Fermentation products of sugar-beet fiber by cecal bacteria lower plasma cholesterol concentration in rats

Plasma cholesterol concentration is reduced by feeding some dietary fibers but the mechanism is not fully understood. We examined whether cecal fermentation products are involved in lowering plasma cholesterol by feeding rats a highly fermentable sugar-beet fiber (SBF) in four separate experiments. These were designed to investigate the effects on plasma cholesterol of oral ingestion of fermentation products on plasma cholesterol, the effects of the products in comparison with that of a short-chain fatty acid (SCFA) mixture, effects of individual SCFA and effects of alteration of energy and nitrogen ratio in the diet by the addition of the SCFA mixture. Cecal contents of rats were cultured with SBF by using a jar fermenter under anaerobic conditions, and the supernatant from the culture medium, containing fermentation products of SBF, was collected and freeze-dried before feeding to rats. Yield of fermentation products as dry weight from the fiber was 80-90%. In rats fed a diet containing fermentation products (80 g/kg diet), plasma cholesterol concentrations were lower than in rats of the fiber-free group 3, 7 and 14 d after feeding the test diet. Major SCFA in the fermentation products were sodium salts of acetic, propionic and butyric acids. Plasma cholesterol concentration in rats fed the diet containing a mixture of equal amounts of the three SCFA salts (66 g/kg diet) as the fermentation products diet was also lower than that in the fiber-free group and was not different from those in rats fed SBF (100 g/kg diet) and the fermentation products. In rats fed an acetate-containing diet but not in rats fed diets without acetate, plasma cholesterol was significantly lower than in the fiber-free group. In conclusion, absorption of SCFA from cecal fermentation products lowers plasma cholesterol. Acetate, and not propionate, may be responsible for lowering plasma cholesterol concentration.