The omega-3 fatty acid is the last double bond with 3 carbon atoms at the end of the methyl. Omega·3 fatty acids are mainly 20 carbon-five-ene acid (EPA) and 22-Hna. Marine fish oil is the most abundant, including the fish in the sea, containing a large number of EPA and DHA. The mechanism of regulating blood lipid of sea fish oil is not very clear. It may inhibit the synthesis of lipid and lipoproteins in the liver and promote the excretion of cholesterol from feces. In addition, it can dilate coronary arteries, reduce thrombosis, delay the progression of atherosclerosis and reduce the incidence of coronary heart disease. This is likely to work by affecting prostaglandin metabolism and improving platelet and leukocyte function. A large number of fish-eating eskimos and Arctic residents have a low incidence of coronary heart disease.