Soy protein and isoflavones: their effects on blood lipids and bone density in postmenopausal women

The effects of soy protein (40 g/d) containing moderate and higher concentr ations of isoflavones on blood lipid profiles, mononuclear cell LDL recepto r messenger RNA, and bone mineral density and content were investigated in 66 free-living. hypercholesterolemic, postmenopausal women during a 6-mo, p arallel-group, double-blind trial with 3 interventions. After a control per iod of 14 d, during which subjects followed a National Cholesterol Educatio n Program Step I low-fat, low-cholesterol diet, all subjects were randomly assigned to 1 of 3 dietary groups: Step I diet with 40 g protein/d obtained from casein and nonfat dry milk (CNFDM), Step I diet with 40 g protein/d f rom isolated soy protein containing 1.39 mg isoflavones/g protein (ISP56), or Step I diet with 40 g protein/d from isolated soy protein containing 2.2 5 mg isoflavones/g protein (ISP90). Total and regional bone mineral content and density were assessed. Non-HDL cholesterol for both ISP56 and ISP90 gr oups was reduced compared with the CNFDM group (P < 0.05). HDL cholesterol increased in both ISP56 and ISP90 groups (P < 0.05). Mononuclear cell LDL r eceptor mRNA was increased in subjects consuming ISP56 or ISP90 compared wi th those consuming CNFDM (P < 0.05). Significant increases occurred in both bone mineral content and density in the lumbar spine but not elsewhere for the ISP90 group compared with the control group (P < 0.05). Intake of soy protein at both isoflavone concentrations for 6 mo may decrease the risk fa ctors associated with cardiovascular disease in postmenopausal women. Howev er, only the higher isoflavone-containing product protected against spinal bone loss.