Fish oils are the fats obtained from fish such as mackerel, tuna, salmon and trout. They are highly polyunsaturated fatty acids that are composed primarily of eicosapentaenoic (EPA, C20:5 (n-3)) and docosahexaenoic acid (DHA, C22:6 (n-3) which belong to the omega-3 family of fats. Fish oils collect in the flesh and skin of fish, where they are required because of their low melting points, as less unsaturated oils would go solid at the low temperatures typical of coldwater fish habitats. Fish accumulate these fatty acids from the algae they eat, and are not able to synthesise them endogenously.When we eat these fish we absorb the fatty acids and they accumulate in out cell membranes. Here the fish oils act as a reservoir for the formation of the series 3 eicosanoids and the series 5 leukotrienes, which both have mild anti-inflammatory effects. In addition the series 3 eicosanoids and the series 5 leukotrienes block the formation of pro-inflammatory series 2 eicosanoids and series 4 leukotrienes.
Fish oils therefore have anti-inflammatory effects, and this explains their ability in some parts to improve insulin sensitivity. As inflammation is a cause of oxidative stress, and oxidative stress in turn decreases insulin resistance, consumption of fish oils would be expected to improve insulin resistance by reducing inflammation. And this appears to be so. However, in addition, fish oils may also increase the oxidation of fatty acids in the visceral fat that has accumulated as a result of consuming a poor quality diet. The exact mechanism is unknown, but fish oils appear to reduce the plasma concentrations of triglycerides, which suggests that they inhibit the de novo lipogenesis pathway in the liver. As this pathway is responsible for the fatty acids that interfere with the insulin signal cascade and decrease insulin sensitivity, fish oils may improve insulin sensitivity through a direct effect on the availability of these fatty acids. Consumption of fish oils may therefore have more than one mechanism by which they improve insulin sensitivity.
RdB
