Absorption of Iron Naturally Present in Soy

Abstract

Plant-based foods can offer sustainable and healthy dietary choices. Soybeans and derivatives (for example, flour, concentrate, or isolate) are the primary protein source for plant-based products, including meat analogs, and are naturally rich in iron. To investigate the nutritional contribution of iron naturally present in soy, this narrative review presents iron bioavailability data from isotope studies in humans aged >3 y. To allow interstudy comparison, we adjusted mean iron absorption for iron status (that is, serum ferritin of 15 μg/L), quantified native iron absorbed, and compared with daily human requirements for absorbed iron where possible. Adjusted iron absorption from soybeans served as part of meals varied widely (4.1%–22.2%), translating to contributions of 13%–70% and 10%–40% to the daily requirements for absorbed iron in adult males and females, respectively. Similar results were found for meals prepared with soy flour (full fat, defatted, and texturized) and soy protein concentrates, whereas iron bioavailability from soy protein isolates may be reduced. Within a meal, partial substitution (≤30%) of meat with soy concentrates and isolates did not meaningfully impair total iron absorption. In all conditions, low phytic acid levels and co-ingestion of ascorbic acid improved the absorption of iron naturally present in soy. Available evidence suggests that soy-based products can provide a meaningful contribution to daily requirements for absorbed iron, especially if phytic acid is below defined thresholds to optimize absorption and/or if products include iron absorption enhancers such as ascorbic acid. Further research is needed to understand the factors affecting iron bioavailability from these products, especially the soy cultivar, the roles of phytoferritin and the protein profiles of different soy protein ingredients, as well as the processes to produce them. Long-term assessments of the impact of soybean-based products on iron status are also warranted.