Are diets high in omega-6 polyunsaturated fatty acids unhealthy?

This article reviews the connection between dietary omega-6 fatty acids and atherosclerosis, carcinogenesis and insulin resistance. These polyunsaturated fatty acids (PUFAs) may be likened to ‘double-edged swords’: on one hand they are considered essential for membrane function and eicosanoid formation necessary for vascular, immune and inflammatory cell function, while on the other they lead to increased susceptibility to lipid oxidation, stimulating neoplastic cell growth in culture and impairing insulin activity. Omega-6 function should not be considered in isolation but as part of a complex of nutrient interactions together with omega-3 fatty acids (shared enzymatic pathways) and antioxidants. Insulin sensitivity might be the common factor relating disease to fatty acid metabolism — both within and between the fatty acid pathways. A high linoleate to arachidonate concentration occurs in insulin resistance, in diabetic complications and also in some tumours. Since the interaction between the omega-6 and omega-3 pathways in neither linear nor stochastic, specific dietary recommendations have to await clarification of these relationships. Adipose tissue fatty acid composition and function may be a suitable biomarker with which to study these questions. Current epidemiological and clinical evidence supports the regular consumption of cold-water fish as part of a balanced diet, in which attention to lifestyle and the quantities eaten (to prevent obesity and the insulin resistance syndrome) may be more critical than the nature of the fatty acids consumed.