Food allergy
There is a difference between food
intolerance and food allergy
Food
intolerance refers to an adverse reaction to food or food additives
In
food allergy the immune system is involved
Food
allergy is more common in children
Symptoms
are usually confined to the digestive tract but other parts of the body may also
be involved
Avoidance
of the offending food is the mainstay of treatmen
What is
the difference between food intolerance and food allergy?
Food intolerance refers to any adverse reaction to food or food
additives. Food allergy is only one such reaction and refers specifically to
food intolerance in which the body's immune (defence) system is directly
involved.
Some
doctors prefer to use the term food intolerance only for adverse reactions to
food in which the body's immune system is not involved (non-immune or
non-allergic).
There
are different types of non-immune reactions to food. The most obvious example is
simple toxicity. Contaminants (substances which get into food during the growth,
harvesting, processing, packaging or storage of food) are occasionally harmful.
In severe cases these contaminants can make food poisonous and anyone eating
them will suffer ill effects. Much less obvious are the adverse reactions of a
few people who lack the enzymes necessary to digest certain foods.
A common
example is lactose intolerance. This is due to the lack of the enzyme lactase,
which is essential for the digestion of the milk sugar lactose. Most people have
adequate levels of the necessary enzyme and tolerate milk.
Another
example of non-allergic food intolerance is the reaction caused by naturally
occurring chemicals in food, or by food additives (chemical reaction). These
reactions are similar to true allergic responses and may be mistakenly labelled
as food allergy.
Food
additives include a variety of substances, such as preservatives, flavouring
agents, colouring agents, etc. Well-known examples are tartrazine, monosodium
glutamate (MSG), sulphur dioxide and benzoates. Chemical reactions to food or
food additives are not true allergic reactions because they do not involve the
immune system.
Another
interesting cause of a non-allergic reaction is psychological reactions to
foods. It has been shown that if one is convinced, perhaps by a past experience,
that one cannot tolerate a certain food, one tends to avoid it. Should one eat
it again in the future, the chances are that one will experience, that one
cannot tolerate a certain food, one tends to avoid it.
Should
one eat it again in the future, the chances are that one will experience ill
effects.
Is true
food allergy common?
True food allergy is less common than popularly believed. It is
estimated that only between 1% and 4% of the general population suffers from a
definite food allergy. Food allergy tends to be more common in children (up to 3
years) than adults. In selected groups, such as children with eczema, the
prevalence of food allergy may be as high as 60%.
What are
the symptoms of food allergy?
The symptoms of food allergy may be confined to the digestive system
only (the most common sort), or involve other parts of the body as well.
Symptoms
of the upper part of the digestive system, which come on rapidly, include
swelling of the lips, and itching and redness around the mouth. Sometimes the
mouth becomes intensely itchy and the uvula (the small "tongue" at the back of
the throat) may become swollen. Foods which most often cause such reactions are
eggs, nuts, shellfish, citrus fruits and berries.
Reactions of the lower part of the digestive tract may take a little longer to
develop such as nausea and vomiting; other common symptoms are stomach cramps
(colic) and diarrhoea.
Other
systems which may be involved in food allergy are the skin, respiratory
(breathing) organs and the central nervous system.
Skin
symptoms include eczema and urticaria (hives or nettle rash) characterised by
raised red and itchy wheals.
The
respiratory organs are less commonly affected than the digestive tract or skin.
Symptoms of the respiratory organs include asthma and hayfever.
The
effects of food allergy on the central nervous system (CNS) is a controversial
area and one which tends to attract a lot of media attention. CNS disorders
which have been linked to food allergy include migraine, the allergic
tension-fatigue syndrome and hyperactivity. The tendency to suffer from migraine
runs in families.
Several
foods have been shown to trigger migraine: chocolate, red wine, yeast extracts,
hard cheeses, coffee, milk and eggs.
Children
with the allergic tension-fatigue syndrome have pale faces with dark rings under
their eyes, giving them a tired look. They may be difficult to rouse in the
mornings and tend to concentrate poorly at school, especially in the mornings.
These
children tend to be irritable and to sleep badly at night. It has been found
that there is a link between this syndrome and an excessive intake of milk, cool
drinks and chocolates. Elimination of these foods from the diet may improve the
symptoms of these children quite dramatically.
How is
food allergy diagnosed?
The diagnosis of food allergy rests more on a careful evaluation of
the patient than on laboratory tests.
The
diagnosis is easy when the reaction occurs soon after a new food is introduced.
If a commonly used food is involved, the diagnosis is more difficult. In this
situation, a variety of tests can be used.
The
final mainstay of diagnosis remains the demonstration of relief of symptoms on
removal of a given food item and recurrence of symptoms on its re-introduction
(elimination-challenge testing).
Before
this is undertaken, skin tests and a test called RAST (which detects IgE
antibodies in the blood) may help to pinpoint the foods that should be tested in
the withdrawal-relief and challenge procedures.
In
general, skin tests and RAST are helpful, especially in children, but they are
far from being totally accurate in the diagnosis of food allergy.
How is
food allergy treated?
Avoidance of the offending food is the mainstay of treatment. At the
same time it is essential to provide a balanced diet which contains enough
protein, calories, minerals and vitamins. Close co-operation between the
patient, the doctor and a qualified dietician is important to ensure this.
Strict
avoidance of offending foods is the key to successful treatment. When dietary
measures do not appear to work, this may be due to one of three reasons:
the diet is not strict
enough; or,
the
patient is eating hidden sources of the offending food;
the reaction might be due to food
additives, such as colouring agents,
or to other naturally occurring
chemicals, such as salicylates and histamine;
the diagnosis of food allergy is not
correct.
If the
diagnosis of food allergy is correct and the recommended diet is not working,
medication may have to be added to the treatment. The doctor will usually decide
on the appropriate medication, depending on the patient's symptoms.
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