Food Allergy & Oral Tolerance

The UK has some of the highest prevalence rates of allergic conditions in the world, with ‘prevalence’ meaning the number of cases that are present at a given time. AllergyUK estimates that a staggering 44% of British adults now suffer from at least one allergy, and the number of sufferers is on the rise. Almost half of sufferers have more than one allergy. Interestingly seven times as many people were admitted to hospital with severe allergic reactions in Europe in 2015 than in 2005. Of those allergies many are to environmental allergens (things to which one could be allergic) including pollen, dust and pets, but a small subsection are to common food allergies.

What Is An Allergy?

An allergy is the tendency for an individual’s immune system to respond excessively to the presence of normally harmless substances, such as pollens, house dust mites, and the certain foodstuffs. Whilse in most people these substances (allergens) pose no problem, in allergic individuals the immune system identifies them as a ‘threat’ and produces an inappropriate response which would ordinarily be reserved for genuine pathogens such as bacteria or foreign objects.

Risk Factors For Food Allergies

A plethora of risk factors are proposed to influence food allergies, including sex (male sex in children), race/ethnicity (increased among Asian and black children compared with white children), genetics (familial associations, and specific genes), vitamin D insufficiency, dietary fat (reduced consumption of omega-3-polyunsaturated fatty acids), reduced consumption of antioxidants, increased use of antacids (reducing digestion of allergens), obesity (being an inflammatory state), increased hygiene, and the timing and route of exposure to foods (9). Allergies are also extremely common in very young children who will typically grow out of them by age 5.

Some of these factors might provide opportunities for prevention, or treatment, of allergies (9). It’s useful for us to know this because we coaches can educate our clients around the importance of vitamin D, omega 3 and antioxidant intake (through fruits and vegetables), and weight management in order to improve a number of health metrics – potentially including the reduction of allergic reaction severity.

Oral Tolerance (The Process Involved In Normal Immune Reaction)

While we now have a basic understanding of what an allergy is, and the pathophysiology that occurs (such as antibody and histamine production), it is also important we understand the physiology of all of this. What is a normal immune reaction to food? And what reduces the risk or prevents an allergy from occurring?

Oral tolerance is the state of local and systemic immune unresponsiveness. A comparable but more local process also regulates responses to friendly bacteria in the large intestine which, of course, would ideally create no response whatsoever. Allergy researchers note that “…oral tolerance appears to prevent intestinal disorders such as food allergies, celiac disease, and inflammatory bowel diseases (2).”

This simply means that ‘oral tolerance’ is the necessary process we need to maintain to minimise our risk of ‘reacting’ inappropriately to food. Oral tolerance occurs when:

1. We have adequate gastrointestinal enzymes digesting our food effectively, (more on this when we discuss food intolerances),
2. The physical barrier of the intestine is intact
3. We have proper immune surveillance of food antigens (13).

While point 1 is partly dependent on point 2, point three is a relatively independent process and is partly influenced by our gut microbiome. Changes in our microbiome have been associated with allergies, with several lines of evidence supporting protection by specific bacteria and their products, likely through sustaining intestinal Treg populations. Treg cells are are a subpopulation of T cells (which is a type of immune cell) that modulate the immune system, maintain tolerance to self-antigens, and prevent autoimmune disease. As such an impaired microbiome that results in a reduced Treg cell population leads to poor modulation of the immune system and the subsequent risk of pathological immune activity.

Let’s take a step back break this down.

Oral tolerance is the term describing the immune system’s ability to tolerate both food, and the bacteria that resides in our gastrointestinal tract. Oral tolerance is dependent on a healthy and diverse microbiome (for healthy Treg cells and thus immune system), and an intact gut barrier.

The reason for the importance of an intact gut barrier in maintaining oral tolerance is that there is an element of ‘the dose makes the poison’. During healthy digestion only a small amount of food antigens (things to which you could be allergic) are taken up into the rest of the body. With increased intestinal permeability (sometimes known as ‘leaky gut’) we get an increased uptake of food antigens, creating an immune-mediated inflammatory response.

Nutritionally a key aspect of managing a healthy microbiome is an adequate dietary fibre intake, ideally from whole plant-based foods. These contain the probiotic substrates needed to ‘feed’ gut bacteria and keep your digestive system healthy. Other steps include adequate vitamin D and A intake, minimizing lifestyle stress and proper sleep. From this we can start to understand why allergies are on the rise – with the use of antibiotics (which dysregulate microbiome diversity and density), poor dietary habits including limited fibre intake and repetitive food choices, chronic stress and lack of sleep all influencing the healthy and integrity of our gut microbiome and gut barrier, resulting in an increased allergy risk on top of that which would be present due to genetic factors.

Listen to Episode 6 of The Alex Manos Podcast (click here) to hear Functional Medicine Practitioner Robyn Puglia go in to further detail around food allergies and autoimmune disease.



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