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United States Department of Agriculture

Agricultural Research Service


Location: Plant, Soil and Nutrition Research

2012 Annual Report

1a.Objectives (from AD-416):
Study food factors and intestinal conditions that enhance and inhibit the bioavailability of iron in staple food crops, food products and food ingredients.

1b.Approach (from AD-416):
Use a combination of in vitro assays and animal studies to identify factors that enhance or inhibit iron bioavailability from foods. We will also employ sophisticated state of the art analytical techniques to measure and profile the minerals and phytochemcals in the foods. We will also use techniques that profile the microflora of the intestine to determine how intestinal bacteria influence iron bioavailability. Coupled together, this combination of in vitro techniques, animal trials and analytical methods will expose the mechanisms of how various food and intestinal factors influence iron bioavailability.

3.Progress Report:

In FY 2012, we continued the use of a poultry model for Fe bioavailability from foods. In the past year, this model was utilized to demonstrate the potential nutritional benefits of feeding high Fe black beans and low phytate sorghum. It is also planned to be used in conjunction with a cell culture model to identify lentil harvest that are high in bioavailable Fe. Indeed, sufficient progress has now been made on the use of this model that we believe it may be useful to exactly match a meal plan for humans. For example, in regions of Bangladesh, the meal plan is relatively monotonous, consisting of a serving of rice, some lentils and a small serving of a vegetable or fish. We now have logistical methods in place to do the same with our poultry model, thus we can match exactly a human meal plan over the course of 6-7 weeks (a typical poultry trial) and thus get an accurate assessment of the Fe bioavailability from prospective human meal plans.

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.

Last Modified: 11/28/2015
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