Effect of dietary fatty acids on tumorigenesis of colon cancer induced by methyl nitrosourea in rats.

We studied the effect of dietary fatty acid composition on the tumorigenesis of colon cancer induced by methyl nitrosourea (MNU) in rats. Five groups of Sprague-Dawley male rats were fed with semi-synthetic diets that contained different proportions of beef tallow, soybean oil, alkana oil, corn oil, and fish oil for 180 days. Each group was matched with a control group fed with the same diet. The experimental groups were given MNU in PBS i.p. 6 times at weekly intervals. The control groups were given PBS only. The incidence of colon cancer, the average volume of the tumors, PCNA, cell kinetics, membrane lipid fluidity, ALP activity, and the content of PGE2 in colonic mucous and the fatty acid distribution in the testis pad fat were measured at the end of the experiment. The results showed that the incidence of colon cancer and the average volume of the tumors in animals fed with diets that contained mainly beef tallow, soybean oil, or alkana oil were significantly higher than that in animals fed with diets that contained mainly fish oil. The diet containing 13.9% of SFA, 16.4% of MUFA, and 68.8% of PUFA showed the strongest inhibition effect. This may be due to the mechanism of protecting the membrane lipid fluidity, decreasing the amount of PCNA in colon cells, the number of propidium iodine-labeled cells in S phase, the activity of ALP and inhibiting the production of AA and thus decreasing the amount of PGE2.