Fiber fermentability in the rat cecum and its physiological consequences

The aim of the study was to compare the fermentability of complex fiber sources in the rat large intestine. The studied sources ranged from predominantly structural fiber (oat fiber and external pea fiber) to more soluble plant storage fibers (beet fiber and internal pea fiber) and were included at levels of about 13% or 26% TDF in the diet. Rats fed the diets containing the more insoluble fibers had a compensatory increase in intake, resulting in similar weight gains in all groups. Beet and internal pea fibers were better fermented, and caused a more pronounced hypertrophy of the cecum and greater absorption of short-chain fatty acids (SCFA). The SCFA profile varied with a higher proportion of butyrate in the cecal contents of rats fed the less soluble fibers and a higher proportion of propionate in those fed the internal pea fiber. Feeding fiber consistently enhanced the transfer of urea nitrogen into the cecum, enhancing fecal nitrogen excretion. The fiber diets elicited an accumulation of Ca and Mg in the cecum, the Ca and Mg absorption was closely correlated with the fermentability of the fibers. Except oat fiber, the studied fibers carried bile acids into the large intestine but also enhanced their cecal reabsorption. It appears that, besides analytical data on fiber solubility, the fermentability of complex fiber source is effectively appreciated by their effects on the parameters of cecal digestion.