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Pollution complicates diet advice
April 10, 2008
Suzanne Havala Hobbs

The more we pollute the environment, the harder it is to make simple dietary recommendations. Advice about eating fish is a good example.

As a concentrated protein source, fish is generally a healthier choice than other meats. It’s low in saturated fat and rich in oils thought to be heart-healthy for some individuals.

Some evidence also points to possible benefits for brain and vision development in infants whose mothers eat fish during pregnancy.

But eating fish also carries risks.

Widespread methylmercury contamination in fish has led the federal government to issue complicated advice about the types and limits on fish that young children and women in their child-bearing years should eat.

Methylmercury can cross from mother to baby and cause learning deficits and developmental delays in children.

Why is advice about mercury in fish directed solely at these groups and not everyone? Are long-term, low doses of mercury OK for men and older women? The truth is nobody knows. In the absence of evidence, the government offers no advice on fish-eating limits for others.

Meanwhile, mercury isn’t the only contaminant in fish. Harmful bacteria and microbes, metals and chemicals also accumulate in fish.

For example, cancer-causing polychlorinated biphenyls, or PCBs, are a particular problem in farmed salmon.

Attempts to issue coordinated, easy-to-understand advice that includes information about benefits and risks of eating fish have been contentious, largely because so many interests are at stake.

One example: A 2001 fish advisory published by the Food and Drug Administration excluded any recommended limits on tuna, a substantial source of mercury in Americans’ diets.

The nonprofit Environmental Working Group criticized what it called undue influence of the fish industry in the drafting of the advisory. The FDA eventually went back and added a warning for canned albacore tuna.

So how is a consumer supposed to trust advice, knowing it’s often a product of scientific and political struggles?

For now, the best advice on fish comes from a 2006 Institute of Medicine report that attempted to create an objective, comprehensive set of guidelines for eating fish. Be warned, the report doesn’t offer clear-cut answers.

“Advice to consumers about balancing the benefits and risks of eating seafood must be based on the best available scientific information,” the report said. “The scientific evidence about both benefits and risks, however, is diverse, somewhat incomplete and uncertain.”

The IOM recommends limits on certain fish for certain people. For everyone else, it suggests spreading the risks by eating a variety of fish rather than a few. Other advice:

* Science suggests that women in their child-bearing years and young children may benefit from eating oily fish – two 3-ounce servings per week up to a limit of 12 ounces per week. Albacore (white) tuna, however, should be limited to 6 ounces per week, and shark, swordfish, tilefish and king mackerel should be avoided.

* It’s possible that healthy teens may lower their future risks for heart disease by eating fish. Anyone eating more than two servings per week, though, should pick a variety of fish to minimize exposure to contaminants from a single source.

* It’s also possible that adults at risk for heart disease may reduce that risk by eating fish regularly, especially oily fish. Again, eating a variety is safer than eating a single type.

Some of the suggested benefits of eating fish haven’t yet been proven. Likewise, the risks have not been adequately measured.

In the absence of clear answers, consumers, environmental groups, the fish industry and governments should aggressively pursue meaningful and effective steps to reduce mercury pollution and other environmental contamination.

Failure to do so promises increasingly complicated dilemmas over what’s safe – and unsafe – to eat.