Soy protein without isoflavones reduces aortic total and cholesterol ester concentrations greater than soy protein with isoflavones compared with casein in hypercholesterolemic hamsters

The present study was designed to investigate the effects of replacing casein with soy protein either containing isoflavones or not on plasma lipids and lipoprotein cholesterol concentrations and early aortic atherosclerosis (measured as aortic cholesterol concentration) in hypercholesterolemic hamsters. Thirty, 8-week-old, male F1B Golden Syrian hamsters were individually housed and fed a semipurified hypercholesterolemic diet (HCD) containing 22% casein, 20% coconut oil, 2% corn oil, and 0.12% cholesterol (wt/wt) for a period of 2 weeks. The hamsters were then divided into 3 groups of 10 based on similar mean fasting plasma cholesterol concentrations and placed on experimental diets for 6 weeks. Group 1 continued on the HCD (casein). Group 2 was fed the HCD with 22% water-washed soybean protein isolate (soy +I) (1.76 mg of isoflavones per gram of protein) in place of casein. Group 3 was fed the HCD with 22% alcohol-washed soybean protein isolate (soy - I) (0.08 mg isoflavones per gram of protein) in place of casein. Compared with hamsters fed casein, hamsters fed both soy diets had significant decreases in their plasma total and non-high-density lipoprotein (very low and low-density lipoprotein)--cholesterol concentrations by week 2, which continued across weeks 4 and 6. However, the hamsters fed the soy -I diet accumulated significantly less aortic total cholesterol compared with the hamsters fed casein and the soy +I diet. In addition, the hamsters fed the soy -I diet accumulated significantly less aortic cholesterol ester compared with the hamsters fed casein only. In conclusion, dietary replacement of casein with soy protein either containing isoflavones or not in hypercholesterolemic hamsters lowers plasma total and non-high-density lipoprotein-cholesterol concentrations; however, only the soy protein without isoflavones reduced aortic cholesterol accumulation.