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Fermentation of Vegetable Fiber in the Intestinal Tract of Rats and Effects on Fecal Bulking and Bile Acid Excretion¹

^* Department of Food Chemistry, Chemical Centre, University of Lund, S-221 00 Lund, Sweden ^** Nestlé Research Centre, Nestec Ltd., Vers-chez-les-Blanc, CH-1000 Lausanne 26, Switzerland

The fermentative breakdown and fecal bulking capacity of dietary fiber from various vegetables (carrots, rutabagas, peas, green beans and Brussels sprouts) were evaluated in balance experiments in rats. The excretion of bile acids, protein and fat was also studied. The addition of blanched vegetables providing 10 g of fiber/100 g of diet caused a two-(rutabagas) to threefold (carrots) increase in fecal dry weight compared to that with a basal fiber-free diet. With green beans and Brussels sprouts, only about 25% of the fecal dry weight could be accounted for as fiber, whereas with the other investigated vegetables, 40–47% was fiber. Of the remaining part, 11% on average was fat, and 18% was crude protein. Fiber in carrots and peas was the least degraded, with approximately 47% of the polysaccharide intake being excreted in feces. By contrast, the breakdown of the fiber in green beans and Brussels sprouts was more extensive, with a mean of 23% of the polysaccharides being recovered. Among individual fiber constituents, glucose, mannose and uronic acids were least fermented, with considerable differences between vegetables. Total excretion of bile acids was reduced only when Brussels sprouts were added, whereas the concentration of fecal bile acids was lowered with all vegetables except rutabagas. However, no uniform change in fecal bile acid pattern could be detected.

KEY WORDS: • vegetable fiber • fiber fermentation • bile acids • rats

¹ This work was supported by the Swedish Council for Forestry and Agricultural Research.

² To whom correspondence should be addressed.

³ Present affiliation: Department of Applied Nutrition, Chemical Centre, University of Lund, S-221 00 Lund, Sweden.

Manuscript received 30 June 1989. Revision accepted 9 October 1989.