PUBLISHED: 16:07 01 September 2008 | UPDATED: 15:25 20 February 2013
The facts about food allergies and food allergy testing
There is no doubt that allergies and intolerances of all types have been on the rise, and around one third of us will visit a doctor about an allergy at some point.
The wrong information and advice can be potentially harmful, so it is important to understand the benefits and limitations of any testing or treatment you choose.
An allergy is essentially an immune system response to a substance, which causes symptoms. The most serious type of food allergy is immediate hypersensitivity, which occurs as a result of IgE antibodies, within two hours of contact with the food. Symptoms can range from a rash or facial and mouth swelling, through to wheezing and full-blown anaphylaxis, a life-threatening situation.This type of allergy can be tested with an IgE blood test fairly reliably; however, the medical history is the most important factor.
Increasingly, it is being recognised that IgE or immediate hypersensitivity is not the only type of food reaction. Other immune mechanisms can also result in symptoms. Such reactions are sometimes known as intolerance, or more recently 'non-allergic food hypersensitivity'. These reactions can be delayed, and they have been attributed to a wide range of symptoms including: rash; abdominal pain; diarrhoea; constipation; nausea; indigestion; headaches; fatigue; and so on.
Many people with asthma, eczema, urticaria and migraine also find that certain foods can precipitate their symptoms. The difficulty is that there are, as yet, no reliable tests for these reactions, and the symptoms could be due to a number of different causes other than intolerance. IgE antibody tests have recently been used, but cannot be wholly relied upon. There are also many tests offered which are considered to lack a convincing evidence base, including: applied kinesiology, hair analysis, leukocytotoxic tests and vega testing. Patch or skin prick testing is not useful for food allergy, though can be very useful in other types of allergy.
I have seen patients who, for many years, have been eliminating a very wide range of foods from their diet because of unreliable tests. The only reliable way to identify food intolerances is through a formal elimination diet, which requires supervision and expert interpretation. There are also less formal low-allergen diets which can be used, with sequential reintroduction of foods, depending on the situation.
Most people with food allergies and intolerances simply omit the offending food. If there is just one food, this is practical, but if there is a wide range of foods from which you experience symptoms, it can be worth considering allergy desensitisation. Many people find that intolerance symptoms are worse when they are under stress, so it is important to address this. Improving the function of the bowel can also help, as can treating nutritional deficiencies.
Make sure that any practitioner you choose is qualified, and has professional indemnity insurance and membership of a professional regulatory body. You may want to ask how long their training was, and whether their training qualifies them to judge whether symptoms could have a cause other than allergy or intolerance. Never agree to a barrage of tests which are not accompanied by detailed medical history taking, and ask about the evidence for, and reliability of, the tests which you are having done. If you are being advised to avoid a large number of foods, your nutritional balance should be considered very carefully, and should only be continued long term if symptoms return on several reintroductions of that food.
Allergy medicine is a very complex speciality. People often ring our clinic to ask if we do allergy tests. Although they are expecting a simple yes or no answer, I always take a deep breath before saying "yes, but...". They are only a part of a range of tools used in the assessment and treatment of allergies and intolerances, and need to be considered in the proper context.
This article is not a substitute for individual medical advice; anyone who has a medical condition, is pregnant, under age or who takes medication should check with their medical practitioner before taking any supplements or medication.
Dr Nicholson has trained in General Practice, Allergy, Nutritional and Environmental Medicine and in Complementary Medicine. She is a partner at The Centre for Balanced Medicine in Chudleigh, 01626 854743, www.balancedmedicine.co.uk.