Test by Elimination Diet

The only fully acceptable way of diagnosing or confirming a 'food intolerance' (as opposed to a 'food allergy') is by an elimination diet.

This test is based on the simple observation that if all likely or possible trigger foods are avoided at the same time, and if food intolerance has been the cause of the patients symptoms, then symptom clearance occurs.  Such a diet is known as an elimination diet, a range of possible trigger foods being disallowed at the same time.  Suspect foods are then introduced one at a time, symptoms observed, and appropriate measurements taken (e.g. a pulse test).  If this period of food avoidance dramatically clears all the symptoms, the recurrence on re-challenge is then more obvious, the period of avoidance also appears to heighten both the rate and the briskness of the symptom response. 

Five to ten days of scrupulous avoidance most reliably produces this response, effectively unmasking the hidden allergy, so that the first eating of the food after the period of avoidance usually produces symptoms within an hour or two.

Experience suggests that attention to detail is needed during this elimination phase.  For example, if sensitivity to corn (maize) is the cause of symptoms (derivatives of corn include corn starch, corn flour, dextrose and other food additives), symptoms may not disappear until all forms are excluded.  This may require the simultaneous avoidance of toothpaste and (where possible) medications whilst on the test diet.  This kind of test is difficult to do on your own.  The assistance of a doctor or dietitian with experience of this kind of testing is invaluable.

Other Tests

It would be very helpful for many people suffering common conditions such as migraine and irritable bowel syndrome if there was an easier test than the elimination diet test.  One result of this has been the proliferation of tests and clinics that offer to 'diagnose' your food intolerance.  Some use measurements of muscle strength (Kinesiology) or electrical activity (Vega test - see left) when you are in close contact with the food.  Some clinics will even offer to test a sample of your hair or urine through the post.  None of these tests has any rational scientific basis and none has been properly compared with the results of elimination diet and sequential food challenge.

Other tests use a blood sample and examine the effects of dilute quantities of the food on the white blood cells (Nutron, Cytotoxic, ALCAT and CAST Elisa tests).  Some measure the production of immune globulin G (IgG Elisa Test).  Whilst these tests may provide pointers to the involved foods, none has been objectively assessed to confirm the level of accuracy.  If these tests are used, the results certainly need to be confirmed, ideally with the help of a doctor or dietitian skilled in the management of food allergy and intolerance.  

Before the results of such tests are accepted, they need to be confirmed by an elimination and challenge test.

Double-Blind Challenge Test

At the other extreme, some doctors have suggested a more rigorous test for food intolerance where small test quantities of suspected foods are hidden in capsules made to look identical to placebo (dummy) capsules that contain an inert substance in place of the food.  The patient then has to take a series of such capsules, neither patient nor doctor knowing which ones contains the suspect food and which ones contain the placebo.  This test is called the double-blind placebo- controlled food challenge (DBPCFC) and has been regarded by some as the 'gold standard' against which all other tests should be compared.

Whilst this test is a valid one for food allergy (the immediate kind), when testing for food intolerance the test has many flaws, the main ones being that firstly the standard DBPCFC test does not employ an adequate elimination diet phase, and secondly the quantity of food tested (normally freeze-dried powder in a capsule) is not sufficient to cause symptoms.  Unfortunately when dealing with food intolerance (as opposed to food allergy) under these circumstances the patient may not get symptoms unless an adequate period of strict elimination has preceded the food challenge, and a sufficiently large portion (or several repeated portions) of the food used for the test.

An examination of the many scientific studies that have properly confirmed the existence of food intolerance shows that all have used elimination diets, and have followed this with properly conducted double-blind placebo-controlled challenge tests.  Studies that have utilised DBPCFC tests without elimination diet (the so-called 'gold standard) and have used this approach in conditions that involve food intolerance have either identified no food reactions at all, or have identified only the immediate food reactions (food allergy).  As a result, the medical scientific community has been divided about the role of food intolerance in common medical conditions.

RAST Blood Test

Last, but not least, amongst tests that may cause confusion if food intolerance is suspected are tests intended for food allergy.  The standard allergy blood test or RAST (radio-allergo-sorbent test), that examines the blood for specific antibodies to many substances foods included, is available through GP's and hospital clinics.  However, in a move that has been heavily criticised by allergy experts, one UK supermarket and several chains of chemist shops are now offering RAST in conjunction with a private pathology laboratory.  This is likely to cause confusion as although such tests may be helpful to confirm a food allergy (the immediate kind), a negative result does not rule out the possibility of food intolerance (the hidden kind)  For this and other reasons, people using these tests should have them interpreted by a doctor or dietitian in conjunction with a case history.