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Allergies and gut-brain interactions

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"Allergy" is one of the most misunderstood terms in medicine. Its original meaning, more than a century ago, was "altered reactivity", and was applied equally to people who over-responded to some exposure from their environment as well as to those who under-responded.

It was not long, however, before "allergy" was applied only to the over-responders, people who developed adverse health effects at exposure levels that did not bother most other people. For nearly half a century, this common use of the word "allergy" was used by doctors and the public alike. A bad reaction was a bad reaction and avoidance was the only cure.

Then doctors used allergy to describe a Type I hypersensitivity reaction involving immunoglobulin E, mast cells, eosinophils and histamine release. At this point, the medical profession and the public diverged in applying the term "allergy".

To this day, most people use the term "allergy" meaning "I have a bad reaction to something that other people don't seem to react to". They tell their doctors that they are allergic to wheat or milk because they suffer headaches, abdominal pain or diarrhoea when they consume that food. Their doctor performs some tests, such as skin prick testing or RAST testing, and tells them that they have no allergies. It is a source of both confusion and tension between patients and doctors.

Classical food allergy is usually associated with a history of infantile eczema (dermatitis or red rash of the skin in the first two years of life) and without such a history food allergy is unlikely. 

Dermatitis developing later in life is more commonly a combination of allergies and altered fatty acids in the protective layers of the skin. Even so, anyone with dermatitis probably deserves to undergo a supervised elimination diet trial and if the dermatitis significantly improves over a period of a few weeks, each of these foods can be reintroduced one at a time to identify the causative agent or agents.

There are many other types of adverse reactions to foods. The diagnosis and treatment of these other types of reactions is divisive and controversial. The category "non-IgE mediated food allergy" covers all the immunological responses to foods not caused by IgE. This includes many of the food reactions assessed by somewhat controversial diagnostic tests such as the "cytotoxic food allergy test"and the ALCAT test. These broader types of immune reactions are devilishly hard to isolate and diagnose and the tests typically identify a broad range of foods as potential candidates for avoidance, often leaving the person with inadequate diets from a nutritional perspective.

One other well-known immunological adverse food reaction is coeliac disease. This is not allergy, but an autoimmune disorder triggered by an immune reaction against grain components called gluten. The reaction is typically triggered only by wheat, rye and barley, even though all grains contain gluten.

Gluten is a complex of two different proteins and the component called the prolamin determines which grains cause coeliac disease and other autoimmune diseases, such as thyroiditis and type II diabetes.

The final big category of adverse food responses is called food intolerance and does not involve the immune system. The best-known is lactose intolerance where there is a deficiency of the enzyme lactase, preventing the normal digestion of the milk sugar lactose. Fructose intolerance falls into this category as well. Sugar can set off fermenting organisms, again causing abdominal discomfort and pain.

Adverse reactions are also common to many food additives such as colours, flavours, preservatives and MSG. For many parents these are the scourges that cause behavioural changes in their children, exacerbating ADHD and sometimes triggering asthma.

Many people find relief in low-salicylate diets, but these restrict nutrition from healthy fruits and vegetables. Salicylates are naturally occurring plant pesticides, manufactured within foods to defend the plant against insect enemies. They exacerbate already existing problems with gut permeability. The focus on salicylate avoidance, therefore, leads to an unsustainable restriction of dietary intake leading to progressive deterioration in health over time. 

While such a diet may be useful in the short term, the focus should be on gastrointestinal repair with probiotics, digestive enzymes and a wide variety of foods in season, and restoration of the normal microbial environment of the gastrointestinal tract.

With some thought about the management of allergy, intolerance and gut permeability, followed by restoration of the joy of eating fresh, organic foods in season with family and friends, the health of most of our patients can be transformed.

Please note: This article is based on the opinions of Dr Mark Donohoe


The information provided on FX Medicine is for educational and informational purposes only. The information provided on this site is not, nor is it intended to be, a substitute for professional advice or care. Please seek the advice of a qualified health care professional in the event something you have read here raises questions or concerns regarding your health. 

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Dr Mark Donohoe

Dr Mark Donohoe is one of Australia’s most experienced and best known medical practitioners in the fields of Nutritional and Environmental Medicine. He has a long history working in the emerging field of “integrative medicine”, and continues to bring orthodox and complementary medicine together in his medical practice. He is a regular guest on the FX Medicine Podcast and in 2019 became the host of FX Medicine's newest podcast series; FX Omics - blending genetics into the modern practice of personalised medicine.