In medicine, food allergy is hypersensitivity to dietary
substances, leading to various types of gastrointestinal
complaints. It occurs mainly, but not exclusively, in
children. It is a common type of allergy, and is usually
treated with an exclusion diet.
Signs and symptoms
Patients present with skin
symptoms, throat tightness, shortness of breath,
lightheadedness and/or stomach symptoms. The symptoms
usually develop within half an hour of ingesting the
Rarely, food allergy can lead
to anaphylactic shock: hypotension (low blood pressure) and
loss of consciousness. This is a medical emergency.
Allergens commonly associated with this type of reaction are
peanuts, nuts, milk, egg and seafoods. Latex products can
induce similar reactions.
Food allergy is thought to develop more easily in patients
with the atopic syndrome, a very common combination of
diseases: allergic rhinitis and conjunctivitis, eczema and
asthma. The syndrome has a strong inherited component; a
family history of these diseases can be indicative of the
The best method for
diagnosing food allergy is to be assessed by an allergist.
The allergist will discuss the symptoms that occured after
the food ingestion. If the allergist feels the reaction is
in keeping with a real food allergy, he/she will perform
allergy skin tests. These skin tests are performed by a
method called skin prick testing. It is generally very safe
and tolerated even by young children. The results are
available within 15 minutes. Another option is to perform
blood testing, called RAST testing, for the foods that are
suspected as allergens.
ELISA tests for Iqe
may also be used.
Lactose intolerance; this
generally develops later in life but can present in young
patients in severe cases. This is due to an enzyme
deficiency (lactase) and not allergy. It occurs in many
Celiac disease; this is an autoimmune disorder triggered by
a specific wheat protein (gliadin).
Irritable bowel syndrome (IBS); although many IBS cases
might be due to food allergy, this is an important diagnosis
in patients with diarrhea in whom no allergens can be
C1 esterase inhibitor deficiency (hereditary angioedema);
this rare disease generally causes attacks of angioedema,
but can present solely with abdominal pain and occasional
allergy for a general discussion of the background of
Generally, introduction of
allergens through the digestive tract is thought to induce
immune tolerance. In individuals who are predisposed to
developing allergies (atopic syndrome), the immune system
produces IgE antibodies against protein epitopes on
non-pathogenic substances, including dietary components. The
IgE molecules are coated onto mast cells, which inhabit the
mucosal lining of the digestive tract.
Upon ingesting an allergen, the IgE reacts with its protein
epitopes and release (degranulate) a number of chemicals
(including histamine), which lead to oedema of the
intestinal wall, loss of fluid and altered motility. The
product is diarrhea.
The eight most common food allergies in North America and
Europe are to eggs, milk, peanuts, soy, fish, shellfish,
tree nuts, and wheat. Any food allergy has the potential to
cause a fatal reaction.
The mainstay of treatment
for food allergy is avoidance of the foods that have been
identified as allergens.
If the food is accidentally
ingested and a systemic reaction occurs, then epinephrine
(best delivered in an Epipen) should be used. It is possible
that a second Epipen dose may be required for severe
reactions. The patient should seek medical care.
At this time, there is no
desensitization or allergy "shots" available for food
For reasons that are not
entirely understood, the diagnosis of food allergies has
become more common in Western nations in recent times. (This
trend seems to apply to asthma as well.) In the United
States, it is believed that about 4% of the population
suffers from food allergies. In children, this number is
believed to be significantly higher.
The most common food
allergens include peanuts, milk, eggs, tree nuts, fish,
shellfish, soy, and wheat - these foods account for about
90% of all allergic reactions.
Various medical specialties
have a differing view on food allergies. What is called
irritable bowel syndrome by many doctors (a
stress-related functional disorder) is often interpreted by
allergists to be food allergy.
In addition, many
practitioners of complementary and alternative medicine
ascribe symptoms to food allergy where most classically
trained doctors would not find a causal relationship.
Examples are headaches, tiredness and hyperactivity.
Nevertheless, hypoallergenic diets can be of benefit in
these conditions, indicating that the current medical views
on food allergy may be too limited. Holford and Brady (2005)
suggest three levels of response; classical immediate-onset
allergy (IgE), delayed-onset allergy (giving a positive
response on an ELISA IgG test but rarely on an IgE skin
prick test), and food intolerance (non-allergic), and claim
the last two to be more common.
Milk and soy allergies in
children can often go undiagnosed for many months, causing
much worry for parents and health risks for infants and
children. Many infants with milk and soy allergies can show
signs of colic, blood in the stool, reflux, rashes and other
harmful medical conditions. These conditions are often
misdiagnosed as viruses or colic.
Many children who are allergic to cow's milk protein also
show a cross sensitivity to soy-based products. There are
infant formulas in which the milk and soy proteins are
degraded so when taken by an infant, their immune system
does not recognize the allergen and they can safely consume