Influence of different dietary constituents of beans ( Phaseolus vulgaris) on serum and biliary lipids in the rat

Abstract

Bean ( Phaseolus vulgaris) components were separated by physical and chemical methods to study their effect on serum and biliary lipids, and on hepatic cholesterol concentration in the rat. Experimental diets were prepared replacing each component of a basic casein diet by each of the constituents obtained from beans: protein, starch, non-soluble fiber, and lipid. Rats fed a whole-bean diet significantly decreased serum cholesterol by 20%, and markedly increased biliary cholesterol output by 200% and hepatic cholesterol esters by 100%. Rats fed the bean starch diet also decreased serum cholesterol by 20%. In these animals, biliary cholesterol saturation increased by 180%, biliary phospholipid output by 100%, and biliary cholesterol output by 400%; hepatic cholesterol esters also increased by 100%. The bean protein and bean lipids had no effect on these parameters. Non-soluble fiber fraction of beans significantly decreased biliary bile acids and biliary phospholipid output, but increased biliary cholesterol saturation. In contrast, serum cholesterol remained unchanged compared with the control group of rats. Saponins, which are known to have hypocholesterolemic effects, were only detected in the whole-bean and starch-bean diets. When 0.3% bean sapogenins were fed to rats for 3 days, biliary cholesterol output increased by 300%. These experiments indicated that the effect of beans on serum, biliary cholesterol, and phospholipid outputs, and on hepatic cholesterol ester concentration are dependent on the starch fraction of beans, presumably on its sapogenin content. Furthermore, this study suggests that increasing biliary cholesterol output by dietary manipulations may induce a significant hypocholesterolemic effect.