Soy Nutrition Institute
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Jul 21, 2015

Adaptation to the iron-inhibiting effects of phytate

Phytate, which is found in whole grains and legumes including soy, is known to inhibit the absorption of divalent minerals such as iron. Since plant-based diets are typically high in these foods some concern has been raised about the iron status of vegetarians. However, nearly all studies show that vegetarian iron status is normal although iron stores are usually lower in comparison to that of nonvegetarians. One reason for the normal iron status may be because new research indicates there is adaption to the mineral-inhibiting effects of phytate. This notion contrasts with findings from a study published nearly 30 years ago.

For this new study, 32 nonanemic females, 18-35 y of age, with normal body mass index but with suboptimal iron stores were matched for serum ferritin concentration and randomly assigned to high-phytate or low-phytate groups, in a parallel design study. Each subject consumed high- or low-phytate foods with at least 2 of their daily meals for 8 weeks and the serum iron response over 4 hours after a test meal containing 350 mg of phytate was measured at baseline and postintervention.  The serum iron response to the test meal increased in the high-phytate group at postintervention, resulting in a 41% increase in the area under the curve (AUC). In contrast, no effect was observed in the low-phytate group (21% decrease in AUC). These results strongly suggest that iron bioavailability from diets rich in high-phytate foods has been underestimated.

Armah SM, Boy E, Chen D, et al. Regular consumption of a high-phytate diet reduces the inhibitory effect of phytate on nonheme-iron absorption in women with suboptimal iron stores. J Nutr. (2015).