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Volume CXXXIII, Number 13 |
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Ask Dr. Jeff
JEFF BENSON, M.D.
COLUMNIST
Dear Dr. Jeff: What's the story with food allergies?
Are they more common- or more dangerous- than they used to be? -JRW
Dear JRW: Although a great many people believe themselves
to be allergic to certain foods, studies show that only 6 percent of children
and 1 or 2 percent of adults actually have true food allergies. True allergies
involve an immune reaction to specific proteins. Other non-allergic reactions
to food include food intolerances (from a lack of digestive enzymes, such
as lactose intolerance), reactions to food additives (like MSG), or naturally
occurring food components (like tyramine in cheese), or actual food poisoning
(caused by microbes contained in the food and not the food itself).
In an allergic reaction to food, certain cells in the gastrointestinal
tract (mast cells) release chemical mediators (especially histamines)
which induce local, and sometimes systemic, allergic symptoms. Initially,
these symptoms might include transient itching and swelling of the lips,
mouth or throat. When the offending food passes into the stomach and intestines,
however, nausea, vomiting, cramping pain, abdominal distention and diarrhea
may result. Allergic reactions to food can also cause hives, swelling
of the hands or feet, or an asthma attack. Rarely, food allergies can
result in anaphylaxis: extreme shortness of breath, heart beat irregularities,
and, if untreated, shock and ultimately death.
Most people with food allergies are allergic to fewer than
4 foods. The most common adult food allergens are peanuts, tree nuts (like
walnuts or almonds), fish and shellfish.
Allergic symptoms generally develop within minutes to 2
hours after eating, but may vary greatly depending on the manner in which
the food was prepared, the amount consumed, and what else was also eaten
during the same meal. For these reasons, foods suspected of being allergens
may fail to provoke consistent allergic reactions. Food allergies are
diagnosed through selective hypersensitivity skin testing or "RAST"
allergy blood tests or through placebo-controlled food challenges or dietary
restrictions.
At present, there is no cure for food allergies. Avoidance
is the only way to prevent an allergic reaction. Sometimes, that can be
more difficult than one might expect. For instance, some "artificial"
nuts, like mandelonas, are sold as peanut substitutes, but in fact are
themselves just peanuts that have been deflavored and then reflavored
(with almond oil, in the case of mandelonas). They are just as potently
allergenic as natural peanuts. Fish-allergic people can react to non-fish
food that has been unknowingly contaminated by a spatula, cooking oil
or grill previously exposed to fish. Worcestershire sauce usually contains
anchovies.
Anaphylactic allergic reactions must be treated promptly
with epinephrine. People with a history of severe food allergies should
always carry a couple of Epipens and should also wear a Medicalert bracelet.
Anaphylactic reactions cannot be reliably prevented by taking antihistamines
before eating, nor by inducing vomiting after food has been ingested.
Those at risk should take epinephrine as soon as they suspect they have
eaten a problem food or feel a reaction starting. Even if the reaction
is stopped by the epinephrine, they should be transported immediately
to the nearest Emergency Room for further evaluation and observation.
It may not have been scientifically demonstrated (at least
yet), but it certainly seems that food allergies are more common nowadays.
This may be a result of the innumerable chemical manipulations of our
food that take place commercially (everything from the genetic modification
of crops to the addition of beef extracts to McDonald's fries). It has
been clearly shown, however, that the most effective primary prevention
of food allergies comes from extended breast feeding of infants and then
delaying and moderating their introduction to table foods.
Stay informed about what you eat!
Jeff Benson, M.D.
Dudley Coe Health Center