Good Fish, Bad Fish
Tuesday, August 8, 2006
The conflicting health information about seafood can make you feel ready to go off the deep end.
First, fish are touted for their health benefits. Then, sometimes soon after, they're condemned for containing too much mercury, PCBs or other contaminants.
Some health experts worry there's enough conflicting advice to make the public avoid fish altogether.
"It's a shame that people are running away from seafood at a time when it gives so many benefits," notes William Lands, a retired National Institutes of Health researcher who has studied the healthy fats found in fish.
That could be a big mistake. The benefits of eating seafood "are likely to be at least 100-fold greater than the estimates of harm, which may not exist at all," according to Walter Willett, professor of nutrition at the Harvard School of Public Health. He notes that "the kinds of levels of contaminants that are being talked about are not a reason for people to reduce their fish intake."
Rich in omega-3 fatty acids, a healthy kind of fat, seafood is known to help protect the heart, the brain and the joints.
Reporting in this month's Journal of the American College of Cardiology, researchers from the Harvard-affiliated Channing Laboratory found that increased fish consumption is linked with a lower risk of irregular heartbeat, which can lead to death. These findings fit with other studies that suggest eating at least two meals of seafood per week has health benefits, including a reduced risk of stroke.
Emerging evidence also suggests that omega-3s, which are most plentiful in deep-ocean fish, could also help prevent, and possibly alleviate, some mood disorders, including depression and bipolar disorder.
The health advantages of eating seafood are sufficiently clear that the U.S. Dietary Guidelines, the American Heart Association, the National Academy of Sciences, and the National Heart, Lung, and Blood Institute recommend fish for at least two meals a week (unless it's deep-fried).
But concerns about mercury and other potential risks continue to muddy the waters. Both the Food and Drug Administration (FDA) and the Environmental Protection Agency warn young children, women who might become pregnant and those who are pregnant or nursing to completely avoid eating shark, swordfish and king mackerel and to limit albacore ("white") tuna, all of which can be high in mercury.
Mercury occurs naturally in the environment and is also spewed into the air by industrial emissions, particularly from power plants. As the mercury drifts down, it accumulates in streams and oceans, where bacteria convert it to a toxic form of the chemical called methylmercury, which is then absorbed by fish.
The higher a fish is on the food chain, the more mercury it accumulates. Experts have worried that this could be damaging, particularly if the mercury crosses the placenta and passes into the fetal brain, where it could affect hearing and intelligence.