Food Allergies and Food Intolerances in Pets. Are They a Real Problem? And What to Do About Them?

Many pet parents can be quick to assume their pets have food allergies when their dog or cat is itching for no apparent reason. There are not a lot of studies that state the true incidence of food allergies and food intolerances in dogs and cats. One published meta-analysis based on several other published papers stated that cutaneous adverse food reactions (CAFR) in all dogs seen in veterinary clinics were between 1-2% based on the data evaluated.¹ For all cats presented to veterinarians in the studies, that number fell to less than 0.2%.¹ The authors declared certain limitations for this analysis, including geographic differences and criteria used to diagnose CAFR. CAFR is a medical description that describes the symptoms of a food allergy. The takeaway is that food allergies and intolerances are not common in our pets and other causes of itchy dogs and cats should be ruled out first.

The most common types of allergies that manifest as skin problems in pets are flea bite allergies. Even though pet parents may not see fleas, a single flea bite to highly allergic individual pets can trigger an immune reaction leading to itchy skin. Other types of allergies include environmental and contact allergies. Environmental allergies can be caused by some of the same things that humans have allergies to such as mold, pollen, and dust mites.² Contact allergies can be due to insecticides, grass, or synthetic material used in cloth or carpet.² One of the biggest differences between flea and environmental allergies in pets is that they can vary during different times of the year. Of course, in some geographies fleas can live year-round and indoor allergens can be present all the time making the differentiation harder.

It is important to rule out flea allergies first by working closely with your veterinarian for strict flea control on your pet as well as in your home. Skin allergy testing can be very effective for diagnosing environmental allergies and can be done by veterinary dermatologists as well as some general veterinary practices. Allergy testing for environmental allergies that relies on blood samples is available but is much less reliable. Additionally, testing with saliva, blood, or hair for food allergy is also considered unreliable. It is important to always rule out flea and environmental allergies before pursuing a food allergy diagnosis in our pets.

Once a pet parent and their veterinarian have eliminated flea and environmental allergies then food allergies or food intolerances can be considered. Food allergies and food intolerances can show some of the same symptoms in our pets but the main difference is that a true food allergy involves the pet’s immune system where a complex response of inflammatory mediators can trigger itchy skin or even gastrointestinal (GI) problems such as diarrhea, gas and even vomiting.³ Food intolerances do not directly involve the pet’s immune system but can be caused by an individual pet having trouble digesting a certain food and can cause some similar GI symptoms as do true food allergies. True food allergies generally develop by repeated exposure to the offending food or ingredient in the food. A food intolerance can be seen immediately when a pet eats a diet with ingredients that can cause the problem. Food intolerances may be easier to manage once the offending food is identified as it can just be avoided in the pet’s diet.

Food allergies are commonly caused by an immune-mediated hypersensitivity to certain proteins found in a pet’s diet.⁴ As the result of various complicated immune system pathways, the pet’s body recognizes a protein as an allergen (substance causing allergic reaction). The pet’s immune system is set into motion. This ultimately causes the symptoms we commonly see with allergies like itchy skin, feet, ears, and GI symptoms. It becomes more complicated when pets are allergic to more than one food or protein ingredient.

If a veterinarian thinks a furry friend may have a food allergy, they will likely want the pet parent to do an elimination diet test for them to try to determine which food(s) could be causing the problem. This is easier said than done. Elimination diets take a commitment on the part of the pet parent to know their pet’s diet history well and share it with their veterinarian and commit to feeding specific diets (sometimes home-cooked) for extended periods of time. The elimination diet study should begin by only feeding a single protein and ideally a single carbohydrate source for a specified period. This elimination diet should be the only thing given by mouth, no other treats, supplements, oral flavored medications, or toothpastes are allowed at this time. This can be called the “wash out” period where the pet’s symptoms hopefully will resolve or lessen to the point where they are improved enough to see a symptom exacerbate when a new food is introduced. There is no true consensus among veterinary experts on how long this period should be. A meta-analysis of studies on dogs and cats with CAFR stated that by 5 weeks in dogs and 6 weeks in cats over 80% of pets had remissions of their allergy symptoms. When that period was increased to 8 weeks greater than 90% of pets showed no allergy symptoms.⁵ However, the longer the “wash out” period the harder it may be for the pet parent to feed the novel (new) food. A veterinarian should recommend the length of time to the pet parent. Once this period of time is complete, the old diet can be reintroduced, and if the allergy signs return, food allergy becomes the main concern. Ideally, at this point, the elimination diet should be re-introduced, and allergy signs should go away again. Now, common food ingredients (usually proteins) are introduced one at a time along with the “wash out” diet to see if the pet’s immune system reacts. If they do not react then it is assumed that the pet is not allergic to that ingredient. Systematically, ingredients are introduced to try to figure out what the pet is allergic to. Some of the most common allergens in dogs are beef, dairy, chicken, and wheat, while for cats the most common food allergens are beef, fish, and chicken.⁶

Once all offending food ingredients are identified, avoiding them in the pet’s diet is critical to keep them from experiencing the allergy symptoms. This can be done by feeding novel ingredient diets that do not contain any of the identified ingredients that caused food allergy reactions. One problem with this can be cross-contamination at both the ingredient supplier level and the manufacturer level. Pet parents can contact a company to see what kind of steps they take to mitigate cross-contamination when selecting the appropriate food.

Another way to manage pets with food allergies is to feed hydrolyzed protein diets. These are pet foods that have had the proteins broken down into smaller pieces of proteins (peptides). When the protein is broken down into small enough pieces, the pet’s immune system should not recognize it as the protein it is allergic to. In a way, this tricks the pet’s immune system. These generally work well in a lot of pets with food allergies but there are always a few pets that may still have problems with hydrolyzed diets. This can be due to cross-contamination as with the novel diets mentioned earlier or it could simply be that the hydrolyzed protein was not broken down into a small enough peptide, triggering the immune response.

Food allergies and intolerances are relatively uncommon. Other causes of the pet’s symptoms should always be ruled out first. When they do occur, food allergies can be difficult to diagnose but with patience, dedication, and good veterinary guidance they can usually be managed to mitigate the uncomfortable symptoms associated with them.

References:

1. Olivry, T., Mueller, R.S. Critically appraised topic on adverse food reactions of companion animals (3): prevalence of cutaneous adverse food reactions in dogs and cats. BMC Vet Res 13, 51 (2016). https://doi.org/10.1186/s12917-017-0973-z
2. Banovic, F. Canine atopic dermatitis: updates on diagnosis and treatment. Today’s Veterinary Practice. 1-2(2018)
3. Pucheu-Haston, C. Cutaneous food allergy in animals. Merck Manual Veterinary Manual Online. Last modified 10:2020. https://www.merckvetmanual.com/integumentary-system/food-allergy/cutaneous-food-allergy-in-animals
4. Siarra, T. et al. Assessment of dog owners’ knowledge relating to the diagnosis and treatment of canine food allergies. Can Vet J. Mar; 60(3): 268-274. (2019)
5. Olivry, T. et al. Critically appraised topic on adverse food reactions of companion animals (1): duration of elimination diets. BMC Vet Res. 11:225. (2015)
6. Mueller, R. et al. Critically appraised topic on adverse food reactions of companion animals (2): common food allergen sources in dogs and cats. BMC Vet Res. 12:9. (2016)

 

Follow us on LinkedIn for the latest updates on all things happening here at BSM Partners.

About the Author

Dr. Bradley Quest, DVM, is the Principal Veterinarian at BSM Partners. He has practiced clinical veterinary medicine, developed and tested hundreds of pet food and health products, performs extensive animal health research, and helps navigate pet food ingredient approval for clients.