284 OLIVE OILS AND HEALTH and Dietetics Associations”), FAO/WHO (“Food and Agriculture Organization of the United Nations / World Health Organization”), EFSA (“European Food Safety Authority”), and Cochrane (an international network for high-quality scientific evidence)], have conducted reviews and issued consensus statements on the health effects of omega-6 fats. With regard to the lipid profile, the evidence suggests that when omega-6 fats replace saturated fats, they lower total blood cholesterol, and their effect appears to be comparable to that of monounsaturated fats. However, there is insufficient evidence to support claims that omega-6 fats increase HDL cholesterol (the “good” cholesterol) or reduce LDL cholesterol (the “bad” cholesterol). They may also have little or no effect on blood triglyceride levels. Furthermore, the majority of studies do not provide conclusive evidence about whether omega-6 fat intake has a positive or negative effect on heart and circulatory diseases, although some data suggest they may be beneficial for individuals at high risk of heart attacks. Omega-6 fat intake has also been associated with a reduced risk of diabetes, although the quality of the supporting evidence is sometimes described as low. There is also considerable controversy regarding the effects of omega-6 fats on cancer. Prospective cohort epidemiological studies generally do not show a significant association between the consumption of omega-6 polyunsaturated fatty acids and the incidence of breast, colorectal, or prostate cancer. However, certain associations do appear when data from multiple studies are pooled in meta-analyses. Moreover, migration studies show that the incidence (cancer incidence) of breast and other cancers increases among Japanese and Inuit -Eskimo- populations (low in their countries of origin), when they move to Western countries. These increases are associated with a shift in dietary patterns, specifically, a reduction in fish consumption (a source of omega-3 fats) and a corresponding rise in omega-6 fat intake. Unlike basic epidemiological studies, experimental studies in animal models have clearly shown that excessive omega-6 fat intake dramatically promotes the progression of breast, and also that of colon, rectal, and prostate cancers. Many of these studies describe various mechanisms, based on structural and functional alterations in cells, that could explain the harmful effects of excessive omega-6 fats. In addition to these specific effects, the excessive intake of any fat also contributes to increased the caloric intake, which can indirectly support cancer growth as a non-specific effect. In this context, it is important to recall that fats, regardless of type, are the most energy-dense nutrients (9 kilocalories/g). Moreover, cancer cells are highly active and have very high energy requirements. Therefore, any type of fat consumed in excess may contribute to the energy supply that fuels tumour development. Conversely, caloric restriction has been shown to slow or even reverse cancer growth. Excessive intake of omega-6 polyunsaturated fats has also been associated with other potentially harmful effects. Several studies suggest that these fats may promote inflammation, particularly when omega-3 intake is low. However, more recent research concludes that there is no solid evidence to support a pro-inflammatory role of omega-6 polyunsaturated fatty acids. In addition, some, mostly experimental, studies suggest that diets high in these fats may increase oxidative stress and be linked to poorer ageing outcomes, although further evidence is needed to confirm this. As with other types of fat, it is important to remember that the observed effects of these lipids are difficult to separate from the overall dietary pattern and lifestyle context in which they are consumed.
RkJQdWJsaXNoZXIy Njg1MjYx