Effects of phytate on mineral bioavailability in mice

Phytic acid (inositolhexaphosphoric acid) constitutes 1-3% by weight of all plant seeds and is present in numerous food commodities. Excessive dietary intake of phytate is thought to suppress the bioavailability of important polycations, such as Fe3+ and Zn2+, through the formation of insoluble metal phytate complexes. However, multiple factors may affect intestinal mineral absorption, and direct interference by phytate is still controversial. Therefore, we decided to investigate the chemical interactions between phytate and Fe3+, Zn2+ and Ca2+ in vitro and to measure the uptake of 59Fe3+ and 45Ca2+ administered to mice by intraduodenal instillation and by gavage, respectively. The results demonstrate that: 1) di- and trivalent cations studied form soluble complexes with phytate at high phytate-to-metal ratios, independent of pH and 2) phytic acid has no substantial effect on the absorption of either Ca2+ or Fe3+. These results may prompt reevaluation of the supposedly adverse effects of dietary phytate on the bioavailability of metallophytate complexes.