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THE BIOLOGY O F
Food Allergies and Intolerances
All of us live with, know, or have heard of somebody who
then marshal an overwhelming systemic response, ramping
call an allergic response. The symptoms vary because differ-
damages the small intestine. The latter condition is common
has had a harrowing allergic reaction to food. There they
it up faster than the pathogen can reproduce. Amazingly,
ent tissues react to histamine and other allergic mediators in
enough—recent studies estimate it affects one in 133 people of
are, enjoying a meal at the kitchen table, a restaurant, or
less than one-trillionth of a gram of viral material is enough
different ways.
European descent—that it has a name: celiac disease, from the
a wedding banquet. Then suddenly, within minutes or
to induce an immune response.
About 80% of people who think they have a food allergy
Greek word for abdomen.
a few hours, they are fighting off a severe, potentially life-
You can think of a food allergy as a malfunction of the
actually have a so-called food intolerance, meaning a reaction
Gluten can be hard to avoid: many restaurants and food
threatening allergic reaction (called anaphylaxis) by jabbing
immune system. Food should not trigger self-destruction.
that occurs by some biological mechanism other than an
products label products that contain wheat but not other
themselves with an adrenaline injector or being rushed to
But in people with food allergies, the immune system reacts
antibody response. Intolerances are even more mysterious
sources of gluten, including many other grains. Cross-
the emergency ward.
to certain food proteins as if they were signs of a dangerous
than food allergies; in many cases, the mechanism is
contamination is a frequent problem. Even some medicines,
Anaphylactic reactions are the most severe manifesta-
microbe. This is why the smallest hint of peanut protein, left
unknown.
vitamin formulations, and lip balms contain the protein.
tions of food allergies. Few countries have any estimates of
on an imperfectly cleaned assembly line and picked up on
Some reactions seem to be set off by irritating chemicals,
Those who suffer the most acute form of celiac disease
deaths due to food-triggered anaphylaxis, but the U.S. is
the wrapper of a peanut-free product, can trigger anaphy-
such as histamine, or by toxins from troublesome bacteria.
remain malnourished no matter how much they eat, as long
one of them. According to government estimates, 100–200
laxis. To the immune cells of a highly allergic person, those
Others occur because a person lacks a particular enzyme
as gluten is part of their diet. Fortunately, there is a simple and
people die annually from anaphylaxis in the United States,
few molecules of protein look for all the world like a life-
needed to digest a component of the food. Probably the best
complete cure: avoid eating gluten. Even so, it can take
where 6%–8% of children and about 4% of adults are
threatening germ.
known and most common example is lactose intolerance.
months for the gut to heal after the offending protein is
allergic to at least one food. Globally, a larger proportion
Some 90% of all people with food allergies respond to
Lactose is a common sugar found in milk and milk products.
removed from the diet. As with other intolerances, the range
of people, when asked whether they think they have an
one of a notorious octet of allergens: shellfish, fish, peanuts,
Lactose-intolerant people are deficient in lactase, an enzyme
of symptoms can vary widely, with some people suffering
allergy, will say that they do, but medical tests generally
cow’s milk, eggs, tree nuts (such as walnuts and pecans),
that breaks down lactose into simpler carbohydrates. To the
major discomfort if they eat tiny amounts of gluten and others
confirm that only 1%–5% of a given population indeed has
soybeans, and wheat. Tree nuts are thought to be the most
normally beneficial bacteria that usually make a quiet living in
able to occasionally down a slice of pizza with no ill effects.
a food allergy.
potent food allergens: vanishingly small amounts of the
the gut, the undigested lactose becomes an abundant source
Other common food intolerances include difficulty pro-
In the vast majority of cases, allergic reactions to food
troublesome proteins, perhaps as little as 10 millionths of
of food, leading to the generation of gas, pain, and other
cessing histamines (present in certain cheeses, wine, and
come and go within minutes or hours. They usually involve
a gram, have triggered serious allergic reactions. According
characteristic symptoms.
fishes including tuna and mackerel), nitrates (ubiquitous in
distressing but easily manageable symptoms, such as hives
to the U.S. Centers for Disease Control and Prevention, 6.9
Gluten intolerance is also widespread. It takes at least two
preserved meats), and sulfites (added as a preservative to wine
or rashes, tingling in the mouth and throat, or coughing and
million Americans are allergic to seafood of some variety
distinct forms. Some people’s bodies simply react to the
and beer but also a naturally occurring constituent of onions,
wheezing. But then there are those 30,000 emergency-
and 3.3 million are allergic to peanuts or tree nuts.
protein gluten as a toxin. In many others, the protein, which is
garlic, and fermented liquids such as vinegars, wines, and soy
room visits each year from people with serious allergies. For
Only a small minority of people who have food allergies
a component in all varieties of wheat, barley, rye, and many
sauce and a frequent contaminant of citric acid and
such a person, ingesting even a trace of an allergenic food
are at risk of anaphylaxis. What sets the stage for an anaphy-
other grains, triggers an inflammatory immune response that
cornstarch).
foments riot within the immune system.
lactic response to food is the ingestion of a particular food
The French physiologist Charles Richot, who won a Nobel
protein and the presence in the body of an errant antibody
Prize in 1913 for his work leading to the recognition of this
that latches onto that protein. Antibodies are proteins made
over-the-top type of immune system response, explained in
his Nobel speech how he came up with the word “anaphylaxis.”
His basis for the word says something about how the
normally life-preserving immune system can go so wrong:
“Phylaxis, a word seldom used, stands in the Greek for
in an enormous variety of subtle variations by the immune
system. They have a bloodhoundlike ability to find and bind
with exquisite selectivity to specific molecules of concern,
such as proteins in a virus’s shell.
For reasons that are not entirely clear, some people
Food labels in the U.S. and some other countries must alert consumers to ingredients
or possible cross-contaminants that may trigger one of the more common allergic
reactions, such as that to peanuts. But such warnings are not comprehensive. They don’t
always cover substances, such as nitrates or sulfites, to which people may be intolerant
or food components that are used during intermediate processing of the product.
protection. “Anaphylaxis” will thus stand for the opposite …
develop antibodies that bind to a food protein. For these
that state of an organism in which it is rendered hypersensi-
people, when that food protein is present, perhaps even
tive instead of being protected.”
from a shiny clean spoon that might previously have been
Such a rapid, feather-trigger, shock-and-awe response is
used to scoop some peanut butter from a jar, it interacts
just what the body needs to fight off viruses and bacteria
with these first-response antibodies.
because just a few of these microscopic pathogens can
The antibodies, in turn, set off a cascade of events in
quickly replicate to legion and lethal numbers if left un-
immune system cells, including basophils in the blood and
checked. In response to that threat, the human immune
mast cells in body tissues. When stimulated by the allergen,
system evolved the ability to detect truly minuscule
these cells release histamine, tryptase, and other biochemi-
amounts of the chemicals that signal an infection and to
cal mediators that produce the wide range of symptoms we
238 VOLUME 1 · HISTORY AND FUNDAMENTALS FOOD AND HEALTH 239