Contents
Adverse reaction to food is a general
term that describes any abnormal reaction to a food
or food additive that is eaten, whether it is caused
by allergic or non-allergic mechanisms. A few specific
foods seem to cause a majority of food allergies. Some
of the most common food allergens are cow's milk, eggs,
peanuts, wheat, and soy.
Reports of food allergies began to
appear in Europe in the early 1900s, and since the
1940s, food allergies have been recognized by doctors
around the world. Up to two million, or 8%, of children
in the U.S. are estimated to be affected by food allergy,
and up to 2% of adults.
With a true food allergy, an individual’s
immune system will overreact to an ordinarily harmless
food. This is caused by an allergic antibody called
IgE (Immunoglobulin E), which is found in people with
allergies. Food allergy often may appear in someone
who has family members with allergies, and symptoms
may occur after that allergic individual consumes
even a tiny amount of the food.
Food intolerance is sometimes confused
with food allergy. Food intolerance refers to an abnormal
physical response to a food or food additive that
is not an allergic reaction. It differs from an allergy
in that it does not involve the immune system. For
instance, an individual may have uncomfortable abdominal
symptoms after consuming milk. This reaction is most
likely caused by a milk sugar (lactose) intolerance,
in which the individual lacks the enzymes to break
down milk sugar for proper digestion. Your allergist
can help you determine the difference between intolerance
and allergy and help you in establishing a management
plan.
Food allergens—those parts of
foods that cause allergic reactions—are usually
proteins. Most of these allergens can still cause
reactions even after they are cooked or have undergone
digestion in the intestines. Numerous food proteins
have been studied to establish allergen content. The
most common food allergens—responsible for up
to 90% of all allergic reactions—are the proteins
in cow’s milk, eggs, peanuts, wheat, soy, fish,
shellfish and tree nuts.
All foods come from either a plant
or an animal source, and foods are grouped into families
according to their origin. Peanuts, black-eyed peas,
kidney and lima beans, and soybeans are some of the
members of the legume family, whereas asparagus, chives,
garlic and onion are, surprisingly, members of the
lily family. In some food groups, especially tree
nuts and seafood, an allergy to one member of a food
family may result in the person being allergic to
all the members of the same group. This is known as
cross-reactivity. However, some people may be allergic
to both peanuts and walnuts, which are from different
food families; these allergies are called coincidental
allergies, because they are not related.
Within animal groups of foods,
cross-reactivity is not as common. For example, people
allergic to cow’s milk can usually eat beef, and
patients allergic to eggs can usually eat chicken. People
allergic to eggs usually react only to the egg white,
which contains several proteins. However, because it
is impossible to completely avoid cross-contamination
between yolk and white, they must avoid eggs completely.
Symptoms of allergic
reactions to foods
The most common allergic skin reaction
to a food is hives. Hives are red, very itchy, swollen
areas of the skin that may arise suddenly and leave
quickly. They often appear in clusters, with new clusters
appearing as other areas clear. Hives may occur alone
or with other symptoms.
Atopic dermatitis, or eczema, a skin
condition characterized by itchy, scaly, red skin,
can be triggered by food allergy. This reaction is
often chronic, occurring in individuals with personal
or family histories of allergies or asthma. Symptoms
of asthma, a chronic disease characterized by narrowed
airways and difficulty in breathing, may be triggered
by food allergy, especially in infants and children.
Gastrointestinal symptoms of food allergy include
vomiting, diarrhea and abdominal cramping, and sometimes
a red rash around the mouth, itching and swelling
of the mouth and throat, nausea, abdominal pain, swelling
of the stomach and gas.
In infants, non-allergic, temporary
reactions to certain foods, especially fruits, cow’s
milk, egg white, peanuts and wheat, are common. For
example, a rash around the mouth, due to natural acids
in foods like tomatoes and oranges, or diarrhea due
to excess sugar in fruit juice or other beverages,
occur with some frequency. However, other reactions
are allergic and may be caused by traces of the offending
food when eaten again. As they grow older, some children
may tolerate foods that previously caused allergic
reactions, with the exception of peanut and tree nut
allergies. Periodic food allergy check-ups with appropriate
food challenges should be carried out under the supervision
of an allergist.
Severe allergic reactions
In severe cases, consuming a food
to which one is allergic can cause a life-threatening
reaction called anaphylaxis—a systemic allergic
reaction that can be severe and sometimes fatal. The
first signs of anaphylaxis may be a feeling of warmth,
flushing, tingling in the mouth or a red, itchy rash.
Other symptoms may include feelings of light-headedness,
shortness of breath, severe sneezing, anxiety, stomach
or uterine cramps, and/or vomiting and diarrhea. In
severe cases, patients may experience a drop in blood
pressure that results in a loss of consciousness and
shock. Without immediate treatment, anaphylaxis may
cause death.
Symptoms of anaphylaxis are reversed
by treatment with injectable epinephrine, antihistamines,
and other emergency measures. It is essential that
anyone with symptoms suggesting possible anaphylaxis
get emergency treatment immediately.
Food intolerance and
additive reactions
Food intolerance reactions are usually
caused by factors in the diet other than the proteins
that make up food allergens. As mentioned, one of
the most common is lactose intolerance. Other food
intolerance reactions may be triggered by drug-like
chemicals in some foods. Symptoms can include nervousness
after consuming caffeine in coffee or soft drinks,
headaches triggered by chemicals in cheese and chocolate,
or various adverse reactions to chemicals and preservatives
added to food, called food additives. These additives
may cause adverse reactions in sensitive people. The
most common food additives that may cause reactions
include aspartame, benzoates, BHA and BHT, FD&C
dyes Yellow No. 5 and Red No. 3, monosodium glutamate
(MSG), nitrates/nitrites, parabens and sulfites. True
allergic reactions to food additives are very rare.
The best way to handle food additive
sensitivity is to know which foods contain certain
additives, and to avoid the additives that cause problems
for you. Your allergist can help you identify those
food items responsible for your symptoms so that you
can eliminate them as much as possible from your diet.
Diagnosis
An allergist is the best qualified
professional to diagnose food allergy. Diagnosis requires
a carefully organized and detailed assessment of the
problem. First, the allergist will take a thorough
medical history, followed by a physical examination.
The allergist will inquire about the frequency, seasonality,
severity and nature of the symptoms, and will ask
about the amount of time that elapses between eating
a food and any reaction.
Allergy skin tests may be helpful
to determine which foods, if any, are triggering a
patient’s allergic symptoms. In skin testing,
a small amount of liquid extract made from the food
is placed on the back or arm. In a test called a prick
test, a needle is then passed through the liquid on
the top layer of the skin. During a scratch test,
small scratches are made through the liquid and the
top layer of skin. If the patient develops a wheal—a
raised bump or small hive—within 20 minutes,
this positive response indicates a possible allergy.
If the patient does not develop a wheal, the test
is negative. It is uncommon for someone with a negative
skin test to have an IgE-mediated food allergy. Skin
tests are not helpful when sensitivity to simple foods
such as sugars or chemical food additives is suspected.
Your doctor may also use blood tests,
called RAST testing or CAP-RAST, to diagnose food
allergies. In certain cases, such as severe eczema
all over the body, an allergy skin test cannot be
done. Your doctor may recommend a food RAST blood
test to obtain the same information that can be found
with a skin test. For diagnosis of milk, egg, peanut
or fish allergy, the CAP-RAST test may be more useful
than skin tests. False positive results may occur
with both food allergy skin testing and blood testing.
Food challenges, described below, are often required
to confirm the diagnosis.
The allergist may suggest that the
patient keep a food diary, which is a detailed record
listing foods eaten, date, time and any symptoms that
occurred after eating the food. When an allergy to
a single food is suspected, the allergist may recommend
eliminating the food for a time. If symptoms are relieved,
the allergist may add the food to the diet once again
to further determine if it causes a reaction (however,
this is never done when the patient has a history
of anaphylaxis).
If the diagnosis of food allergy remains
in doubt, the allergist may recommend a "blinded"
food and/or food additive challenge test. These tests
are conducted in the allergist’s office, or
at times, in the hospital under close observation.
Usually, the suspected food or a neutral food, called
a placebo, is fed to the patient in colorless capsules,
or in a non-allergenic slush or pudding. Neither the
patient nor the doctor knows whether the suspected
food or the placebo is being eaten. This is called
a "double-blind" challenge. When properly
performed, these challenges are very reliable in establishing
a concrete cause and effect relationship between a
food and an allergy symptom.
Treatment
| 1. |
Avoid the food. The
best way to treat food allergy is to avoid the
specific foods that trigger the allergy.
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2. |
Ask about ingredients. To avoid
eating a "hidden" food allergen away
from home, food-allergic individuals must always
inquire about ingredients when eating at restaurants
or others’ homes.
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3. |
Read food labels. It is important
for food-allergic people to read food labels carefully
and to become familiar with technical or scientific
names for foods. For example, milk may not be
listed as an ingredient on a label; rather, the
label may list casein (a milk protein), sodium
caseinate or milk solids. Not every food that
contains wheat identifies it as such; sometimes
wheat is listed as gluten. Similarly, egg white
is frequently listed as albumin. Government agencies
have been working toward improving food ingredient
labeling so food-allergic consumers can more easily
determine which foods they may need to avoid.
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4. |
Be prepared for emergencies.
Anaphylactic reactions caused by food allergies
can be potentially life-threatening. Those who
have experienced an anaphylactic reaction to a
food must strictly avoid that food. They may need
to carry and know how to use injectable epinephrine
and antihistamine to treat reactions due to accidental
ingestion. Those with food allergies should also
wear an identification bracelet that describes
the allergy. If you have an anaphylactic reaction
after eating a food, it is essential that you
have someone take you to the emergency room, even
if symptoms subside. For proper diagnosis and
treatment, make sure to get follow-up care from
an allergist.
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Video
If you have a food
allergy, the world of eating may seem filled
with challenges and frustrations. The same foods
that others around you enjoy every day can have
unpleasant and even dangerous effects if you're
allergic.
What can you do to take care of your health
without living in fear?
Watch the video
about food allergies,
how they work and why you have them.
Topics
will include:
|
• |
Why do some people develop
allergies? Can they be prevented? |
|
• |
Why are some allergies more common in
certain countries than others? |
|
• |
What emergency procedures should everyone
with a food allergy know? |
|
• |
What can you do to help protect your
child from food allergies? |
Would
You Like to View the Video on Food Allergies?
|
 |
|
Egg
Egg is one of the
most allergenic of all foods, and minute
amounts of egg can result in symptoms
within minutes, including life-threatening
anaphylaxis. This is also seen after
contact with egg through non-oral routes.
Reactions may occur the first time a
child is given egg.
TABLE
I -
Labels that may indicate the presence
of egg protein
|
Albumin
|
Globulin
|
Ovamucoid
|
Binder
|
Lecithin
|
Ovovitellin
|
Coagulant
|
Livetin
|
Powdered
egg |
Egg white
|
Lysozyme
|
Vitellin
|
Egg yolk
or yellow |
Ovalbumin
|
Whole
egg |
Emulsifier
|
Ovamucin
|
----- |
|
TABLE
II -- Foods that may contain egg
protein
|
Baked goods
(most except some breads)
Baking mixes
Batters
Bearnaise sauce
Bouillon (in restaurants to
clear it)
Breakfast cereals
Cake flours
Candy (see Sweets)
Cookies
Creamy fillings
Custard
Egg noodles
Eggnog
French toast
Hollandaise sauce
Ice cream
Lemon curd
Macaroni
Malted cocoa drinks (e.g.,
Ovaltine) |
|
Marshmallows
Mayonnaise
Meringues
Muffins
Noodles (egg)
Omelettes
Pancakes
Processed meat products (e.g.,
bologna, meat loaf, meatballs,
sausages)
Puddings
Salad dressing (creamy)
Sherbets
Souffles
Soups
Spaghetti
Sweets (e.g., fondant creams,
truffles, marshmallows, etc.)
Tartar sauce
Turkish Delight
Waffles
Wines (if cleared with egg
white) |
|
Although ovalbumin,
ovomucoid, and ovotransferrin have been
identified as the major allergens in
egg white, 10 other unnamed allergens
of lesser importance have been identified.
These allergens are also present in
egg yolk but in lesser quantities. This
is important because components of egg
may be individually used for specific
actions in food preparation. For example,
hen's egg lysozyme is used as a preservative
in food; and in some countries, notably
Japan and Switzerland, lysozyme is used
in medications. Individuals sensitive
to hen's egg have been shown to be allergic
to lysozyme produced from hen's egg.
A variety
of descriptions may indicate the presence
of egg protein in a product (Table I)
. The function that egg performs in
a product may be named on the ingredient
panel (e.g., binder, emulsifier, or
coagulant). Because legislation may
permit a manufacturer not to list an
ingredient constituting less than a
specific percentage of the total product,
noodles containing egg may not have
egg listed on the ingredient panel.
A similar situation may occur when egg
white is used to give pretzels, bagels,
and other baked goods their shiny appearance.
In most products, lecithin is derived
from soy, but sometimes it may be egg-derived.
Provitamin A (extracted from egg) may
be used and described as a colorant,
but its antigenic properties are unknown.
In addition
to food products (Table II) that may
be dangerous to egg-sensitive individuals,
egg proteins are also found in cosmetics,
shampoos, and pharmaceuticals, such
as the laxative Agarol. A patient allergic
to egg should avoid buying fried foods
from vendors who use the same frying
surface for preparing multiple types
of food. Recent evidence suggests that
egg-sensitive children can receive measles
immunization safely.
Although
rare, avian proteins can induce egg
allergy in susceptible individuals.
It has been suggested that duck egg
be substituted for hen's egg in egg-sensitive
individuals. These individuals are able
to tolerate cooked chicken.
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