Food Allergy and Diet Trials

Food allergies are a known cause of skin irritation in the dog and cat, and up to 50% of these animals may also show signs of gastrointestinal disease. Dogs that are food allergic often display their symptoms early in life. Any breed and sex can be affected. Some of the more commonly incriminated foods driving food allergies are shown in this paper:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4710035/

Clinical signs of food allergies

It is important to understand that the pattern of itching and lesions seen with food allergy can mimic any case of environmental allergy (atopy), flea allergy dermatitis, and sarcoptic mange.
Approximately half the dogs with food allergies that have itchy skin will also have gastrointestinal disease, although this these signs are often mild and may not be seen as abnormal by their owner. The most common sign is an increased number of bowel movements per day (it appears that 3 movements per day should make us suspicious of food allergy, 4 movements per day is certainly abnormal). Vomiting and diarrhoea are seen in less than 15% of the cases of food allergy that presents with skin signs.

Tests for food allergy

Over the years there have been supposed breakthrough blood tests and skin tests that have promised to provide a straightforward diagnosis of food allergy. Hair and saliva testing in dogs for food allergies has been proven to be an unreliable testing modality:
https://onlinelibrary.wiley.com/doi/abs/10.1111/jsap.12952

In fact, to date, all in vitro nor in vivo tests have been shown not to be reliable tests:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5577833/

Currently, the gold standard to diagnose food allergies in the dog and cat is an elimination diet trial, which must involve subsequent “provocation” or “re-challenge.” Without the provocation – the diet trial is of no practical use.

The elimination diet trial

Your pet receives a novel protein diet which consists of proteins that they have never ingested before, or proteins that the body cannot recognise. To provide reliable information, elimination diet trials must be correctly devised by your dermatologist and strictly followed at home, for 8 weeks. During this time, absolutely nothing is fed to your pet other than the prescribed diet, and water! This is easily achievable, once everybody in the house is on-board with the plan. For some pets I can provide a shortened feeding trial which still provides the same results, but in as little as 4 weeks.

Re-challenge phase of the diet trial

Performing an elimination diet trial and showing improvement in clinical signs supports the diagnosis, but the diagnosis is very strongly supported through re-feeding the suspect foods that are may be driving the allergy. So, at the conclusion of the advised trial period, we proceed with a “smorgasbord” re-challenge, where your pet is fed a thorough mix of all the foods fed prior to the elimination diet starting. Then, if reactions occur, with correct guidance, we can test single ingredients to devise a list of allergens that need to be avoided.

Which ingredients are best known to cause food allergy?

In Australia and the USA, these components are most commonly:
-beef, dairy products, chicken, wheat and lamb in dogs.
-beef, fish and chicken in the cat.

In each patient, we know fairly well that:
40% of patients are allergic to a single component of the diet
40% are allergic to 2 components
20% of patients are allergic to 3 or more components

Once we have composed a list of agents that are causing your dog or cat to develop skin disease, avoiding the suspect foods can make a huge difference and, in most cases, will significantly reduce the need for supporting treatments (such as anti-itch medications).  Life for you and your pet is then so much simpler.