Suspect a food allergy? Run an elimination diet trial-and do it right!
Beef? Eggs? Wheat? Lamb? Dairy? How to find out which foods are no-nos for your food-allergic veterinary patients. (Illustration by Mindy Valcarcel)You are working up a dog or cat that presents with skin or gastrointestinal (GI) signs, and you have reached the point in your diagnostic flow chart that calls for a food elimination trial. For any number of reasons-including pressure from the client to use OTC products, multipet households, children who drop food or flavored medications-food elimination trials are at best challenging. Fortunately, CVC speaker Rebecca Remillard, PhD, DVM, DACVN, of Veterinary Nutritional Consultations Inc. in Hollister, North Carolina, has a few tips to help make sure your trial is a success.
Tip 1: Know whether you are dealing with a food intolerance or a food allergy.
Dr. Remillard says a food intolerance is limited to non-immunologic GI disturbances (will not involve the skin), such as nausea, loose stool or gas. Causes of food intolerance can include:
Food intolerance can happen after first exposure to the offending substance.
In contrast, a food allergy is an abnormal immunologic response to a food antigen and can cause GI signs, dermatologic signs, or both Dr. Remillard tells us. The animal has developed an abnormal immunologic response to what should be a safe protein. Food allergies are most common in animals 2 to 6 years of age. With a food allergy, it is subsequent exposure to the offending allergen that puts the animal over the edge and causes signs ranging from pruritus to vomiting and diarrhea. The most reported allergens are beef, dairy, wheat, lamb, eggs, soy and chicken, not because these are inherently allergenic but because they are common in OTC pet foods. To complicate matters, just because beef causes a problem doesn't mean dairy does, and the same goes for chicken and eggs.
Tip 2: A diet trial is the only way to go.
Other than a food elimination trial, there is still no reliable way to test for food allergy. No blood, urine, saliva or skin test is considered to be diagnostic. Dr. Remillard describes these tests by saying, “Even a broken clock is right twice a day.” If you suspect a food allergy, do not waste the client's money on any further tests and go straight to a food elimination trial. The gold standard is a food trial with a rechallenge of offending protein.
How long does the food elimination trial last?
For animals that have only GI signs, Dr. Remillard recommends a four-week trial since that is long enough to see if the vomiting, gas or diarrhea clears up. For animals with dermatologic signs, Dr. Remillard recommends a minimum of 12 weeks for the trial, as it takes that long for the skin to turn over.
Hydrolyzed diet or novel protein?
Dr. Remillard recommends using a protein therapeutic diet that is novel for that patient. You can use a hydrolyzed chicken or soy product, but if the patient is allergic to chicken liver or soy, that animal will still have an immunologic reaction to a hydrolyzed diet because the components the hydrolyzation process produces are in the range of Dalton size.
Tip 3: Stand your ground.
Those of us in private practice will understand how difficult it can be to get clients to switch from their maintenance diet to a therapeutic diet. And it can be even harder to get them to finish out the trial, especially if they are not seeing any results immediately. Some patients will not respond positively for 10 weeks. From the client's point of view, OTC diets are cheaper, have seemingly higher-quality ingredients and are more convenient. According to the client, therapeutic diets conversely are more expensive, seem to have lower-quality ingredients and are less convenient. It can feel like a huge uphill battle.
Having said that, Dr. Remillard is adamant on using a therapeutic diet designed for food trials, and I can see why. Several studies in the past 10 years have used enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) tests on OTC pet food ingredients against label claims, and the results are not surprising: foods labeled to be soy-free and beef-free tested positive for both.1-3 In another study, PCR or microscopy analysis, or both, identified discrepancies in the results compared with the ingredients listed on label.4 The ingredients listed on the label matched those found in testing in just two of the 12 diets. Cross-contamination is allowed in pet food manufacturing and is unavoidable even under good processing practices.
The take-home point for you and your clients is that what is on the label does not necessarily reflect what is in the diet. Another way to communicate this point is by telling clients that running a food elimination trial with an OTC product is a waste of their time and money. If they are going to invest in a food elimination diet, for the next four to 12 weeks, they will be feeding a therapeutic diet that you choose together. Fortunately, there is a wide array of products available using truly novel (kangaroo, alligator, insect) proteins.
All gelatin capsules in the United States contain either beef or pork antigens. In additional, natural and artificial flavors contain protein antigens that may not agree with labeling. For example, “beef flavoring” can be made from pork or soy-no beef needed. If your patient is receiving medications or supplements, you should contact the manufacturer of any oral therapeutics before beginning a food elimination diet or prescribing oral therapeutics to known food-allergic patients.
Tip 4: Don't forget about allergens in medications.
A 2014 study examined whether there was soy, pork and beef antigens in flavored OTC products and medications.5 Three OTC products and four veterinary therapeutics were tested using ELISA for the presence of soy, pork and beef antigens, in addition to positive and negative controls. All the OTC products tested produced ELISA results in agreement with their ingredient lists, but the veterinary therapeutic products did not agree with ingredient lists or product inserts because of other ingredients that need not be listed.
1. L'Hocine L, Boye JI, Munyana C. Detection and quantification of soy allergens in food: study of two commercial enzyme-linked immunosorbent assays. J Food Sci 2007;72:C145-C153.
2. Willis-Mahn C, Remillard R, Tater K. ELISA testing for soy antigens in dry dog foods used in dietary elimination trials. J Am Anim Hosp Assoc 2014;50:383-389.
3. Raditic DM, Remillard RL, Tater KC. ELISA testing for common food antigens in four dry dog foods used in dietary trials. J Anim Physiol Anim Nutr (Berl) 2011;95:90-97.
4. Ricci R, Granato A, Vascellari M, et al. Identification of undeclared sources of animal origin in canine dry foods used in dietary elimination trials. J Anim Physiol Anim Nutr (Berl) 2013;97 (suppl):32-38.
5. Parr JM, Remillard RL. Common confounders of dietary elimination trials contain the antigens soy, pork, and beef. J Am Anim Hosp Assoc 2014;50:298-304.