FOOD ALLERGY

What is it?

Food allergy results from the presence of IgE antibodies. Contact with certain foods stimulate an allergic reaction.

The definition of food allergy adopted by the Royal College of Physicians and the British Nutrition Foundation is:

a form of food intolerance in which there is evidence of an abnormal immunological reaction to the food.

The most common allergy causing foods are dairy products, fish, nuts and wheat, although almost any food can be implicated.

Who gets it?

Food allergies are common in childhood and also limit the diet of many adults.

A substantial number of adults restrict their diet in the belief that particular items of food upset them. Possibly even more children have their diet limited in some way because they are perceived to be intolerant to one or more items of food.

What are the symptoms?

Food allergy can involve any system of the body, although it most frequently presents with gastro-intestinal symptoms. Colic and abdominal distension may be manifestations of food allergy. Recurrent bleeding from the gut mucosa is now recognised as a sign of allergy to cows' milk.

Uurticaria is a feature of anaphylaxis with immediate onset. Food allergy may cause an exacerbation of eczema.

Some children with recurring rhinitis may be food allergic.

The most dramatic consequence of food allergy is immediate anaphylaxis. The sudden onset of extreme distress, perhaps associated with swelling of the tongue, glottic spasm or wheezing, with a generalised urticarial rash, and accompanying hypotension and sensation of imminent demise, is extremely frightening. The patient should be educated to anticipate and manage any recurrence of the life-threatening experience.

What tests will the Doctor want to do?

The history will often identify the offending food.

When food allergy is strictly defined, the mechanism is usually IgE mediated. Therefore, the affected individual will have an increase in specific IgE to the offending foods. This may be revealed by skin-prick tests.

Alternatively, specific IgE may be measured by the more protracted and less sensitive method of RAST. This measures specific IgE antibody in serum, and the correlation with skin-prick testing is close.

The definitive test of food allergy is claimed to be the double-blind, placebo-controlled, food challenge. The food is usually administered concealed in capsules and the patient is carefully observed for any reaction.

What is the short-term treatment?

The only real treatment of food allergy is avoidance of the offending foods.

The importance of a dietician in the management of food allergy cannot be overemphasised to ensure that required nutrients are not omitted from the diet.

Will I need long-term treatment?

Many food allergies, particularly those occurring early in infancy, are of limited duration. The physician and dietician can advise how and when previously offending foods can be introduced into the diet.

Where food produces a major reaction or anaphylaxis, the individual, parent or other carer should have available, and know how to administer, adrenaline 1:1,000, 0.25-0.5 ml subcutaneously, repeated if necessary after 10-15 minutes. Some individuals with multiple and ill-defined food allergy may need to use their adrenaline on many occasions. The majority will never require it, and their greatest problem will be to remember to keep the adrenaline in date, as it has a shelf-life of only 9-18 months.

At present, immunotherapy, or desensitising, has not been established as a safe or effective option for the treatment of food allergy.