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In Vitro Production of Short-Chain Fatty Acids by Bacterial Fermentation of Dietary Fiber Compared with Effects of Those Fibers on Hepatic Sterol Synthesis in Rats^1,2,

The Hebrew University of Jerusalem, Faculty of Agriculture, Department of Biochemistry and Human Nutrition, Rehovot 76100, Israel

The aim of this study was to determine the effects of fiber feeding on short-chain fatty acid (SCFA) production in laboratory rats and in an in vitro fermentation model using fecal inocula from rats adapted to a high fiber diet. In addition, the effect of fiber intake on endogenous sterol synthesis was evaluated. Twenty male Sprague-Dawley rats were divided into four groups and fed a control or 30% fiber diet (cellulose, pectin or pea fiber) for 4 wk. In vitro fermentation was compared with measurements of cecal SCFA content of fiberadapted rats. Sterol synthesis in isolated hepatocytes was determined in groups of five to seven rats fed 15% dietary fiber for 4 wk. Cellulose was poorly fermented in both the in vitro and in vivo experiments. Pectin fermentation produced high levels of propionate, whereas pea fiber was associated with notable butyrate production. Adaptation to pectin produced seven times more SCFA in rat cecal contents (515 ± 78 µmol) in comparison to a fiber-free diet (70.6 ± 4.9 µmol), with similar results observed in vitro. Sterol synthesis in hepatocytes of rats fed pectin was significantly greater than in those of control or cellulose-fed rats. Despite significantly higher rates of SCFA production in pectin-fed rats, cholesterol synthesis was not inhibited, suggesting that SCFA are not the cholesterol-lowering factor of highly fermentable fiber sources.

KEY WORDS: • dietary fiber • fermentation • rats • short-chain fatty acids • cholesterol synthesis

¹ Supported by the Israeli Ministry of Health.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ To whom correspondence should be addressed.

Manuscript received 15 March 1993. Initial review completed 5 April 1993. Revision accepted 27 July 1993.