It’s normal that every now and then, all of us might suffer some sort of digestive discomfort after eating. This might range from trivial, infrequent and frustrating to restrictive and sometimes frightening. Any abnormal reaction occurring after eating food is called an adverse food reaction. It can be the result of either a food intolerance (often called sensitivity) or a food allergy. It seems more and more of us are quick to jump to the conclusion that we are suffering from some kind of adverse food reactions leading us to exclude many common staples from our diet. So, what’s really going on? Is it an allergy or an intolerance? And more importantly - why does it matter?
True food allergies are rare but potentially deadly, triggered even by trace amounts. Despite somehow becoming a catch-all self-diagnosis, estimates suggest <4 % of UK adults have true food allergies. Unlike intolerances, allergies are caused by our normal immune defences, usually reserved for fighting infections, go awry. Instead of ‘tolerating’ food and remaining switched off, this safety mechanism fails (1). Immune cells release special antibodies (called IgE) that stick to Mast cells lining our digestive tract where they are poised and ready to respond when the offending food is next eaten. Once we have an allergy, the lifelong symptoms run the gamut from annoying hives and swelling to anaphylactic shock, a life-threatening whole-body reaction.
While we can't say for sure why allergy rates are increasing. Genetics are one culprit but they may be a by-product of modern lifestyles: pollution, diet, vitamin D, exposure to microbes. The "dual allergen exposure" theory posits food allergy development is down to how and when our immune system ‘sees’ the food (3). Oral tolerance to allergens can be broken through skin exposure to foods (2). Breastfeeding transfers antibodies to the baby’s gut that teach the immune system to tolerate foods (2). Avoiding certain foods in early life actually doesn’t pay off in preventing food allergies since early exposure is actually protective (4).
A food intolerance is a non-immune response of your digestive system to a food and easy to confuse with allergies (5). Unlike a food allergy, intolerances are generally occur because your body cannot properly break down food properly or the food irritates your digestive tract. Broadly categorised as physiological (e.g. lactose enzyme deficiency), functional (e.g. irritable bowel syndrome in response to FODMAPs) or pharmacological which is sensitivity occurs to food additives or components of foods (e.g. sulfites) (8). Intolerances can also be psychological (e.g. eating disorder) or in some cases without a defined cause (idiosyncratic). Self-diagnosis of intolerances are common with up to 20% of the UK population estimated to have altered their diet to exclude foods based on a perceived ‘intolerance’. One study found 34% of parents reported food allergies in their children but only 5% were found to have an allergy (6). Implementing these unnecessarily restrictive diets are actually leading to malnutrition (7).
There are VALID evidence-based tests for IgE-mediated allergies (11) involving a skin prick challenge in conjunction with a detailed clinical history, followed by double-blind placebo-controlled challenge. Food allergies can be life threatening so these tests need to be performed by registered health professionals in medical facilities. Normally treatment of a true allergy is complete exclusion. Oral antihistamines are used to treat mild reactions and injectable adrenaline or resuscitation for severe cases. Immunotherapy is sometimes an option but is currently tested and trialed under research conditions because safety risks (12).
Food intolerances are real and deserve to be taken seriously but more problematic to diagnose. The underlying mechanisms are broad and not well understood. To make matters worse, the use and marketing of non-valid tests - all with NO valid evidence - is growing fast (11, 13, 14). Intolerances are non-immune, but confusingly much of the diagnostic ‘science’ is driven by reported increases in IgG antibodies. IgG testing does have analytical validity (i.e. valid method to check for IgG) but lacks clinical validity. In fact having IgG in our blood is actually an indicator of food tolerance not intolerance.
Intolerances are confirmed by cutting out suspect food(s), observing symptoms followed gradual monitored re-introduction. Short-term removal of offending food(s) may give immediate relief, long-term exclusion of foods without professional guidance can feel unmanageable, mask other problems or anxieties and put you at risk of nutrient deficiencies. What's more, a developing concern is that a significant proportion of people who embark on highly restrictive diets because of a perceived food intolerance represents a newly described form of eating disorder: Avoidant/Restrictive Food Intake Disorder (ARFID) (9, 10). Diagnosing an intolerance is meticulous and time consuming. But with supervision of a registered nutrition professional, you can ensure a well-balanced diet through the process. Few food intolerances are lifelong and in most cases people can eat small amounts without causing problems.
A food allergy is...
an adverse response by your immune system
something that usually comes on suddenly
triggered by a small amount of food
something that happens every time you eat the food regardless of how much or frequently
something that can be life-threatening
A food intolerance is...
not mediated by your immune system
usually comes on gradually
often relates to the amount of food
often relates to the frequency of eating the food
is not life threatening
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2) Ohsaki, A., Venturelli, N., Buccigrosso, T. M., Osganian, S. K., Lee, J., Blumberg, R. S., & Oyoshi, M. K. (2018). Maternal IgG immune complexes induce food allergen-specific tolerance in offspring. The Journal of Experimental Medicine, 215(1), 91–113. https://doi.org/10.1084/jem.20171163
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