Bioavailable iron in typical Thai meals: Comparative studies between radioactive in vitro and in vivo food iron absorption measurements

Presently available in vivo methods for assessing iron absorption in human subjects, although physiologically acceptable and accurate, are not practical for screening large numbers of food and diet samples. A simple in vitro method for determining the amount of iron available for absorption was therefore investigated. It is based on the common pool concept of food iron absorption using radioactive Fe-59 as a marker of the iron present in the bioavailable iron pool. The ionizable iron was measured after an initial peptic digestion by using pepsin/HCl at pH 1.35 followed by an increase of the pH to 6.0 to simulate duodenal alkalinity. The method was proved to be simple, reproducible and applicable either to single food items or whole meals of varying composition. It is able to detect known enhancers or inhibitors of food iron absorption. The percent ionizable iron among 5 different meals with the inclusion of inhibitor or enhancer was shown to correlate closely with the percentage of iron absorbed in human subjects (r=0.9197, p<0.001). A high correlation between the in vivo and in vitro methods was also observed when the results were expressed as absorption ratios and ionizable ratios (r=0.9192, p<0.001). The method is expected to be useful for improving diet composition to increase the iron availability of some typical meals in developing countries, including those which are known to contain considerable amounts of inhibitors of iron absorption. 39 refs, 1 fig., 13 tabs