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 dietar y fish oil and vegetable oil high in omega-3 polyunsaturated fatty aci ds (PUFAs) suppress the risk of colon cancer. The optimal amount to pr event colon carcinogenesis with perilla oil high in omega-3 PUFA alpha -linolenic acid in a 12% medium-fat diet was investigated in female F3 44 rats. For comparison, safflower oil high in omega-6 PUFA linoleic a cid was used. Methods. Thirty or 25 rats at 7 weeks of age in each gro up 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 wee k 35 was 40%, 48%, and 32% in the rats fed the diets with 3% perilla o il 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% safflowe r oil. The amount of diet consumed and the body weight gain were ident ical 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 r esults suggest that a relatively small fraction of perilla oil, 25% of total dietary fat, may provide an appreciable beneficial effect in lo wering the risk of colon cancer.