ASSESSMENT OF FOOD CHEMICAL INTOLERANCE IN ADULT ASTHMATIC SUBJECTS

Background - Identification of food chemical intolerance in asthmatic subjects can be reliably assessed by changes in the forced expiratory volume in one second (FEV(1)) in response to double blind, placebo con trolled challenges on a strict elimination diet. However, this method is cumbersome and time consuming. A study was undertaken to determine whether changes in bronchial responsiveness to histamine following foo d chemical challenge without an elimination diet might be a faster, mo re convenient method. Methods - Eleven adult asthmatic subjects were c hallenged twice with metabisulphite, aspirin, monosodium glutamate, ar tificial food colours, sodium nitrite/nitrate, 0.5% citric acid soluti on (placebo), and sucrose (placebo) on separate days. During the first set of challenges subjects consumed a normal diet. Bronchial responsi veness to histamine was assessed 90 minutes after each challenge. A gr eater than twofold increase in bronchial responsiveness was considered positive. For one month prior to and during the second set of challen ges subjects followed a strict elimination diet and FEV(1) was monitor ed during and for two hours after each challenge. A fall in FEV(1) of 20% or more was considered positive. Results - Of the 77 food chemical challenges performed on an unmodified diet, 20 were positive (six pla cebo responses). In two subjects it was not possible to perform a hist amine test after one of the chemical challenges because of poor spirom etric function. Of the 77 food chemical challenges performed on an eli mination diet, 11 were positive (no placebo responses). Excluding the two challenges in which there were no corresponding histamine tests, o nly on two occasions did the positive responses in both methods coinci de, giving the unmodified diet method a sensitivity of 22%. Conclusion - Strict dietary elimination and measurement of FEV(1) after double b lind food chemical challenge remains the most reliable method for the detection of food chemical intolerance in asthmatic subjects.