Video: Too much mercury in fish?

By Elisa Zied, R.D.
msnbc.com contributor
updated 1/29/2008 6:39:51 PM ET 2008-01-29T23:39:51

Clarification: An earlier version of this story said it is safe to eat up to 12 ounces of fish a week. The statement should have noted that the government recommends that pregnant women, nursing mothers and young children should eat a variety of fish and shellfish that are lower in mercury, but not exceed 12 ounces a week. The story should have also specified that tuna sushi is most often linked to high levels of mercury.

Concerns about the safety of eating sushi were raised this week after reports surfaced over the high levels of mercury in tuna and swordfish. Lab tests commissioned by the New York Times found so much mercury in tuna in 20 Manhattan restaurants and stores that eating six pieces a week would exceed acceptable levels set by the Environmental Protection Agency, the newspaper reported.

On Friday, the group that conducted the tests, the Environmental and Occupational Health Sciences Institute, in Piscataway, N.J. told TODAY that the findings would likely be similar in other cities around the country.

The report generated a strong response from the seafood industry. TODAY’s Matt Lauer quoted a statement from the National Fisheries Institute, saying “The public deserves to have all the facts about the benefits of eating fish, and that is why scaring consumers with misinformation is so irresponsible.”

The government recommends that Americans eat fish at least two to three times a week as a good source of low-fat protein. But is it OK to eat sushi? Read on if you're confused about whether you should keep eating fish and what types are safest.

Q. Lab tests found high levels of mercury in sushi fish, particularly tuna and swordfish. Are there risks in eating raw fish in general?

A. Fish provides high-quality protein, as well as healthful omega-3 fats . But there are many risks associated with consuming it raw. As we know, raw fish can contain high levels of chemical contaminants, including methylmercury. Mercury occurs naturally in the environment, but is also a by-product of pollution that enters oceans and lakes. When it gets into the water, mercury gets converted into methylmercury and builds up in fish. Too much methylmercury in the bloodstream can damage the developing nervous system in fetuses, infants, and young children. In adults, it can cause vision problems, memory loss, headaches and hair loss.

Sushi tuna is most often linked to high levels of mercury, but don't panic if you’ve eaten a lot recently. According to the Food and Drug Administration, one week's consumption doesn’t change the level of methylmercury in the body much at all. If you eat a lot one week, you can cut back the next week or two and you’ll be fine.

There are other problems with eating raw fish. Other contaminants that accumulate in raw fish include polychlorinated biphenyls (PCBs) and dioxins, which some studies suggest can be carcinogenic and have other adverse health effects.

Eating raw fish can also make you susceptible to a variety of foodborne illnesses caused by bacteria, which causes diarrhea, cramping and vomiting, and also viruses such as Hepatitis A, and Norwalk-like viruses. Parasites can also be passed on via raw fish but, fortunately, can be killed when fish is frozen before consumption.

In rare cases some bacteria that accumulates in the diets of fish can produce toxins which can lead to illnesses including scombroid poisoning, the most common form of fish poisoning in the United States. Symptoms, which include diarrhea, flushing, sweating, headache, and vomiting, can begin within two minutes to two hours after eating the contaminated fish.

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Q. Is it safer to consume cooked fish?

A. Unfortunately, cooking fish does not remove mercury. However, cooking fish with the fat trimmed and skin removed, and cooking on a grill that drips away some fat can limit your exposure to these contaminants.

Q. Are there people who are at high risk who should avoid fish?

A. Women who plan to become pregnant, those who are already pregnant or nursing, children up to age 12, elderly people, and anyone with liver disease or any other disease or condition that compromises their immune system should steer clear of raw fish.

It’s also prudent for those at high risk to heed the advice of the FDA and Environmental Protection Agency and stay away from high-mercury fish. The fish highest in mercury are shark, swordfish, king mackerel and tilefish.

Q. Are there health benefits from eating sushi?

A. Sushi dishes made with cooked fish can be a relatively low-calorie, low-fat, nutrient-dense meal — as long as you watch the soy sauce and other add-ons that can contribute a lot of sodium. Cooked salmon, for example, is a good source of vitamin D. Sushi rice provides complex carbohydrates. If you order brown rice instead of white, you’ll get an added bonus of whole grains and extra fiber.

But you should eat sushi only at or from reputable and clean places. Don’t be afraid to ask the chef or vendor a lot of questions, so you have a better idea of what you’re getting.

Q. What types of fish are high in omega-3s and other nutrients, but are known to be lower in contaminants?

A. Wild salmon (fresh, frozen and canned), herring, sardines, sablefish, anchovies, and farmed oysters are good options. You can also choose shrimp, canned light tuna, pollock, and catfish.

The bottom line is eat fish, but mix it up. Have different types each week, keep portions small and cook it!

Elisa Zied, R.D., is a spokesperson for the American Dietetic Association. She is the co-author of “Feed Your Family Right!” and “So What Can I Eat?!”

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