The facts about food allergies

Food allergies are one of the most misunderstood of all dog health problems. This partly caused by the enormous amount of misinformation on the internet, much of it coming from pet food companies! As a veterinarian and a pet food company founder I think its really important for all dog owners to have a good understanding of the evidence we have around food allergies in dogs.

What is a food allergy?

A food allergy is a hypersensitivity reaction which occurs when a dog’s immune system overreacts to a particular food ingredient and mounts an immune response to that substance. This is most commonly a protein, but can also be a complex carbohydrate.

How common are food allergies in dogs?

True food allergies (also known as adverse food reactions or cutaneous adverse food reactions) are thought to make up only around 5% of all skin disease in dogs and about 15% of all allergic skin problems in dogs. So, they’re not as common as you might think. Fleas (flea allergy dermatitis) and canine atopic dermatitis (a genetic predisposition to reacting to allergens in the environment) are the most common causes of skin disease.

Unfortunately, canine atopic dermatitis, presents very similarly to food allergies in dogs and this can be a real challenge for diagnosis. To make things even more confusing studies have shown that 13-30% of dogs with food allergies have concurrent atopic dermatitis. So, atopic dermatitis is an important differential diagnosis to consider in any itchy dog and I will cover this in more detail in some future blogs.

What foods are most likely to cause allergies?

The internet will tell you that ‘grains’ cause most food allergies. In actual fact, research has long shown that proteins are the leading cause of food allergies. Here are the results from a recent paper (Fiora et al, 2013):

* It is also important to note here that it is extremely uncommon for dogs to be allergic to gluten, with the exception of Irish Setters (who present with gastrointestinal symptoms not skin problems) and possibly Border Terriers.

Symptoms of food allergies in dogs

Dogs can present with signs of food allergies at any age, but they most commonly seen before 6 months of age and over 6 years of age. This can be useful when trying to differentiate food allergies from atopy, which more commonly presents in dogs between the age of 6 months and 3 years.

There is no doubt that food allergies make dogs pretty itchy. Vets use the term pruritis for this. Our dogs show us they are itchy by scratching, rubbing, chewing, licking, scooting along on their bottoms and head shaking. Common sites affected are the paws, ears, armpits, groin and around the anus. And you guessed it, a similar pattern of distribution is seen with atopic dermatitis.

Dogs presenting with these clinical signs may also have secondary bacterial and/or fungal infections caused by self-trauma and chronic inflammation. By the time we see these secondary signs we usually have a pretty smelly, sore, sad pooch.

Food allergies can also cause gastrointestinal signs such as vomiting, diarrhoea, straining to pass a bowel motion, increased frequency of bowel motions and flatulence.

Food allergies are non-seasonal. So as long as the dog is eating the same food they will occur year round. In contrast, many of the environmental allergens which dogs with atopy react to, such as pollens, tend to be more seasonal, although things like dust mites will be present all year round.

Diagnosis – The Elimination Diet

Diagnosis of food allergy can be tricky as, despite what you might read on the internet, there are no commercially available tests that are actually accurate. The only way to truly rule in or out a food allergy is to do a dietary elimination trial.

An elimination trial involves putting the dog onto a diet that it is highly unlikely to be allergic to for 8-12 weeks and assessing whether the symptoms settle down. If there is a marked improvement in clinical signs you then refeed the dog with the original diet and if there is a flare up of symptoms then you can conclude that the dog is allergic to an ingredient in that diet. We then pop them back on the elimination diet until the skin has settled again and then run some provocation trials. This involves selectively introducing 1 new ingredient at a time back into the diet to see what the dog will react to. The decision on what ingredients to use is usually based on what the diets the dog has previously eaten or that prevalence table above.

The most accurate way to do an elimination diet trial is to use a prescription diet such as RC Anallergenic or Hills Z/D. These are hydrolysed diets, meaning their constituent proteins have been broken down, using a special enzymatic process, to be of a size that the body’s immune system cannot react to. In addition, the companies that make these diets have strict quality control and testing procedures to ensure that there are no trace amounts of other ingredients in their diets, which may affect the validity of the trial.

This is all pretty technical, so I’ll write a more detailed post on this in the future.

Hypoallergenic diets for dogs

Once we’ve finished our elimination diet and provocation trials we will know what foods an individual dog is actually allergic too. We then select a diet that doesn’t contain any of those ingredients. With the huge variety of dog foods now on the market is has become a lot easier to select a diet with the right ingredient profile for individual allergic dogs.

If you don't want to commit to the time and expense of an elimination trial you can attempt to rule out potentially offending ingredients by trying a range of ‘hypoallergenic’ or low allergy diets. These are diets which have been specifically formulated using ingredients that are less likely to cause food allergies. This is a much less accurate method and involves more trial and error than undergoing a strict diet elimination trial using a prescription product.

Our Ocean Fish formula contains NZ King Salmon and fish meal as its protein source and rice as its carbohydrate source and so is ideal to try if you are in this situation.

Most grain free foods will tout themselves as being hypoallergenic, blaming wheat as the main cause of food allergies. But from our table above we can see that protein source is by far the more likely cause of a food allergy. So a grain free food containing beef, chicken or lamb is unlikely to be true to this claim.

Take home messages

Having read all this, I’m hoping that you’ve picked up these key messages:

• Allergic skin diseases are not always simple to fix, as you may be dealing with more than one underlying cause
• If you are having ongoing skin issues, your vet is the best place for advice and a properly structured dietary elimination trial is the ideal approach
• Grain free does not equal hypoallergenic! If you have an itchy dog don’t choose a food based on whether it is ‘grain free’ or not, especially as we know that these foods are causing heart issues in some pets.
• If you haven’t done an elimination trial then choose a food based on what the protein source is, as that is by far the most likely culprit for causing a food based skin or gut problem