Long-term effects of fermentable fibers on rat colonic pH and epithelial cell cycle.

The long-term effects of fermentable fibers on colonic luminal pH and the epithelial cell cycle were compared in 50 male Sprague-Dawley rats fed either a defined basal fiber-free diet or the basal diet supplemented with 10% pectin, cellulose or guar or with 20% oat bran. After 8 mo, in vivo pH measurements revealed that acidification of luminal contents occurred in the cecum and in mid and distal colons of rats fed fiber-supplemented diets when compared with the fiber-free controls (P less than 0.05). Pectin and guar produced the greatest acidification of luminal contents, the largest increase in cecal surface area and the highest percentage of colonic cells in S-phase, as measured by flow cytometry. In the proximal colon of the pectin group 9.2 +/- 0.5% of cells were in S-phase (6.3 +/- 0.8% with the fiber-free group) (P less than 0.05) and in the distal colon of the guar group 10.9 +/- 1.4% were in S-phase (7.1 +/- 0.5% with the fiber-free group) (P less than 0.05). Even though the most fermentable fibers produced the greatest mitogenic response, there was no site-specific correlation between pH and mucosal cell growth except in the cecum. This suggests that fibers may act as colon cell growth factors by some mechanism other than extracellular pH changes.