Prostate protection? This is fishy.

A wealth of studies has pointed to the heart benefits of diets rich in fish. A Swedish study now finds another reason for male diners to request finned fare: prostate protection.

Researchers have inhibited prostate cancer in animals by feeding them the omega-3 fatty acids that characterize fish oil. Paul Terry and his colleagues at the Karolinska Institute in Stockholm wanted to find out if the same held true in men, so they focused on 3,100 pairs of male twins born between 1886 and 1925.

Thirty-four years ago, each of the men had filled out a detailed dietary questionnaire. As of 4 years ago, 466 of the participants had been diagnosed with prostate cancer. Roughly three-quarters of these men died of the disease.

In the June 2 LANCET, Terry's team reports finding that men who regularly ate lots of fish appeared to derive substantial protection against prostate cancer. Moreover, this anticancer effect was even stronger when the scientists accounted for other possibly confounding risks, such as differences in the groups' smoking and drinking habits.

Overall, those who frequently ate fish were only half as likely to be diagnosed with prostate cancer--and only one-third as likely to die of it--as were men who habitually eschewed fish. Men eating intermediate amounts of fish exhibited cancer risks somewhere between the two groups.

How much fish confers measurable protection against prostate cancer? Says Terry, "It boils down to three or four servings a week--or eating it every other day."

Swedes routinely consume fatty fish, such as salmon, herring, and mackerel. Indeed, the fat in these fish makes them well adapted for cold waters. Terry says his team is now testing the hypothesis that diets rich in fish oil may also inhibit other hormone-dependent malignancies--such as breast and uterine cancers.