Fermentable polysaccharides that enhance fecal bile acid excretion lower plasma cholesterol and apolipoprotein E-rich HDL in rats

The effect of different polysaccharides fermented in the large intestine and liable to lower plasma cholesterol was investigated in rats. Male rats were assigned to one of five treatment groups: control diet or a diet containing pectin, guar gum, gum arabic or beta-cyclodextrin. The four compounds were effectively fermented, yielding cecal short-chain fatty acids (SCFA) concentrations in the range of 130 to 170 mmol/L. Relative to controls, the cecal concentration of propionate was significantly higher in rats fed all fibers, especially those fed guar gum (+190%) or beta-cyclodextrin (+385%). All the fermented carbohydrates elicited a significant cholesterol-lowering effect, which was most potent in rats fed guar gum or beta-cyclodextrin, the two fibers that also significantly depressed plasma triglycerides. These two carbohydrates significantly lowered LDL and HDL1 cholesterol, triglyceride-rich lipoprotein triglycerides and apolipoprotein E levels. Apolipoprotein B was lowered only by beta-cyclodextrin. The microsomal activities of hydroxymethylglutaryl (HMG) CoA reductase and of cholesterol 7 alpha-hydroxylase were markedly elevated in rats fed guar gum or beta-cyclodextrin and, to a lesser extent, in those fed pectin compared with controls. Increased bile acid excretion seems to be essential in the cholesterol-lowering effect of soluble fibers and related compounds. This effect is connected to induction of HMG CoA reductase and lowering concentrations of apolipoprotein E-containing particles.