Food allergic dog and cat patients can represent some of the greatest challenges, but also some of the most rewarding outcomes, in small animal practice. Summarized below are some practical considerations, under hopefully engaging and/or intriguing headers, to help you better aid your clients and patients when a food allergy is suspected or ruled in.
Behold the pruritic threshold
Allergic patients are not limited to reacting to one antigen source. However, they may only show dermatologic symptoms like itching, licking, and chewing when enough antigenic stimulation of the immune system occurs. Therefore, a patient with flea allergy dermatitis and atopy or environmental allergies may concurrently have a food allergy.
Flea adulticide and a diet change may be easier to implement than avoidance of environmental allergens or the use of antihistamines/steroids and/or hyposentization therapy. Thus, feeding a limited ingredient, novel or uncommon proteins, or hydrolyzed protein diet may lower a patient to a state below the threshold where pruritus manifests.
Hyporexia, sialorrhea, borborygmi: More than “$20 words”
In veterinary school, some professors used to quip one should learn multisyllabic medical terms as you can charge more when you know how to use them. We are not advocates of increased fees based on terminology, but do believe clients say very valuable observations. GI symptoms of a food allergy, or more formally and expansively, an adverse reaction to food that includes not only immune reactions, are generally perceived as easy to spot.
However, vomiting and diarrhea are often later stage signs, and perceptive clients may notice a decrease in willingness or enthusiasm to eat a meal, increased salivation, gut sounds, and/or flatulence prior to vomiting and/or diarrhea developing. These early signs can be helpful in recognizing the development of a new reaction or the incomplete response to current treatment.
Diagnosis in doubt
Definitive diagnosis of a food allergy is made with an elimination-challenge diet trial. Supportive diagnostics may include vitamin B-12 and folate blood concentrations and biopsies via endoscopy or surgery. Concerns of other similar conditions like pancreatitis or some type of fat intolerance, such as lymphangiectasia, can and should be ever present as symptoms can be similar and diagnostics not completely discerning, if even performed.
From a practical perspective, there are scant options when novelty/hydrolyzation and leanness are needed in one diet. The specificity and sensitivity of blood and salivary testing for food allergies remains controversial and awaits new technology and research to support their use in all cases. Often one is left solely with a supportive elimination diet that was found effective and used as the sole support for a presumptive diagnosis.
Diet history: An untold story
Collecting a complete and accurate diet history is an art, even with the best of client historians. Diets change, memories fade, and treats go unreported, all leading to gaps and potential for foods to be identified as novel or new to the patient when they are not. Uncommon antigen foods that have a lower likelihood of having been fed given their scarcity in the pet food industry become a potential, but partial solution for cases. Hydrolysates that can be actually hypoallergenic hold promise (see more below).
Ultimately, a diet history is a partial guide and incomplete one, and patient response to the best initial choice(s) supersedes even an unabridged diet history.
Dampen, suppress, and inhibit
Immunosuppressive medications can be vital to treatment and “calming” the immune system enough to allow for nutritional management to be effective. However, the immune system in cases of food allergy has lost oral tolerance for some food antigens/proteins and is reacting as if there is a massive invasion by parasites, bacteria, or viruses.
One can appreciate the degree of dampening or inhibition needed for the immune system to completely surrender to a BID or TID bolus of such a large amount of life-threatening infectious material. Therefore, the mainstay of treatment must be removal of the offending dietary protein (from animals and/or plants) until immunotherapy becomes a treatment option in the future (e.g., Palforzia in humans with peanut allergies).
OTCs all over
With a presumptive or definitive diagnosis of food allergy, treatments are often actively searched for given the potential relief they can provide to the patient and the human caretaker alike. With an ever-growing number of exotic or uncommon pairings, over-the-counter (OTC) foods become an obvious and attractive solution especially to the laity. Unfortunately, given their intended use in healthy pets, they commonly can legally and ethically have “rework” or material included from previous production runs unless systems are segregated and/or completely cleaned, sanitized, and tested between lots.
Such a labor-intensive practice is not justified for OTC offerings. This does result in proteins/antigens being present that are not declared on ingredient lists (see Raditic & Remillard 2010, Horvath-Ungerboeck C et al. 2017), and can still result in a reaction in very sensitive patients. This is why human food packaging warnings of shared equipment or facility have become so prevalent.
Cross-contact & cross-reactivity—making one cross
The challenges of cross-contact noted above is not unique to OTC foods and has been reported in some therapeutic foods as well (see Pagani et al. 2018, Ricci et al. 2018). However, some therapeutic foods, including notably hydrolysates, have proven superior to OTC options (Horvath-Ungerboeck C et al. 2017). Cross-reactivity is an additional concern with limited veterinary research, but it is known, especially in humans, that past exposure is not needed to have an immune response if the antigen is from a closely related food species. For example, one can react to duck without having ever eaten duck if allergic to chicken. This can inform choices where one, for example, might avoid bison as a first choice in cases with a known beef allergy.
Hydrolysates—is the key still there?
Hydrolysates, which are proteins that have been broken into small molecular peptides, are theoretically hypoallergenic, unlike any untreated, intact or exotic/uncommon protein. However, the hydrolyzation process is an imperfect one.
This means the molecular size of the “key” or epitope from the hydrolyzed protein can remain present and large enough to still “work” on an existing “lock” or antibody. Thus, if using a soy or chicken hydrolysate, and the patient is allergic to these proteins, there may still be enough intact or large enough protein to elicit an immune reaction. The only completely hypoallergenic solution is one composed of purified amino acids, as is found in “elemental” diets for humans, which are cost prohibitive in veterinary medicine currently.
A resistance to some very good and proven, commercially produced therapeutic foods can exist with some clients. Most often they are concerned about other ingredients that are present to make the food shelf stable and/or complete and balanced. This can be especially true as highly processed and purified protein and carbohydrate-rich foods are used to avoid additional concerns of antigenicity and cross contact and as a consequence need to be highly fortified using synthetic and purified minerals and vitamins.
If commercially prepared, therapeutic uncommon antigen or hydrolysate pet foods are ineffective or exhausted, homemade pet food can increase available options. They also may provide a solution when a concurrent condition like fat intolerance is of concern.
Care must be taken in their formulation and preparation, and support from a board-certified veterinary nutritionist’s solution or consultation is recommended (see referral section below). It should be realized that homemade food has drawbacks which include costing more than extruded food (a.k.a. kibble; but typically costs less than retorted or frozen food) and “diet drift.” This is the phenomenon where clients shift away from the specifics of a formulated recipe to different ingredients or amounts and omit parts that result in a diet no longer being nutritionally appropriate for long-term feeding.
Listen to your patient
The best history and diagnostics are meaningless if the treatment they inform proves ineffective in practice. Thus, if one’s patient presents with early signs of a reaction as noted above, or with ongoing clinical signs, efforts must be taken to adjust treatment and try different foods/antigens, after ruling out the possibility of any other underlying disease(s) and/or exposure to foods/antigens (e.g., lapses in adherence, flavored medications, toothpaste, supplements with flavorings) not part of the elimination diet. It must also be remembered that new reactions can develop within weeks to initially tolerated foods.
Palatability concerns not related to a reaction can be addressed at times with a sweet and savory approach (in dogs only; with the addition of sugar and salt), increasing dietary fat, the use of warm water/gentle heating to release aromas, and/or a change in format (extruded/retorted/frozen/homemade). Stool quality issues, especially with highly digestible homemade foods, may benefit from the addition of dietary fiber notably insoluble fiber like powdered cellulose (as loose stool should not always be ascribed to a reaction if no other signs support such a concern).
Crisis and sacrificial diets
In the midst of a crisis, where inflammation is severe, the feeding of a “sacrificial” protein diet (often using very exotic and at times expensive ingredients) may be indicated. This approach is based on the theory that the gut especially may be more likely to develop antibodies to ingested dietary protein at these times. If one doesn’t want to eliminate a protein or food that one wishes to feed later, it should be avoided at these crucial times.
A time for every referral
General practitioners are well-equipped with the knowledge and tools to manage food allergic patients. However, refractory cases, ones with intense or passionate clients, or that have multiple co-morbidities in need of potentially conflicting nutritional management can benefit from referral to a board-certified veterinary nutritionist. (See acvn.org or vetnutritionist.com for directories.)
Sean J. Delaney, BS, DVM, MS, DACVN, is a board-certified veterinary nutritionist and the founder of BalanceIT.com.
Yuki Okada, BA, DVM, PhD, is co-owner of Seven Hills Veterinary Hospital in San Francisco. She sees clinical nutrition referral cases weekly as part of her ACVN residency with Dr. Delaney at Pet Emergency & Specialty Center of Marin.