Evaluation in rats of the dose-response relationship among colonic mucosal growth, colonic fermentation, and dietary fiber.

The dose-response relationship among dietary fiber, colonic fermentation, fecal weight, and mucosal growth were evaluated in this study. The morphometric parameter of total mucosal volume was used to assess diet-induced differences in colonic mucosal growth. Dietary fibers with a wide range of fermentability and that have previously been shown to inhibit the development of colonic neoplasia in rats were used. Sprague-Dawley rats were fed Purina Rodent Chow, AIN-76a fiber-free diet, or an AIN-76a diet supplemented with three different dietary fibers, (cellulose, guar gum, or wheat bran) at 2, 5, 10, or 15% of the diet. Diets were fed for 28 days. Total colonic mucosal volume was determined using stereologic principles and computerized image analysis; 48-hr fecal weight was measured; and the concentration of short-chain fatty acids (SCFA) in colonic contents was determined at study termination. Each type of fiber induced a dose-dependent increase in total mucosal volume of the colon and fecal weight. Mucosal volume and fecal weight were closely correlated (R2 > 0.95). Total mucosal volume was not correlated with the concentration of total SCFA or butyrate in the colon. These results indicate that diet-induced change in colonic mucosal growth, as measured by total mucosal volume, is positively correlated with fecal weight and not related to alterations in colonic fermentation. Enhanced colonic mucosal growth occurs in rats fed dietary fibers that have previously been shown to inhibit the development of genotoxin-induced colonic neoplasia in rats.