Challenges and Techniques for Measuring Iron Bioavailability in Foods.

Iron biofortification requires accurate assessment of Fe bioavailability to identify and characterize the factors that influence Fe absorption from staple crops and food products. Iron bioavailability from a diet should also be evaluated to estimate the contribution of absorbable Fe from various sources. In addition, released cultivars require monitoring for sustainability of effect. In vitro techniques, animal models and isotopic labelling approaches have been applied to such research for well over 50 years. In vitro studies started with Fe solubility as a measure of bioavailability; however, solubility often does not equate with bioavailability due to the complex nature of Fe binding in foods. In vivo studies have used metabolic balance studies, which are imprecise and labor intensive. The majority of in vivo studies have used isotopic Fe labelling, via extrinsic or intrinsic techniques. Extrinsic labelling requires the assumption that the extrinsic Fe fully exchanges with the intrinsic Fe of the food or meal. Many studies show that complete isotopic exchange often does not occur, and thus accuracy of extrinsic labelling is questionable. Intrinsic labelling of food crops, although theoretically more accurate, is expensive as it requires hydroponic greenhouse growth and produces limited amounts of material. Also, hydroponically grown plants may not represent those grown in soil and adverse environmental conditions. As a result of the above, an in vitrodigestion/Caco-2 cell bioassay has evolved that circumvents the need for isotopic labelling. This model is cost effective and has repeatedly demonstrated accurate measurement of Fe bioavailability from staple crops and food products. When coupled with an established poultry model of Fe bioavailability, these tools represent an established approach that are now thoroughly validated via direct parallel comparison with human trials. This presentation will summarize and illustrate the above issues, providing specific examples of how these established techniques can address Fe bioavailability.