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.