Chicago - Middle-aged men who eat a weekly meal of "fatty" fish such as tuna, salmon, mackerel or shellfish cut in half their risk of suffering a sudden, deadly heart attack, a study published yesterday said. Researchers at Brigham Hospital in Boston studied the dietary habits and health of 20,551 male physicians, aged 40 to 84 years, and found that those who ate seafood containing the n-3 fatty acid at least once a week had a 52 per cent lower risk of sudden cardiac death compared to those who ate fish less than once a month.