Many people confuse food intolerances with food allergy, but they have different causes. This article is intended to help the reader understand those differences.
If you have a food allergy, your immune system overreacts to a food by producing antibodies called Immunoglobulin E (IgE). These antibodies travel to cells that release chemicals causing an allergic reaction, which can occur rapidly and to minute exposures of the food. We now know that there are also food allergies which do not involve IgE but are still caused by an over-reaction of the immune system. These are called non-IgE mediated food allergy. They tend to be of slower onset, with symptoms taking up to two days to occur, and are often confused with food intolerances.
Food intolerances do not involve the immune system. The symptoms are often much slower to occur, involve larger doses and often happen because the body is unable to process the food effectively. Many food intolerances involve the digestive system. For example, lactose intolerance is a condition where a sugar called lactose is poorly digested and absorbed. Histamine and salicylates within foods can also cause symptoms.
Other causes of food intolerances are less well understood and may involve mechanisms outside the digestive tract.
The symptoms caused by food intolerance are varied. Digestive symptoms may include bloating, diarrhoea, nausea or vomiting. Other signs may include fatigue, sluggishness or joint pains.
As no validated test for food intolerance has been devised, a diagnosis can be extremely difficult to reach. It is important to get expert medical advice, and the doctor should bear in mind that the approach in the case of a child may be different to that taken with an adult patient. Tests used to diagnose food allergy – skin prick tests and blood tests – are not able to diagnose a food intolerance. On our view, over-the-counter testing, or methods suggested on the Internet, should be viewed with great suspicion. However a well-trained healthcare professional may be able to tell from what the patient reports whether the reaction is driven by the immune system or not; and if a food intolerance is suspected, an elimination and reintroduction diet may be suggested. This is where the suspect food is cut out of the diet and later reintroduced to see if symptoms occur.
If you believe you may suffer from a food intolerance, it is important not to restrict your diet without getting expert advice.
Another common cause of symptoms triggered by a food is a psychological aversion to that food, usually the result of an adverse experience earlier in life. For example, if you become sick after eating a food you might have an aversion to that food in the future – even if the illness was not caused by the food. Symptoms of food aversion occur only when the food is knowingly eaten. This is not allergy.
This article has been reviewed by Prof John Warner, early years theme lead for the CLAHRC for north west London (Collaboration for Leadership in Applied Health Research and Care). Other members of the Anaphylaxis Campaign’s expert clinical panel also offered views.
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Disclaimer – The information provided in this Factsheet is given in good faith. Every effort has been taken to ensure accuracy. All patients are different, and specific cases need specific advice. There is no substitute for good medical advice provided by a medical professional.
Published: June 2016
Review date: June 2019