The most important thing you need to know is that the benefits of eating fish far outweigh the risks for most people, according to researchers at Harvard University. Fish is high in protein and rich in vitamin D, and it may well lower your chances of developing heart disease. The exceptions are those who are pregnant or nursing or have young children or are planning to: They need to watch what they eat because some fish are contaminated with mercury, which can cause neurological damage to children. (The toxin is mostly produced by industrial sources, like coal-burning power plants, which release mercury into the air.) If you’re in one of these groups, the U.S. Food and Drug Administration suggests you avoid fish that are high in mercury (those marked with * on the Healthy-Seafood Guide) and limit your general intake to 12 ounces (two meals) a week.