Food allergy, preservatives and Asthma
	One of the marvels of the human body is that it can defend itself against harmful invaders such as viruses or bacteria. But sometimes the body's defences (immune system) are too aggressive, and harmless substances such as house dust, pollen and certain foods are mistakenly identified as dangerous.

Which foods cause allergic reactions?

Few foods can trigger allergic reactions. Among the most common are cow's milk, eggs, wheat, soya, peanuts and fish. Allergic reactions to food may occur anywhere in the body, but usually in the digestive system, the skin, and occasionally in the nose and lungs - the places where the special immune system cells are stationed to fight off invaders that are inhaled, swallowed or come in contact with the skin. In most cases, foods cause reactions in allergy-prone individuals if they are swallowed. In certain people, food may cause reactions such as asthma if inhaled. For example, flour can cause asthma in bakers who are allergic to this substance.

How common in asthma in persons with food allergy?

Food allergy is generally uncommon. It affects about 1% of children (1 in 100) and 0.05% of adults (5 in 1000). Skin symptoms such as eczema and hives and symptoms of the digestive tract such as stomach cramps, vomiting and diarrhoea are more common in food allergy than asthma. Asthma may develop in less than 5% (5 in 100) of individuals who suffer from food allergy. In general, inhaled allergens such as house-dust mites, cat fur and pollen are more likely to trigger asthma than foodstuffs.

Diagnosis

The diagnosis of food allergy is easy when the adverse reaction occurs soon after ingestion of an uncommonly used food item but more difficult if the reaction occurs several hours or days later, or if commonly used food is involved. In this situation a variety of diagnostic tests (skin prick test, RAST) can be used. At present there are no definite and reliable tests to diagnose food allergy. The final mainstay of diagnosis is the demonstration of the relief of symptoms on removal of a given food item and recurrence of symptoms on its re-introduction (eliminate-challenge testing).

How is asthma due to food allergy treated?

The most effective approach to treating asthma related to food allergy is to avoid the offending food(s) in the first place. However, identifying the offending food may not be easy or it may not be possible to completely avoid it. In this situation, medication to control asthma must be taken by the patient. A number of new and effective medications are available to treat asthma and food allergy.

PRESERVATIVES

Are additives safe?

The vast majority of additives and preservatives appear to be safe. They have been tested by many laboratories throughout the world before being used in foods. However, individuals may be "sensitive" to various additives and preservatives. Government agencies control which substances, and the amounts, which may be used in the production of food. In South Africa, the Department of Health, controls the use of additives and preservatives.

Who do they affect?

In the majority of cases, individuals with some form of allergy, e.g. asthma, hay fever, urticaria etc will be affected by these substances. A few additives and preservatives can affect non-allergic people. Some of these substances cause more reactions than other. For example, reactions to sulphur dioxide and sodium benzoate occur more commonly in asthmatics than reactions to the colourant tartrazine.

What additives result in side effects?

We cannot hope to cover all the additives and preservatives that may result in reactions, but these are some of the more important ones.

• Preservatives
  Sulphur dioxide and sodium benzoate often cause tight chests in individuals who have asthma. Many people also complain of a scratchy feeling at the back of their throats. Although these are the common reactions, others such as rashes may also occur. Sulphur dioxide may be labelled as sodium metabisulphite, potassium metabisulphite, sodium or potassium bisulphite or sulphite.
  • Foods that may contain sulphur dioxide include (shortened list): Some fruit juices, concentrated soft drinks, dried fruit, boerewors, dried wors, wine, beer, some sauces, pickles, hamburger patties.
  • Foods that may contain sodium benzoate include (shortened list): Fruit juices, soft drinks, foods with fruit.
• Colourants
  Colourants may be natural or synthetic. Reactions, although not common, can occur with both types. The best known colourant is tartrazine. Tartrazine is an azo dye, so if you react to this colourant, you should avoid all of the azo dyes. Although many people are concerned that they may be affected by colourants, not many individuals are in fact affected. Thus not all asthmatics need to avoid tartrazine. Whether tartrazine or other colourants can result in hyperactivity in children is still controversial.
  • Foods that may contain colourants include: Fruit juices, soft drinks, sweets, desserts, toppings, syrups, cooking oils, sauces and pickles.
• Flavour enhancers
  The most famous of these is monosodium glutamate, commonly called MSG. Eating foods with this additive may result in tight chests in asthmatics. This reaction may occur immediately or 6 to 12 hours later. Typical symptoms include headache, a burning sensation along the back of the neck, chest tightness or pain, nausea, sweating and a sensation of facial pressure. "Pins and needles" or tingling may be experienced in the limbs or face and head. It is not a common condition.
  • Foods that may contain MSG include: Oriental food, packet soups, sauces, soya sauce, seasoning. Aromat. MSG is also thought to occur naturally in mushrooms and tomatoes.
• Salicylates
  Acetyl salicylic acid found in aspirin may result in a tight chest.
  In some instances, the reaction will immediately follow the ingestion of an additive or preservative, as with sulphur dioxide and sodium benzoate. In other cases, the reaction may be delayed for 6 to 24 hours.

What can I do to see if I am affected?

You may have to keep a diary and record all the food you eat, the time it was eaten, and when the reaction occurred. You will need to see if there is a pattern to the reaction. Unfortunately, there is no blood or skin test available to check whether you are affected. Your doctor may suggest a "challenge" with the substance to see if you are indeed affected.

What treatment must I take if I am affected?

Read labels on foods very carefully and avoid all food that contains the preservative or additive that you are affected by. The Food Intolerance Databank* has lists of foods that are "free from" a variety of preservatives and additive free diet for at least two weeks to check whether you are indeed affected or not. Your local dietician will assist you in drawing up a suitable diet.

You can also contact the:
Food Intolerance Bank
c/o Association for Dietetics in Southern Africa
PO Box 4309
Randburg 2125
Telephone (011) 886-8130/Fax (011) 886-7612.

5 key points to remember

Food allergy

• Food allergy is generally uncommon, affecting 1 in 100 children and 5 in 1000 adults.
• Allergic reactions to food occur more commonly in the digestive system and the skin, and rarely in the lungs and nose.
• Asthma develops in less than 5 in 100 individuals with food allergy.
• Common foods causing allergy are cow's milk, eggs, wheat, soya, peanuts and fish.
• The most reliable way to diagnose food allergy is by elimination-challenge testing.

Preservatives and additives

• Preservatives and additives cause chemical and not allergic reactions.
• Only some asthmatics will react to these substances.
• There are no reliable tests to confirm sensitivity to these chemicals.
• Keep a diary of what you eat when reactions occur to look for a pattern.
• Read all food and ingredient labels carefully.

Written by: Dr Cas Motala, Dr Harris Steinman