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

Author: Potter SM et al
Publication: Am J Clin Nutr. 1998 Dec;68(6 Suppl):1375S-1379S

The aim of this study was to find influence of the consumption of soy protein and isoflavones on cardiovascular health and bone loss of postmenopausal woman.

A daily dosage of 40 g soy protein with different levels of isoflavones was used. The effect was measured on on blood lipid profiles, mononuclear cell LDL receptor messenger RNA, and bone mineral density and content. A total of 66 postmenopausal woman participated in this study during six months in a double-blind trial with 3 interventions.

At the beginning of the experiment all women followed during 14 days an identical diet (National Cholesterol Education Program Step I low-fat, low-cholesterol diet). The women were divided in 3 group, all groups received Step I diet but the 40 g protein was from different origin:
– group 1: protein obtained from casein and nonfat dry milk.
– group 2: soy protein (isolated soy protein) containing 55 mg isoflavones
– group3: soy protein (isolated soy protein( containing 90 mg isoflavones.

The non-HDL cholesterol for both group 2 and 3 was reduced compared with the group 1 (P < 0.05). HDL cholesterol (= good cholesterol) and mononuclear cell LDL receptor mRNA increased in both group 2 and 3 (P < 0.05). Significant increases in both bone mineral content and density in the lumbar spine was observed in group 3 (P < 0.05).

It can be concluded that soy protein may decrease the risk factors associated with cardiovascular disease in postmenopausal women. Only the diet with the highest isoflavones content (90 mg isoflavones per day) protected against spinal bone loss.