Adverse Food reactions and Allergies in Dogs and Cats


             By Dr. Michael W. Fox

This commentary is based in part on the excellent review by Drs. Jon Hardy and Isuru Gajanayake, “Diagnosis and management of adverse food reactions in dogs and cats” published in the Veterinary Record, vol 190, p 196-203, 2022 There were several issues that they did not address and which I have included in this review.

Too many dogs and cats suffering from adverse food reactions and less common food allergies are improperly diagnosed and treated for a skin issue such as “atopic dermatitis”, as with prednisone and immunosuppressants like Apoquel, rather than having their diets investigated and changed as needed.

Adverse food reactions can be signaled by various dermatological and gastrointestinal conditions. True food allergies, often associated with inflammatory bowel disease in dogs can be caused especially by beef, dairy, chicken and fish. And in cats, beef, fish and chicken. Wheat can cause seizures in some dogs.

Adverse food reactions may be more common in some breeds such as German shepherds, Boxers, Rhodesian ridgebacks, Labradors, Golden retrievers and Pugs.

Adverse food reactions involving the external body include various inflammatory and itchy skin conditions, ear inflammation and secondary infection, anal gland problems and symmetric lupoid onychitis—inflamed nails fall off. Cats may develop eosinophilic granulomas which can be in the throat, lips or other body regions. Most common signs in cate are vomiting soon after eating, and excessive grooming, licking and scratching, and fur-pulling. The latter behaviors can also be associated with fleas, mites, separation anxiety and hyperthyroidism.

Adverse food reactions and allergies in dogs and cats can cause vomiting, diarrhea, inflammatory bowel disease, flatulence and poor growth in young animals. Gluten and gliadin sensitivity (from grains and pulses) causing gastrointestinal problems is common in some breeds such as Irish setters and Wheaten terriers. Dogs and cats may also develop conjunctivitis, excessive salivation, respiratory difficulties and hyperactive behavior.

Inflammatory bowel conditions can lead to the so-called leaky gut syndrome. The gastrointestinal tract is one of the body’s primary defenses against the external environment. The loss of these intestinal defenses is commonly called “leaky gut.” Increased intestinal permeability (“leakiness”) can contribute to chronic inflammatory disease and increase the risk of food allergy or food sensitivity reactions. In most cases, normal permeability can be restored once the causative factors are identified and corrected. Treatment with probiotics and prebiotics and even fecal microbiome inoculation can be curative provided responsible dietary ingredients are identified and eliminated and inflammatory and dysbiotic conditions corrected with short term corticosteroid and antibiotic treatment along with elimination of possible parasites, especially giardia.

Food additives such as monosodium glutamate (MSG/hydrolyzed protein//”natural flavors”) can cause gastrointestinal and metabolic problems and possibly obesity and even brain damage and seizures in dogs ( Niaz, K., Zaplatic, E., & Spoor, J. (2018). Extensive use of monosodium glutamate: A threat to public health?. EXCLI journal, 17, 273–278.

Carrageenan can also cause gastrointestinal and other problems. ( Tobacman JK (2001) Review of harmful gastrointestinal effects of carrageenan in animal experiments .Environ Health Perspect 109(10):983-9). Also, herbicide residues, especially of glyphosate in high-cereal-content pet foods, may be a contributing factor to gut microbial dysbiosis. ( Barnett, J.A. and Gibson D.L., Separating the Empirical Wheat From the Pseudoscientific Chaff: A Critical Review of the Literature Surrounding Glyphosate, Dysbiosis and Wheat-Sensitivity Front.Microbiol., 25 September 2020

Diagnosing and treating adverse food reactions and food allergies are not generally effective or reliable according to Drs. Hardy and Gajanayake and the best approach is to provide suspected cases, after also considering seasonal pollen, flea-bite and in-home dust mite allergies where skin problems are presented, a single-protein diet. This can be challenging since many cat and dog foods tested for single animal proteins were found to contain other animal proteins.

As authors Hardy and Gajanayke advise, a home-prepared diet of known ingredients, additive-free may be the best first step. Or a hydrolyzed protein diet. I am concerned that hydrolyzed protein diets could be problematic for some animals because they are intolerant of the main protein ingredient and because MSG may be included. (see Flavoring and Coloring Agents: Health Risks and Potential Problems Muthusamy Ramesh, Arunachalam Muthuraman, in Natural and Artificial Flavoring Agents and Food Dyes, 2018)

For more details see Diseases of the Small Intestines Debra L. Zoran, in Handbook of Small Animal Practice (Fifth Edition), 2008 She emphasizes that if homemade diets are used in dogs, well-cooked rice, potatoes, and tapioca are highly digestible, gluten-free carbohydrate sources.

Immunosuppressive doses of prednisone reduce the inflammatory and immunological stimulus within the GI tracts once infectious or parasitic causes are ruled out. A few animals are eventually maintained with diet alone, but these are likely to be animals with a primary dietary sensitivity, not idiopathic eosinophilic inflammatory bowel disease (IBD). Antibacterial therapy is generally justified in IBD since secondary overgrowth of bacteria or development of antibiotic responsive enteritis is relatively common, and because bacterial antigens are believed to be of major importance in the development of IBD. Metronidazole is the preferred drug in both dogs and cats for initial therapy. Tylosin may also be effective and has immunomodulatory effects (similar to metronidazole). In severe cases of IBD, fluoroquinolones (enrofloxacin) may be indicated. Read full chapterView PDFDownload book.

In cases of severe pruritis many dogs are given Apoquel and other immunosuppressive drugs, long term and all too often with no significant benefit for what owners are often told is “atopic dermatitis”. A survey by the American College of Veterinary Dermatology revealed “across all the dermatological diagnoses made by primary care veterinarians, 46% did not match the veterinary dermatologist’ diagnoses. The top 3 diagnosis mismatches [i.e. mistakes] were food allergy, breed-associated genetic skin condition and skin allergy.” ( Hanna,B., Earlier dermatology referral rewards primary care practice (part1): easing client expenses and enhancing patient care. DVM360 May 2022, Vol 53: 42-43

It is notable that ElleVets Sciences has published research findings of its CBD+CBDA oil’s efficacy on dogs with atopic dermatitis. The results displayed that over 65% of the dogs participating in the study had a substantial improvement in skin itchiness. (Loewinger M, Wakshlag JJ, Bowden D, Peters-Kennedy J, Rosenberg A. The effect of a mixed cannabidiol and cannabidiolic acid based oil on client-owned dogs with atopic dermatitis. Vet Dermatol. 2022. doi: 10.1111/vde.13077.)

Dogs diagnosed with seasonal skin allergies, notably “hot spots” benefit from weekly shampoos and anecdotally, supplements of vitamin B complex or Brewer’s yeast (which may repel fleas) and local bee pollen or honey daily in their food.

Skin and other health problems in dogs, cats and humans can be associated with in-home dust mites ( that thrive on shed skin cells from us and our pets); and from fire-retardant and stain-proofing chemicals in carpets and upholstery which have also been identified as endocrine disruptors and potential carcinogens.

Supplements providing omega 3 essential fatty acids such as fish oils, marine algae, flax seed oil and oil of primrose can improve general skin health and barrier functions. This can help dogs with skin problems associated with diabetes mellitus, hypothyroidism and Cushing’s disease. Secondary bacterial and fungal infections of the skin are best treated with dermatopical shampoos containing miconazole or chlorhexidine. Dogs diagnosed with atopic dermatitis can benefit from such medicated shampoos along with oral immunosuppressing drugs such as lokivetmab, oclacitinib, glucocorticoids and cicisporin. (Prost, K. Making Rash Decisions When Choosing a Treatment Plan for Your Canine Dermatology Patients? Don’t Forget Dermatopicals. DVM360.May 2022 53: 67-73,)