Stimulation of Absorption of Volatile Fatty Acids and Minerals in the Cecum of Rats Adapted to a Very High Fiber Diet

Abstract

The effects of a high fiber diet containing about 50% pectin, gum, crude potato starch and the fiber components of wheat bran and soya seed cake on the cecal absorption of substrates were studied by parallel measurements of cecal arteriovenous differences and blood flows. Rats fed the high fiber diet had heavier cecae and higher cecal wall weight and blood flow than rats fed a fiber-free diet. Very high arteriovenous differences in volatile fatty acids (VFA) were observed and VFA absorption in cecal vein reached 17.5 μmol/min in the high fiber diet group. This process was concomitant to a moderate absorption of Na⁺ and partly offset by a secretion of Cl^-. In contrast, K⁺, Mg²⁺ and Ca²⁺ were absorbed in large amounts along a favorable concentration gradient. About 10% of arterial urea was removed, and there was a substantial reabsorption of ammonia, despite the lower cecal ammonia and the acidic pH in the cecum when the high fiber diet was fed. The present study suggests that rats may tolerate large amounts of diversified fibers or related compounds in the diet. Such a model could contribute to the assessment of the role of VFA in the effect of fiber.