used in dietary elimination trials. J Anim Physiol Anim Nutr (Berl). 2011; Feb;95(1):90-7.
2. Horvath-Ungerboeck C, Widmann K, Handl S. Detection of DNA from undeclared animal species in commercial elimination diets for dogs using PCR. Veterinary Dermatology. 2017;28:373–e386.

Dr. Sheinberg is a veterinary dermatologist with Dermatología Especializada Centro Veterinario Mexico and practices in Mexico City.

Dr. Galia Sheinberg and her dog Obic

Dr. Galia Sheinberg and her dog Obic

Purina Pro Plan Veterinary Diets VETgirl blog elimination diet

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