Blood lipid and oxidative stress responses to soy protein with isoflavones and phytic acid in postmenopausal women.

Background: Postmenopausal women are at risk of cardiovascular disease (CVD) as a result of unfavorable blood lipid profiles and increased oxidative stress. Soy protein consumption may help protect against these risk factors.

Objective: Our objective was to ascertain the effect of the soy protein components isoflavones and phytate on CVD risk in postmenopausal women.

Design: In a double-blind 6-wk study, 55 postmenopausal women were randomly assigned to 1 of 4 treatments with soy protein (40 g/d) isolate (SPI): low phytate/low isoflavone (LP/LI); normal phytate/low isoflavone (NP/LI); low phytate/normal isoflavone (LP/NI); or normal phytate/normal isoflavone (NP/NI). Blood lipids (total, LDL, and HDL cholesterol and triacylglycerol) and oxidative stress indexes (protein carbonyls, oxidized LDLs, and 8-iso-prostaglandin-F(2alpha)) were measured at baseline and 6 wk.

Results: The oxidative stress indexes were not significantly affected by either phytate or isoflavones. Phytate treatment had a minimal but nonsignificant effect in reducing protein carbonyls and 8-iso-prostaglandin-F(2alpha); the reductions were 6-8% and 4-6% in the NP/LI and NP/NI groups and 1-4% and 3-4% in the LP/LI and LP/NI groups, respectively. Similarly, circulating lipids were not significantly affected by either phytate or isoflavones. The decline in total (6%-7% compared with 2%-4%) and LDL (10%-11% compared with 3%-7%) cholesterol did not differ significantly between the normal- and low-isoflavone groups, respectively.

Conclusion: In postmenopausal women, neither phytate nor isoflavones in SPI have a significant effect of reducing oxidative damage or favorably altering blood lipids.