How Fish may NOT be Good for You

October is National Seafood Month. This month-long celebration highlights the commercial and recreational fishing industries and its positive impact on the economy.  That’s great news, because fish are good for you?  Or are they?  Doctors and dieticians almost always advise: “Eat more fish,” and the American Heart Association recommends eating fish at least two times per week as part of a healthy diet. But we are also hearing more and more about the importance of where our fish come from,  if they’re sustainable or not, the dangers of overfishing, etc.

The biggest health risk to eating some kinds of fish is that they can be very high in mercury, notably fattier ocean fish like gmackerel, swordfish and some tuna (bluefin and albacore), because their fatty tissue absorbs and holds the mercury in the seawater. “All fish do contain some mercury,” sasys Julia Zumpano, RD, LD, a registered dietitian specializing in nutrition therapy for preventive cardiology and rehabilitation at the Center for Human Nutrition, Cleveland Clinic, Cleveland, Ohio. “Mercury occurs naturally in the environment and as a result of industrial pollution. It collects in the air and can collect in streams and oceans where it’s converted into methylmercury.”

She specifically named four fish with some of the highest levels of mercury—shark, tilefish, king mackerel, and swordfish—that should be limited or avoided. Even so, one serving of one of these fish per week is OK for most people, according to the FDA. Most people. However, there are some populations who are more susceptible to high levels of mercury.

One of these populations are pregnant women.  Pregnant/nursing mothers should completely avoid eating fish that are high in mercury, and should limit their consumption of other types of fish to 12 oz per week (in other words, a 4 oz. serving, three times a week).

For children, you can keep them from exceeding the safe limits for mercury by having them eat fish from the FDA’s “best choices” category two times a week according to these recommended serving sizes by age group:

  • Age 2: 1 oz serving
  • Age 6: 2 oz serving
  • Age 9: 3 oz serving
  • Age 11 and up: 4 oz serving

Are freshwater fish safer than saltwater fish?  “Not necessarily—it really depends on the condition of the water. Freshwater fish are exposed to mercury, dioxins, and PCBs [polychlorinated biphenyls] just as saltwater fish are,” says Zumpano. “It’s best to eat a variety of fish from both sources that are known to have the fewest contaminants. You can check your local fish advisories through the EPA.”


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