That was the message from the advisers as they grappled with exactly what the Food and Drug Administration should tell women.
The advice Wisconsin health officials offer pregnant women may be the right approach until the FDA gets better data, the panelists concluded: Two 6-ounce cans of tuna per week is fine if that's the only fish they eat, or a single can if other seafood, which also can contain mercury, is part of their diet.
"Nobody wants to tell people to stop eating tuna fish," said the panel chairman, Sanford Miller of Virginia Tech University. "We're trying to balance the very positive virtues of fish, including tuna fish, with the harms. It's a very hard balance to make."
Indeed, tuna provides high-quality protein for pregnant women who might instead opt for higher-fat bologna, added panelist Joseph Hotchkiss, a Cornell University food scientist.
The FDA already tells pregnant women not to eat four fish species that contain the highest levels of mercury: shark, swordfish, king mackerel, and tilefish, also known as golden or white snapper.
But those women should eat up to 12 ounces a week of a variety of other cooked fish, including canned tuna, shellfish and smaller ocean fish, the FDA advises. Canned tuna and those other species contain far less mercury than types on the don't-eat list.
But the FDA's advice, issued last year, caused an uproar as consumer advocates charged that tuna should be limited, too — because as the nation's most popular seafood, women may eat enough to add up to risky mercury levels.
The U.S. Tuna Association declined comment on the panel's conclusion. But the food industry testified that very few pregnant women eat enough fish, much less tuna, today to absorb worrisome mercury levels. The FDA's advice last year was sound, said Rhona Applebaum of the National Food Processors Association.
Fish is very nutritious. The American Heart Association recommends people eat it twice a week to absorb heart-healthy fats; it also contains fats important for fetal brain development.
But different species also harbor different amounts of mercury, a metal believed harmful to the growing brains of fetuses and young children. Typically, the largest fish contain the most mercury.
About 8 percent of U.S. women of childbearing age have enough mercury in their blood to be at risk of having babies with subtle learning disabilities, the Centers for Disease Control and Prevention estimates. Eating seafood is considered the main source.
Pregnant women would have to eat more than two cans of tuna a day for weeks to really be at risk, FDA scientist Michael Bolger argued Thursday.
But the FDA's advisory panel, ending a three-day inquiry into the controversy, countered that no one knows what proportion of the mercury in a woman's diet tuna actually contributes to.
In fact, women could absorb far more mercury if they also eat freshwater fish that friends or family catch in local lakes or rivers. Some state waters are heavily polluted with mercury, and the FDA doesn't regulate recreationally caught fish.
The FDA should quickly research just how big a risk canned tuna truly is, but in the interim urge that pregnant women — and young children, too — take extra care by limiting their consumption, the panel decided.
It also urged FDA to work more closely with the Environmental Protection Agency and states issuing advice that takes into account recreationally caught fish — and to do a better job of educating women about what seafood they should eat.
Consumer advocates called the decision a victory.
"The advisory committee says FDA can't leave consumers in the dark about mercury in their favorite fish, tuna," said Caroline Smith DeWaal of the Center for Science in the Public Interest.
The FDA deems safe fish that contain less than 1 part per million of methylmercury. The average commercial fish contains 0.12 ppm. Canned tuna on average contains only slightly more than that, but amounts can vary to as much as 0.75 parts per million, Bolger said.