Iron absorption from soybean ferritin in nonanemic women

Background: Dietary ferritin, a protein cage around an iron mineral, is an underestimated source of bioavailable iron. Plant ferritin, the most common dietary ferritin, has not been studied. Iron from animal ferritin is absorbed as well as is iron from FeSO4 in women. Objective: The objective was to examine iron absorption from purified soybean ferritin. Design: Healthy, nonanemic women (n = 16) were fed a standardized meal (bagel, cream cheese, and apple juice) containing 1 mu Ci Fe-59/meal as FeSO4 or (extrinsically labeled) as iron-free soybean ferritin reconstituted with the high phosphate characteristic of plant ferritin (iron: phosphorus = 4:1). Iron-free, apo-soybean ferritin was prepared (with the use of thioglycolic acid and extensive dialysis) from purified ferritin. In a randomized crossover design, the other labeled meal, which contained FeSO4 or ferritin, was given after 4 wk. The subjects received 140 mu g Fe as ferritin (2.5 mg) or as FeSO4. After 28 d, whole-body Fe-59 and Fe-59 in red blood cells were measured before and after dosing. Results: There was no significant difference in whole-body iron absorption from soybean ferritin (29.9 +/- 19.8%) and that from FeSO4 (34.3 +/- 23.6%) or in iron absorption calculated from red blood cell incorporation (33.0 +/- 20.1% for soybean ferritin and 35.3 +/- 23.4% for FeSO4), which confirmed previous results with animal ferritin that was mineralized and labeled similarly. An inverse relation was observed between serum ferritin and iron absorption from both ferritin and FeSO4, which suggested that sensors regulating iron absorption respond similarly to iron provided as ferrous salts or as ferritin mineral. Conclusion: Iron from soybean ferritin is well absorbed and may provide a model for novel, utilizable, plant-based forms of iron for populations with a low iron status.