ALLERGY AND INTOLERANCES
allergies or food intolerances affect nearly everyone at some point.
People often have an unpleasant reaction to something they ate and
wonder if they have a food allergy. One out of three people either
say that they have a food allergy or that they modify the family
diet because a family member is suspected of having a food allergy.
But only about three percent of children have clinically proven
allergic reactions to foods. In adults, the prevalence of food allergy
drops to about one percent of the total population.
difference between the clinically proven prevalence of food allergy
and the public perception of the problem is in part due to reactions
called "food intolerances" rather than food allergies. A food allergy,
or hypersensitivity, is an abnormal response to a food that is triggered
by the immune system. The immune system is not responsible for the
symptoms of a food intolerance, even though these symptoms can resemble
those of a food allergy.
is extremely important for people who have true food allergies to
identify them and prevent allergic reactions to food because these
reactions can cause devastating illness and, in some cases, be fatal.
Allergic Reactions Work
allergic reaction involves two features of the human immune response.
One is the production of immunoglobulin E (IgE), a type of protein
called an antibody that circulates through the blood. The other
is the mast cell, a specific cell that occurs in all body tissues
but is especially common in areas of the body that are typical sites
of allergic reactions, including the nose and throat, lungs, skin,
and gastrointestinal tract.
ability of a given individual to form IgE against something as benign
as food is an inherited predisposition. Generally, such people come
from families in which allergies are common-not necessarily food
allergies but perhaps hay fever, asthma, or hives. Someone with
two allergic parents is more likely to develop food allergies than
someone with one allergic parent.
an allergic reaction can occur, a person who is predisposed to form
IgE to foods first has to be exposed to the food. As this food is
digested, it triggers certain cells to produce specific IgE in large
amounts. The IgE is then released and attaches to the surface of
mast cells. The next time the person eats that food it interacts
with specific IgE on the surface of the mast cells and triggers
the cells to release chemicals such as histamine. Depending upon
the tissue in which they are released, these chemicals will cause
a person to have various symptoms of food allergy. If the mast cells
release chemicals in the ears, nose, and throat, a person may feel
an itching in the mouth and may have trouble breathing or swallowing.
If the affected mast cells are in the gastrointestinal tract, the
person may have abdominal pain or diarrhea. The chemicals released
by skin mast cells, in contrast, can prompt hives.
allergens (the food fragments responsible for an allergic reaction)
are proteins within the food that usually are not broken down by
the heat of cooking or by stomach acids or enzymes that digest food.
As a result, they survive to cross the gastrointestinal lining,
enter the bloodstream, and go to target organs, causing allergic
reactions throughout the body.
complex process of digestion affects the timing and the location
of a reaction. If people are allergic to a particular food, for
example, they may first experience itching in the mouth as they
start to eat the food. After the food is digested in the stomach,
abdominal symptoms such as vomiting, diarrhea, or pain may start.
When the food allergens enter and travel through the bloodstream,
they can cause a drop in blood pressure. As the allergens reach
the skin, they can induce hives or eczema, or when they reach the
lungs, they may cause asthma. All of this takes place within a few
minutes to an hour.
adults, the most common foods to cause allergic reactions include:
shellfish such as shrimp, crayfish, lobster, and crab; peanuts,
a legume that is one of the chief foods to cause severe anaphylaxis,
a sudden drop in blood pressure that can be fatal if not treated
quickly; tree nuts such as walnuts; fish; and eggs.
children, the pattern is somewhat different. The most common food
allergens that cause problems in children are eggs, milk, and peanuts.
Adults usually do not lose their allergies, but children can sometimes
outgrow them. Children are more likely to outgrow allergies to milk
or soy than allergies to peanuts, fish, or shrimp.
foods that adults or children react to are those foods they eat
often. In Japan, for example, rice allergy is more frequent. In
Scandinavia, codfish allergy is more common.
someone has a life-threatening reaction to a certain food, the doctor
will counsel the patient to avoid similar foods that might trigger
this reaction. For example, if someone has a history of allergy
to shrimp, testing will usually show that the person is not only
allergic to shrimp but also to crab, lobster, and crayfish as well.
This is called cross-reactivity.
interesting example of cross-reactivity occurs in people who are
highly sensitive to ragweed. During ragweed pollination season,
these people sometimes find that when they try to eat melons, particularly
cantaloupe, they have itching in their mouth and they simply cannot
eat the melon. Similarly, people who have severe birch pollen allergy
also may react to the peel of apples. This is called the "oral allergy
A differential diagnosis means distinguishing food allergy from
food intolerance or other illnesses. If a patient goes to the doctor's
office and says, "I think I have a food allergy," the doctor has
to consider the list of other possibilities that may lead to symptoms
that could be confused with food allergy.
possibility is the contamination of foods with microorganisms, such
as bacteria, and their products, such as toxins. Contaminated meat
sometimes mimics a food reaction when it is really a type of food
are also natural substances, such as histamine, that can occur in
foods and stimulate a reaction similar to an allergic reaction.
For example, histamine can reach high levels in cheese, some wines,
and in certain kinds of fish, particularly tuna and mackerel. In
fish, histamine is believed to stem from bacterial contamination,
particularly in fish that hasn't been refrigerated properly. If
someone eats one of these foods with a high level of histamine,
that person may have a reaction that strongly resembles an allergic
reaction to food. This reaction is called histamine toxicity.
cause of food intolerance that is often confused with a food allergy
is lactase deficiency. This most common food intolerance affects
at least one out of ten people. Lactase is an enzyme that is in
the lining of the gut. This enzyme degrades lactose, which is in
milk. If a person does not have enough lactase, the body cannot
digest the lactose in most milk products. Instead, the lactose is
used by bacteria, gas is formed, and the person experiences bloating,
abdominal pain, and sometimes diarrhea. There are a couple of diagnostic
tests in which the patient ingests a specific amount of lactose
and then the doctor measures the body's response by analyzing a
type of food intolerance is an adverse reaction to certain products
that are added to food to enhance taste, provide color, or protect
against the growth of microorganisms. Compounds that are most frequently
tied to adverse reactions that can be confused with food allergy
are yellow dye number 5, monosodium glutamate, and sulfites. Yellow
dye number 5 can cause hives, although rarely. Monosodium glutamate
(MSG) is a flavor enhancer, and, when consumed in large amounts,
can cause flushing, sensations of warmth, headache, facial pressure,
chest pain, or feelings of detachment in some people. These transient
reactions occur rapidly after eating large amounts of food to which
MSG has been added. Sulfites can occur naturally in foods or are
added to enhance crispness or prevent mold growth. Sulfites in high
concentrations sometimes pose problems for people with severe asthma.
can give off a gas called sulfur dioxide, which the asthmatic inhales
while eating the sulfited food. This irritates the lungs and can
send an asthmatic into severe bronchospasm, a constriction of the
lungs. Such reactions led the U.S. Food and Drug Administration
(FDA) to ban sulfites as spray-on preservatives in fresh fruits
and vegetables. But they are still used in some foods and are made
naturally during the fermentation of wine, for example.
are several other diseases that share symptoms with food allergies
including ulcers and cancers of the gastrointestinal tract. These
disorders can be associated with vomiting, diarrhea, or cramping
abdominal pain exacerbated by eating.
intolerance is associated with the disease called gluten-sensitive
enteropathy or celiac disease. It is caused by an abnormal immune
response to gluten, which is a component of wheat and some other
people may have a food intolerance that has a psychological trigger.
In selected cases, a careful psychiatric evaluation may identify
an unpleasant event in that person's life, often during childhood,
tied to eating a particular food. The eating of that food years
later, even as an adult, is associated with a rush of unpleasant
sensations that can resemble an allergic reaction to food.