But a new study suggests that advice may be flawed.
The study found that children born to women who ate more than two servings of fish a week during pregnancy — more than federal guidelines recommend — were about half as likely as kids born to women who ate less fish to have trouble with attention and hyperactivity at school.
The study can’t prove more fish was the only reason kids could function better at school. But fish are rich sources of omega-3 fatty acids, which are important for healthy brain development.
“This is only one study. More studies should look at this. But if indeed eating more fish does seem to be protective across different studies, that’s an important public health message,” Sagiv says.
But the good news about fish comes with a big catch.
The study also found that children exposed to high levels of mercury in the womb were more likely than those who were not to show signs of attention deficit hyperactivity disorder (ADHD) in school.
Where does the mercury come from? Mostly from fish in mom’s diet.
“Eating fish is good for brain development,” Sagiv says. “But eating fish high in mercury is a risk for brain development.”
What that means, Sagiv says, is that pregnant women should eat fish, but should try to stick to species that are lowest in mercury.
Good choices include catfish, mullet, trout, sardines, sole, tilapia, and wild-caught salmon, according to the Natural Resources Defense Council, a nonprofit environmental group that publishes a guide to mercury in fish.