Dietary Fiber Modulates Colon Cell Proliferation by Altering Luminal Concentrations of Short-Chain Fatty Acids

To compare the effects of various types of dietary fiber on microbial production of short-chain fatty acids (SCFA) and on colon cell proliferation which is used as an intermediate biomarker for colon carcinogenesis, groups of 10 male Sprague-Dawley rats were fed one of four fiber-supplemented diets (6% cellulose, 6% pectin, 6% polydextrose, and a mixture of 3% cellulose and 3% polydextrose) for three weeks. As a control, a fiber-free diet was fed to a separate group of 10 rats. Cell proliferation was measured by in vivo incorporation of bromodeoxyuridine into DNA in the proximal and distal colon, respectively. Luminal concentrations of SCFA were measured by gas chromatography. Dietary fiber significantly influenced microbial production of SCFA in the colon; pectin supplementation produced the highest concentrations of luminal SCFA in both the proximal and distal colon (p<0.05). The degree of individual SCFA production was characterized by a relatively higher increase in butyrate production by the pectin-supplemented diet, and in propionate production by the polydextrose-supplemented diet, resulting in alterations of the molar ratios of acetate, propionate and butyrate. There were significant differences in colon cell proliferation among the diet groups; the pectin-supplemented diet produced a significantly higher effect on cell proliferation of distal colonic epithelial cells (p＜0.05), and the polydextrose-supplemented diet produced an intermediate effect compared to the fiber-free or cellulose-supplemented diet. Increased cell proliferation was correlated to increased luminal concentrations of butyrate in the proximal colon and to increased luminal concentrations of propionate and butyrate in the distal colon (p<0.05). Therefore, these data suggest that dietary fiber may modulate colon cell proliferation by altering luminal SCFA concentrations, particularly butyrate and perhaps propionate. In addition, the present study is the first finding that has demonstrated a relative increase in colon cell proliferation due to supplementation with polydextrose, suggesting that the overuse of this artificially synthesized polysaccharide in food processing technology needs to be carefully evaluated from the public health point of view.