Abstract: Objective: To study the hypocholesterolemic effects of rice and soybean protein isolate on estrogen deficiency-induced hypercholesterolemia in ovariectomized rats. Methods: 24 Wistar femal rats were divided into four groups. Three groups were double ovariectomized and fed the diets containing rice and soybean protein isolates as two experimental groups with 20% casein as control. The other group was sham-overiectomized and fed the diets containing 20% casein as control. All rats were dissected afer 4 weeks of feeding to assay concentrations of cholesterol, triacylglycerides in serum and liver and fecal excretion of bile acids and apparent protein digestibility. Results: Concentrations of cholesterol, triacylglycerides in serum and liver are significantly increased in OVX rats. Concentrations of serum total cholesterols, LDL and cholesterol are significantly lower in soybean isolate feed group than in casein feed group(p<0.05), but triacylglycerides are effected with no significant difference. Liver weight, liver total lipids, total cholesterol, free cholesterol and total triacylglycerides are also significantly decreased. However, fecal excretion and fecal excretion of bile acids are being increased and apparent protein digestibility of soybean protein isolate group is higher than that of casein and rice protein isolate groups. Rice protein isolate group has no apparent effect on decreasing serum lipids, but liver total lipids, total cholesterol, free cholesterol and triacylglycerides of rice protein isolate group are significantly lower than those of casein group. But fecal excretion, fecal excretion of bile acids and apparent protein digestibility of rice protein isolate group has no apparent difference with casein group. Conclusions: Resistant protein may significantly decreasethe serum cholesterol concentration in estrogen deficiency-induced hypercholesterolemia rats, because the hypocholesterolemic effect of resistant protein appears to be interfered with bile acids metabolism and fecal excretion increase in the intestinal pool.

Key words: resistant protein, soybean protein isolate, rice protein isolate, ovariectomized rats, serum lipids