Differences in food intolerances vs allergies: Dietary diagnostic and treatment
By Dr. Shiva Greenhalgh (RAnNutr)
In the last decade, the premiumisation of pet care has increased at an astronomical rate, largely driven by the humanisation of pet nutrition and care. This shift has been a positive for pets, as their welfare outcomes are improved through greater accountability of pet owners and manufacturers alike.
However, when it comes to pet nutrition specifically, humanisation can be stretched in areas such as food allergies. Here, we look at the state of food intolerances and allergies within the context of pet food.
There is no denying that food allergies in pets can and do occur, however their prevalence is significantly low, with <2% occurring in dogs and <1% in cats1. Intolerance and allergy are often described as one and the same – current diagnostic methods are not clear cut, with compliance in elimination diets extremely low.
More concerning in the humanisation of pet food are ‘cure diets’ and fear-mongering which can be unacceptably misleading. This form of marketing heightens the belief that a pet has an allergy with an adamancy in owner diagnosis and treatment. While this may seem harmless, it can cloud the owner’s judgment in seeking appropriate and effective veterinary aid.
Intolerance vs allergy
Globally, food allergies in pets is a common issue among owners. Diagnosis is difficult to determine, with the term frequently and incorrectly used to describe all adverse reactions following food intake. Reactions are varied but are typically cutaneous or digestive in nature. These reactions can occur as a result of an immunologic or non-immunologic response to a dietary ingredient. Non-immunologic is typically regarded as an intolerance, but food idiosyncrasies are also included, and they can be due to toxic reactions that are associated with histamine (scombroid fish), tyramine (old cheese) and bacterial toxins (botulism)3.
Food allergies are immunological reactions following food intake. In human medicine, immunoglobulin E (IgE) allergy antibodies type 1 appear to play a role in the pathogenesis of food allergy. In cats and dogs, the immunologic mechanisms are not as well understood, but they are believed to be types 1, 3 and 4 hypersensitivity reactions:
- Type 1 is an immediate reaction, usually occurring within a few minutes of ingestion.
- Type 2 is intermediate, with the animal reacting after a few hours of ingestion.
- Types 3 and 4 are classified as delayed and occur several hours to days after ingestion.
There are numerous potential food allergens, and because of the large number of ingredients in a typical commercial food, it is unlikely to implicate which one might be a causative allergen for each animal suspected of having an allergy. The most commonly implicated food allergens in dogs include beef, dairy, lamb, egg, chicken, and soy. In cats they are beef, lamb, fish, chicken, and dairy.
Dietary diagnostics and treatment
In human studies, double-blinded, placebo-controlled food challenges represent the current gold standard and the only way to establish or rule out adverse reactions to food2.
Unfortunately, this method is not feasible in veterinary medicine, as single-food extracts are not easily available commercially, with no specific serological or intracutaneous tests for the diagnosis available. Therefore, an elimination diet trial remains the gold standard for the diagnosis of food allergies in pets2.
An elimination-diet trial is the most important and only reliable diagnostic test to evaluate for and diagnose food allergies in dogs and cats. This involves feeding a chosen diet for a period of time with the exclusion of suspected ingredients for a minimum of eight weeks and maximum 12 weeks. Once complete, the animal is then challenged with the original diet. If clinical signs return upon reintroduction and subside again upon elimination diet, a diagnosis of allergy is confirmed.
During an elimination diet trial, all previous food items are removed and a new trial that meets certain criteria is decided. The trial diet should contain a limited number of novel proteins or a hydrolysed protein. The proteins used should be ones that are low in vasoactive amines (histamine, tyramine, and phenylalanine).
A common issue with this elimination diets is owner compliance. Eliminations diets require a strong commitment by the owner to strictly adhere to the guidelines of the diet including the challenge-diet reintroduction. It is a lengthy process but is the most reliable method.
Hypoallergenic, hydrolysed and grain-free diets
Hypoallergenic is a term that every pet owner has come across and is understood by most as a diet for those that have allergies or sensitivities. However, such a food does not exist, and this is because what one dog may be allergic or sensitive to will differ to another, and the ingredients of a branded ‘hypoallergenic’ may actually cause very adverse reactions for some.
Most hypoallergenic foods do contain proteins that most pets have been exposed to. The key to hypoallergenic foods is in two forms: the protein used must be novel for that animal, and the second is through hydrolysed proteins. Hydrolysis is a naturally occurring chemical reaction that breaks down large protein molecules into peptides, which the immune system does not typically respond to due to how small the molecule size is.
A hypoallergenic food does not have to be commercial. In fact, many opt for a home-cooked approach as it ensures full transparency in the ingredients used and minimal issues of cross-contamination. The only concern with such diets is that most – if not all – are unbalanced without the guidance of a certified vet or animal nutritionist.
Grain-free diets are another option offered to pets with suspected allergies and intolerances, but some pet owners opt for this diet despite no benefit in doing so. Many manufacturers have no option other than to produce this product as grains have been condemned, yet grains are a very beneficial ingredient to include in a pet’s diet.
Not only do grains provide carbohydrates, but they also provide an array of vitamins and minerals, as well as being an economical source of protein. When grains are combined, the biological effectiveness of the protein is enhanced, bringing a completeness and balance in amino acids. However, for pets that do indeed show intolerances and allergy towards grains, alternatives are available – including sorghum, quinoa, and legumes.
Allergies and intolerances are not easily identifiable until after the age of six months. As the animal gets older, the likelihood of an adverse reaction increases, particularly if their exposure to foods as a puppy or kitten was limited or not exposed at all.
Oral tolerance is a phenomena whereby prior exposure to an antigen through enteric route induces a specific immunological unresponsiveness on subsequent systemic to the same antigen through a supressing mechanism in the gut-associated lymphoid tissue. The importance in this is that from when cats and dogs are weaned, the introduction of various foods should be encouraged repeatedly as a long-term strategy to decrease allergic or intolerant responses as an adult.
The prevalence of food allergies in cats and dogs is largely unknown and likely underestimated, however the distinction between allergy and intolerance is important in the treatment and future feeding of pets.
Allergic response is often inherent, however through exposure to a variety of foods as a young dog or cat, allergies and intolerances are more likely to be reduced by the time they are an adult through oral tolerance. Therefore, we need to avoid imposition of our dietary requirements or philosophy on them, and this includes the introduction of grains, soy products, various proteins, and carbohydrates. Their dietary appetite and ability to utilise modern ingredients is through evolutionary mechanisms which will only further develop through greater exposure.
Cats and dogs that are suspected of having allergies are best to validate through elimination diets, which are the current gold standard in diagnosis.
1. Olivry T, Mueller RS. Critically appraised topic on adverse food reactions of companion animals (3): prevalence of cutaneous adverse food reactions in dogs and cats. BMC Vet Res. 2017 Feb 15;13(1):51.
2. Fischer N, Spielhofer L, Martini F, Rostaher A, Favrot C. Sensitivity and specificity of a shortened elimination diet protocol for the diagnosis of food-induced atopic dermatitis (FIAD). Vet Dermatol. 2021 Jun;32(3):247-e65.
3. Fascetti, Andrea J. and Sean J. Delaney. Applied veterinary clinical nutrition. 2012.