The hypocholesterolemic effect of high amylose cornstarch in rats is mediated by an enlarged bile acid pool and increased fecal bile acid excretion, not by cecal fermented products.

Sham-operated and cecectomized rats were fed for 21 d a cholesterol-free purified diet containing (200 g/kg) either normal cornstarch (CS) or high amylose cornstarch (HACS). In both types of rats, those fed the HACS diet had a significantly lower plasma total cholesterol concentration and a significantly larger intestinal bile acid pool than those fed the CS diet. In cecectomized rats, those fed the HACS diet had significantly lower plasma HDL and LDL cholesterol concentrations, a significantly greater fecal bile acid excretion and a significantly lower hepatic 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase mRNA concentration than those fed the CS diet. The plasma triglyceride concentration and LDL-receptor mRNA concentration were not affected by the diet or cecectomy. In sham-operated rats, the propionate concentration in the cecal contents was significantly greater in those fed the HACS diet than in those fed the CS diet. Compared with sham-operated rats, cecectomized rats had significantly enhanced cholesterol 7alpha-hydroxylase activity. In intact rats, biliary bile acid flux into the small intestine was significantly greater in those fed the HACS diet than in those fed the CS diet. Thus, the hypocholesterolemic effect of HACS appears to be mediated by accelerated fecal excretion of bile acids and increases in the intestinal pool and biliary flux of bile acids, and not by cecal fermentation products.