It seems that our interest in food and our digestion has never been greater than it is now.
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 resulting from either a food intolerance (often called sensitivity) or a food allergy. While more and more of us are jumping to the conclusion of having several intolerances leading us to exclude many common staple foods, true food allergies are rare (the best estimates suggest less than 4 % of UK adults), yet have somehow become a catch-all self-diagnosis for adverse food reactions.
The distinction between food allergy and food intolerance can be confusing and it is easy to see where the misunderstanding stems from; both food allergies and food intolerances involve well… food. There is a muddled distinction between their many shared unpleasant symptoms: bloating, nausea, stomach pain, diarrhoea, vomiting or even rashes joint pain and headaches.
Why does it matter?
Well, shared symptoms are where the similarities end. While there is no doubt allergic reactions can be life-threatening, excluding foods without professional guidance can feel unmanageable and leave you miserable, mask other problems or anxieties and out you at risk of nutrient deficiencies.
Digestive system vs. immune system
A food intolerance is a response of your digestive system to a food. Unlike a food allergy, intolerances do not involve the immune system and generally occur because your body cannot properly break down food properly during digestion or the food irritates your digestive tract. Food intolerances are broadly categorised as physiological (e.g. due to a true enzyme deficiency in the case of lactose), functional (such as irritable bowel syndrome in response to dietary FODMAPs) or pharmacological which is sensitivity occurs to food additives or naturally occurring components of foods (e.g. sulfites). Intolerances can also be psychological (in the case of an eating disorder) or in some cases foods trigger adverse reactions without a defined cause (known as idiosyncratic). Eating a food that you are intolerant to could leave you feeling miserable and uncomfortable but in most cases, people can eat small amounts of the food without causing problems.
Unlike food intolerances, allergies are caused by our immune system. They are the result of our normal immune defences, usually reserved for fighting infections, going awry and inappropriately react to a harmless component of food.
So how do we develop a food allergy?
Normally our digestive system interacts with the food that we eat without generating an immune response. This is because our immune system has switches in place to recognise that food is harmless and not an infection. It remains switched off and instead tolerates food components because they pose no threat. This is termed ‘immunological oral tolerance’. So with this oral tolerance in place, food is well tolerated by the immune system.
So how do we become allergic?
Sometimes a failure to develop or a breakdown in oral tolerance leads to our immune system mistakenly seeing a food as a threat and becomes sensitised to the food. It responds by releasing a particular type of antibody known as immunoglobulin E (IgE) which sticks to Mast cells lining our digestive tract. Here they are poised and ready to mount an inflammatory reaction when the offending food is next eaten. Once we have an allergy, the symptoms can run the gamut from annoying to life-threatening whole body reaction known as anaphylactic shock. Although we don’t know the reasons for the breakdown in oral tolerance, it is an area of intense research. Allergies tend to run in families so we know genetics are one culprit in the development of allergies. But elements of our lifestyle and environment play a considerable role in manipulating our oral tolerance to the things we eat.
Diagnosis and treatment
With such a broad range of potential triggers and causes, diagnosing any adverse food reactions is complicated. Unlike food intolerances, there are VALID food allergy tests, one key test includes an IgE blood test in the context of a medical history and followed by double-blind placebo controlled food challenge. Food allergies can be life threatening and normally require strict avoidance so definitely see your GP if you suspect this. Oral antihistamines are used to treat mild cases and injectable adrenaline for severe cases. Desensitisation (or immunotherapy) involves giving gradually increasing doses of extracts of the offending food as an injection or under the tongue and is currently only being tested and trialled under research conditions because of the risk of anaphylaxis.
While food intolerance is a real condition that deserves to be taken seriously, they are more problematic to diagnose. The underlying mechanisms are broad and not well understood so there are no reliable tests available (with the exception of that for lactose). However, that hasn’t stopped them being marketed, though. From applied kinesiology to IgG blood tests, there is a growing number of commercial food intolerance tests available all with NO evidence of diagnostic validity. Consequently self-willed intolerances are growing.
While most of us can eat whatever we want with no ill effects providing we eat it in moderation. Focussing so heavily on unusual ‘reactions’ to foods risks that message getting lost. Much of the ‘science’ of diagnosing food intolerances is driven by reported increases in blood IgG antibodies to certain foods. While intolerances are non-immune, confusingly, this type of test does have analytical validity (i.e. it is a valid method of testing for changes in IgG antibodies in the blood) but lacks clinical validity (having a positive test does not have any correlation to clinical status). In fact, unlike IgE antibodies which are the cause of a true allergy, having IgG antibodies in our blood is actually an indicator of immunological oral tolerance to food, which may in fact be protective in preventing us from responding to that food.
If a true allergy is ruled out, an intolerance can often be identified with guidance of a healthcare professional by cutting out the suspect food, waiting for symptoms to improve and then gradually reintroducing while monitoring the symptoms. A food diary, to correlate what you are eating with symptoms, is useful. Cutting out the food completely may not always be necessary and only a very small proportion of food intolerances are lifelong so most can be managed with proper guidance.
What you need to know
A food allergy is
- an adverse response by your immune system.
- usually comes on suddenly.
- triggered by a small amount of food
- happens every time you eat the food regardless of how much or frequently
- can be life-threatening
A food intolerance is
- not mediated by your immune response
- usually comes on gradually
- often relates to the amount of food
- often relates to the frequency of eating the food
- is not life threatening