Food Allergies and Sensitivities
Presenter: Steve L. Taylor, Ph.D.
University of Nebraska
Department of Food Science & Technology
Food Allergy Research & Resource Program Lincoln, NE
This SciTalk made possible through an educational grant from the Institute
of Food Technologists
The ancient Roman poet and philosopher, Lucretius, was quoted as
saying: "One man's food may be another man's poison". This quote applies
rather nicely to food allergies and sensitivities. While most foodborne
illnesses have the potential to affect everyone in the population, food
allergies and sensitivities affect only a few individuals in the population.
The most serious type of illness among these individualistic adverse
reactions to foods are the true food allergies that are the subject of this
Sci-Talk. Food allergies involve an abnormal response of the immune system
to a particular food or food component, usually a naturally-occurring
protein component of the food, which is safe and nutritious for the vast
majority of consumers.
The most common and severe form of food allergy involves the
development, in susceptible individuals, of IgE antibodies that are able to
recognize and react with a protein component of a specific food. In
IgE-mediated food allergies, allergen-specific IgE antibodies are produced
in the body in response to exposure to a food allergen, usually a protein.
These IgE antibodies are highly specific and will recognize only a specific
portion of the protein that they are directed against. Occasionally, IgE
antibodies produced against one particular protein in a specific food will
confer sensitivity to another food either because the food is closely
related or because it shares a common segment with the allergenic protein.
Some food proteins are more likely to elicit IgE antibody formation than
others. While exposure to the food is critical to the development of
allergen-specific IgE, exposure will not invariably result in the
development of IgE antibodies even among susceptible people. Many factors
including the susceptibility of the individual, the immunogenic nature of
the food and its constituent proteins, the age of exposure, and the dose,
duration, and frequency of exposure are likely to influence the formation of
allergen-specific IgE antibodies.
Once they are produced by immune cells in the body,
allergen-specific IgE antibodies attach to the outer membrane surfaces of
two types of specialized cells: MAST CELLS, which are found in many
different tissues, and BASOPHILS, which are found in the blood. In this
so-called "sensitization" process, the mast cells and basophils are
sensitized and ready to respond to subsequent exposure to that specific food
allergen. However, the sensitization process itself does not result in any
symptoms. No adverse reactions will occur without subsequent exposure to the
specific allergenic protein or some closely related protein. Once the mast
cells and basophils are sensitized, subsequent exposure to the allergen
results in the allergen cross-linking with IgE antibodies on the surface of
the mast cell or basophil membrane. This interaction between the allergen
and the allergen-specific IgE triggers the release of a host of chemical
mediators of allergic disease which are either stored or formed by the mast
cells and basophils. Histamine is one of the primary mediators of
IgE-mediated allergies and is responsible for many of the early symptoms
associated with allergies. The interaction of a small amount of allergen
with the allergen-specific IgE antibodies results in the immediate release
of comparatively large quantities of the various mediators into the
bloodstream and tissues. Thus, exposure to extremely small amounts of
allergens can elicit symptoms. This IgE mechanism is involved in many
different types of allergies to foods, pollens, mold spores, animal danders,
bee venom, and pharmaceuticals. Only the source of the allergen is
IgE-mediated food allergies are sometimes called immediate
hypersensitivity reactions because of the short onset time (a few minutes to
a few hours) between the ingestion of the offending food and the onset of
symptoms. Since the mediators released from the mast cells and basophils can
interact with receptors in a number of different tissues in the body, a wide
variety of symptoms can be associated with IgE-mediated food allergies. The
most common symptoms associated with food allergies are those involving the
skin (hives, eczema, itching) and the gastrointestinal tract (vomiting,
diarrhea). Respiratory symptoms (rhinitis, asthma) are less frequently
involved with food allergies than with various inhalants such as pollen and
animal dander allergies. However, asthma is a very serious, though
uncommon, respiratory manifestation of food allergies. Fortunately, most
food-allergic individuals suffer from only a few of the many possible
symptoms. Anaphylactic shock is, by far, the most serious manifestation of
food allergies. Anaphylactic shock involves gastrointestinal, cutaneous, and
respiratory symptoms in combination with a dramatic fall in blood pressure
and cardiovascular complications. Death can ensue within minutes of the
onset of anaphylactic shock. Fortunately, very few individuals with food
allergies are susceptible to such severe reactions after the ingestion of
the offending food.
The severity of an allergic reaction will be dependent to some
extent on the amount of the offending food that is ingested. Severe
reactions are more likely to occur when an allergic individual inadvertently
ingests a large amount of the offending food, especially if that individual
happens to be exquisitely sensitive. However, exposure to even trace
quantities can elicit noticeable reactions due to the large release of
mediators. Some food-allergic individuals are at risk of death if they
inadvertently ingest their particular offending food. Recent research on
deaths associated with food allergies indicates that teenagers are at
greatest risk of death because they tend to take risks with the foods that
they consume, fail to carry medications that might reverse the severe
reactions, and no longer are reliant on their parents for their safety. The
most common allergenic foods are peanuts, tree nuts (walnuts, almonds,
etc.), cashews, soybeans, cows' milk, eggs, fish, crustacea, and wheat.
Peanuts and the various tree nuts cause most of the deaths but deaths have
also been attributed to milk, eggs, soybeans, fish, and crustacean shellfish
(shrimp, lobster, etc.).
Peanut allergy is the most common food allergy especially in
the U.S. where peanuts are a popular dietary item and peanut butter is
introduced at an early age. Throughout the world, cows' milk allergy is the
most common food allergy among infants due to the widespread ingestion of
milk during the first months of life. Any food which contains protein has
the potential to elicit an allergic reaction in someone. The most common
allergenic foods tend to be foods with high protein content that are
frequently consumed. The exceptions are beef, pork, chicken, and turkey
which are uncommonly allergenic despite their frequent consumption and high
The prevalence of IgE-mediated food allergies is not precisely
known. The overall prevalence of food allergies in the developed countries
of the world ranges from 4-8% in infants to perhaps 1% in adults. Thus, many
infants and young children outgrow their IgE-mediated food allergies. The
reasons for the development of tolerance to previously allergenic foods are
not fully understood. Allergies to some foods such as cows' milk and eggs
are more frequently outgrown than allergies to other foods, such as peanuts.
The specific avoidance diet is the primary means of treatment for
IgE-mediated food allergies. For example, if allergic to peanuts, don't eat
peanuts. With IgE-mediated food allergies, very low amounts of the offending
food can be tolerated by most allergic individuals. However, severe
reactions have resulted from the trace amounts that would result from the
use of a shared eating utensil or cooking equipment such as using a knife
that had been previously used with peanut butter. Thus,the construction of
a safe and effective avoidance diet can be quite difficult. Food-allergic
patients must have considerable knowledge of food composition. For example,
casein, whey, and lactose are common food ingredients that are derived from
cows' milk. These milk ingredients would likely be hazardous for
milk-allergic individuals. The ingredient must contain the specific
allergenic protein to be hazardous to the allergic consumer. For example,
peanut oil and soybean oil, despite being derived from allergenic sources,
do not contain protein and would not be hazardous for peanut-allergic or
soy-allergic individuals unless the oils had become contaminated during use.
The careful reading and complete understanding of food labels is critical to
the implementation of a safe and effective avoidance diet. Of course, the
manufacturers of packaged foods have the responsibility to assure that the
label statements on packages are accurate. However, restaurant and other
food service meals can present an even bigger challenge for food-allergic
individuals. Residues of allergenic foods can arise from the use of shared
food preparation equipment.
Many inadvertent exposures occur among allergic consumers who are
attempting to avoid their offending food(s). Individuals affected by severe
food allergies should carry emergency medications to counteract a reaction
in case their attempts at avoidance are not entirely successful.
Self-injectable epinephrine or adrenalin (sometimes referred to as a bee
sting kit) can be a life-saving drug for such individuals when the offending
food is inadvertently ingested. Parents and friends of individuals with
severe food allergies should learn how to administer the epinephrine also
because immediate administration is advantageous.
Recently, some concerns have been expressed regarding the
potential allergenicity of genetically modified foods. Such foods contain
novel genes and the novel proteins that are expressed from those genes.
Obviously, if a gene was selected from a peanut and cloned into another food
crop such as tomatoes, then the possibility would exist that this gene might
code for an allergenic peanut protein. However, in commercial practice,
genes are usually selected from biological sources that have no history of
causing allergies. In such circumstances, the risk of developing a novel
allergenic food would be very small. Even so, developers of such modified
crops are expected to test the novel proteins for their potential
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Metcalfe, D.D., Sampson, H.A., and Simon, R.A., ed. (1991). "Food
Allergy-Adverse Reactions to Foods and Food Additives".
Blackwell Scientific Publications, Boston.
Taylor, S.L., and Hefle, S. L. (2002). Allergic reactions and food
intolerances. in "Nutritional Toxicology", 2nd ed. (F.N. Kotsonis, and M.
Mackey, eds.). Taylor and Francis, New York, p. 93.
Taylor, S. L., Hefle, S. L., and Munoz-Furlong, A. (1999). Food
allergies and avoidance diets. Nutrition Today 34:15.
Zeiger, R.S., and Heller, S. (1995). The development and
prediction of atopy in high-risk children: follow-up at age seven
years in a prospective randomized study of combined maternal and
infant food allergen avoidance. J. Allergy Clin. Immunol. 95:1179.
TABLE 1. Symptoms of IgE-Mediated Food Allergies
|| Anaphylactic shock
|| Laryngeal edema
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