Prescription hypoallergenic diets may help more than just food allergy!
The diagnosis of food allergy unfortunately is not performed by a quick laboratory test. There is no simple blood or skin test that can accurately make the diagnosis. Attempts have been made via skin testing, IgG/IgE serum testing, and hair and saliva testing all to no avail.[1] In fact we keep coming back to the elimination diet as the “gold standard” for accurately assessing food allergy in our patients. It has been shown that 90% of food allergy cases in either dogs or cats require a restrictive diet fed for 8 weeks.[2] 80% of food allergic dogs may respond within 5 weeks and in cats, 6 weeks.[3] But did you know that by feeding a prescription hypoallergenic diet to your atopic patients, you may be helping to reduce their atopic flareups?
First a bit of collective information on food allergy and how it differs in dogs and cats. Food allergy incidence in dogs is unknown possibly due to not being recognized by owners but is reported to be anywhere from 14-33%.[4] Most dogs (33%) start with symptoms at < 1 year of age (true for humans as well).[5] There is no breed predilection but breeds such as German shepherds, West Highland white terriers, and Labrador and Golden retrievers account for 40% of affected dogs.[6] Food allergy in cats may occur in 10-49% of patients with the age of onset anywhere from 6 months of age up to 12 years of age. There is no breed predilection but one study found 1/3rd of food allergic cats to be Siamese or Siamese crosses.[7]
Aside from dermatological symptoms in dogs with food allergy such as pruritus of the face, feet, axilla, perineum, recurrent pyoderma, and otitis externa (25% of the time being unilateral [8]), keep in mind that food allergy may also play a role in noncutaneous signs such as gastrointestinal issues, seizures[9], erythema multiforme, lupoid onychodystrophy, vasculitis, and pemphigus. In addition to pruritus, cats may experience eosinophilic granuloma lesions, miliary dermatitis, seborrhea, pyoderma-bacterial or Malassezia, and/or otitis. Noncutaneous signs may include flatulence, diarrhea, vomiting, salivation, conjunctivitis, and/or sneezing.[10]
Since food allergy in both species can have the same symptoms as atopy, they often exist together making it difficult to reach a diagnosis. A recent paper[1]found 10 of 53 dogs with a diagnosis of nonseasonal atopic dermatitis flared when challenged with their former diet when off prednisolone resulting in a diagnosis of food-induced atopic dermatitis. Information in humans and now, in dogs, suggests that foods may trigger symptoms of atopy (“food-induced atopic dermatitis”).[2] Evidence in the literature shows cross reactivity between certain pollens and foods as well as unrelated allergens such as house dust mite and shellfish.[3]For these reasons, it may be prudent to advise a prescription hypoallergenic diet for your atopic patients. A former study of dogs allergic to house dust mites showed that they had less flareups when fed a prescription diet (Hill’s Z/D).[4] Choosing an elimination diet for food allergy testing requires knowledge of what the pet has eaten in the past. “If you haven’t been exposed to something, you can’t be allergic to it” is a common belief. Obtaining a thorough dietary history from the owner is essential and if former diets are unknown (such as in a rescued pet), a hydrolyzed protein diet may be the option. Also, one needs to take into consideration the age of the pet, as only a few prescription elimination diets are labelled for growth: Cats-Royal Canin PR dry, PD dry, PV dry, Rayne rabbit maintenance, Blue Buffalo NP. Dogs-Royal Canin HP dry, PD dry, Rayne rabbit maintenance, Blue Buffalo NP. Over the counter (OTC) “limited ingredient” diets are NOT SUITABLE for use as elimination diets because up to 83% of OTC diets may contain ingredients in the food which are not listed on the label.[5] Raw diets are also not suitable as one study showed 78% of canine diets and 56% of feline diets contained other meat species.[6] For owners wanting to feed a vegetarian diet, Royal Canin Vegetarian (RCV) was helpful in eliminating pruritus in 3 food allergic dogs.[7] Insect-based diets (mealworm) fed for 12 weeks in 7 dogs not only helped with pruritus but also reduced trans epidermal water loss (TEWL) which is essential in maintaining good skin barrier function.[8] Thankfully there is a plethora of commercial novel prescription elimination diets to choose from-most manufacturers including Blue Buffalo, Royal Canin, and Rayne perform PCR or ELISA-TEK testing during manufacturing and of the final product to rule out contaminant proteins in their diets. Hydrolyzed protein diets where the long-chain proteins are cleaved to reduce allergenicity are either soy (Purina HA, Royal Canin HP), salmon (Blue Buffalo HF), chicken (Hill’s Z/D), or poultry-feather (Ultamino) based. However, up to 50% of chicken or soy allergic patients may still react to hydrolyzed protein diets containing either of those 2 proteins.[9] Home-cooked elimination diets are also suitable if done under VETERINARY SUPERVISION as one study showed when owners composed the diets, proteins, minerals, and omega-3 levels were deficient, and the calcium: phosphorus ratio was erroneous.[2]
So, what can you do?
- Consider a prescription elimination diet in atopics to reduce flareups but don’t forget food allergy can play a role in other systemic diseases as mentioned above.
- Choose a PRESCRIPTION elimination diet be it novel protein or hydrolyzed protein or a supervised home cooked diet and feed it for 8 weeks. When challenged with the offending protein, cats and dogs will flare immediately or within 7 or l4 days, respectively.
- OTC “limited ingredient” diets and raw diets are NOT SUITABLE for testing.
- In young, growing dogs, be sure the prescription diet is labelled for growth.
- It is not enough to advise an owner to avoid a certain protein when feeding OTC foods or treats as up to 83% may contain other ingredients not listed on the label.
[1] Bizikova P, Olivry T. A random double blinded crossover trial testing 2 hydrolyzed poultry diets in dogs with chicken allergy. Vet Derm 2016;19(5), 280-287.
[2] Stockman J, et al. Evaluation of recipes for home-prepared maintenance diets for dogs. JAVMA 2013;242(11), 1500-1505.
[1] Favrot C, et al. The usefulness of short-course prednisolone during the initial phase of an elimination diet trial in dogs with food-induced atopic dermatitis. Vet Derm 2019;30(6), 498-e149.
[2] Favrot C, et al. The usefulness of short-course prednisolone during the initial phase of an elimination diet trial in dogs with food-induced atopic dermatitis. Vet Derm 2019;30(6), 498-e149.
[3] Thursday K, et al. Oral allergy syndrome in shrimp and house dust mite allergy. The Journal of Allergy and Clinical Immunology: In Practice 2018;6(6), 2163-2164.
[4] Fiora P, et al. A retrospective study on the prevalence and causative allergens of food-induced atopic dermatitis in France. Abstracts 2013 ESVD and ACVD. Vet Derm 24, 377-397.
[5] Olivry T, Mueller R. Critically appraised topic on adverse food reactions of companion animals (5): discrepancies between ingredients and labeling in commercial pet foods. BMC Vet Res 2018;14(24).
[6] Cox A, et al. Detection of DNA for undeclared animal species in commercial canine and feline raw meat diets using PCR. ACVD meeting presentation, April 2019.
[7] Aufox E, et al. PCR analysis of a prescription diet used in 3 dogs with cutaneous food reactions. Vet Derm 2018;29(4): 345-e122.
[8] Lee K, et al. Hypoallergenicity of an insect-based diet in the treatment of canine cutaneous adverse food reaction. Abstract 2020 World Congress of Veterinary Dermatology.
[9] Bizikova P, Olivry T. A random double blinded crossover trial testing 2 hydrolyzed poultry diets in dogs with chicken allergy. Vet Derm 2016;19(5), 280-287.
[1] Jeffers JG. Diagnostic testing of dogs for food hypersensitivity. JAVMA 1998;198(2), 245-250.
[2] Olivry T, et al. Critically appraised topic on adverse food reactions of companion animals (1): duration of elimination diets. BMC Vet Res 2015;11(225).
[3] Olivry T, et al. Critically appraised topic on adverse food reactions of companion animals (1): duration of elimination diets. BMC Vet Res 2015;11(225).
[4] Verlinden A, et al. Food allergy in dogs and cats: a review. Critical Review in Food Science and Nutrition. 2006;46(3), 259-73.
[5] Tsakok T, et al. Does atopic dermatitis cause food allergy? A systematic review. Journal of Allergy and Clinical Immunology. 2016;137(4), 1071-1078.
[6] Olivry T, Mueller R. Critically appraised topic on adverse food reactions of companion animals (7): signalment and cutaneous manifestations of dogs and cats with adverse food reactions. BMC Vet Res 2019;15(140).
[7] Carlotti D, et al. Food allergy in dogs and cats. A review and report of 43 cases. Vet Derm 1990;1(2), 55-62.
[8] Gaschen F, et al. Adverse food reactions in dogs and cats. Vet Clinics of NA Small Animal Practice 2011;41(2), 361-379.
[9] Rosser E. Diagnosis of food allergy in dogs. JAVMA 1993;203(2), 259-262.
[10] Mueller R, Olivry T. Critically appraised topic on adverse food reactions of companion animals (6): prevalence of noncutaneous manifestations of adverse food reactions in dogs and cats. BMC Vet Res 2018;14(341).