Food allergies

03 August 1999

Surveys show about 20% of all adults believe they have food allergies. When a full evaluation and diagnosis has been performed, however, only 1 to 2% of people suffer from allergies. Because their immune systems are not yet fully developed, young children are likely to be more affected than adults.

What is food allergy?

A food allergy is an adverse reaction to a food or food component that involves the body's immune system. Other adverse reactions to foods involve the body's metabolism but not the immune system. These are known as food intolerance and can include reactions to food poisoning and enzyme deficiencies, which prevent proper digestion of certain food components such as lactose (milk sugar).

A true allergic reaction involves three primary components: Contact with the food allergen (a reaction provoking substance, usually a protein) Increased Immunogloblin E (IgE - an antibody in the immune system that reacts to allergens) Mast cells (tissue cells) and basophils (blood cells) which when in contact with IgE antibodies release histamine or other substances causing allergic symptoms.

When the body's immune system recognises an allergen in a food, it produces antibodies to block this foreign invasion. At the same time, the body exhibits physical symptoms such as swelling of the lips, stomach cramps, vomiting and diarrhoea, hives, rashes or eczema, a running nose and breathing problems. A more serious but rare reaction is anaphylactic shock which is life threatening and requires immediate medical attention.

Allergic reactions to food are rare but may be caused by just about any food. ILSI (the International Life Sciences Institute) has categorised a list from a CODEX proposal of recognised food allergens: 'Critical' allergen: peanut 'Major' allergens: cereals containing gluten (oats, wheat, barley, rye spelt), shellfish (excluding molluscs), eggs, fish, soya, milk protein, tree nuts (almonds, hazelnuts, pistachios, pecan nuts, pine kernels, brazil nuts, cashew nuts, macadamia nuts) and sesame seeds. 'Minor' allergens: buckwheat, celery, fruits with stones (apricots, cherries, peaches and plums).

What to do when food allergy is suspected?

If an allergy to a food is suspected, it is best to avoid eating that food until a doctor is consulted to establish the causes, as factors such as one's medical condition may also produce similar symptoms. If however, the symptoms are associated with a food allergy, evaluation by an allergist is essential. The only reliable diagnosis of a food allergy is a combination of skin tests (application of the suspect food to the skin) and double blind oral challenges (eating food or a placebo in the form of a capsule while both the patient and the doctor are unaware of either capsule's contents).

Living with a food allergy

Presently, no adequate treatment exists to cure food allergies permanently. Once diagnosed, the only effective treatment is the so-called 'avoidance' diet -removing the food in question from a person's diet. We should be aware that the removal of foods, especially staple foods, may require medical advice because of potential dietary imbalances, particularly in children.