Vol. 2, #15
April 16, 2005
Q: What are "food allergies" , do they really exist, and what can be done about them? - Technical
A: Food allergy is a reaction of the body's immune system to something in a food or an ingredient in a food; usually a protein. It can be a serious condition and should be diagnosed by a board-certified allergist. A true food allergy (also called "food hypersensitivity") and its symptoms can take many forms.
Symptoms of food allergy differ greatly among individuals. They can also differ in the same person during different exposures. Allergic reactions to food can vary in severity, time of onset, and may be affected by when the food was eaten.
Common symptoms of food allergy include skin irritations such as rashes, hives and eczema, and gastrointestinal symptoms such as nausea, diarrhea and vomiting. Sneezing, runny nose and shortness of breath can also result from food allergy. Some individuals may experience a more severe reaction called anaphylaxis.
Anaphylaxis is a rare but potentially fatal condition in which several different parts of the body experience allergic reactions. These may include itching, hives, swelling of the throat, difficulty breathing, lower blood pressure and unconsciousness.
Symptoms usually appear rapidly, sometimes within minutes of exposure to the allergen, and can be life threatening. Immediate medical attention is necessary when anaphylaxis occurs. Standard emergency treatment often includes an injection of epinephrine (adrenaline) to open up the airway and blood vessels.
- These are the most common clinical manifestations of an allergic
reaction to a food or food additive.
- Symptoms range from acute urticaria (most common) to exacerbations of
- In addition, angioedema and flushing can be due to IgE-mediated food
- Food allergy is rarely an etiology for chronic urticaria or
- Significant controversy surrounds the role of food allergy in the
pathogenesis of atopic dermatitis. Studies show that a significant subset of
patients with chronic atopic dermatitis (35-40%) have IgE-mediated food
allergy contributing to their skin disease.
- Both food-specific IgE-mediated and cellular mechanisms appear
responsible for chronic eczematous inflammation.
- Removal of a specific food allergen leads to resolution of clinical
symptoms in affected patients; reintroduction of the food exacerbates the
- Prophylactic studies show that avoiding particular foods (eg, cow milk,
eggs, peanuts) helps prevent the onset of atopic dermatitis.
- This is an unusual form of non-IgE cell-mediated hypersensitivity
related to celiac disease. It manifests clinically with a chronic and
intensely pruritic rash with a distribution that has some similarities to
the typical rash distribution of atopic dermatitis.
- Elimination of gluten from the diet often leads to resolution of skin
- IgE-mediated gastrointestinal food allergy
- In their classic form, these food allergy reactions include immediate
hypersensitivity and the oral allergy syndrome.
- Specific gastrointestinal symptoms include nausea, vomiting, abdominal
pain, and cramping. Diarrhea is found less frequently.
- The patient may develop a sensation of itching or tingling of the lips,
tongue, palate, and throat following the ingestion of certain foods. In
addition, edema of the lips, tongue, and a sensation of tightness in the
throat may be observed. In fewer than 5% of cases, symptoms progress to more
- In this syndrome, certain pollen and food allergy sensitivities are
related. For example, individuals with ragweed allergy may experience oral
allergy syndrome following the ingestion of bananas or melons, and patients
with birch pollen allergy may experience this syndrome following the
ingestion of raw carrots, celery, potato, apple, hazelnut, or
- Mixed IgE/non-IgE gastrointestinal food allergy (eosinophilic
- Typical symptoms include postprandial nausea, abdominal pain, and a
sensation of early satiety.
- One of the hallmarks in children is weight loss or failure to thrive.
- CBC count and differential findings may show eosinophilia in
approximately 50% of patients; however, this is not diagnostic. Typically,
endoscopy and biopsy must be performed in order to establish the presence of
eosinophils in the intestinal wall. While a dense eosinophil infiltrate may
be seen anywhere from the lower esophagus throughout the large bowel,
involvement is patchy and variable.
- Ultimately, an elemental or oligoantigenic diet is necessary to aid in
- If the patient does not respond to the elemental diet, a trial of
systemic oral corticosteroids can be useful for resolving the clinical
- Non-IgE-mediated gastrointestinal food allergy
- Dietary protein enterocolitis is a syndrome that typically manifests in
the first few months of life in a child who has severe projectile vomiting,
diarrhea, and failure to thrive.
- Cow milk and soy protein formulas are usually responsible for these
reactions, which occur 2 or more hours after food ingestion.
- Infants typically appear lethargic, wasted, and dehydrated. To establish
the diagnosis, an oral challenge study must be performed.
- Severe anaphylactic reactions or fatality
- Following the ingestion of food, severe anaphylactic reactions (ie,
systemic allergic reactions) or fatality can occur.
- Symptoms may include the following:
- Oropharyngeal pruritus
- Angioedema (eg, laryngeal edema)
- A feeling of impending doom
- Cardiovascular collapse
- Risk factors include the following:
- The presence of asthma, especially in patients with poorly controlled
- Previous episodes of anaphylaxis with the incriminated food
- Failure to recognize early symptoms of anaphylaxis
- Delay or lack of immediate use of emergency medications (eg,
Of all the individuals who have any type of food sensitivity, most have food
intolerances. Fewer people have true food allergy involving the immune system.
Other reactions to foods are called food intolerance and food idiosyncrasy. Food
intolerance and food idiosyncrasy reactions are generally localized, temporary,
and rarely life threatening, whereas food allergy can cause life-threatening
Adverse food reactions can be classified into 2
categories. The first is hypersensitivity that is an immunologically mediated
adverse food reaction and is unrelated to any physiologic effect of the food or
food additive. These reactions include disorders mediated by immunoglobulin E
(IgE) antibodies (eg, IgE-mediated reaction to peanuts), which occur more
immediately, and others resulting from non-IgE mechanisms (eg, non-IgE-mediated
reactions such as protein-induced enterocolitis syndrome), which generally take
several hours to appear clinically.
The second category is food intolerance. These reactions include any adverse
physiologic response to a food or food additive that is not immunologically
mediated (eg, lactose intolerance, bacterial food poisoning).
Allergic reactions to food are IgE-mediated or non-IgE-mediated. Immune
responses mediated by specific IgE antibodies are the most widely recognized
mechanism of food hypersensitivity. Patients with atopy produce IgE antibodies
to specific epitopes in the food allergen. These antibodies bind to
high-affinity IgE receptors on tissue mast cells and basophils that are present
in the skin, gastrointestinal tract, and respiratory system. Subsequent allergen
exposure binds these IgE antibodies and initiates the release of many mediators,
including histamines, prostaglandins, and leukotrienes. This results in
vasodilatation, smooth muscle contraction, and mucus secretion, which, in turn,
lead to a spectrum of clinical symptoms observed in persons with allergic
reactions to food.
Food allergens are typically water-soluble glycoproteins with molecular
weights of 10-70 kd. These characteristics facilitate the absorption of these
allergens across mucosal surfaces. Moreover, food allergens are generally
resistant to proteolysis and are heat-stable. Several food allergens are
purified and well-characterized, such as peanut Ara h1, Ara h2, and Ara h3;
chicken egg white Gal d1, Gal d2, and Gal d3; soybean-Gly m1; fish-Gad c1; and
shrimp-Pen a1. Closely related foods frequently contain allergens that
cross-react immunologically (ie, specific IgE antibodies determined by skin
prick or in vitro testing) and only rarely cross-react clinically. Finally,
cross-reactive allergens have been identified among certain foods and airborne
pollens Conserved homologous proteins likely account for this
Food intolerance is an adverse reaction to a food substance or additive that
involves digestion or metabolism (breakdown of food by the body) but does not
involve the immune system. Lactose intolerance is an example of food
intolerance. It occurs when a person lacks an enzyme needed to digest milk
sugar. If a person who is lactose intolerant eats milk products, they may
experience symptoms such as gas, bloating and abdominal pain.
Food idiosyncrasy is an abnormal response to a food or food substance. The
reaction can resemble or differ from symptoms of true food allergy.
Idiosyncratic reactions to food do not involve the immune system. Sulfite
sensitivity or sulfite-induced asthma is an example of a food idiosyncrasy that
affects small numbers of people in the population. However, sulfite-induced
asthma can be potentially life threatening.
Other suspected adverse reactions to foods such as to corn, high fructose
corn syrup and sugar have rarely been demonstrated as true food allergies. Some
foods contain a variety of either naturally occurring or added components that
can cause a chemical, or drug-like reaction. The "burning" sensation when eating
foods like chili peppers is an example of a chemical food reaction.
You should see a board-certified allergist to get a diagnosis. An allergist
and dietitian can best help the food-allergic patient manage diet issues with
little sacrifice to nutrition or the pleasure of eating.
Making a diagnosis may include:
- A thorough medical history;
- The analysis of a food diary; and
- Several tests including skin-prick tests, RAST tests (blood test) and food
challenges (using different foods to test for allergic reactions).
Once a diagnosis is complete, an allergist will help set up a response plan
to manage allergic reactions that may occur. A response plan may include taking
medication by injection or drops ( sublingual-under the tonue) to control
Food additives may also induce allergic reactions. Misconceptions abound
regarding allergy to food additives and preservatives. Although some food
components have been shown to trigger asthma or hives in certain people, these
reactions are not the same as those observed with food.
- Severe anaphylactic reactions, including fatality, can occur following the
ingestion of food. Typical symptoms observed in a food-induced anaphylactic
reaction involve the respiratory tract and include oropharyngeal pruritus,
angioedema (eg, laryngeal edema), stridor, cough, dyspnea, wheezing, and
dysphonia. Food allergy is confirmed in approximately one third of the
patients with anaphylaxis presenting to the emergency department at the Mayo
- Peanuts, tree nuts, and shellfish are usually implicated in food-induced
- Risk factors for food-induced anaphylaxis include (1) the presence of
asthma, especially in patients with poorly controlled disease; (2) previous
episodes of anaphylaxis with the incriminated food; (3) a failure to recognize
early symptoms of anaphylaxis; and (4) a delay or lack of immediate use of
emergency medications (eg, epinephrine, antihistamines) to treat the allergic
Because food allergy can be life threatening, the allergy-producing food must
be completely avoided. If you, or someone else, are experiencing a severe food
allergic reaction, call 911 (or an ambulance) immediately and execute your
Most life-threatening allergic reactions to foods occur when eating away from
the home. It is important to explain your situation and needs clearly to your
host or food server. If necessary, ask to speak with the chef or manager.
The Food and Drug Administration (FDA) requires that ingredients are listed
on most food labels. Be sure to look at the listings on labels to determine the
presence of the eight major allergens. Since food and beverage manufacturers are
continually making improvements, food-allergic persons should read the food
label for every product purchased, each time it is purchased. The same
equipment to manufacture one food product may be used to manufacture another
food product so even though the offending food is not in the other product, it
may contain enough residue to produce fatal reactions as has happened numerous
times with peanut contamination.
Many different foods can cause food allergic reactions. However, most
reactions to foods are not food allergies but some other type of food
- Serum testing for specific IgE antibodies to foods
- Specific IgE antibodies to foods can be measured by in vitro laboratory
methods (eg, IgE radioallergosorbent testing), which offers advantages when
dermatographism, generalized dermatitis, and a clinical history of severe
anaphylactic reactions to a given food limit skin testing.
- This form of testing provides information similar to prick skin tests,
but it is more expensive and generally less specific.
- The recently developed CAP System fluorescent-enzyme immunoassay (FEIA)
(Pharmacia Diagnostics, Uppsala, Sweden) provides a more quantitative method
of determining allergen-specific IgE to food allergens.
- Compared with the outcome of well-controlled oral food challenges,
results of the CAP system FEIA are generally similar to those of prick skin
tests in predicting symptomatic food allergy.
- Quantitating food-specific IgE antibodies with this automated system can
help identify patients who are highly likely to have allergic reactions
- Published positive and negative predictive values using this system are
available, and these values aid in making the diagnosis.
- Currently, the predictive values of CAP System FEIA results are limited
to several major food allergens (ie, egg, milk, peanut, fish) and based on a
population of children with moderate-to-severe atopic dermatitis.
- This type of testing may eliminate the need to perform oral food
challenges in some patients suggested to have an IgE-mediated food
- Peripheral serum measurements of eosinophils or total IgE concentrations:
Results from these tests may support the diagnosis of food allergy, but normal
values do not exclude diagnosis.
- Basophil histamine-release assays: These tests are mainly limited to
research settings and have not been shown conclusively to provide reproducible
results useful for diagnostic testing.
- This is a chronological record of all food eaten and any associated
adverse symptoms. It is inexpensive to undertake and allows patients to
focus on their diet.
- This record is occasionally helpful for identifying the food implicated
in an adverse reaction; however, it is not usually diagnostic, especially
when symptoms are delayed or infrequent.
- This is mainly used in the treatment and prevention of food
- It requires complete avoidance of certain foods or groups of foods for a
given time period, usually 7-14 days, and also may be used in the diagnostic
approach to food allergy.
- Success depends on identifying the correct food allergen and completely
eliminating it in all forms from the diet. This can be difficult if multiple
foods are under consideration.
- Additional limitations of this method include potential effects of
patient or physician biases, questionable patient compliance, and the
time-consuming nature of the endeavor.
- Prick and puncture tests are the most common screening tests for food
allergy and can even be performed on infants in the first few months of
life. However, the reliability of the results depends on multiple factors,
including the testing technique, interpretation of the reaction, and
concomitant use of medications (eg, antihistamines).
- When used in conjunction with a standard criterion of interpretation and
appropriate controls (eg, histamine: positive, saline: negative), these
tests provide useful and reproducible clinical information in a short period
(ie, 15-20 min).
- This is a reliable method of excluding IgE-mediated food allergies. The
negative predictive accuracy is greater than 95%; however, the positive
predictive accuracy is generally less than 50%, which limits clinical
interpretation of positive skin test results.
- Positive skin test and clinical history findings must be confirmed by an
oral food challenge unless the patient has a convincing history of
significant food allergy.
- The risk of inducing a systemic reaction during this type of testing is
increased when compared to the prick or puncture method, and this
intradermal skin testing should be avoided.
- In addition, the results from this method are less specific compared to
those from prick or puncture testing.
- Tests with uncertain diagnostic value: The diagnostic value of performing
the following tests is not currently supported by objective scientific
- Results from food-specific immunoglobulin G (IgG) or IgG subclass
antibody concentration testing have not been proven to be helpful with
- Testing for food antigen-antibody complexes has no proven diagnostic
- Performing leukocyte cytotoxic tests is not supported by objective
- Results from subcutaneous provocation and neutralization testing have
not been proven to be helpful for diagnosis.
- Kinesiology-based testing is not recommended because objective
scientific evidence has indicated this type of testing does not aid in
- Food challenge confirmation of food allergy
- This includes properly conducted elimination of and oral challenge with
foods suggested to cause allergic reactions as based on the medical history,
skin testing results, or in vitro testing results.
- Of these procedures, the double-blind placebo-controlled food challenge
(DBPCFC) is the best method to help diagnose and confirm food allergy and
other adverse food reactions.
- Conduct any food challenge in a clinic or hospital setting with
available personnel and equipment for treating a systemic allergic reaction.
Patients undergoing a food challenge must not be on beta-blocker
medications. Obtain intravenous access in patients with history findings
that indicate the potential for a systemic reaction.
- If the history of the patient suggests an anaphylactic reaction is
possible following food ingestion, do not perform an oral food
- This test involves the patient ingesting the suspected food, which is
prepared in its usual, customary fashion (ie, the challenge food is not
disguised in any way).
- Both the patient and the observer (eg, physician, nurse) are aware of
the food contents.
- The open food challenge is best used in clinical practice when patient
or physician bias is minimal.
- This type of challenge is typically used when the skin test results for
the suspect food are negative or if a specific food reaction is
- Whenever the results are equivocal, perform a blinded
- Patients should never perform an open food challenge at home, even if
the chance they will develop severe symptoms is remote.
- Single blinded food challenge
- This challenge involves the patient ingesting the suspected food, which
is disguised so the patient is unaware of the contents.
- This type of challenge, which is suitable for clinical practice and some
research investigations, is designed to reduce patient bias during the
procedure. However, subjective attitudes regarding the outcome of the
challenge cannot be completely eliminated.
- This test may be useful for screening the patient for entry into studies
in which history findings will be unequivocally confirmed by DBPCFC results.
- Trained personnel and equipment necessary to treat anaphylactic shock
must be available prior to undertaking this procedure because it may result
in allergic reactions.
- Double-blind placebo-controlled food challenge
- DBPCFC involves ingestion of the suspected food, which is disguised so
the patient and observer are unaware of the contents of the
- This type of challenge is designed to reduce patient and observer bias
and subjective attitudes during the procedure.
- Always perform this challenge in a clinic or hospital
- Consider this the criterion standard for diagnosing food allergy,
especially in research investigations. Currently, it is the only completely
objective method for determining the validity of the history of an adverse
reaction to a food.
- Do not perform a challenge if the patient has a clearly convincing
history of a severe life-threatening anaphylactic reaction following the
isolated ingestion of a specific food.
- Consultation with a nutritionist or nutrition service is invaluable in the
overall management. The restriction diet can be reviewed and appropriate
substitutions can be recommended. Dietary deficiencies can be anticipated and
- Consultation with a gastroenterologist is also useful in the workup of
selected patients. For example, patients presenting with possible anatomic
gastrointestinal abnormalities, eosinophilic esophagitis or gastroenteritis,
failure to thrive, and malabsorption syndromes may benefit from consultation
with both an allergist and a gastroenterologist.
- A properly managed well-balanced elimination diet (eg, allergen
restriction) can lead to resolution of symptoms and can help avoid nutritional
- Educate the patient and family how to properly read food labels and to
identify common words for the food allergen of concern (eg, casein and whey
- With elimination diets, only exclude those foods confirmed to provoke the
- Recognize obvious and hidden sources of food allergens. Be aware of
noningestion exposures or contact (eg, airborne allergens).
- Anticipate the likely candidates for food allergen cross-contamination,
such as the following:
- Eggs and chicken (<5%)
- Cow milk and beef (10%)
- Cow milk and goat milk (>90%)
- Fish (>50%)
- Peanuts and related legumes (<10%)
- Soy and related legumes (<5%)
- Tree nuts and other nuts (>50%)
- Avoid high-risk situations (eg, buffets, picnics), where accidental or
inadvertent ingestion of food allergens can occur.
- Developing intolerance
- In general, most infants and young children outgrow or become clinically
tolerant of their food hypersensitivities.
- Well-controlled prospective investigations of food allergy in infants
and children demonstrate that by following proper elimination diets, 85% of
confirmed symptoms are resolved by age 3 years.
- Adults with food allergy also lose their clinical allergic reactions to
foods after implementation of appropriate food elimination diets.
- Approximately one third of all children and adults lose their clinical
reactivity to specific food allergens after 1-2 years of appropriate food
allergen elimination therapy. Patients with allergies to peanuts, tree nuts,
fish, and shellfish rarely lose their clinical reactivity.
- Avoidance of allergen
- How well the patient complies with the allergen avoidance diet seems
directly associated with the ultimate clinical outcome (ie, development of
- Patients with allergic reactions to peanuts, tree nuts, shellfish, and
fish rarely lose their clinical reactivity.
- While exclusive breastfeeding is frequently promoted as a means of
preventing food allergy and atopic disease in general, considerable
controversy remains regarding the effectiveness of this practice.
- Some investigations suggest that lactating mothers should eliminate
highly allergenic foods (eg, peanuts, tree nuts, shellfish) that may induce
life-long allergic sensitivity in their infants. Many allergenic foods can
cross from the mother's blood into the mother's milk.
- Further studies are needed to clarify the role of early elimination
diets and breastfeeding in the prevention of food allergy.
- Recent scientific data support the routine 1-dose administration of the
measles-mumps-rubella vaccine to all patients with egg allergy, even those
with severe anaphylactic reactions following egg ingestion.
- If the patient has a clinical history of egg allergy and has experienced
systemic reactions (eg, anaphylaxis) following the ingestion of egg, the
administration of the influenza vaccine requires special diagnostic
consideration. Test the patient's skin with diluted preparations of the
influenza vaccine (ie, puncture skin testing and, if needed, intradermal
skin testing). If skin test results with the vaccine are positive, the
vaccine can be safely given in a graded, multidose scheme. If results are
negative, the vaccine may be administered in the routine 1-dose
Food sensitivities may be a...
- food allergy,
- food intolerance, or
- food idiosyncrasy.
The eight most common food allergens are milk, eggs, peanuts (legumes,
NOT nuts) , tree nuts, soy, wheat, fish and shellfish.
If you, or someone else, are having a serious allergic reaction to a food,
CALL 911! (or call an ambulance).
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DISCLAIMER: The information in this column, is NOT intended to diagnose and/or treat any health related issues and is provided solely for informational purposes only. Consult the appropriate healthcare professional before making any changes to your healthcare regime. Even what may seem like simple changes in the diet for example, can interact with, and alter, the efficiency of medications and/or the body's response to the medications. Many herbs and supplements exert powerful medicinal effects. Neither the author, nor the website designers, assume any responsibility for the reader's use or misuse of this information.
© 2002 Nature's Corner