Effects of a Soluble Fraction of Soybean on Lipid Profiles in Ovariectomized Rats Fed a Cholesterolemic Diet

The increases in serum lipid profiles at the onset of menopause are regarded as a risk factor for cardiovascular disease. This study was designed to clarify the effects of a dried aqueous soybean extract and ovariectomy on lipid parameters in rats fed with cholesterolemic diet. Twenty-four 9-week-old female Sprague-Dawley rats were divided into two groups of 12 each and either sham-operated or ovariectomized. The ovariectomized and sham groups were then subdivided into groups of six and fed a semipurified casein-based diet (control diet) or the same diet containing dried soybean extract (0.5%) at the expense of sucrose (experimental diet). Total isoflavone content was 4.52 mg/g of soy extract. Ovariectomized groups showed significantly greater weight gain and food intake than sham groups, while uterus weight was markedly lower in ovariectomized groups. Although ovariectomy significantly increased the concentration of serum triacylglycerol, the concentration of serum total cholesterol was not affected by the operation. Soybean extract restored the concentration of serum triacylglycerol in the ovariectomized groups to the level observed in the sham groups. On the other hand, liver cholesterol levels were significantly higher in the ovariectomized groups compared to the sham group, without effects of the diet. This study suggests that soybean extract supplementation modulates the level of serum triacylglycerol induced by ovariectomy in rats, and furthers the possibility that dietary cholesterol may be a crucial factor in determining liver cholesterol in the presence of ovarian hormone deficiency.