One downside of increasing the amount of fish you eat is potential exposure to mercury, a toxin that can affect brain development in fetuses and young children, and in excess may affect the health of adults as well.
At the same time, though, women of childbearing age (especially those who are pregnant or breastfeeding) and children are encouraged to eat fish to get the omega-3s that support growing brains, and everyone should be eating fish to boost their heart health.
“It’s healthy to eat fish, and you can even eat a lot of fish. You just need to pay attention to which fish are high or low in mercury,” says Jean Halloran, director of food policy initiatives for Consumers Union, the advocacy division of Consumer Reports. “There are acute neurological risks of too much mercury, even for adults—from mental fuzziness to tremors and loss of balance.”
The AHA urges people to choose fatty fish that are highest in omega-3s for their two servings a week. Its list includes salmon, mackerel, herring, lake trout, sardines, and albacore tuna.
But some of those recommendations are at odds with the Food and Drug Administration’s guidelines for women of childbearing age and children. The FDA lists albacore tuna as a “once a week choice.” And while Atlantic mackerel is low in mercury and okay to eat two or more times a week, King mackerel is a high mercury fish that the FDA recommends avoiding.
The authors of the AHA advisory did not find that mercury had any adverse effects on cardiovascular disease and concluded that the heart-health benefits of eating fish twice a week outweigh any risks, especially if you consume a variety of seafood. Rimm notes, however, that they did not look at pregnant women or children in their review of the research.
Consumer Reports recommends getting your omega-3s from low-mercury fish. Fortunately, some of these are rich sources of omega-3s: Atlantic mackerel, sardines, salmon (including canned), and trout. “Although other low-mercury fish, such as catfish, flatfish and sole, shrimp, and tilapia don’t supply as much omega-3s, they do contain some,” Halloran says.
As for tuna—the most popular type of seafood next to shrimp—Halloran notes that previous Consumer Reports analysis of mercury levels in tuna suggests that pregnant women shouldn’t eat it at all. Everyone else should opt for chunk light which has one-third the mercury of albacore and about one-fifth of the mercury in sushi tuna (such as bigeye), and not make tuna the only type of seafood they eat.