THE EFFECTS OF DIETARY FIBER FROM LAGENARIA-SCINERARIA (YUGAO-MELON) ON COLONIC CARCINOGENESIS IN MICE

Background. The increasing trend of colon cancer in Japan is attribute d to changes in dietary habits, that is, increased amounts of fat and decreased amounts of fiber in the diet. The effects of Japanese dietar y fiber from Lagenaria scineraria (yugao-melon) on colonic carcinogene sis in mice were examined. Methods. Eighteen ICR mice in each group we re fed with either a basal diet or a diet containing 5%, 10%, or 20% o f yugao powder for 35 weeks. All the mice received a weekly intraperit oneal injection of 1,2-dimethylhydrazine (DMH), 10 mg/kg body weight f or 10 weeks. The effects of yugao powder on the mucosal and luminal va riables involved in colonic carcinogenesis were then compared with tho se of wheat bran in the mice without any carcinogen treatment. Results . The incidence of colon tumors (adenocarcinomas) was lower in the yug ao powder diet groups than in the basal diet group at week 35 (24% vs. 50%, P < 0.05). The bile acid concentration in the colon was reduced in all the fiber diet groups except for the 5% yugao powder diet group . The colonic luminal pH acidified as yugao powder contents also incre ased in the yugao powder diet groups. The findings on the colonic shor t chain fatty acids, microflora, and mucosal fatty acids and ornithine decarboxylase activity were all inconsistent with a tendency to eithe r develop or to inhibit carcinogenesis in both the fiber diet groups. Conclusions. Dietary fiber from yugao-melon suppressed DMH-induced col onic carcinogenesis in mice by lowering the bile acid concentration an d pH in the colon. The results of the luminal and mucosal variables ex amined also suggested that the mechanisms of action of yugao powder ag ainst colonic carcinogenesis differed from those of wheat bran.