Family doctor

What is a food allergy?

Food allergy is the result of an immune reaction by the body to normally harmless substances in foods. These substances are called antigens or allergens. For a variety of reasons some children's immune systems release antibodies and histamines in response to these allergens.

Reactions may occur within minutes of eating the allergen (Type 1 hypersensitivity), or be delayed up to 48 hours after consuming the food (Type 4 hypersensitivity).

The release of histamines in the body may cause a variety of symptoms:

Type l - occurs within 60 minutes of exposure. Reactions include:

• Abdominal cramps
• Colic
• Vomiting
• Diarrhoea
• Difficulty in breathing
• Low blood pressure, fainting
• Itching (rashes, welts, swelling, hives)

Type 4 - occurs within hours or days of exposure and may be dependent on the amount of allergen consumed. Reactions include:

• Eczema, dermatitis
• Asthma, hay fever, sinusitis, persistent cough, runny nose, ear infections
• Constipation
• Sweating
• Poor appetite, feeding difficulties
• Behaviour and mood changes, rocking, hyperactivity, poor attention
• Sleep problems

Why do allergies occur?

Typically a reaction occurs because a foreign protein (antigen or allergen) is absorbed from the digestive system into the blood. The production of antibodies and histamines are the body's protective mechanism against these.

Children may inherit tendencies towards allergies. The stronger the family history of allergies e.g. asthma, eczema, hay fever - the earlier the child is likely to develop these.

Sensitivity may also develop when the digestive system of the child is immature and comes into contact with new foods and substances.

Allergy prevention

Where there is a known family history the mother should avoid suspected foods throughout her pregnancy and breastfeeding. To avoid the possibility of nutrient deficiencies she should consult a registered dietitian for dietary guidance.

Breastfeeding exclusively up to the age of six months helps to reduce the possibility of allergies developing for any child. For infants requiring bottle feeding before the age of six months, look for hypoallergenic (low allergy) formulas.

Care must be taken with all infants at the introduction of solids. Because the digestive system is very immature it may allow the absorption of foreign proteins which would normally not be allowed to pass into the blood system.

Do not be in a hurry to start feeding different foods. Introduce one new food per week. All foods should be cooked. The least allergenic foods to start with are rice, pears, yellow and root vegetables.

By the age of 8 to 9 months start to introduce:

• Oats
• Green vegetables
• Unprocessed meat and chicken

From 9 to 12 months

• Wheat
• Soy
• Dairy e.g. plain yoghurt, cottage cheese, goats milk products
• Beans, lentils, chickpeas
• Tomatoes
• Citrus and other fruits

From 18 to 24 months

• Eggs
• Berry fruits

From age 3

• Peanuts, nuts
• Fish and shellfish

Avoid processed meats e.g. ham and bacon, also chocolate, spices, colourings, artificial flavourings, fruit drinks and juices. Be cautious with cow's milk and cheese, pork, beef, citrus fruits, and all gluten containing grains (e.g. wheat and rye; rice and millet are gluten free).

Suspect a food allergy? Here's what to do:

Your health practitioner can arrange for various skin and other food sensitivity tests. These are not considered to be completely reliable however and may return false negative and false positive results in some cases. Do not depend on them completely to alter your child's diet.

Careful elimination of the suspected foods give the best results and allow for less reduction of important nutrient containing foods. The advice of a registered dietitian is important to prevent any nutrient deficiencies developing.

Suspected foods should be removed from the diet for four to six weeks then reintroduced while carefully noting any recurrence of symptoms. Introduce suspected foods one week apart to allow for delayed reactions.

Further information:

For advice and support contact your local Allergy Awareness Association. Registered dietitians can provide dietary guidelines, food substitute guidance, packaged and takeaway food "free from" lists, and food additive lists.