Adverse Food Reactions

Adverse Food Reactions

Deciding which diet to feed your pet can feel daunting at times. This decision can be further complicated if your pet suffers from a food allergy or intolerance Dog with a bowl of vegetables and bowl of meat . Environmental allergies and flea allergies are much more common than food allergies or intolerances, but we certainly do see adverse food reactions in veterinary medicine. And while these adverse food reactions are a very real issue, owners are often faced with misinformation and misconceptions in this arena. Partnering with your veterinarian to better understand adverse food reactions will help you work together to choose a healthy diet for your pet.

Defining the Terms

First of all, it is important to differentiate the different causes of adverse food reactions we can see in pets:

A true food allergy refers to a scenario in which a pet’s immune system mounts a hypersensitivity reaction in response to a specific food ingredient. In essence, the body reacts too strongly because it responds to the ingredient as a threat. These reactions occur soon after eating, usually within minutes (or up to 1 hour after eating). If your pet has a food allergy y, you may see signs like extreme itchiness (especially in cats), hives, or redness and swelling of the mouth and throat. There may be gastrointestinal signs evident, such as vomiting or diarrhea. Nausea and abdominal pain may be present, but can be harder to identify. In cats, it is possible to see signs of asthmatic flare-ups.

In contrast, a food intolerance does not involve an immune response, and is much more common than true food allergies in animals. Food intolerance usually shows itself as gastrointestinal signs (such as a decreased appetite, vomiting, or diarrhea). A good example of food intolerance in people would be lactose intolerance (which, incidentally, can also be seen in animals). A pet may be intolerant to a primary ingredient, or to a component added for flavor, coloring, or protection from bacterial contamination.

Cat ScratchingClinical Signs

Now that we have discussed different causes of food reactions, let’s delve a little deeper into the types of signs they may cause. There are two main categories: gastrointestinal signs and skin conditions (otherwise known as cutaneous adverse food reactions, or CAFRs). As we mentioned before, GI signs may include vomiting, diarrhea, abdominal pain, or decreased appetite. Skin conditions (CAFRs) may include many different types of signs, such as itchiness, ear infections, skin lesions, and secondary skin infections. The itchiness associated with food reactions is usually non-seasonal (meaning it does not change in intensity dependant upon the season). With food reactions, the areas that are most frequently itchy are the ears and rear end.


High Protein foods: Bowl of eggs, bowl of beans, bowl of nuts, steak, chicken and fish If you or your veterinarian suspects your pet may be suffering from an adverse food reaction, how can you test to be sure? Unfortunately, there is no quick and easy way to diagnose food reactions. Diagnostics such as skin testing or blood tests are not effective at diagnosing food reactions, the way they would be for environmental allergies. Therefore, it is necessary to begin a diet trial, or food elimination trial. Pursuing a diet trial requires commitment and dedication on your part, or it will not be successful. However, the time and effort are well worth it in order to identify and better control the cause of a pet’s signs. The goal of the diet trial is to identify if a pet is indeed reacting to a food ingredient, and to eventually isolate that ingredient so that it can be avoided in the future. Most of the time, the offending ingredient is an animal protein source. Common protein sources which may cause adverse signs in pets include beef, chicken, dairy, and eggs. Fish is also a common offending agent in cats. It is important to note that grains are very rarely the cause of adverse food reactions in animals.

If you are pursuing a diet trial, make sure you do so under the guidance of your veterinarian. He or she will begin with a thorough history of what your pet has been fed. Be sure to include your pet’s main diet, treats, snacks, medications (including oral parasite prevention), and any human food your pet may receive.

Choosing the Right Trial Food

A hydrolyzed protein is a protein that has been broken into tiny pieces When it’s time to begin the food trial, your veterinarian will present you with a few options regarding diet. One option is to feed a completely novel (or “new”) protein source. This means choosing a protein source that your pet has absolutely never eaten before. This can be tricky, because most pets have already been exposed to common protein sources like beef and chicken. Even sources like lamb, duck, and salmon are becoming more commonly found in over-the-counter (OTC) pet foods. If the trial food contains a protein source that a pet has previously eaten, the trial will not be accurate or effective. Some examples of novel protein sources may include rabbit, venison, kangaroo or emu. These novel protein diets can be purchased commercially (directly from your veterinarian, or with a prescription), or can be formulated as homemade diets. If you choose to make a homemade diet, it is very important that your primary veterinarian or a veterinary nutritionist oversees the formulation. Usually the diet will consist of one protein source and one carbohydrate source. In cats, we can often use just a protein source for the short term. Over-the-counter diets are not a good choice for a food elimination trial. This is because cross-contamination is very common, and the foods very often contain ingredients not included on the label. In other words, just because an over the counter diet is labeled as “venison,” does not mean that it contains only venison. Not only do over-the-counter diets frequently contain other protein sources, they often contain many additional ingredients, which can interfere with the trial. For an elimination diet trial, a good rule of thumb is “the simpler, the better.”

If selecting a novel protein diet (either commercial or homemade) seems overwhelming, another very good option is to use a hydrolyzed diet. This is a commercially formulated prescription diet in which the protein source is hydrolyzed, or broken down in such a way that the body does not recognize it as that protein. This is a very good choice for many owners and pets, especially those with a complex dietary history.

The Diet Trial

Once an appropriate diet is chosen, the diet trial may begin. Trials are generally 8 to 12 weeks long, though if a pet’s signs are primarily GI-specific, we can sometimes see results within just a few weeks. During the diet trial, the pet may be fed the new food only. Nothing else flavored may pass through the pet’s lips! This includes other pet foods, treats, table scraps, flavored medications (including flavored heartworm prevention), pill pockets, or human food. There are prescription hydrolyzed treats that may be fed under the supervision of your veterinarian. You can also bake the trial food into biscuits or feed pieces of the trial kibble for treats if necessary. There are topical and non-flavored heartworm prevention medications that can be administered during the diet trial to avoid compromising the trial, and your veterinarian will be sure to prescribe only non-flavored medications when necessary. It is important that anyone living in the household with the pet or who has contact with them is on board with the diet trial commitment. Even giving a “little treat” or “table scrap” here or there will make the trial moot. You would hate to waste all of your hard work and investment for just one little “cheat”!

Next Steps

Once your pet has completed the trial period, your veterinarian will direct you to challenge your pet, which means feeding a previous food or ingredient. We will often re-introduce just one ingredient at a time, then monitor for one to two weeks for the adverse signs to come back. This allows us to identify exactly which component was causing the signs. When signs do come back, we revert to the trial diet again to get the pet back to a controlled state before introducing another component.

Once we identify what ingredient(s) are causing trouble for your pet, there are a few options. You may continue a hydrolyzed prescription diet long term, as it is completely balanced and safe for your pet (as long as there are no other underlying medical issues requiring specific dietary modifications). Or, you can find a commercial limited-ingredient diet that does not contain the offending ingredient(s). Feeding a homemade diet long term is usually not a good option, as it may not be completely balanced for your pet’s health (unless the diet is formulated and balanced by a veterinary nutritionist). Making and feeding a good homemade diet long term can also be very time and cost-intensive.

Dog allergy FAQs

Dietary FAQs

There are a few questions commonly posed by owners as they think about food allergies or intolerances in their pets. First, people often wonder if it would be beneficial to feed a grain-free diet to their pets. It’s important to realize that gluten allergies are extremely rare in animals. They have never been identified in cats, and only two dog breeds (Irish Setters and Border Terriers) have been documented to have gluten sensitivities. Grain-free diets for pets are, in essence, a fad with little scientific backing. If a gluten sensitivity is truly suspected in a dog, there is a specific test which can be run to help diagnosis. Feeding a grain free diet for most dogs is unlikely to actually address the underlying problem, and these diets have not been shown to be healthier than grain-containing diets.

Owners will sometimes ask if they should frequently rotate foods, or feed more unusual protein sources in order to help prevent their pet from developing a food allergy or intolerance. The answer to those questions is “no.” Feeding a more unusual protein source will not decrease your pet’s risk of developing a food allergy; rather, it will just make it more likely that if an allergy does occur, it will be to that protein source (instead of a more common ingredient). Similarly, feeding many different types of diets and protein sources does not decrease a pet’s risk of developing adverse food reactions. If a reaction does develop, however, it will be much harder to find a novel protein when it is time to pursue a diet trial.


Though adverse food reactions are much less common than environmental allergies and flea allergies, we certainly do see them in our veterinary patients. If a food allergy or intolerance is suspected, the best way to proceed is with an elimination diet trial under the guidance of your veterinarian. Together, you can work to find a diet that results in the happiest, healthiest, and most comfortable pet (and pet parent)!

Our ACMP Blog is filled with interesting articles on topics pertaining to your pet’s health. Visit our website at


  1. Bowlin CL. Novel proteins & food allergies. Clinician’s Brief. 2010: (3)37-40.
  2. Freeman LM, Linder EM, Heinze CR. “What every pet owner should know about food allergies.” Cummings Veterinary Medical Center at Tufts University. Web. 27 Jan 2017. 6 Oct 2017.
  3. Hall EJ, Batt RM. Development of wheat-sensitive enteropathy in Irish setters: morphologic changes. Am J Vet Res. 1990;51(7):978-982.
  4. Lenox C. Food trials. Clinician’s Brief. 2013: (10):31-32.
  5. Lowrie M, Garden OA, Hadjivassiliou M, et al. The clinical and serological effect of a gluten-free diet in border terriers with epileptoid cramping syndrome. J Vet Intern Med. 2015;29(6):1564-1568.
  6. Paterson S. 2016: Diet-related canine skin conditions. Clinician’s Brief. 2016: (12)18-21
  7. Pet Myths & Facts. Purina ProPlan Veterinary Diets. Web. n.d. 6 Oct 2017
  8. Witzel A. Can gluten sensitivity be a multisystem disorder? Clinician’s Brief. 2017: (6): 50-51.