Professor of Nutritional Immunology University of Southampton Southampton, United Kingdom
Abstract: The omega-6 vs omega-3 fatty acid debate assumes that one family of fatty acids is harmful and the other helpful. This is simplistic and makes the assumption that all omega-6 fatty acids are the same and that all omega-3 fatty acids are the same. This is clearly not true. Amongst the omega-6 fatty acids, linoleic (LA), gamma-linolenic, dihomo-gamma-linolenic (DGLA) and arachidonic (AA) acids are functionally different from one another. Compared with saturated fatty acids, LA lowers total and LDL-cholesterol and in this regard is healthy. LA is an essential component of skin ceramides. Eicosanoids produced from DGLA are anti-inflammatory. AA has important roles in brain development and function and AA gives rise to eicosanoids that are involved in blood clotting, immunity, inflammation, bone turnover, fertility and parturition. These are physiological roles, although excessive production of these eicosanoids links to disease and many anti-inflammatory pharmaceuticals target AA metabolism or metabolites. However, the view that AA is pro-inflammatory is simplistic: some AA-derived eicosanoids have anti-inflammatory actions and AA gives rise to pro-resolving lipoxins. Thus, not all omega-6 fatty acids are the same and not all of their actions are harmful. On the omega-3 side, alpha-linolenic acid (ALA), stearidonic acid, eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) all have different roles and potencies. DHA has unique roles in visual and cognitive development and function. EPA, DPA and DHA are all anti-inflammatory and give rise to pro-resolving mediators. EPA is an antagonist of AA and so affects blood clotting. The principal role of ALA seems to be as a precursor to EPA. ALA also generates lipid mediators with biological actions. Any discussion on pros and cons of polyunsaturated fatty acids needs to focus on individual fatty acids and on specific physiological targets; we cannot make statements based on fatty acid families.
