Elimination diets for adverse food reactions

It’s relatively uncommon for a pet to have an adverse food reaction due to a true food allergy, although gastrointestinal upset due to sensitivity to a food ingredient may occur more often. Adverse reactions to food include true allergies, which are due to the immune system responding to the ingredient, and food intolerances, which are not immune-mediated, such as lactose intolerance. 

©Waltham Petcare Science Institute

Food ingredients that cause allergies are known as allergens. The most common reactions are skin (cutaneous) problems such as itching or redness, or gastrointestinal signs including vomiting and/or diarrhea and can also include increased gas and abdominal discomfort. There are many documented dietary allergens – the most common offenders in the USA in cats which cause skin problems include dairy products, beef and fish. The most common ingredients causing gastrointestinal signs have not been reported. Note that these are all protein sources. They are the ingredients causing the most reactions due to their frequent inclusion in foods rather than an inherent allergenicity, and they can vary by country depending on what ingredients are commonly fed. There have been no confirmed cutaneous adverse food reactions to food additives.

A comprehensive diet history is required for determining what ingredients have been fed and to aid in selection of ingredients for a suitable elimination trial diet. While labels are required to list ingredients, labeling regulations in some countries allow for less specific ingredient lists or category labeling rather than specific foods (eg “meat” rather than “beef”).

If a diet labeled as having a single protein source is made in a processing plant that handles other protein sources accidental cross-contamination is possible in “over the counter” diets. In order to avoid cross-contamination, the manufacturers of high-specification therapeutic elimination diets and hydrolyzed protein diets deep-clean their production lines to ensure only select and labeled ingredients are included in their product. This is one reason for the greater expense of these diets.

The diagnostic tool of choice is an elimination diet using a hydrolyzed protein diet or a limited ingredient protein and carbohydrate source not previously fed (ie novel). The use of hydrolyzed protein diets may be the better choice to determine if sensitivity to food is part of the problem. Improvement on such a diet, deterioration on re-challenge with the previously fed food and improvement again on the elimination diet confirms the diagnosis of adverse food reaction.

Tests of blood, serum, saliva and hair are not useful for diagnosis of food allergy as there are currently no reliable, sensitive or specific blood or salivary tests. Testing for serum food-specific immunoglobulins shows a highly variable accuracy, which means that the test may indicate a pet cannot eat an ingredient which does not cause a problem, or less frequently, that it can eat an ingredient which may cause problems.

Pets with adverse reactions to foods may need to be on restricted diets long term, especially if they have skin disorders, although some pets can eventually return to the original diet if they have gastrointestinal signs without skin problems. In one study, 80% of dogs with gastrointestinal problems which responded to an elimination novel protein diet were able to return to their previous diet after 14 weeks of eating the elimination diet.

The simplest solution can be to avoid the particular protein sources and possibly carbohydrate sources in the diet which cause the problem. Many pet foods contain a mixture of different protein sources and so choosing a new diet for your allergic pet may not be easy and you should discuss it with your veterinarian. If the diet used in the diet trial was complete and balanced, eg commercial therapeutic limited protein or hydrolyzed diets, they can be fed long term.

Some animals which have been allergic to one part of their diet may develop other reactions to another ingredient, so be watchful for the signs recurring. In some cases there may not be a suitable commercial diet available and you should consult a veterinary nutritionist™ to formulate a home-cooked diet for your pet.

A diet is only hypoallergenic for your pet if it has never been exposed to any of the proteins incorporated in it. No intact protein can be described as hypoallergenic for every pet. This concept of low allergenicity is more appropriate for hydrolyzed diets (see below) as each individual pet will have been exposed to multiple dietary protein sources throughout their life and may develop an adverse reaction to any of them.

Hydrolyzed protein diets are produced by specialist veterinary nutrition companies. Reactions to food components are usually against large molecules like glycoproteins. Enzymatic hydrolysis breaks apart the protein to its smaller components of amino acids and very low molecular weight peptides (short chains of amino acids). It is common to recommend using these products for exclusion diet trials, especially those made from proteins unlikely to be fed to our pets such as feathers and soya; diets with hydrolyzed chicken are also available. These diets are formulated to be complete and balanced and can be fed long term. A disadvantage for some pets is that they may be less palatable than diets with complete intact proteins.

Feeding raw meat-based diets to pets has become an increasingly popular trend amongst pet owners. Owners who desire to provide the best for their pets should seek veterinary opinion about this food option. It should be noted that raw diets have not been proven to cause either more or fewer adverse reactions to food, and do have inherent risks of bacterial contamination. There is sufficient evidence available that veterinarians should feel obligated to discuss the human and pet health implications of a client’s decision to use a raw meat-based food for their pet. It is proven that owners who feed their pets a raw diet have a higher risk of infections with pathogenic (disease causing) bacteria such as Salmonella, Listeria, Campylobacter and E. coli. Humans who are more vulnerable to these potentially severe problems include young children, elderly people, pregnant women, and immune-compromised individuals (eg chemotherapy, or those with immune disorders). These individuals are at a higher risk of infection and illness if exposed to pathogenic bacteria. Similarly pets that are more prone to risks of infection include those pets receiving chemotherapy or other immunosuppressive therapies (eg corticosteroids), very old or very young pets, and those with immune-mediated diseases.

If your veterinarian recommends a diet trial, the following instructions can be followed:

Elimination diet trial feeding instructions

1. It is essential that either a hydrolyzed protein diet or only one novel protein and carbohydrate diet is fed exclusively throughout the whole 6-12 week trial if your pet has skin problems. If your pet is showing vomiting, diarrhea or other signs of gastrointestinal disease without skin problems a two week food trial period is usually adequate.

2. The choice of a limited ingredient protein source is dependent on the animal’s dietary history; hydrolyzed protein diets can be used for any pet. Slow transition to the diet over 3-5 days is usually recommended to improve acceptance.

3. Free access to water (only).

4. No flavored (‘palatable’) medications or toothpastes, human foods, scraps, treats, food-based dental chews, or food used to give medications should be fed.

5. If treats are required, for example for training purposes, then a small portion of the trial diet, or an oven-baked portion of the protein source, may be given if a single protein source diet is chosen.

6. Use separate feeding equipment for the patient being tested if there is more than one pet in the house and the others are on different diets. Wash all items used in feeding (bowls, scales, measuring cups) with soap and thoroughly rinse after every meal. Ensure the food bag is completely sealed between meals and in a clean, dry place.

7. Friends, relatives and neighbors may be supplying the pet with foods or treats. Their cooperation is often vital to the success of the trial. The only way to be certain that a perfect diet trial has been performed with a cat is to confine him/her in your house throughout the trial and usually to feed in contact cats with the trial diet also.

8. Keep a diary – scoring itchiness or gastrointestinal signs and noting down any inadvertent access to other foods such as scavenging, treats, or food stealing.

Diet trial phases (Exclusion-Provocation)

In order to identify the ingredient causing the problems and avoid coincidences an elimination diet trial is followed by provocation by feeding individual ingredients. When the elimination diet successfully alleviates clinical signs, some clients choose to not continue on to return to the previous diet or to challenge the pet with other ingredients. If the trial diet was complete and balanced, the pet may stay on that diet.

1. Challenge: this phase is intended to identify the specific ingredients that cause a flare of signs. The patient continues eating the strict elimination diet while being offered previously fed ingredients (usually protein sources, which are the most commonly problematic) as treats or diet toppers. Small amounts (<10% of caloric intake) of one previously fed ingredient at a time are offered for up to 2 weeks while the pet is monitored for recrudescence of signs. In many cases the signs reoccur much more quickly, eg within a day. If a thorough diet history was undetermined (eg poor client recollection, multiple people feeding the pet, new pet with unknown history), a starting point would be foods commonly reported to cause allergies if there is a problem with the skin.

2. If no signs are noted, the ingredient can be fed; if signs are noted, the ingredient should be avoided.  The only way to definitively diagnose a problem food is systematic testing of each ingredient.

3. If clinical signs are noted, transition back to the elimination diet.

4. Challenging with previously fed ingredients helps determine problematic foods to avoid, which significantly improves prognosis. Knowing which ingredients are off-limits may enable clients to feed less expensive over-the-counter diets in the future, although again the potential for cross-contamination of these diets exists and may pose problems in sensitive individuals. In addition, if an allergy to the diet arises in the future, transitioning to another diet with previously tested and tolerated ingredients may avoid another lengthy dietary elimination trial.

5. Maintenance: feeding a fixed formula (ie specific listed ingredients on the label) or hydrolyzed protein complete diet avoiding the offending specified protein sources.

In cases with allergic skin disease, partial improvement with the elimination diet, relapse with provocation foods, and a second partial improvement with re-feeding the elimination diet likely indicates adverse food reaction in combination with other allergies.