Dietary fat and fiber modulate colonic cell proliferation in an interactive site-specific manner.

A 3 x 3 factorial experiment was conducted to examine how dietary fiber and fat interactively affect cell proliferation in the colon in rats. Groups of 10 male Sprague-Dawley rats were fed one of nine experimental diets for three weeks: three types of fat at 15% by weight (beef tallow, corn oil, and fish oil) x 2 types of fiber (pectin and cellulose) plus a fiber-free diet as a control. Cell proliferation was measured by in vivo incorporation of bromodeoxyuridine into DNA. The main effect of dietary fiber on cell proliferation was found in the proximal colon, where the pectin diet stimulated cell proliferation compared with the cellulose and fiber-free diets (p < 0.05). In comparison, the main effect of dietary fat was in the distal colon, where the beef tallow diet was more promotive with respect to cell proliferation than the fish oil diet and the corn oil diet had an intermediate effect (p < 0.05). In the proximal colon, however, the effect of fiber on cell proliferation was highly dependent on the source of fat in the diet. Pectin exerted a hyperproliferative effect when the source of fat in the diet was corn oil, but not when beef tallow or fish oil was the fat source. These data indicate that dietary fiber and fat modulate cell proliferation of the colon in an interactive site-specific manner.