Soy protein, phytate, and iron absorption in humans

Am J Clin Nutr. 1992 Sep;56(3):573-8. doi: 10.1093/ajcn/56.3.573.

Abstract

The effect of reducing the phytate in soy-protein isolates on nonheme-iron absorption was examined in 32 human subjects. Iron absorption was measured by using an extrinsic radioiron label in liquid-formula meals containing hydrolyzed corn starch, corn oil, and either egg white or one of a series of soy-protein isolates with different phytate contents. Iron absorption increased four- to fivefold when phytic acid was reduced from its native amount of 4.9-8.4 to less than 0.01 mg/g of isolate. Even relatively small quantities of residual phytate were strongly inhibitory and phytic acid had to be reduced to less than 0.3 mg/g of isolate (corresponding to less than 10 mg phytic acid/meal) before a meaningful increase in iron absorption was observed. However, even after removal of virtually all the phytic acid, iron absorption from the soy-protein meal was still only half that of the egg white control. It is concluded that phytic acid is a major inhibitory factor of iron absorption in soy-protein isolates but that other factors contribute to the poor bioavailability of iron from these products.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Absorption / drug effects
  • Adult
  • Dietary Proteins / administration & dosage*
  • Female
  • Humans
  • Iron / pharmacokinetics*
  • Male
  • Phytic Acid / administration & dosage
  • Phytic Acid / pharmacology*
  • Plant Proteins / administration & dosage*
  • Plant Proteins / chemistry
  • Soybeans*

Substances

  • Dietary Proteins
  • Plant Proteins
  • Phytic Acid
  • Iron