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Food Allergy

Food allergy occurs in around 1 in 20 children and in about 1 in 100 adults. The majority of food allergies in children are not severe, and will disappear with time. However, peanuts, tree nuts, seeds and seafood tend to cause life-long allergies. Some food allergies can be severe, causing life-threatening reactions known as anaphylaxis.

Many people think they are allergic to food, but many are wrong...

The term "allergy" is often misused to describe annoying (but ultimately harmless) symptoms such as headaches after overindulging in chocolate or red wine, or bloating after a milkshake. The result is a widespread impression (in both the lay and medical community) that all food allergies are trivial. Unfortunately, when severe reactions do occur, they are frightening for patients and those involved in their care, and may be life-threatening.

What is allergy?

Underneath the lining of the skin, gut, lungs, nose and eyes are mast cells. These are designed to kill worms and parasites. Mast cells are like Bean bags filled with irritant chemicals including histamine. Mast cells are armed with proteins called IgE antibodies, which act as remote sensors in the local environment. A person allergic to peanut, for example, will have IgE antibodies capable of recognizing the shape of peanut protein (the allergen), in much the same way that a lock "recognizes" the shape of a key. When this happens, mast cells are triggered to dump their contents (such as histamine) into the tissues, causing an allergic reaction.

Symptoms of food allergy are usually obvious

Many allergic reactions are mild and limited to localized hives or swelling. The most serious symptoms are breathing difficulties or a drop in blood pressure (shock), either of which can be life threatening. Anaphylaxis is the most severe form of allergic reaction. Other symptoms include swelling of the face or throat, dizziness, difficulty thinking, an intense sense of fear, a runny or blocked nose, tightness in the chest, wheezing, stomach pains, vomiting or diarrhoea.

Sometimes food allergy may be less obvious

Less common manifestations of food allergy include infantile colic, reflux of stomach contents, eczema, chronic diarrhoea and failure to thrive.

Food allergy can sometimes be dangerous

Anaphylaxis is the most severe form of allergic reaction. It results in potentially life-threatening symptoms such as difficulty breathing, hives, stomach upset or a drop in blood pressure (shock). Deaths from food allergy are rare in Australia. The most common foods causing life-threatening anaphylaxis are peanuts, tree nuts and shellfish.

Allergies to cow's milk, soy, eggs, peanuts and tree nuts are the most common in children.

Food is the most common cause of severe allergy in young children, particularly cow's milk, soy, egg, peanuts, tree nuts and wheat. Peanuts, tree nuts, shellfish, fish, seeds and egg are the most common food allergens in older children and adults, although other triggers such as herbal medicines, fruit and vegetables have been described. Nevertheless, almost any food can cause allergic reactions in older patients.

When does food allergy develop?

One first has to be exposed to something to become allergic to it.
It is currently believed that some infants may become sensitized after birth to small amounts of food passing intact through breast milk.

Identifying the cause

Your doctor will normally ask a series of questions that may help to narrow down the list of likely causes such as foods or medicines consumed that day, or exposure to stinging insects. This approach will also help to exclude conditions that can sometimes be confused with anaphylaxis. Skin or blood (RAST) allergy testing help confirm or exclude potential triggers. Sometimes a temporary "elimination diet" under close medical and dietetic supervision will be needed, followed by challenges to identify the cause. Long term unsupervised restricted diets should not be undertaken, as this can lead to malnutrition.

Unorthodox so-called "allergy tests" are unproven

There are several methods of unorthodox "tests" for food allergy. Examples include cytotoxic food testing, Vega testing, kinesiology, iridology, pulse testing, Alcat testing and Rinkel's intradermal skin testing. These have no scientific basis, are unreliable and have no useful role in the assessment of allergy.

Most people grow out of their food allergy

Most children allergic to cow's milk, soy, wheat and egg will be able to tolerate it by the the time they reach school age, often before. By contrast, allergic reactions to peanut, tree nuts, seeds and seafood persist in the majority (~ 75%) of children affected. When food allergy develops for the first time in adults, it usually persists.

Reactions may be mild or severe, depending on a number of factors:

The severity of the allergy
The amount eaten
The form of the food (liquid is absorbed faster)
Whether it is eaten on its own or mixed in with other foods
Exercise around the same time as the meal may worsen severity.
Cooked food is sometimes better tolerated
The presence of absence of asthma

Can food allergies be prevented?

There are few studies of allergy prevention, and even fewer examining food allergies. Therefore even if you follow the following advice, this may not result in prevention of allergy.

Where possible breast feed your child for at least the first six months
If breastfeeding isn't possible use a partially hydrolysed formula
Don't smoke during pregnancy
Avoid exposure to tobacco smoke in the home
Delay the introduction of solids until the age of 6 months (see weaning guide below).

GUIDE FOR WEANING

From 6 months
Introduce new solid foods one at a time (every one to two weeks) so that allergic or other adverse reactions can be more readily identified:

Rice cereal or rice
Pureed fruit (such as pear or apple)
Vegetables (such as carrot, sweet potato, green beans, celery, cabbage, pumpkin and potato).

From 8-12 months
Introduce other foods one at a time:

Other vegetables (such as broccoli, cauliflower, cucumber and zucchini)
Other fruits (such as bananas, avocado, melons, grapes and stone fruits)
Meat (chicken, veal, lamb)
Wheat products (such as bread, egg-free pasta)

From 12-24 months
Delay the introduction of foods which are more likely to cause allergic reactions until at least 12 months:

Egg and products containing eggs
Fish
Dairy products (other than formula*)

From 24 months
Delay the introduction of foods which can be highly allergenic until at least 24 months (or up to 5 years in children with a family history of allergy to these foods):

Peanuts and tree nuts
Shellfish

* When breastfeeding isn't possible, a suitable formula should be given up until 12 months to ensure adequate nutrition. Even in children with confirmed cow's milk and soy allergy, appropriate formula is available on prescription from your doctor. This formula is usually based on cow's milk that has been processed to break down most of the proteins which cause symptoms in infants who are cow's milk allergic.

Living with your food allergy

Since there is currently no way of "switching off" food allergy, the principles of managing food allergy are to:

Identify and avoid the cause (if possible)
Recognize the early symptoms of an allergic reaction
Know what to do if it happens again

Further information on food allergy and anaphylaxis is provided in accompanying articles in this series and on the ASCIA website http://www.allergy.org.au/

References

1. Kemp AS. Food allergy in children. Aust Fam Physician 1993; 22(11): 1959-633.
2. Sampson HA. Food allergy. part 1: Immunopathogenesis and clinical disorders. J Allergy Clin Immunol 1999, part 1; 103 (5 Pt 1): 717-284.
3. Sampson HA. Food allergy. part 2: Diagnosis and management. J Allergy Clin Immunol 1999; 103 (6): 981-95.
4. Sampson HA. Infantile colic and food allergy: fact or fiction? J.Pediatr 1989; 115: 583-584
5.

Disclaimer:

The content of this brochure has been reviewed by ASCIA members, represents the available published literature at the time of review, is not influenced by its sponsors and is not intended to replace professional medical advice. Any questions regarding a medical diagnosis or treatment should be directed to a medical practitioner.

For further information on allergy, asthma or immune diseasesvisit http://www.allergy.org.au/ - the website ofASCIA is the peak professional body of Clinical Allergists and Immunologists in Australia and New Zealand.