How are food allergies diagnosed and treated?

The way your vet will approach diagnosing your dog’s AFR will depend on the clinical signs. Because both skin and gastrointestinal signs can mimic lots of other diseases, your vet may need to do skin scrapes and swabs and skin allergy testing. Ruling other things out is as important as ruling food allergy or intolerance in. With skin symptoms particularly, this can be a lengthy process, so be patient with your vet.

The main goal in diagnosing and managing food allergies or intolerances is to find and avoid the food ingredient responsible. The most practical and accurate method is a food elimination trial. There are two common approaches to this:

• Hydrolysed diets. These are diets in which the protein source has been hydrolysed. This means that it has been broken into tiny parts that are too small for the body’s immune system to recognise as proteins. The carbohydrate sources will usually have been purified to take out the protein components and just leave the carbohydrate. 

• Novel protein diet. These diets are, as they sound, aimed at feeding your dog a protein that they have never been exposed to before, such as venison or duck.

• Hydrolysed diets tend to be preferred for two main reasons. Firstly, in theory, you can feed these foods to any dog with any food allergy. Secondly, many people do not know exactly what proteins their dog has been exposed to, so finding a novel one may be a little uncertain.

Doing a food elimination trial

• Transition to the new food. Your vet will ask you to gradually change your dog’s food over 5-7 days. You can do this by replacing a ⅕ of your dog’s old food the first day and then increasing the proportion of new food each day until they are eating only that food.

• Cut out ALL extras. It’s essential during the trial that your dog only eats the therapeutic diet your vet has recommended. Treats, extras and chews should all be removed. Your vet may be able to recommend hypoallergenic treats or give you a recipe to make baked treats at home from the special diet.

   

• Stay the course! It’s very important that you follow your vet’s instructions for how long the trial needs to be. For gut symptoms like vomiting and diarrhoea, this may only be 3-4 weeks, but for skin symptoms, you will need to stick with it for around 12 weeks to give the skin cycle time to show improvement.

Never try to simply remove ingredients from your dog's diet because you could easily end up malnourishing them.

What next?

When you get to the end of the elimination trial, you should have your answer as to whether your dog has an AFR or not. If not, then your vet will continue their work-up. If your dog is miraculously better, then you can both breathe a sigh of relief! What you do next depends on whether you want to know exactly what your dog is reacting to. If so, you can challenge your dog by adding a single protein source to the therapeutic diet for a couple of weeks. For example, add some cooked chicken breast every day and see what happens, then try beef or wheat, etc.

Many pet parents are so relieved that their dog feels better that they choose to simply stay on the special food. It keeps things simple!

While food allergies can be tricky to diagnose and cause a real headache (or tummy ache) for you and your dog, once they have been diagnosed, most dogs can go on to have normal lives by simply avoiding the offending food.

If your dog doesn’t respond to a food elimination trial, your vet may continue the process of ruling other skin and allergy issues in or out. This can take a while, so be patient and work with your vet to get to the bottom of things. Of course, your dog may have more than one type of allergy and may respond partially to a food trial but need more care for a different issue.

FAQs

1. What are the first signs of food allergies in dogs?
   Some dogs get itchy skin and ears, while others have gastrointestinal symptoms like vomiting and diarrhoea – and some unlucky individuals get both!

2. How do vets diagnose food allergies and intolerances?
   Ultimately by doing a food elimination trial. Your vet may do other tests as well to rule out other diseases, depending on your dog’s symptoms.

3. What’s the best diet for dogs with food allergies?
   This will depend on what your dog is allergic to. Hydrolysed diets can be fed to any dog with an adverse food reaction. Your vet will advise you about your individual dog.

4. How long does it take to see an improvement on a hypoallergenic diet?
   Gastrointestinal symptoms usually resolve in 3-4 weeks, sometimes sooner. Skin symptoms can take up to 12 weeks, as the skin is much slower than the gut to heal and recover.

5. Can you blood test for food allergies?
   While there are blood tests available for food allergies, these are not currently reliable and are best avoided.

Reviewed by Dr. Hein Meyer, DVM, PhD, Dipl-ECVIM-CA and Dr. Emma Milne BVSc FRCVS.