“Not only are fish relatively low in fat and cholesterol, but they also contain omega-3 fatty acids (commonly called fish oils). These are very long-chain, polyunsaturated fatty acids that seem to have cardiovascular benefits. Large population studies have shown that groups of people who eat fish regularly have fewer heart attacks than those which do not, and omega-3 fatty acids are believed in part responsible for this protection. The omega-3 fatty acids have an anti-thrombotic effect, which means that they cause blood to take longer to clot. Since most heart attacks ultimately occur when a blood clot forms and becomes lodged in a narrowed coronary artery, a reduced tendency to clot is an obvious advantage. Omega-3 fatty acids can also help lower an extremely elevated serum triglyceride level (the fat in the bloodstream). Omega-3 fatty acids occur in marine phytoplankton, which are eaten by small fish and work their way up the food chain. All fish and shellfish have some, but cold-water fish have a higher total fat content and more omega-3 fatty acids than fish found in warmer water.” (p.430)
Benson, H. and Stuart, E. 1992. The Wellness Book. New York, N.Y.: Simon & Schuster.