The other night I had dinner with a friend who’s expecting a baby. The conversation turned to seafood — what’s safe to eat and why it’s important during pregnancy. I was reminded that there’s a lot of confusion about seafood for pregnant women — even in an area where so many of us have an intimate knowledge of local fish. Emily Oken is a researcher with the Harvard Medical School and has been working to understand the role of seafood consumption in pregnancy since the early 2000s.
"Right around at that time when I was embarking on my research career, the federal government released guidance for pregnant women encouraging them to limit their fish consumption because of concern about mercury exposure in pregnancy," said Emily.
The concern with mercury is that it bioaccumulates — in fish and then in our bodies — and at high levels, it can cause developmental problems for babies. The guidance was meant to point women to species of fish that were safe to eat during pregnancy but instead it put a lot of women off seafood entirely.
"What we found is that women did know a lot about the fish that they’re supposed to not eat but they were very unclear about which fish were safer to eat," she said. "And so as I think is common for a lot of us and especially for pregnant women they thought it was a better bet to just eliminate any possible chance of harm by not eating fish or eating less fish rather than taking the chance on eating the wrong fish."
This sounds smart. But it turns out that not eating fish isn’t great either. This is because seafood contains essential nutrients:
"It’s the only natural source of long chain fatty acids, the omega-3 fatty acids," said Emily.
Omega-3 fatty acids are essential fats — meaning we need them to survive. They’re especially important during pregnancy for fetal brain development and our bodies can’t make them; we have to get omega-3 fatty acids through our diets.
"So there are omega-3 fatty acids in nuts and some grains but they’re the short-chain version that our bodies have to convert to the long-chain version. And so since we need them for a lot of healthy organ function and we have to get them in our diet and fish are the only natural source, fish consumption is especially important."
Emily says fish is different from a lot of things we talk about being good or bad during pregnancy. Take smoking for example. Not smoking at all is the best thing for mothers and babies. But because of the important nutrients in fish, even with some risk of eating mercury, most seafood is still worth consuming. It’s nuanced, and recommendations for fish consumption during pregnancy have started changing:
"The guidance is first of all that women should eat fish and should feel comfortable eating fish and the main thing is to eat a variety of fish," she said. "So most of the kind of flakey white meat fish and there are a lot of different kinds of flakey white meat fish most of those tend to be quite low in mercury. So pollock and cod and things like that flounder, salmon and trout are both low in mercury and also high in omega-3 fatty acids."
Locally, Atlantic mackerel is probably the fish with the most beneficial balance that we can still get from local fisheries. Atlantic herring and salmon are both even higher in omega-3 fatty acids and low in mercury, but their populations are so low there’s a moratorium on fishing. Cooked oysters are another good local source of omega-3 fatty acids, as are lobster meat and scallops. Dr. Oken says the most critical thing for pregnant women to know about eating seafood is the importance of variety.
"The people who have historically gotten in trouble with higher mercury levels are really those who eat a lot of one type of fish so they eat you know canned albacore tuna five days a week every day for lunch for example or they eat tuna steak or swordfish very frequently."
Just like with most diets, it seems diversity and moderation are the key.
—
Learn more about omega-3 fatty acids in different seafood types:
https://ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional/
Here is the latest FDA guidance for eating seafood during pregnancy:
