A fish diet helps prevent heart attacks, three teams of researchers reported Wednesday. One study found it cuts the risk in half.
''The consumption of as little as one or two fish dishes a week may be of preventive value in relation to coronary heart disease,'' one of the research groups said.
The protective effect appears to be due to an unusual class of oils found in fish, the researchers reported in the New England Journal of Medicine. These oils seem to prevent the formation of artery-blocking deposits much better than vegetable oils, the scientists said.
Heart experts got interested in fish diets several years ago because of reports of remarkably low rates of heart attacks among Eskimos, who eat about 400 grams (about 15 ounces) of fish a day. High fish consumption also is believed to be related to the low incidence of heart attacks in Japan.
The three studies looked at the relationship between fish consumption and heart attacks on progressively more complex levels.
One study, by a group at the University of Leiden in the Netherlands, looked at diet and heart attack deaths in a group of 852 men for 20 years.
Over the course of the study, 78 men died of heart disease. However, the more fish the men ate, the less likely they were to die from this disease.
The researchers found that those who averaged at least an ounce of fish daily were less than half as likely to die of heart disease than were those who never consumed fish.
''The fish-oil diet led to decreases in both blood cholesterol (27 percent) and triglycerides (64 percent) as compared with the control diet,'' they reported.
Obesity, cigarette smoking, high blood pressure, high cholesterol levels and physical inactivity are among conditions and habits associated with heart trouble. However, the researchers found that none of these could explain the link they found between fish and health.
In the third study, researchers at Harvard looked at the molecular effects of fish oils, which contain chemicals called omega-3 fatty acids. Fish oils appear to cause chemical changes that reduce the tendency of white blood cells to form clots, they said.
The fish oil chemicals also seem to prevent the thickening of artery walls that can lead to blockage of the blood vessels, they said.