The effects on plasma lipid concentrations of beta-conglycinin, one of the two major storage protei (213 mumol v. 22 mumol/day) and soyasaponins (2176 mumol v. 23 mumol/day) and the mechanism of beta-conglycinin to affect plasma lipid levels were investigated in mildly hypercholesterolemic women. A significant reduction of plasma total and LDL cholesterol occured after 14 and 28 days during ingestion of beta-conglycinin but only when it contained high levels of isoflavones and soyasaponins. A slight but nonsignificant increase in excretion of fecal bile acids and neutral sterols may have contributed to these changes. This study suggests that isoflavones and soyasaponins may to be needed companions for beta-conglycinin to exert a cholesterol lowering effect;The beneficial effects of daidzein, genistein, or glycitein on plasma lipid concentrations were investigated in female Golden Syrian hamsters fed these compounds for 4 weeks. Glycitein significantly lowered plasma total and non-HDL, cholesterol levels compared with casein (P < 005). The percentage of urinary recovery of each isoflavone was glycitein > daidzein > genistein (P < 0.05). These results suggest that glycitein's greater cholesterol-lowering effect was due to greater bioavailability, as reflected in urinary recovery of glycitein compared with the other purified isoflavones;An animal study was conducted to determine if group B soyasaponins affect plasma lipid concentrations by increasing excretion of fecal bile acids and neutral sterols, to investigate the relationship between group B soyasaponin metabolite and plasma lipid concentrations, and to identify group B soyasaponin metabolites. Compared with casein, hamsters fed soyasaponins significantly lower plasma total Cholesterol, non-HDL cholesterol, and triglycerides. Cholesterol-lowering was probably by a mechanism involving greater excretion of fecal bile acids and neutral steroids (P<0.05). Two fecal soyasaponin metabolite excretion phenotypes were observed. The high producer of soyasaponin metabolite showed significantly lower total/HDL cholesterol ratio compared low-producers (P < 0.03). Greater production of soyasaponin metabolite in hamsters was associated with improved lipid profile;These findings suggest that both soy isoflavones and soyasaponins in nutritionally relevant concentrations contribute to the cholesterol-lowering effects of soy foods and soy protein ingredients.