Wheat fiber, phytates and iron absorption

Abstract

The marked inhibitory effect of bran on iron absorption can almost completely be explained by its content of phytates. There are other inhibiting factor(s) as well in bran but they play only a minor role especially in meat containing meals. Several studies were made to clarify the role of phytates. Enzymatic dephytinization of bran almost fully removed its inhibiting effect. The same was observed when washing bran with hydrochloric acid. A “physiological” mixture of monoferrric, potassium and magnesium phytates showed the same inhibition of the absorption of iron as bran with the same phytate content.

There was a strong semilogarithmic relationship (r = 0.99) between the inhibition of iron absorption and the amount of phytates. As little as 5-10 mg phytate phosphorus added to a wheat roll containing 3 mg iron inhibited iron absorption by 50 per cent. Ascorbic acid as well as meat strongly counteracted this inhibition.

It was concluded that if bran is used to increase the dietary fiber intake that would interfere with the absorption of iron. However, if the intake of ascorbic acid and/or meat are sufficiently increased in the bran containing meals that would effectively counteract the inhibition of the iron absorption by the phytates in bran (wheat fiber).