WASHINGTON — The federal government on Friday warned that pregnant women and young children should limit their intake of tuna and other types of seafood because the mercury content can harm developing nervous systems.
But the advisory by the Food and Drug Administration and the Environmental Protection Agency also said tuna -- that staple of school lunches and diet menus -- offered health benefits that should not be ignored.
That triggered a political food fight, with consumer and environmental groups complaining the advisory did not go far enough, and a tuna industry official accusing critics of trying to scare people away from a food that was low in fat at a time when America faced an obesity epidemic.
A member of an FDA advisory group resigned in protest, saying the agency should have discouraged more strongly the consumption of albacore tuna by pregnant women.
The debate underscored a dilemma facing Washington: how to guide Americans on eating food that offered health benefits and was important to the U.S. economy but also could harm the nervous systems of fetuses and young children.
"This message has to be a balance between the nutritional benefits of fish and the potential risks from exposure to mercury in fish," said Dr. David Acheson, chief medical officer of the FDA's center for food safety and applied nutrition.
"That's where it gets difficult. Because you have to strike this balance," he said.
Most people can and should eat fish frequently because of its high protein content and other nutrients, the federal advisory said.
But women who are pregnant, nursing or may become pregnant should, "as a matter of prudence," limit their consumption of fish likely to contain mercury to 12 ounces -- or two average meals -- a week.
The consumer guidelines listed canned light tuna, shrimp, salmon, pollock and catfish as varieties that should be eaten in the restricted quantities.
The same group of women, the advisory said, should consume no more than six ounces a week of albacore or white tuna, which has more mercury than canned light tuna.
Although the warning is limited, its scope may be significant because tuna is so popular. About 2.3 billion cans of tuna are sold in the United States each year.
Federal officials urged parents to follow the recommendations when feeding fish to children, but to serve smaller portions. Because the scientific data are inconclusive, the advisory did not specify how much smaller the portions should be, or the age range of children that should be covered.
According to the guidelines, children as well as women who are pregnant, nursing, or planning to become pregnant, should avoid eating shark, swordfish, king mackerel and tilefish altogether because they contain high levels of mercury.
In addition, those at-risk groups were urged to check local advisories about the safety of fish caught in local waters; if no advice was available, they should limit eating such fish to six ounces -- or one average meal -- per week and avoid consuming any other types of fish during the week.
Lester M. Crawford, the FDA's deputy commissioner, said the advisory would "help Americans continue to consume and enjoy the health benefits of fish while lowering the risk of any harmful effects of mercury."
The guidelines come a month after an EPA analysis found that more than 600,000 of the roughly 4 million babies born annually in the United States -- double the previous estimate -- might be exposed to dangerous levels of mercury in the womb. Mercury in children can cause neurological damage and learning problems.
Consumer and environmental groups called the advisory a generally positive step, but said the federal government should go further.
They said warnings should be required on supermarket shelves and distributed to doctors' offices.
And they urged officials to act more aggressively to reduce mercury pollution, especially from coal-burning power plants.
FDA officials said they planned to launch an educational program this year.
Diana Zuckerman, president of the National Center for Policy Research For Women & Families, a Washington research and advocacy group, called the advisory a compromise.
Although her group favors a "more cautious" approach to consumption than the government laid out Friday, Zuckerman said, "it's still a victory for women and families, because they will finally have information about the risks of canned white tuna. Now they can use that information to protect their babies and young children from dangerous levels of mercury."
H. Vasken Aposhian resigned from his temporary position on an FDA food-safety advisory committee, complaining that the guidelines did not do enough to protect pregnant women and their fetuses.
The Environmental Working Group, a research and advocacy organization, accused the government of kowtowing to the tuna industry and making a "bad situation worse by encouraging consumption of albacore tuna at clearly unsafe levels."