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Allergies - food allergies and intolerances
Allergies - food allergies and intolerances


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Immune system; digestive system
The terms food allergies and food intolerances are often used to describe an inability to eat a certain type of food, and it is often assumed that the two terms mean the same thing. However, a food allergy is not the same as a food intolerance.

A food allergy is an over-reaction by the body's immune system to substances in the food that are usually harmless to most people. These substances are called allergens and they are capable of triggering an allergic reaction very quickly, soon after the person has eaten even only tiny amounts of the food. In some cases, the allergic reaction can be life-threatening.

A food intolerance is an inability of the body's digestive system to process certain foods properly. The unpleasant reactions develop slowly, often hours or even days after the food has been eaten. The more of the offending food that is eaten, the greater is the reaction. Food intolerances are never directly life-threatening.

Reports of the number of children with an allergy to food or an intolerance to food vary, but both tend to be exaggerated when compared with results from scientific studies. About 5% to 8% of children will really have a food allergy and the number declines to about 2% once they reach adulthood.

There is evidence to suggest that the number of children with food allergies is increasing in line with an increase in other allergies such as eczema and asthma.

As many as 30% of people believe that they have an intolerance to food, but while it is not possible to be precise, the true figure is likely to be less than 10%.
The most common causes of food allergies in children are nuts (especially peanuts), fish, shellfish, eggs, cow's milk, wheat, citrus fruits and tomatoes. These foods contain proteins that the body's immune system wrongly recognises possibly as proteins found in bacteria and parasites. As a defence mechanism, the immune system tries to protect the body against these proteins, and it is this mistake by the immune system that eventually gives rise to an allergic reaction.

It would appear that this defect in the immune system runs in families as children whose parents are prone to allergies have a higher risk of developing allergies, including eczema and asthma, than children whose parents are without allergies.

An allergic reaction does not occur the first time that a child is exposed to the protein or allergen in the food. It has to be exposed two or more times. This process is known as sensitisation and, after it has developed, the child is said to have become sensitised to the allergen.

During the sensitisation process, when the allergen first comes into contact with the body's immune system, special proteins are produced against the allergen by the immune system. These special proteins, called antibodies or immunoglobulins (IgE) are highly specific to each allergen, capable of recognising just that allergen. More and more IgE is produced each time the immune system is exposed to the allergen, eventually excessive amounts of IgE circulate in the blood stream. When food containing the allergen is eaten, the allergen binds to IgE causing the release of large amounts of histamine and other chemicals from cells called mast cells. It is the release of these chemicals that cause the symptoms of an allergic reaction.

In contrast, food intolerances occur because of a defect in the digestive system and an inability to break down foods properly. In order to absorb and make use of the nutrients in foods, the food has to be broken down or digested by the action of digestive enzymes in the stomach and intestines. There are a large number of different enzymes, capable of breaking down sugars, proteins and fats. If any of these enzymes is missing or is not working properly, then the food will not be broken down and absorbed. Instead, the food may remain in the digestive system where it can cause symptoms such as wind, bloated stomach and diarrhoea.

For example, some children are intolerant to cow's milk because of a deficiency of the enzyme lactase. Lactase is responsible for breaking down a sugar called lactose in milk. If lactase is absent or deficient, the lactose is not absorbed but is fermented by bacteria present in the large intestines, releasing large amounts of gas that cause wind, bloating and stomach pains. Excess lactose in the intestine also has a laxative effect, so the child may have diarrhoea. Signs of lactose intolerance generally first start to appear after the child has reached about 2 years of age, when lactase levels start to decline.
An allergic reaction to a food can occur almost instantly, as soon as the food enters the mouth and even before it has been swallowed. Symptoms can include wheezing, coughing, sneezing, skin rashes, swollen lips and stomach cramps. In severe cases, the child may suffer what is called an anaphylactic reaction where the child's throat and tongue may swell making breathing difficult, or the child may lose consciousness because of a drastic fall in blood pressure. An anaphylactic reaction is life-threatening.

The symptoms of food intolerance are far less dramatic and tend to develop hours or even days after the food has been eaten. They include wind, bloating, stomach pain, nausea, vomiting diarrhoea or constipation. Food intolerances are never directly life threatening. However, if the missing enzyme prevents the absorption of certain essential nutrients, or prevents these nutrients from being used properly by the body, the child may fail to put on weight and develop normally.
As an allergic reaction can be triggered by even the smallest amounts of food, it is important that you learn to identify the problem foods and exclude them from your child's diet. Make sure your child also knows which foods to avoid because you cannot be with them all of the time. Remember too that it is the allergen in the food and not the food itself that is the cause of the problem. For example, if your child has a peanut allergy, she or he can suffer an allergic reaction by eating biscuits that, although do not appear from the label to contain peanuts, have been produced in a factory where peanuts are made into other products. Similarly, if your child has a fish allergy, it will be to all types of fish and all types of fish products. Get into the habit of double-checking food labels, looking for the ingredients and for any warnings.

About 90% of children will grow out of mild allergies to foods such as cow's milk, fruit and vegetables by the age of three, but for some, especially those allergic to peanuts and nuts, the allergy will persist into adulthood and remain a potential threat.

If your child has suffered an anaphylactic reaction, make sure that you have self-injectable adrenaline always close at hand, and you, your child and other close relatives know how to give the injection if an emergency should occur. Also, draw up an action plan that provides instructions to others such as relatives, teachers and baby-sitters telling them which foods to avoid and what to do in case of an emergency.

Food intolerances can usually be recognised if symptoms disappear when the suspect food is removed from the diet. Once identified, the intolerance can be managed simply by excluding the food from the diet. However, children need essential nutrients to help them grow and develop. Consequently, no food group should be totally eliminated from a child's diet without taking advice from a doctor or dietician.
When to consult your pharmacist
Your pharmacist will be able to give you general advice about food allergies and food intolerances and which foods you should try to avoid. He or she will also be able to give more specific advice about nutritional supplements that may be necessary to supplement your child's diet.
When to consult your doctor
If you suspect that your child has a food allergy or a food intolerance you should visit you doctor. Your doctor will ask you to describe the symptoms and when they occur, so it would be helpful if you kept a diary of the foods that your child has eaten and made a note of any symptoms and when they occurred.

If the doctor suspects an allergy or an intolerance, there are skin tests and blood tests that can be performed that will confirm the diagnosis and establish which are the problem foods.

If your child has suffered a severe allergic reaction or an anaphylactic reaction, talk to your doctor about providing you with self-injectable adrenaline to use in an emergency.

If your child is intolerant to certain foods, your doctor may refer your child to a dietician to provide advice on how to avoid problem foods and recommend alternative foods to maintain a balanced healthy diet for your growing child.