Hypoallergenic diets. Help or hype?

Food allergy or intolerance?

An adverse reaction to a food is an abnormal or exaggerated clinical response to the ingestion of a food or food additive. It may be immune mediated (called food allergy or hypersensitivity) or not immune mediated (called food intolerance, possibly the result of a metabolic defect, for example lactose intolerance). 

Adverse food reactions in cats and dogs are mainly expressed by itchy skin or ear and gastrointestinal signs. However, food allergies have to be distinguished from multiple other causes of these issues. Flea allergies and environmental allergies (dust mites, pollen, grasses) are much more common in pets than food allergies, but all can have similar symptoms.

Therefore, environmental allergies and food allergies are often confused, and changing a pet’s diet may not make a difference.

Diagnosis of food allergies

There is no proof that tests using blood, saliva or hair can reliably diagnose food allergies or ‘sensitivities’. The only tool (the gold standard) to diagnose food allergy is an elimination diet, in which the ingredients in the current diet are replaced with one protein and one carbohydrate source that pet has never been fed. 

The best option for this is a home-made diet or a veterinary hydrolysed diet, where proteins have been broken down into smaller components. After signs have disappeared during the trial, ideally it should be confirmed by a challenge test, that is, the reintroduction of the suspected ingredient from the old diet. 

Allergen-free dog food?

All products containing intact protein can potentially cause adverse reactions in predisposed animals. Dogs and cats can be allergic to pretty much any ingredient that can be found in pet food.  

Feeding a diet with exotic proteins like kangaroo or venison will not prevent food allergies – they are no less allergenic than more common foods like chicken or beef. It is simply that they are seldom found in pet food, so allergies to them are uncommon. 

In fact, most protein-containing ingredients have the potential to induce allergic reactions if they are regularly fed to dogs and cats. Rotating diet ingredients does not prevent food allergies, but it can limit the diet choices in a dietary elimination trial.

There are no diets that are completely ‘hypoallergenic’, meaning that they will not cause allergies (except special diets with hydrolysed proteins as the sole source of protein). Intact proteins are part of all products made by the industry including all pet foods. 

Common allergens

The most commonly reported food allergies in dogs and cats are beef, dairy, chicken and egg, simply because these ingredients have been the most common ingredients in pet foods for the past few decades, so pets often have been exposed to them. 

Contrary to the popular belief, grains are actually uncommon causes of food allergies – protein sources are more often to blame than grains. Sometimes pets are allergic to plant ingredients, but it is less common than an allergy to an animal protein.

Over-the-counter pet foods 

Many pet food companies have introduced over-the-counter products that are marketed as being good for dogs with allergies. This trend has emerged in the pet food world in the form of limited-ingredient diets. They are made up of only one meat and usually one carbohydrate source, but may still be contaminated with some other ingredients.

Several studies have shown the ingredient lists may contain protein sources not listed on the label, potentially from sharing machinery in a plant with other diets, without thorough cleaning in between. Because of the risk of cross-contamination, OTC foods are not ideal for food-allergic animals, at least in the early stages of diagnosis and treatment.

Manufacturers and retailers need to consider any ‘hypoallergenic’ marketing claims with great care.