Dogs do indeed get food allergies, however, the terminology in this area can be confusing. In this blog, we’ll break down what a food allergy is, what signs your dog may have, and what can be done. 

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What causes a food allergy?

It is an abnormal reaction by the body’s immune system to an allergen in the food. Normally the allergen is a protein, that at first meeting stimulates the production of antibodies towards it. When this protein is eaten again, the antibodies react causing an inflammatory reaction, most commonly causing skin signs. 

Is this the same as a food intolerance?

Food intolerance is a sensitivity to a certain food. Normally localized to gastrointestinal signs, and is triggered by several different mechanisms that are distinctly different from the immune system’s overreaction that is responsible for a true food allergy.

Lactose intolerance is a relatively common metabolic reaction in dogs and cats. Diarrhoea can develop when given cow’s, or even goat’s milk, due to the lactose content. Many adult dogs and cats lack the enzymes needed to break down milk sugars. Gluten-sensitive enteropathy has been well documented in Irish setters, as, again, these dogs lack the ability to break down gluten. Certain compounds added to food to enhance taste, provide colour, or protect against the growth of microorganisms can also produce signs.

Food allergy and food intolerance are often lumped together, using the name “adverse food reaction”. 

What are the signs of a skin allergy?

The dog typically becomes very itchy especially on the back, face, feet and belly. Confusingly, it may occur alongside other types of skin allergies such as allergies to pollen and may mimic many other skin diseases. The dog may even get a sudden hive-like skin reaction or lick a certain area in response to a certain food. 

Only a maximum of one-third of dogs with a food allergy that produces skin disease also show signs of gastrointestinal disease. This may be in the form of diarrhoea, or an urgent need to go; but may also be more subtle, such as an increased frequency of passing faeces, where the dog will pass motions up to six times a day, straining, or “accidents” at night.

How can it be diagnosed?

The signs of food allergies could be mistaken for many other skin or gastrointestinal disorders. 

After looking at the history of the signs, and performing an examination, your vet may want to perform tests to rule out other causes. There is no specific test for a food allergy. The use of blood and skin tests for food allergy remains controversial.

If your vet suspects a food allergy, they may suggest a food trial.

What is a food trial?

Protein is the most common culprit in allergic reactions, although some carbohydrates can also be responsible. A diet trial is where your dog is fed a protein and carbohydrate never before encountered (known as a “novel source”). If the dog’s symptoms improve, then a food allergy would be suspected. No treats, flavored toys, medications, or toothpaste are allowed. This diet trial must be strict or it will fail. 

Where do I get this diet from?

A diet could be home cooked, or a hypoallergenic diet can be bought.

The search for novel protein has become harder as pet foods contain more and more varied ingredients. Chicken was once a safe choice, but is now a relatively common ingredient in pet food and cause of food allergies. So the simple rice-and chicken diet has metamorphosed over the years from fish and corn, to salmon and potato. We now have kapolin and tapioca, duck and vegetable, and even pork and lentil. The list goes on. 

It is hard to create a home cooked diet that is nutritionally complete. Most lack a source of calcium, essential fatty acids, vitamins and other micronutrients and can contain excessive levels of protein. They can also be time consuming to make. So, while a home-cooked diet may be useful for a short term trial, longer term a proprietary diet may be better. Speak to your vets about a suitable trial. 

I am finding it difficult to think of a ‘novel protein’ for my dog, what can I do?

If it is difficult to find a protein that your dog has never had, then hydrolysed diets produced by some manufacturers may be an alternative. The principle of these diets is that the protein molecules are broken down into tiny fragments so small they are no longer capable of inducing an allergic reaction. 

The theory is that even an animal allergic to, say, beef can eat a hydrolysed beef diet without getting any symptoms – and usually, that’s true. Hydrolysed diets aren’t always the answer. A very small group of patients (reportedly less than 10%) don’t respond, for some reason. Possibly due to a rare phenomenon called “antigenic uncovering”. However, the vast majority of dogs will show at least a partial improvement on them.

How long do I need to feed this diet for?

It can take up to eight weeks to see the full response to dietary change. Most will start to show signs of improvement within four weeks. To make a definitive diagnosis of a food allergy, it is essential to re-introduce previous foods to see if the signs recur. If they do, a diagnosis can be made and a lifelong diet change will be needed.

Only if food allergy is the sole causal agent will the signs 100% disappear. Patients with concurrent skin disease or gut disease may only partially respond to an elimination trial.

What is the role of a gluten-free diet?

Gluten is a general name for the proteins found in grains such as wheat, rye, and barley.

Some families of Irish setters, for example, suffer from a gluten-sensitive enteropathy that results in diarrhoea. There are reports that gluten may cause issues for certain Wheaten Terriers, and Border terriers. Other than these cases, little data exists on gluten sensitivity in dogs and it has been reported infrequently. In pets with gastrointestinal signs, a trial with a gluten-free diet may be worth a try. However, this may not result in an improvement. 

In summary, food allergies do occur, but the subject is complicated by differing terminologies such as food allergy, food intolerance and adverse food reaction. The water is muddied further as these conditions may occur alongside other conditions affecting the skin and gut, as just part of a bigger clinical picture. Diet trials are important for diagnosis, and long term treatment. 

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