Women with low iron stores absorb iron from soybeans

Background: Worldwide, 30% of the population, a greater proportion of whom are women and children, is iron deficient. Soybeans are a major source of nonheme iron in many human diets, but information on iron bioavailability is still conflicting. Because much of soybean iron is in ferritin [distinct from the poorly bioavailable iron in cereals resulting from interactions between calcium, Fe(III), phytate, and proteins in the meal], soybeans provide a target for manipulating seed iron composition to achieve increased iron bioavailability. Objective: The aim was to reevaluate soybean iron bioavailability. Design: Eighteen women, most with marginal iron deficiency, consumed meals with intrinsically labeled (⁵⁵Fe) soybeans (hydroponically grown and nonnodulating) as soup (n = 11) or muffins (n = 7) and a reference dose of ⁵⁹Fe as ferrous sulfate in ascorbate solution. The radioactivity in red cells was measured 14 and 28 d later. Results: The mean ⁵⁵Fe absorption from either soup or muffins was 27% and that from the reference dose was 61%. ⁵⁵Fe was distributed approximately equally between protein (49.3 ± 3.0%) and phytate, a contrast with nodulating soybeans likely caused by a high phosphate content in the growth medium. There was an expected inverse correlation (r = -0.793, P < 0.001) between red cell radioactivity and serum ferritin concentration. Conclusions: These results show that soybeans appear to be a good source of nutritional iron in marginally iron-deficient individuals. More study is needed on the effect of plant nodulation on the form of soybean iron, aimed at enhancing bioavailability to combat iron deficiency in at-risk populations.