Even so, the government needs to help consumers figure out which seafood is safer, an Institute report said.
"The confusion may have scared people out of eating something that is beneficial for them and maybe for their offspring," said Jose Ordovas, a Tufts University researcher and member of the report committee.
"Our goal was to put both things in perspective and see where is the balance," Ordovas said.
The findings from the Institute, which advises the government on health policy, are in line with widely accepted government advice that eating fish and shellfish may reduce people's risk of developing heart disease, the leading cause of death in the United States.
Interestingly, researchers said it's unclear how eating fish fights heart disease. It may be that beneficial omega-3 fatty acids offer some protection. Or the answer may be simpler, that people eat less saturated fat and cholesterol when they choose leaner seafood instead of fatty cuts of meat.
Americans generally eat too much saturated fat and cholesterol and too little of the good omega-3 fatty acids, the report said. And evidence shows that eating seafood rich in omega-3s can contribute to vision and cognitive development in babies and help expecting moms carry babies to term, researchers said.
The Tuna Foundation and other industry groups issued a statement saying the report tells consumers not to let fears of mercury exposure stop them from enjoying the nutritional benefits of regular fish consumption.
Critics said the report will only worsen confusion about which people should avoid which fish.
Environmental and consumer groups say it should have listed "good fish" and "bad fish," which the researchers said would be too difficult.
If the researchers really wanted to help consumers, they would have supported posting mercury notices in stores, as many companies already do, said Caroline Smith-DeWaal of the Center for Science in the Public Interest.
"Labeling, both through notices at the seafood counter and directly on packages of fish, would take away the confusion at the fish counter," she said.
Seafood is the main source of people's exposure to methylmercury, which is linked to learning disabilities and developmental delays in children and to heart, nervous system and kidney damage in adults.
"This report is not balanced, and it's taken on more of an advocacy role, rather than a balanced presentation of facts," said Gerald Leape of the National Environmental Trust. "It's a real disservice to consumers."
Critics were also alarmed the report offers similar guidance for pregnant women and for young children.
"They seem to be unaware that children are smaller than adults," said Jean Halloran, director of food safety at Consumers Union, which publishes Consumer Reports magazine. "That advice, which they have featured prominently, could result in young children getting excessive doses of mercury."
For pregnant women and children younger than 12, the report said:
--They may benefit from eating seafood, especially seafood with higher amounts of omega-3 fatty acids.
--They may eat six to 12 ounces of seafood a week, and that can include up to six ounces of albacore tuna. For children, a reasonable intake would be two 3-ounce servings "or age-appropriate servings, but they can safely consume 12 ounces per week."
--They should avoid big predatory fish such as shark, swordfish, tilefish or king mackerel, which have higher mercury levels.
For healthy teenagers and adults and those at risk of heart disease, the report said eating seafood may reduce the risk of heart disease. And if people eat more than two servings of seafood a week, they should be sure to eat different kinds of seafood to reduce the risk of exposure to contaminants, the report said.
While the report does not list "good" or "bad" fish, it does describe broad categories
--In all seafood, levels of dioxin, PCBs and other contaminants do not pose health risks when eaten in government-recommended amounts.