Food allergy and intolerance

Food intolerances which do not produce classic allergic symptoms are controversial in the medical world. Official figures suggest that only 2 per cent of adults, and up to 8 per cent of children, have one of the five medically accepted food allergies or intolerances, but as many as one in three people recognises that he or she cannot eat certain foods without developing problems.

The accepted types of food allergy are:

Severe anaphylactic reactions ? in which life-threatening symptoms such as falling blood pressure, breathing difficulties and tissue swelling can be triggered by eating certain foods, notably peanuts.

Hypersensitivity ? in which a widespread, itchy rash (urticaria), eczema, asthma, vomiting, abdominal pains or diarrhoea can occur in some people after eating certain foods, such as strawberries, eggs or shellfish.

Food sensitivity ? in which, for example, chemicals found in chocolate, cheese or red wine can trigger migraine.

Lactose intolerance ? those who do not produce enough lactase cannot digest lactose and suffer bloating, abdominal pain and diarrhoea.

Gluten intolerance ? in which sensitivity to gliadin (a protein found in wheat and some other cereals) causes bloating, abdominal pain, bulky stools, malabsorption and weight loss.

Food and the immune system

Substances that trigger idiosyncratic allergic reactions are known as allergens. The traditional way to test for allergies is to look for the presence of a type of antibody known as immunoglobulin E (IgE), which binds to the walls of immune cells in the skin, lining of the stomach, lungs and upper respiratory tract and triggers the release of immune mediators. It is these mediators, such as histamine, that are responsible for the classic physical symptoms of allergy such as itching, swelling, rash and wheeziness. Almost anything can act as an allergen, but the most common are pollen, moulds, exhaust fumes and other environmental pollutants, and, among the “indoor factors”, smoking, viral infections, foods, dust mites and domestic pets.

Many researchers now believe another type of antibody ? IgG ? is responsible for the less severe symptoms associated with food intolerance, such as excess mucus production, dry scaly skin, headache and irritable bowel syndrome.

IgG food intolerance testing acts as a short-cut to a traditional food elimination diet, whereby the subject eats nothing but a single meat, a single source of carbohydrate and a single fruit, and drinks spring, mineral or distilled water for up to three weeks, before the eliminated foods are reintroduced one by one, usually at three day intervals, to see which triggers a recurrence of symptoms.

Anti-food IgG antibodies can be detected in a pin-prick sample of blood using an immune ELISA test, in which a blood sample is exposed to up to 113 different food antigens and the strength of any antigen-IgG reactions measured. This gives an indication of the severity of the food intolerance, and of which foods should be avoided. An audit conducted on behalf of Allergy UK shows that around 52 per cent of allergy sufferers who alter their diet significantly as a result of the test experience a reduction in long-term symptoms, and more than 70 per cent of these report continued health improvements one year later. Interestingly, many people have managed to re-introduce problem foods a year or two after their symptoms have gone without further ill effects.

A double-blind, randomised, placebo-controlled clinical trial at the University of York has shown the benefit of this approach in people with irritable bowel syndrome. Researchers investigated the effectiveness of a three-month exclusion diet, based on the YorkTest FoodScan, in 150 people with irritable bowel syndrome. Volunteers were randomised to receive either a diet excluding all foods to which they had IgG antibodies, or a sham diet excluding the same number of foods but not those to which they were sensitive. Symptom severity and quality of life were recorded at the beginning and at the end of the trial. The results showed that the true diet was significantly better than the sham diet in reducing symptom severity scores, and the researchers concluded that a clinically significant improvement can be achieved in some patients with IBS using a food elimination diet based on IgG food antibodies.

Dr Sarah Brewer is a member of the British Society for Allergy Environmental and Nutritional Medicine, Tel: 0906 3020010, whose members are doctors with a specific interest in this field.

She is the medical director of YorkTest Laboratories, who provide the FoodScan IgG test and other home testing kits www.homeinonhealth.com

Allergy UK  Helpline: 020 8303 8583 www.allergyuk.org