Altaf Mahmud, M.Sc. Biology 2012

An investigation of the relationship between dietary fiber, fecal bacterial composition, and colon cancer


Colon cancer (CC) is the second leading cause of all cancer-related deaths in North America. Dietary fiber (DF) may be an important risk factor in the aetiology and pathogenesis of CC. The anticancer effects of dietary fiber were investigated with a focus on fecal bacterial diversity and toxicity of bacterial metabolites in the aqueous phase of feces (fecal water: FW) that contains bile acids, short chain fatty acid, lactate, succinate, etc. Briefly, male Fischer-344 rats were randomized to one of 3 diets: alphacel (control), fructooligosaccharides (FOS) or wheat bran (WB) with a total fermentability level of 3% (wt/wt). Rats were injected with saline or azoxymethane (AOM) to induce tumors. FW toxicity was tested on HCT-116 cells. Rats fed alphacel and FOS diets had significantly more colon tumors than those fed WB. FW from both FOS and alphacel significantly increased apoptosis and DNA damage, and induced cell cycle arrest in HCT-116 cells after a 48 hr treatment whereas FW of WB had no effect on those cell parameters. Lower pH of FW was associated with more tumors incidence and higher cell toxicity. FOS diet was significantly associated with more Allobaculum sp. whereas Lactobacillus sp. and Clostridium XI sp. were associated with WB diet. These results suggest that dietary fiber can be an influence in CC development. This seems to be related to changes in bacterial population and bacterial metabolic activities.