An elimination diet, also known as exclusion diet, is a diagnostic procedure used to identify foods that an individual cannot consume without adverse effects.
Adverse effects may be due to food allergy, food intolerance, other toxins,
or a combination of these.
ED involves 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.
Reasons for undertaking an elimination diet: suspected food allergies and suspected food intolerances.
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.
Food allergy is an immunological hypersensitivity which occurs most commonly to food proteins: egg, milk, seafood, shellfish, tree nuts, soya, wheat and peanuts: characterized by an increased production of IgE (immunoglobulin E) antibodies.
Food intolerance on the other hand does not activate the immune response system.
A food intolerance generally requires a normal serving size to produce symptoms similar to an IgE immunologic response.
Food intolerances may be mistaken for a food allergy, but they are thought to originate in the gastrointestinal system, and are usually caused by the individual’s inability to digest or absorb foods or food components in the intestinal tract: 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.
Pharmacological reactions are generally to low molecular weight chemicals.
These chemicals 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).
Such toxic chemicals cause biochemical responses in susceptible individuals, and may be naturally in food or released by bacteria or from contamination of food products.
It is possible that psychological reactions involve clinical symptoms caused not by the food but by emotions associated with the food.
In such cases symptoms do not occur when the food is given in an unrecognizable form.
While elimination diets are useful to assist in the diagnosis of food allergy and pharmacological food intolerance, metabolic, toxic and psychological reactions are diagnosed by other means.
Food allergy is principally diagnosed when reactions occur immediately after certain food ingestions.
The diagnosis can be documented by 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.
If false positive results occur when using the SPT or when diagnosis of a particular food allergen is hard to determine, the exclusion of the suspected food or allergen from the patient’s diet, followed by an appropriately timed challenge can establish a diagnosis.
Food intolerance due to pharmacological reaction is more common than food allergy.
Food intolerance estimated to occur in 10% of the population.
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.
Specific food components are not readily known and the reactions are often delayed up to 48 hours after ingestion, it can be difficult to identify suspect foods.
With chemicals there is often a 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).
The elimination diet must be comprehensive.
It should contain only those foods unlikely to provoke a reaction in a patient.
An elimination diet must provide complete nutrition and energy for the weeks it will be conducted.
While on the elimination diet, records are kept of all foods eaten, medications taken, and symptoms that the patient experiences.
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 is 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.
Challenge testing is carried out after all symptoms have cleared or improved significantly for five days after a minimum period of two weeks on the elimination diet.
Food challenges on wheat and milk can be carried out first, then followed by challenge periods with natural food chemicals, then with food additives.
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 before recommencing challenges.
The diet restricts only those compounds to which the patient has reacted and over time liberalization is attempted.