Eating Fish Protects against Some Cancers: Epidemiological and Experimental Evidence for a Hypothesis

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Abstract
Further epidemiological, ecological and experimental evidence is presented which is consistent with the hypothesis alluded to in recent years that fish eating is protective against the development of certain cancers. At present the evidence for this relationship is strongest for colorectal cancer and breast cancer, but there is also evidence for lung cancer and prostatic cancer. Although the biologic mechanism of this protective effect is unclear and the active nutrients involved in this protection against various cancers are uncertain, the long-chain polyunsaturated omega-3 fatty acids contained mainly in fish have been implicated. If these fatty acids are involved, their anti-neoplastic effects may well be at several levels, which include a direct inhibition on tumour cell division, a modulation of cellular lipid metabolism, an inhibition of prostaglandin E2 synthesis, a modification of the immune response, as well as other alterations in lipid metabolism. In human diets, omega-3 fatty acids are mainly obtained from fish meat, as there are none in the meat of domesticated animals. There is evidence that prehistoric man, with the exception of coastal dwellers, probably obtained most of these nutrients from eating wild game, whereas modern man can best obtain these nutrients from eating fish. Further epidemiologic research should be conducted to unravel this potentially important area of nutritional protection against some cancers.