Basically, food allergy reactions involve your immune system, whereas food intolerances do not. Food allergies occur when the body’s immune system wrongly thinks that a food protein is harmful and acts against it, creating Immunoglobulin E (IgE) antibodies. Classic symptoms are an itchy rash, swelling and in some cases vomiting and diarrhoea. The reaction is immediate (within two hours of eating the food) and can be life-threatening, due to difficulty in breathing and collapse (known as anaphylaxis).
There are also food allergies where symptoms can appear up to several days after eating a food. These are a different type of reaction, involving other cells of the immune system, and are known as non-IgE mediated food allergies. Symptoms are usually gut-related (vomiting, diarrhoea, constipation) or skin-related (atopic eczema).
In adults, the most common foods involved in allergy reactions are apples, stone fruit and nuts. Fish, shellfish, legume and seed allergies are also seen.
What types of diagnostic tests are there for food allergies?
There are three diagnostic tests that can be used for food allergies. These are:
- The Skin Prick Test,
- The RAST (Radio Allergo Sorbent Test)
- Oral food challenge done under strict medical supervision where medical facilities and resuscitation equipment are available.
These three tests are evidence-based and performed by registered health professionals in alongside a full clinical history. These tests are only for IgE-mediated food allergies (the “immediate reaction” type).
Unlike immediate food allergy, delayed type food allergies do not involve the production of IgE antibodies, and there are currently no diagnostic tests for this type of food allergy. Dietary exclusion plays an important role in the diagnosis of this kind of allergy. For any suspected food allergy, specialist input is required for diagnosis and management.
What about food intolerances?
Food intolerances do not involve the immune system. This term describes a number of unpleasant reactions people may have after certain foods, and may vary widely for different people. If you’re intolerant to a food, the symptoms usually develop more slowly than with a food allergy. It can take hours or sometimes days for symptoms to appear and how severe these are usually depends on how much of the food you’ve eaten. Symptoms are usually related to your gut, such as diarrhoea, constipation and abdominal pain, as well as skin conditions such as eczema.
If you think you may have a food intolerance, see your GP. You may need further tests to rule out other conditions (such as coeliac disease) and your GP may refer you to a dietitian for specialist advice.
It is important to bear in mind that your symptoms may be part of a bigger picture, rather than down to individual foods.
Beware of food intolerance tests
THERE ARE NO AVAILABLE TESTS FOR FOOD INTOLERANCES (with the possible exception of the hydrogen breath test for lactose intolerance).
However, there are many companies who advertise tests which claim to diagnose food allergies and intolerances.
These include the IgG blood test, Kinesiology, hair analysis, the Leucocytotoxic or Cytotoxic blood test, the Pulse test and the Electrodermal (or “Vega”) tests.
All of these tests should be AVOIDED as they have no scientific basis at all, and results have been shown to be no better than chance. They often suggest a list of multiple foods to be avoided, risking an unbalanced diet and nutritional deficiencies. They are also usually quite expensive! Commercially available tests are NOT recommended by the British Dietetic Association or by the NHS.
What to do instead
If a food allergy is suspected, you should seek medical advice and discuss the use of evidence-based, conventional allergy testing. Alternative allergy testing should be avoided as it has no scientific basis.
If you suspect a food intolerance, then a registered Dietitian such as myself can explore this with you, and use a structured food exclusion and re-introduction procedure to help you to identify any problem foods, whilst still ensuring a well-balanced nutritional intake which will fit in to your lifestyle.
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