Abstract
This study investigated the effect of different dietary fats and fibers on colon tumor incidence and cell proliferation, the levels of eicosanoids and polyamines in colonic mucosa of DMH-treated rats. The experiment was conducted on male Sprague Dawley rats using a 2 $\times$3 factorial design with two fats (corn oil and DHA-rich fish oil) and two fibers (cellulose and pectin) and a fiber-free control. The rats were find an experimental diet containing 15% (w/w) dietary fat and 6% (w/w) fiber for 25 weeks. Tumor incidence was Bower in rats fed fish oil as opposed to corn oil. The levels of arachidonic acid (AA) and eicosanoids ($PGE_2, and TXB_2$) in normal colonic mucosa were significantly lower in rats fed fish oil and there was a concomitant increase of docosahexaenoic acid (DHA). The levels of eicosanoids and AA in tumor tissues were significantly higher than those of normal colonic mucosa. The level of polyamines in normal colonic mucosa was not affected by dietary fats but was significantly lower than that in rumor tissues. Dietary fiber did not have a significant effect on rumor incidence and the levels of AA, eicosanoids and polyamines. Overall, fish oil rich in DHA reduced cell prolifiration and thus inhibited colon carcinogenesis through its effect on the distribution of AA and production of eicosanoids in normal colonic mucosa. However, its effect on colon carcinogenesis revealed a lack of consistency depending on the type of dietary fiber in diet.