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% safflower 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.