Definitions
and Causes
Food allergy is often mistaken for food intolerance. It is important to
note that allergy is only one of a number of possible reasons for food
intolerance.
Food intolerance can be defined
as a condition where particular adverse effects occur after eating
a particular food or food ingredient. Genuine food intolerance is different
from psychologically based food aversion, where a person strongly dislikes
a food and believes that a food produces a particular reaction.
A genuine food allergy is when
a specific immune reaction occurs in the body in response to consuming
a particular food. Allergies often run in families, and people who
are allergic to some foods may also be allergic to other environmental
factors, such as house dust, animal fur and pollen.
A true allergic response involves
an altered or abnormal tissue reaction to an antigen. An antigen can
be a protein, a substance bound to a protein, a food additive or less
commonly, a polysaccharide. The antigen combines with an antibody and
produces an immune response, which results in cell damage and the release
of histamine. The immune system plays an essential role in our bodies
in protecting us from the invasion of harmful substances. An allergy
occurs when the mechanism operates inappropriately in response to a
harmless substance such as a particular food protein.
Food intolerances, other than
allergies, can occur for a variety of reasons including:
 Non
allergic histamine release
The signs are very similar to
an allergy and include headache, swelling, urticaria, vomiting and
diarrhoea. A substance called histamine is released (it is also released
in true allergic reactions) in response to foods such as shellfish
or strawberries.
Metabolic
defects
A lack or deficiency of enzymes
responsible for the digestion of food can cause many types of food
intolerance. For example, a deficiency in lactase, the enzyme responsible
for digesting milk, causes intolerance to milk.
Coeliac disease is a gut intolerance
to a protein found in wheat, called gluten, it would not be considered
an allergy. The symptoms of coeliac disease are controlled by following
a gluten-free diet. It is unknown exactly
why or how gluten harms the gut, although it is now thought to be an
abnormal immunological response rather than an enzyme deficiency. It
is still not considered to be a food allergy in the true sense of the
definition.
Pharmacological
effects
Some food substances can act
like drugs, particularly if taken in large quantities. The most familiar
of these substances is caffeine, found in tea, coffee, chocolate and
cola drinks. A large intake of caffeine can cause tremor, migraine
and palpitations. Other pharmacologically active substances found in
food include histamine, tyramine, tryptamine and serotonin, which may
be consumed in foods such as red wine, cheese, yeast extract, avocados
and bananas. In susceptible people, these foods can trigger urticaria,
facial flushing and headaches.
Food
intolerance of unknown origin
Reactions can be provoked by
many foods and food products which we cannot be clear about. They may
or may not be allergic reactions. Food additives, particularly tartrazine
and sodium benzoate, can provoke urticaria, rhinitis and asthma. Yeasts
can provoke a number of reactions in some people, particularly skin
disorders.
Common Causes
of Food Intolerance
The most common food intolerances, in order of frequency are milk, eggs,
nuts, fish/shellfish, wheat/flour, chocolate, artificial colours, pork/bacon,
chicken, tomato, soft fruit, cheese and yeast.
Whilst not all food intolerances
are related to meat and dairy products, it can be seen from the above
list that vegetarians, and particularly vegans, will suffer less from
food intolerance because they already eliminate some of the most common
causes of intolerance.
Symptoms
The most common symptoms of allergy include asthma, gastro-intestinal symptoms
(nausea, vomiting, and diarhhoea), eczema, urticaria (hives), rhinorrhea
(heavy discharge from the nose), and angio-oedema (swelling of the blood
vessels). Other more long-term symptoms include can depression, anxiety,
fatigue, migraine, sleeplessness and hyperactivity in children. Treatment
As it is sometimes quite difficult to distinguish between a genuine food
allergy and a food intolerance, treatment is often similar. The first step
is to diagnose the food intolerance. This should not be done without medical
supervision as some reactions to food intolerance can be dangerous.
Sometimes the cause of a particular
food intolerance is obvious, by the immediate effect that occurs on
eating a particular food. In this case the treatment is simply to avoid
that particular food. In most cases the suspected food is more difficult
to track down. A diary kept of foods eaten and symptoms experienced
can sometimes help detect the offending food or foods. Other factors
such as the weather, menstrual cycles and difficult relationships can
affect the symptoms. Sometimes simple exclusion diets are advised where
record keeping suggests a particular food may be the cause. So, for
example, milk, egg or wheat may be avoided to see if symptoms improve.
Other more restrictive diets
may be advised, which only include a limited amount of foods which
rarely cause a reaction. These diets are usually called exclusion diets.
The idea of an exclusion diet is to identify an allergy or intolerance,
by limiting the food to a very small choice, checking for symptoms
and then very gradually introducing test foods to see if there is a
reaction. An exclusion diet should not be followed without sound nutritional
advice.
Further Information
Action
Against Allergy, PO
Box 278, Twickenham, Middlesex, TW1 4QB Tel: 0208 892 2711.
Fax: 0208 8924950. E-mail: aaa@actionagainstallergy.co.uk Web: www.actionagainstallergy.co.uk
Coeliac
Society, PO
Box 220, High Wycombe, Bucks, HP11 2HY.
National
Society for Research into Allergy, PO
Box 45, Hinckley, Leicestershire.
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