The effects of omega-3 polyunsaturated fatty acids against cancer

The modifications which have taken place in dietary habits over the centuries have deeply changed the ratio of omega-3 (ω-3) to omega-6 (ω-6) polyunsaturated fatty acids (PUFAs) present in the diet. Among western populations this change, which has taken place progressively since prehistoric times, has become dramatic over the past two centuries. That has been attributed to the progressive enrichment of the western diet with vegetable oils containing high levels of ω-6 PUFAs accompanied by the concomitant decreased consumption of fish, rich in ω-3 PUFAs. All these variations in the diet could be related initially to changed socio-economic conditions, such as the industrialization and concentrations of population in urban areas, and, more recently, to the health recommendations that, by 1970s, had advised the public to avoid the consumption of animal fat because of its high content in deleterious saturated fatty acids and cholesterol. This might have led to dramatic effects on our health, because a low dietary ω-3/ω-6 PUFA ratio has been hypothesized to contribute to the promotion of many chronic diseases including cancer, which are occurring at an increasing rate among western populations. The development of some types of cancer, such as colon, breast and prostate cancer seems particularly related to the amount and type of fat ingested. For this reason considerable effort has been expended in searching whether any inverse association could exist between the increased intake of ω-3 PUFAs and the risk of these cancers. Plenty of results obtained by studying both animal models of cancer or cancer cells cultured in vitro concur to suggest a potential remarkable role for these dietary fatty acids as anticancer agents. Several mechanistic studies have been performed with the aim of understanding which modifi cations in cellular functions and molecular pathways induced by these fatty acids could protect the cells from the deregulated growth which leads to cancer. In spite of all the encouraging results obtained, the picture deriving from the human studies, however, does not appear completely clear. The present chapter will deal with the antineoplastic effects of the long-chain ω-3 PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), because they are the more widely ω-3 PUFAs studied and because there is large agreement on the effi cacy of their antineoplastic action, at least according to the results of the experimental studies. Moreover, only mammary, prostate and colon cancers will be discussed, being, among the most frequent cancers, the most susceptible to the infl uence of dietary fat.