So why is it that the rate of heart disease among men living in Japan is less than half that of men living in the U.S. and that Japanese men tend to have less artherosclerosis -- the artery-clogging plaque that leads to heart attacks and strokes?
A new study suggests that the answer may be found in the sea.
Because they ate more fish, men living in Japan who participated in the study had twice the levels of omega-3 fatty acids in their blood as white men and Japanese men living in the U.S. They also had less severe degrees of atherosclerosis.
The finding lends support to the hypothesis that omega-3, which is found primarily in fatty fish like tuna, mackerel, and salmon, protects against plaque buildup in the arteries.
Sources of omega-3 fatty acids are fish oils, which contain docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), and plant sources. Alpha-linolenic acid (ALA), which is converted into omega-3 fatty acids in the body, is a plant-source omega-3 fatty acid.
Studies have generally used fish oils. While plant sources with ALA may have the same benefits, less is known about them.
"The extremely high intake of fish in Japan may explain the much lower rate of atherosclerosis and subsequent coronary heart disease," researcher Akira Sekikawa, MD, PhD, tells WebMD. "This study does not prove that omega-3 is protecting these men, but we showed that artery thickness decreased as omega-3 levels went up."
The Japanese diet has become increasingly westernized since the end of World War II, but fish consumption in Japan is still among the highest in the world.
People in Japan eat an average of 3 ounces of fish every day, while the average American finds it difficult to manage the two servings of fish a week recommended for heart health by the American Heart Association, omega-3 researcher William Harris, PhD, tells WebMD.