Soy protein, phytate, and iron absorption in humans

Area of Science:

• Nutritional Science
• Food Chemistry

Background:

• Soy protein isolates are a common protein source.
• Phytate in soy can inhibit mineral absorption, particularly iron.

Purpose of the Study:

• To investigate the impact of reducing phytate content in soy protein isolates on nonheme-iron absorption.
• To determine the threshold of phytate reduction necessary for improved iron bioavailability.

Main Methods:

• Human subjects (n=32) consumed liquid formula meals with varying phytate levels from soy protein isolates.
• Iron absorption was quantified using an extrinsic radioiron label.
• Meals also contained hydrolyzed corn starch, corn oil, and either egg white or soy protein isolates.

Main Results:

• Iron absorption increased four- to fivefold when phytic acid was reduced from 4.9-8.4 mg/g to <0.01 mg/g.
• Significant iron absorption improvements were observed when phytic acid was <0.3 mg/g isolate (<10 mg/meal).
• Even with minimal phytate, iron absorption from soy protein was half that of the egg white control.

Conclusions:

• Phytic acid is a primary inhibitor of iron absorption in soy protein isolates.
• Other unidentified factors in soy protein also contribute to reduced iron bioavailability.
• Further research is needed to identify and address these additional inhibitory factors.