Differential dietary effects on colonic and small bowel neoplasia in C57BL/6J Apc Min/+ mice

The effects of fiber on colon cancer are controversial. Twenty 5-week old C57BL/6J Apc Min/+ mice were fed for 60 days with a commercial mouse diet (Teklad LM-485) and eight semidefined diets containing 5-10% various fibers and 20% soybean oil. Ten additional C57BL/6J congenic litter-mates were fed each diet to assay colonic SCFA. SCFA, stool bulk, and colonic tumor incidence differed only slightly among the semidefined diets despite variations in fiber content and source. However, food consumption, caloric intake, stool bulk, and SCFA were substantially increased by the Teklad diet compared with all other groups. The Teklad diet significantly increased the number of mice with colonic tumors, average number of tumors/mouse, total tumor burden, colonic atypical hyperplasia, and small bowel tumors. Mice fed high-fat, no-fiber diets had more small bowel tumors (29.8 +/- 3.1) than mice fed diets with fiber (8.2 +/- 2.1) or with low fat and no fiber (18.1 +/- 3.4) (P < 0.05 for each group). These studies suggest that fat predisposes to and fiber protects against small bowel tumors but not colon tumors in these mice. Thus, diets high in fiber or yielding high colonic luminal SCFA may not necessarily protect against colonic cancer. Furthermore, the effects of dietary fiber in Teklad appear overshadowed by some other biologically active factors in this animal model.