Elimination Diet - Diagnosis

Diagnosis

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. 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.

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 sensitiveity. 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.