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What
Is a Food Allergy?
A
food allergy is an immune system response. It occurs
when the body mistakes an ingredient in food -- usually
a protein -- as harmful and creates a defense system
(antibodies) to fight it. Allergy symptoms develop when
the antibodies are battling the "invading"
food. The most common food allergies in adults are shellfish,
peanuts, fish, and eggs. The most common food allergies
in children are milk, soy products, peanuts, and shellfish.
What
Is Food Intolerance?
Food
intolerance is a digestive system response rather than
an immune system response. It occurs when something
in food irritates a person's digestive system or when
a person is unable to properly digest, or breakdown,
the food. Intolerance to lactose, which is found in
milk and other dairy products, is the most common food
intolerance.
What
Are the Symptoms of Food Allergy?
Symptoms
of a food allergy can range from mild to severe, and
the amount of food necessary to trigger a reaction varies
from person to person. Symptoms of food allergy may
include:
Rash
or hives
Nausea
Stomach pain
Diarrhea
Itchy skin
Shortness of breath
Chest pain
Swelling of the airways to the lungs
Anaphylaxis
What Are the Symptoms of Food Intolerance?
Symptoms
of food intolerance include:
Nausea
Stomach pain
Gas, cramps, or bloating
Vomiting
Heartburn
Diarrhea
Headaches
Irritability or nervousness
How Common Are Food Allergies and Intolerances?
Food
allergies affect about 1% of adults and 7% of children,
although some children outgrow their allergies. Food
intolerances are much more common. In fact, nearly everyone
at one time has had an unpleasant reaction to something
they ate. Some people have specific food intolerances.
Lactose intolerance, the most common food intolerance,
affects about 10% of Americans.
What
Causes Food Allergies and Intolerances?
Food
allergies arise from sensitivity to chemical compounds
(proteins) in food. Food allergies develop after you
are exposed to a food protein that your body thinks
is harmful. The first time you eat the food containing
the protein, your immune system responds by creating
specific disease-fighting antibodies (called immunoglobulin
E or IgE). When you eat the food again, it triggers
the release of IgE antibodies and other chemicals, including
histamine, in an effort to expel the protein "invader"
from your body. Histamine is a powerful chemical that
can affect the respiratory system, gastrointestinal
tract, skin or cardiovascular system.
As
a result of this response, allergy symptoms occur. The
allergy symptoms you have depend on where in the body
the histamine is released. If it is released in the
ears, nose, and throat, you may have an itchy nose and
mouth, or trouble breathing or swallowing. If histamine
is released in the skin, you may develop hives or a
rash. If histamine is released in the gastrointestinal
tract, you likely will develop stomach pains, cramps,
or diarrhea. Many people experience a combination of
symptoms as the food is eaten and digested.
Food
allergies often run in families, suggesting that the
condition can be inherited.
There
are many factors that may contribute to food intolerance.
In some cases, as with lactose intolerance, the person
lacks the chemicals, called enzymes, necessary to properly
digest certain proteins found in food. Also common are
intolerances to some chemical ingredients added to food
to provide color, enhance taste, and protect against
the growth of bacteria. These ingredients include various
dyes and monosodium glutamate (MSG), a flavor enhancer.
Substances
called sulfites, which may occur naturally, as in red
wines, or may be added to prevent the growth of mold,
also are a source of intolerance for some people. The
FDA has banned the use of spray-on sulfates to preserve
fruits and vegetables, but sulfates are still found
naturally in some foods. Salicylates are a group of
plant chemicals found naturally in many fruits, vegetables,
nuts, coffee, juices, beer, and wine. Aspirin also is
a compound of the salicylate family. Foods containing
salicylates may trigger symptoms in people who are sensitive
to aspirin. Of course, any food consumed in excessive
quantities can cause digestive symptoms.
How
Can You Tell the Difference Between a Food Allergy and
Intolerance?
Food
allergies can be triggered by even a small amount of
the food and occur every time the food is consumed.
People with food allergies are generally advised to
avoid the offending foods completely. On the other hand,
food intolerances often are dose related; people with
food intolerance may not have symptoms unless they eat
a large portion of the food or eat the food frequently.
For example, a person with lactose intolerance may be
able to drink milk in coffee or a single glass of milk,
but becomes sick if he or she drinks several glasses
of milk. Food allergies and intolerances also are different
from food poisoning, which generally results from spoiled
or tainted food and affects more than one person eating
the food. Your healthcare provider can help determine
if you have an allergy or intolerance, and establish
a plan to help control your symptoms.
How
Are Food Intolerances Diagnosed?
Most
food intolerances are found through trial and error
to determine which food or foods cause symptoms. You
may be asked to keep a food diary to record what you
eat and when you get symptoms, and then look for common
factors.
Another
way to identify problem foods is to go on an elimination
diet. This involves completely eliminating any suspect
foods from your diet until you are symptom-free. You
then begin to reintroduce the foods, one at a time.
This can help you pinpoint which foods cause symptoms.
Seek the advice of your healthcare provider or a registered
dietitian before beginning an elimination diet to be
sure your diet provides adequate nutrition.
How
Are Food Intolerances Treated?
Treatment
is based on avoiding or reducing your intake of problem
foods and treating symptoms when they arise.
Can
Food Intolerances Be Prevented?
Taking
a few simple steps can help you prevent the symptoms
associated with food intolerance.
Learn
which foods in which amounts cause you to have symptoms,
and limit your intake to amounts you can handle.
When you dine out, ask your server about how your meal
will be prepared. Some meals may contain foods you cannot
tolerate, and that may not be evident from the description
on the menu.
Learn to read food labels and check the ingredients
for problem foods. Don't forget to check condiments
and seasonings. They may contain MSG or another additive
that can lead to symptoms.
Reviewed
by the doctors at The Cleveland Clinic Department of
Pulmonary, Allergy and Critical Care Medicine.
Edited
by Charlotte E. Grayson, MD, Feb. 2004, WebMD.
Portions
of this page © The Cleveland Clinic 2000-2004
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