Fish: What You Need to Know About Eating Fish (cont.)
Fish at the top of the food chain -- pike, bass, older or large tuna, tilefish, king mackerel, shark, and swordfish -- tend to have higher levels of mercury, from one to 1 million times greater than the amount in the waters, according to the EPA.
If you're eating a lot of fish, mercury accumulates in your bloodstream over time. While the body naturally gets rid of mercury, it may take a year for the levels to drop significantly. Thus, it may be present in a woman even before she becomes pregnant. This is the reason why women who are trying to become pregnant -- or pregnant women -- should also avoid eating certain types of fish.
For women wanting to switch to other omega-3 sources, there are options, says Julie Redfern, RD, a registered dietitian in obstetrics at Brigham & Women's Hospital in Boston. She has counseled thousands of pregnant or soon-to-be-pregnant women.
"It's one of those questions that comes up almost every day ? mercury and fish," Redfern tells WebMD. "Some women are very well-read, and they say they are not going to eat any fish. Others say, 'I love fish,' and want to know what's safe. I give them the FDA's list of safe fish. I ask them what fish they usually eat, and look for it on the list. I also talk to them about canned tuna, about the different kinds of tuna -- and what's on the 'avoid' list."
Overall, she says, "I feel very comfortable reassuring them that if they keep it to the 'safe' fish -- and eat no more than two servings a week -- they'll be fine."
But, flaxseed oil, walnuts, canola oil, wheat germ, and omega-3-fortified eggs are excellent food sources for these fats. Also, a couple of new prenatal vitamins -- and a 200 mg supplement -- contain an algae-derived form of omega-3 fats, she adds.
"These are from vegetable plants, so the fats are not quite the same ? the body converts them more slowly. But if someone doesn't want fish, it still works."
Redfern identifies with those who love fish and hate to cast it from their diet entirely. "With them, I advise making sure you're not eating as much as in you once did. You don't want to frighten them, make them not eat fish at all."
Another Issue: PCBs in Farmed Fish
The content of PCBs in fish has not received as much attention. These are synthetic chemicals released into the environment through commercial manufacturing activities. Even though PCB chemicals have been banned in the U.S. since 1979, they continue to be a threat because it does not biodegrade quickly; PCBs continue to "live" in groundwater and soil.
PCBs are a likely cause of cancer, the EPA says. At high levels, PCBs kill lab rats, cause developmental problems, or cause damage to the liver, kidney, and nervous and endocrine systems.
"I think all marine and freshwater fish have PCBs," says Goyer, who has retired to live in Chapel Hill, N.C. "The North Carolina EPA advisory board is more concerned about PCBs than mercury in fish. There is potential for neurological damage." However, in his NAS study, "we determined that mercury was more critical than PCBs. That's not to say that PCBs don't have an affect."
Bottom line: "It's prudent for women of childbearing age to limit their intake fish," he tells WebMD.
Published March 21, 2005.
SOURCES: WebMD Public Information from the Environmental Protection Agency: "What You Need to Know About Mercury in Fish and Shellfish." Robert Goyer, MD, professor emeritus and chairman of pathology, University of Western Ontario. Julie Redfern, RD, registered dietitian, Brigham & Women's Hospital, Boston. WebMD Feature: "Is It Still Safe to Eat Seafood?" WebMD Medical News: "Mercury in Fish No Problem in Pregnancy."
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