Food as an invader

If you were to lay your small intestine flat on the ground, its surface area would equal that of a small football pitch! This barrier is the gateway between your body and the outside world – your ‘inner skin’. Only food substances on the guest list, such as vitamins, minerals, amino acids from digested proteins and so on are allowed through – at least in theory. The police force guarding your inner gateway is your immune system.

A food allergy develops when your immune system treats a food you’ve eaten as an invader, not as a friend. This can happen for a number of reasons. In some cases, the food may contain a kind of protein that the body doesn’t like. For example, many people’s immune system will react to gliadin, a protein abundant in wheat, rye and barley. This can be an inherited condition.

In most cases, food allergies develop when the inside lining of the digestive tract becomes permeable or abnormally ‘leaky’ because of antibiotic use, excess alcohol consumption, gut infection, excessive physical or emotional stress or other reasons. The leakiness enables food proteins to’gatecrash’ your bloddstream and immune system will react to these outright strangers by attacking them.

This reaction happens on a number of fronts. Your immune system attaches the equivalent of handcuffs to it, called antibodies; attacks and destroys it with specialised cells such as phagocytes; and releases all sorts of reactive chemicals, such as histamine, which also cause many of the symptoms we experience as allergic reactions.

The two most common type of allergic reaction, namely the immediate-onset and much more common delayed-onset, involve two different families of antibodies, called IgE and IgG respectively. The ‘Ig’ stands for immunoglobulin, while ‘E’ and ‘G’ is the type or family of immunoglobulin.

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