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Procedure to identify foods that produce adverse effects

An elimination diet, also known as exclusion diet, is a diagnostic procedure
used to identify foods that an individual cannot consume without adverse
effects.[1] Adverse effects may be due to food allergy, food intolerance, other
physiological mechanisms (such as metabolic or toxins),[2] or a combination of
these. Elimination diets typically involve entirely removing a suspected food
from the diet for a period of time from two weeks to two months, and waiting to
determine whether symptoms resolve during that time period. In rare cases, a
health professional may wish to use an elimination diet, also referred to as an
oligoantigenic diet, to relieve a patient of symptoms they are experiencing.[3]

Common reasons for undertaking an elimination diet include suspected food
allergies and suspected food intolerances. An elimination diet might remove one
or more common foods, such as eggs or milk, or it might remove one or more minor
or non-nutritive substances, such as artificial food colorings.

An elimination diet relies on trial and error to identify specific allergies and
intolerances. Typically, if symptoms resolve after the removal of a food from
the diet, then the food is reintroduced to see whether the symptoms reappear.
This challenge–dechallenge–rechallenge approach has been claimed to be
particularly useful in cases[clarification needed] with intermittent or vague
symptoms.[4]

The exclusion diet can be a diagnostic tool or method used temporarily to
determine whether a patient's symptoms are food-related. The term elimination
diet is also used to describe a "treatment diet", which eliminates certain foods
for a patient.[2] [5][6]

Adverse reactions to food can be due to several mechanisms. Correct
identification of the type of reaction in an individual is important, as
different approaches to management may be required. The area of food allergies
and intolerances has been controversial and is currently a topic that is heavily
researched. It has been characterised in the past by lack of universal
acceptance of definitions, diagnosis and treatment.[2][7]


CONTENTS

 * 1 History
 * 2 Definitions
 * 3 Diagnosis
 * 4 Challenge testing
 * 5 See also
 * 6 References


HISTORY[EDIT]

The concept of the elimination diet was first proposed by Dr. Albert Rowe in
1926 and expounded upon in his book, Elimination Diets and the Patient's
Allergies, published in 1941.[8]

In 1978 Australian researchers published details of an 'exclusion diet' to
exclude specific food chemicals from the diet of patients. This provided a basis
for challenge with these additives and natural chemicals. Using this approach,
the role played by dietary chemical factors in the pathogenesis of chronic
idiopathic urticaria (CIU) was first established and set the stage for future
DBPCT trials of such substances in food intolerance studies.[9][10]


DEFINITIONS[EDIT]

"Food hypersensitivity" is an umbrella term which includes food allergy and food
intolerance. [11] [12] [13]

Food allergy is defined as an immunological hypersensitivity which occurs most
commonly to food proteins such as egg, milk, seafood, shellfish, tree nuts,
soya, wheat and peanuts. Its biological response mechanism is characterized by
an increased production of IgE (immunoglobulin E) antibodies.[14]

A food intolerance on the other hand does not activate the individual's immune
response system. A food intolerance differs from a food allergy or chemical
sensitivity because it generally requires a normal serving size to produce
symptoms similar to an IgE immunologic response. While food intolerances may be
mistaken for a food allergy, they are thought to originate in the
gastrointestinal system. Food intolerances are usually caused by the
individual's inability to digest or absorb foods or food components in the
intestinal tract.[14] One common example of food intolerance is lactose
intolerance.

 * Metabolic food reactions are due to an inborn or acquired errors of
   metabolism of nutrients such as in diabetes mellitus, lactase deficiency,
   phenylketonuria and favism. Toxic food reactions are caused by the direct
   action of a food or additive without immune involvement.[15]
 * Pharmacological reactions are generally to low molecular weight chemicals
   which occur either as natural compounds such as salicylates, amines, or to
   artificially added substances such as preservatives, coloring, emulsifiers
   and taste enhancers including glutamate (MSG).[16] These chemicals are
   capable of causing drug-like (biochemical) side effects in susceptible
   individuals.
 * Toxins may either be present naturally in food or released by bacteria or
   from contamination of food products.[17][18]
 * Psychological reactions involve manifestation of clinical symptoms caused not
   by the food but by emotions associated with the food. The symptoms do not
   occur when the food is given in an unrecognizable form.[19] Although an
   individual may have an adverse reaction to a food, this is not considered a
   food intolerance.

Elimination diets are useful to assist in the diagnosis of food allergy and
pharmacological food intolerance. Metabolic, toxic and psychological reactions
should be diagnosed by other means.[2][20][21]


DIAGNOSIS[EDIT]

Food allergy is principally diagnosed by careful history and examination. When
reactions occur immediately after certain food ingestion then diagnosis is
straight forward and can be documented by using carefully performed tests such
as the skin prick test (SPT) and the radioallergosorbent test RAST to detect
specific IgE antibodies to specific food proteins and aero-allergens. However,
false positive results occur when using the SPT when diagnosis of a particular
food allergen is hard to determine. This can be confirmed by exclusion of the
suspected food or allergen from the patient's diet. It is then followed by an
appropriately timed challenge under careful medical supervision. If there is no
change of symptoms after 2 to 4 weeks of avoidance of the protein then food
allergy is unlikely to be the cause and other causes such as food intolerance
should be investigated.[21][22][23] This method of exclusion-challenge testing
is the premise by which the Elimination Diet is built upon, as explained in the
sections below.

Vega machine testing, a bioelectric test, is a controversial method that attempt
to measure allergies or food or environmental intolerances. Currently this test
has not been shown to be an effective measure of an allergy or intolerance.[24]

Food intolerance due to pharmacological reaction is more common than food
allergy and has been estimated to occur in 10% of the population. Unlike a food
allergy, a food intolerance can occur in non-atopic individuals. Food
intolerances are more difficult to diagnose since individual food chemicals are
widespread and can occur across a range of foods. Elimination of these foods one
at a time would be unhelpful in diagnosing the sensitivity. Natural chemicals
such as benzoates and salicylates found in food are identical to artificial
additives in food processing and can provoke the same response. Since a specific
component is not readily known and the reactions are often delayed up to 48
hours after ingestion, it can be difficult to identify suspect foods. In
addition, chemicals often exhibit dose-response relationships and so the food
may not trigger the same response each time. There is currently no skin or blood
test available to identify the offending chemical(s), and consequently,
elimination diets aimed at identifying food intolerances need to be carefully
designed. All patients with suspected food intolerance should consult a
physician first to eliminate other possible causes.[2][20]

The elimination diet must be comprehensive and should contain only those foods
unlikely to provoke a reaction in a patient. They also need to be able to
provide complete nutrition and energy for the weeks it will be conducted.
Professional nutritional advice from a dietitian or nutritionist is strongly
recommended. Thorough education about the elimination diet is essential to
ensure patients and the parents of children with suspected food intolerance
understand the importance of complete adherence to the diet, as inadvertent
consumption of an offending chemical can prevent resolution of symptoms and
render challenge results useless.

While on the elimination diet, records are kept of all foods eaten, medications
taken, and symptoms that the patient may be experiencing. Patients are advised
that withdrawal symptoms can occur in the first weeks on the elimination diet
and some patients may experience symptoms that are worse initially before
settling down.

While on the diet some patients become sensitive to fumes and odours, which may
also cause symptoms. They are advised to avoid such exposures as this can
complicate the elimination and challenge procedures. Petroleum products, paints,
cleaning agents, perfumes, smoke and pressure pack sprays are particular
chemicals to avoid when participating in an elimination diet. Once the procedure
is complete this sensitivity becomes less of a problem.

Clinical improvement usually occurs over a 2 to 4 week period; if there is no
change after a strict adherence to the elimination diet and precipitating
factors, then food intolerance is unlikely to be the cause. A normal diet can
then be resumed by gradually introducing suspected and eliminated foods or
chemical group of foods one at a time. Gradually increasing the amount up to
high doses over 3 to 7 days to see if exacerbated reactions are provoked before
permanently reintroducing that food to the diet. A strict elimination diet is
not usually recommended during pregnancy, although a reduction in suspected
foods that reduce symptoms can be helpful.[2]


CHALLENGE TESTING[EDIT]

Challenge testing is not carried out until all symptoms have cleared or improved
significantly for five days after a minimum period of two weeks on the
elimination diet. The restrictions of the elimination diet are maintained
throughout the challenge period. Open food challenges on wheat and milk can be
carried out first, then followed by challenge periods with natural food
chemicals, then with food additives. Challenges can take the form of purified
food chemicals or with foods grouped according to food chemical. Purified food
chemicals are used in double blind placebo controlled testing, and food
challenges involve foods containing only one suspect food chemical eaten several
times a day over 3 to 7 days. If a reaction occurs patients must wait until all
symptoms subside completely and then wait a further 3 days (to overcome a
refractory period) before recommencing challenges. Patients with a history of
asthma, laryngeal oedema or anaphylaxis may be hospitalised as inpatients or
attended in specialist clinics where resuscitation facilities are available for
the testing.

If any results are doubtful the testing is repeated, only when all tests are
completed is a treatment diet determined for the patient. The diet restricts
only those compounds to which the patient has reacted and over time
liberalisation is attempted. In some patients food allergy and food intolerance
can coexist, with symptoms such as asthma, eczema and rhinitis. In such cases
the elimination diet for food intolerance is used for dietary investigation. Any
foods identified by SPT or RAST as suspect should not be included in the
elimination diet.[2][7][20][21][22][23][25][26][27][28][29]


SEE ALSO[EDIT]

 * List of diets
 * Lactose intolerance
 * Gluten sensitivity
 * Salicylate sensitivity
 * Multiple chemical sensitivity
 * Sodium phosphates
 * Allergy
 * Allergy testing
 * Canada's Food Guide
 * Food pyramid (nutrition)
 * Self-experimentation
 * Self-experimentation in medicine


REFERENCES[EDIT]

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