Carcinogenesis and Metastasis Are Affected by Dietary n-6/n-3 Fatty Acids

Summary

The mortalities from cancers common in the West (lung, mammary gland, colorectal, and others) have been increasing rapidly during the past several decades in Japan, following the increased intake of animal fats and vegetable oils. We have shown in animal experiments that high linoleic (n-6) safflower oil stimulates carcinogenesis (mammary, colon, kidney) and spontaneous mammary tumorigenesis as well as metastasis of tumor cells, but perilla seed oil with a low linoleate (n-6)/α-linolenate (n-3) ratio suppresses carcinogenesis. Oleic acid (n-9), a major fatty acid of animal fats, has been shown not to stimulate carcinogenesis, although a high oleic olive oil was reported to stimulate colon carcinogenesis, possibly due to minor components other than triacylglycerol. The relationship between the increased incidence of mammary tumor and the increased intake of linoleic acid (n-6) in the past 40 years in Japan fits well with the dose-dependency evaluated in animal experiments [Ip et al. (1985) Cancer Res 45:1997–2001]. Based on these observations, we propose that the intake of linoleic acid (n-6) should be decreased to the levels of 40 years ago [~3 energy % (en%)] and that of n-3 fatty acids should be increased to ~3 en%, for the prevention of Western type cancers.