Dietary polyunsaturated fatty acids and cancers of the breast and colorectum: emerging evidence for their role as risk modifiers

The hypothesis that a high-fat diet promotes the development of postmenopau sal breast cancer is supported by international data showing a strong corre lation between fat intake and breast cancer rates and a modest positive ass ociation with high-fat diet in case-control studies. Dietary fat intake was found to be unrelated to the risk of breast cancer in cohort studies. In v iew of these conflicting findings it has been difficult to make nutritional recommendations for the prevention of breast cancer. Studies in animal mod els and recent observations in humans, however have provided evidence that a high intake of omega-polyunsaturated fatty acids (PUFAs), stimulates seve ral stages in the development of mammary and colon cancer, from an increase in oxidative DNA damage to effects on cell proliferation, free estrogen le vels to hormonal catabolism. In contrast, fish oil-derived omega-3 fatty ac ids seem to prevent cancer by influencing the activity of enzymes and prote ins related to intracellular signalling and, ultimately, cell proliferation . In this commentary, current evidence from experimental and human studies is summarized that implicates a high intake of omega-6 PUFAs in cancer of t he breast, colon and, possibly, prostate and which indicates that omega-3 P UFAs and monounsaturated fatty acids such as oleic acid (omega-9) are prote ctive. Plausible mechanisms for modulation of steps in the multistage carci nogenesis process by fats are discussed. Properly designed epidemiological studies are now needed, that integrate relevant biomarkers to unravel the c ontributions of different types of fat, their interactions with hormonal ca tabolism, protective nutritional factors and human cancer risk.