Nutrition experts agree that fish is a good source of protein and healthy fats, but these health benefits often come with a down side. Many fish species, from deep-ocean varieties like tuna to river-bound species like carp, also contain high levels of mercury, which the fish absorb from polluted waters. Because studies have shown that mercury, a heavy metal, can be toxic to neurons in the brain, a draft of FDA recommendations advise pregnant women or women expecting to become pregnant to avoid high-mercury fish altogether when they're expecting.
But scientists at the Environmental Working Group (EWG) show that even if women follow the government’s advice on which types of fish to eat while they're pregnant, they may be exposing themselves and their unborn babies to unsafe levels of mercury — and not gaining the benefits of the omega-3 fats that they believe they're getting from the fish.
The reason, the EWG charges, is that the list of high-mercury fish is incomplete or inaccurate. Specifically, canned light tuna is listed as a lower-mercury fish, but some studies show it’s still high in mercury and it makes the National Resources Defense Council’s list of high-mercury seafood. Plus, it contains relatively low amounts of the healthy omega-3 fats, which means its risks may outweigh its benefits.
“It’s misleading to name canned light tuna as one of the low-mercury species that women are encouraged to eat,” says Sonya Lunder, senior analyst at EWG who wrote the report. It can take months for mercury in the body to get fully eliminated, so doctors should also be advising women to avoid eating too much of the high-mercury fish for at least six months before they become pregnant.
An FDA spokesperson said in a written response to questions that the agency “will update our advice” after more than 200 comments submitted by the public on its draft recommendation. In a statement, the National Fisheries Institute disagreed with the conclusions in the report, calling it a ‘slickly packaged marketing piece designed to drive traffic to its mercury calculator; promotional click bait.’"
EWG asked 254 women of child-bearing age who ate more than the government’s recommended amount of fish to record their seafood consumption and submit hair samples for mercury testing. Among women following this preliminary advice of two to three servings of different types of fish a week three out of 10 women sampled were exposed to levels of mercury deemed unhealthy by the EPA.
“There’s no reason why the government shouldn’t be doing a better job at providing clearer information for women who seek it out,” she says. The FDA-EPA guidelines, which aren’t final and still in draft form, only mention swordfish, king mackerel, tilefish and shark as species for pregnant women to avoid, and suggest limiting albacore tuna to six ounces per week.
To help women to lower how much mercury they’re getting exposed to in their food, she says, “you need a longer list of things to be aware of.”
But other government advice gets it right, says Lunder. The recent dietary guidelines for Americans, while controversial for other reasons, advises all adults to eat at least eight ounces of a variety of seafood a week. To avoid mercury exposure, the guidelines provide a list of low mercury seafood, which include salmon, anchovies, herring, shad, sardines, Pacific oysters, and trout. That list should be part of the FDA-EPA advice as well, says EWG scientists, so that women who are pregnant have more complete information about which types of seafood are safer for them while they are expecting — and not just a limited list of what not to eat.
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As the data on the mercury content of some fish continues to grow, doctors are staring to avoid making blanket recommendations to just eat more fish. Everyone needs to be more aware of balancing the benefits of seafood against its potential risks, and that means considering options, like salmon, that provide the benefits of omega-3s while minimizing exposure to toxins like mercury.