For many years, nutritionists assumed you lost weight when you ate fish because it has fewer calories, pound-for-pound, than red meat. Now however, it appears that reasons go above and beyond calories. Most important, the type of fat found in fish appears to enhance the efficiency of the hormone leptin. This protein circulates in your bloodstream and, like the hormone insulin, is a key hormone in the weight-management equation. Leptin regulates your food intake as well as your body's energy expenditure. When cells in your brain sense a rise in leptin, they signal other parts of your nervous system to turn down your appetite and turn up your metabolism.
The omega-3 fats support healthy heart, a healthy brain and nervous system and possibly enhance the efficiency of leptin, helping you boost your metabolism and control appetite. It hardly gets better than this. While all fish have more omega-3 fats than a hot dog, the fatty fish like salmon, black cod, herring, sardines, mackerel, halibut, fresh tuna and shellfish are highest in omega-3 fats.