Location: Plant, Soil and Nutrition Research
2012 Annual Report
Iron bioavailability studies typically involve isotopic labeling of the food sample in order to track the absorption of the iron. The assumption in this method is that extrinsically added iron mixes and equilibrates fully with the intrinsic Fe of the food sample. If this assumption is accurate, then the iron absorption from the food can be properly monitored. We believe that this assumption has never been adequately tested, even though it has historically been applied to many human iron absorption studies. Our current research is challenging this assumption as we have recently documented in maize. Our initial results from this work indicate that extrinsic labels do not equilibrate adequately with crops such as colored beans. Corn, lentils and white beans show better equilibration but still less than complete. Additional testing is planned for these crops in the coming year.
Over the past year, we have also developed methods to determine the major polyphenolic compounds from the seed coats of black beans and determine their effects on Fe bioavailability. From experience, we suspected that certain polyphenols are potent inhibitors of Fe bioavailability and that some are possible promoters of Fe bioavailability. Our current research indicates that myricetin is a strong inhibitor of Fe bioavailability and is present in relatively high amounts within the seed coat of black beans. Caffeic acid and epicatechin appear to be promoters of Fe bioavailability and are also present in relatively high amounts within the black bean seed coat. These results are potentially valuable to bean breeders as we may be able to modify the concentration of these compounds to improve Fe bioavailability in this crop.
Geophagy, the deliberate consumption of earth, is strongly associated with Fe deficiency. It has been hypothesized to be both a means of increasing Fe intake and a cause of decreased Fe absorption. In collaboration with faculty from Cornell University, we conducted experiments to determine if geophagic earth can provide bioavailable Fe and to examine if geophagic earth can inhibit absorption of Fe in food. For that, 11 geophagic earths consumed in Zanzibar, Tanzania were assessed. Fe content and Fe bioavailability were measured using our cell culture bioassay for Fe bioavailability. The soil samples were extremely high in Fe but provided no significant amount of bioavailable Fe. In fact, our cell culture studies suggested that some types of soil, if consumed with a food could actually reduce Fe absorption from that food. In a subsequent animal feeding trial using poultry, our preliminary results indicate that geophagy provided no significant benefit in terms of Fe status. Additional analysis of the results from the poultry trial are ongoing. Overall, geophagy does not appear to alleviate Fe deficiency and is more likely to be a contributor to the problem. More research is needed to confirm these results.