Hypocholesterolemic effect of dietary fiber: relation to intestinal fermentation and bile acid excretion

Rat cecal contents were static-cultured with three kinds of dietary fibers and examined for the production of short-chain fatty acids after 24h of cultivation. The total amount and molar ratio of acetate, propionate and butyrate (n = 8) were 7.20 +/- 0.62 mM and 38:19:43 with indigestible dextrin (ID), a low-viscosity, water-soluble dietary fiber, 10.88 +/- 0.46 mM and 49:5:46 with pectin (PE), a high-viscosity, water-soluble dietary fiber, and 1.83 +/- 0.19 mM and 64:11:25 with corn fiber (CF), a water-insoluble dietary fiber, respectively (the corresponding values obtained with glucose were 10.59 +/- 0.37 mM and 15:27:58). Next, rats were kept on a cholesterol- and bile acid-free high-sucrose diet. At the completion of the 8-week feeding period, the serum total-cholesterol levels were significantly lower, at 57.6 +/- 3.8 (n = 8), 63.2 +/- 4.67 (n = 7), and 77.8 +/- 3.7 mg/dl (n = 9), in the ID-, PE-, and CF-supplemented diet groups, respectively, than in the control group given no dietary fiber (92.7 +/- 3.8 mg/dl, n = 7). The cecal propionate production was significantly increased in both the ID and PE groups, while the fecal excretion of bile acids was increased in all three fiber groups compared to the control group. In addition, there was a significantly negative correlation between the serum total-cholesterol level and cecal propionate production in the ID group, between the serum cholesterol level and bile acid excretion in the CF group, and between the serum cholesterol level and cecal propionate production or bile acid excretion in the PE group. These results suggest that the degree of intestinal fermentation and bile acid excretion, which are considered to be associated with the hypocholesterolemic action of dietary fiber, varies with each kind of dietary fiber.