Colon cancer prevention with a small amount of dietary perilla oil high in alpha-linolenic acid in an animal model

Background. Epidemiologic and experimental studies suggest that dietary fish oil and vegetable oil high in [omega]-3 polyunsaturated fatty acids (PUFAs) suppress the risk of colon cancer. The optimal amount to prevent colon carcinogenesis with perilla oil high in [omega]-3 PUFA [alpha]-linolenic acid in a 12% medium-fat diet was investigated in female F344 rats. For comparison, safflower oil high in [omega]-6 PUFA linoleic acid was used. Methods. Thirty or 25 rats at 7 weeks of age in each group received an intrarectal dose of 2 mg N-methyl-N-nitrosourea 3 times weekly in weeks 1 and 2 and were fed the diets with various levels of perilla oil and safflower oil throughout the experiment. Results. The incidence of colon cancer at the termination of the experiment at week 35 was 40%, 48%, and 32% in the rats fed the diets with 3% perilla oil plus 9% safflower oil, 6% perilla oil plus 6% safflower oil, and 12% perilla oil plus 0% samower oil, respectively, whereas it was 67% in the rats fed the control diet with 0% perilla oil plus 12% safflower oil. The amount of diet consumed and the body weight gain were identical in all of the dietary groups. The ratios of [omega]-3 PUFA to [omega]-6 PUFA in the serum and the colonic mucosa at week 35 were increased in parallel to the increased intake of perilla oil. Conclusions. The results suggest that a relatively small fraction of perilla oil, 25% of total dietary fat, may provide an appreciable beneficial effect in lowering the risk of colon cancer.