How Much Fish is Too Much?

But, as researchers are discovering, too much of a good thing can be bad. Eating too much saltwater sporting fish such as tuna, one of the most popular sources for omega-3s, may put you at risk of exposure to mercury, a toxic substance. The price of eating too much of this fish may be serious long-term health problems.

"Humans depend on omega-3 fatty acids for survival. In fact, they are as essential as the vitamins and minerals," said Dr. Robert Keith, an Alabama Cooperative Extension System nutritionist and Auburn University professor of nutrition and foods.

"They may play a role in reducing heart disease. One study, for example, revealed that women who ate fish only twice a month reduced their heart disease risk by as much as 50 percent."

There is also an anti-clotting effect associated with omega-3s --- a factor that seems to reduce the risk of heart disease and stroke among people prone to clotting, Keith said.

And there's more. Research has also uncovered a link between omega-3 consumption and healthy brain tissue, especially in cases where DHA, a type of omega-3 fatty acid, is involved. Research has shown that children who obtain adequate amounts omega-3 enjoy healthier cognitive development. In addition, omega-3 fatty acids may help reduce the risk of developing Alzheimer's disease later in life, Keith said.

Our remote ancestors obtained ample amounts of omega-3 fatty acids from game animals, fish and plants. But for modern individuals who derive most nourishment from processed foods, obtaining enough omega-3's can be challenging. Many Americans, in fact, may border on the edge of deficiency and without even knowing it, Keith said.

Since it's no longer possible to eat like our distant ancestors, we're encouraged to make up for this deficiency by eating more fish.

Here's where health-conscious Americans encounter the catch-22. With more salt water fish consumption comes higher exposures to mercury, especially in cases where people are consuming more than two meals a week comprised of ocean-caught sporting fish, such as tuna and salmon.

"There really is a negative side to all of this, especially in cases where the fish being consumed is higher up the food chain, such as tuna," Keith said. "Some have turned up with surprisingly high levels of mercury."

Mercury exposure is an especially serious health risk because of its tendency to accumulate in the body over time. The consequence of this long-term exposure can be damage to the central nervous system. Another effect may be heart disease.

Studies have shown pregnant women and very young children may be especially susceptible to mercury.

"We don't want pregnant women eating too much fish during this critical time in their lives because of the developing fetus," Keith said. "Children are another problem. Because of their size, we just don't know what a harmful dose is."

As for the vast majority of adult Americans who don't fall into these categories, the problems associated with fish pose a dilemma.

"Do we continue eating fish because it's good or do we quit eating the food because it may contribute to a long-term exposure to a toxic chemical? That's a very good question," he said.

"Yes, there is a risk that comes with eating ocean-caught fish high up on the food chain. But do we want people to stop eating fish entirely? Absolutely not. We should keep eating moderate amounts of fish to get adequate levels of omega-3 fatty acids."

Moderation is the lesson here, Keith said. To gain the benefits of omega-3 fatty acids, while avoiding high risks of mercury exposure, he recommends limiting fish consumption to two meals per week.

(Source: Dr. Robert Keith, Alabama Cooperative Extension System Nutritionist, 334-844-3273.)

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