Estimation of nonheme-iron bioavailability from meal composition

Background: Considerable data are available on the individual effects of di etary factors on nonheme-iron absorption, but their combined effect when th ey are present in the same meal is not known. Objective: Our objective was to predict the bioavailability of iron from co mplex meals that are consumed commonly in the United States on the basis of the contents of factors that are known to promote or inhibit food iron abs orption. Design: Radioisotopic measurements of nonheme-iron absorption from 25 meals were made in 86 volunteer subjects by using extrinsic radioiron labeling. The meal contents of nonheme iron, calcium, ascorbic acid, polyphenols, and phytic acid were determined by biochemical analysis; energy and protein co ntents were estimated from food-composition tables. Animal tissue content w as based on weight or was obtained from the manufacturer. Results: After adjusting iron absorption for differences in iron status, th e significant biochemical predictors of iron absorption as determined by mu ltiple regression analysis were the contents of animal tissue (P = 0.0001), phytic acid (P = 0.0001), and ascorbic acid (P = 0.0441). Collectively, th ese 3 variables accounted for 16.4% of the variation in absorption. On the basis of the multiple regression analysis, we developed the following equat ion to estimate iron absorption: Ln absorption, % (adjusted to serum ferrit in concentration of 30 mu g/L) = 1.9786 + (0.0123 x animal tissue in g) - ( 0.0034 x phytic acid in mg) + (0.0065 x ascorbic acid in mg). Conclusion: For the 25 meals evaluated, only the contents of animal tissue, phytic acid, and ascorbic acid were useful for estimating nonheme-iron abs orption.