Effect of bean polyphenols on iron absorption in humans

Iron deficiency and iron deficiency anaemia are major public health problems in many developing countries. Common beans are a staple food in various Eastern African countries. Beans contain high amounts of iron, but the iron is poorly absorbed due to the presence of the iron absorption inhibitors polyphenols and phytic acid. With the overall aim of increasing the intake of bioavailable iron from beans by plant breeding strategies, this study evaluates the importance bean polyphenols on iron absorption. In common beans the polyphenols are concentrated in the bean hulls. Therefore bean hulls were used as a source of natural bean polyphenols and added in three different amounts to a non-inhibitory test meal (phytic acid free bread rolls). Iron absorption from the test meals was measured in three groups of 16 apparently healthy female volunteers using stable iron isotope techniques. Each volunteer consumed a test meal with and a test meal without bean polyphenols extrinsically labeled with ⁵⁷Fe and ⁵⁸Fe respectively. Iron absorption was determined based on the incorporation of iron stable isotopes into red blood cells 14 days after administration. Isotopic analysis was performed by thermal ionization mass spectrometry. The results of the absorption studies showed a dose dependent negative effect of bean polyphenols on iron absorption in humans. At the lowest polyphenol content tested (20 mg per test meal) no impact on iron absorption was found (p 0.92). A polyphenol content of 50 mg reduced the mean iron absorption significantly from 20.3% to 17.3% (p 0.044). The highest polyphenol content of 200 mg significantly reduced the mean iron absorption from 14.3% to 7.9% (p 0.0001). Further studies are planned to evaluate the relative effect of polyphenols and phytic acid on iron absorption from beans to provide guidance for breeding beans with improved iron bioavailability. (author)