Japan's Heart-Healthy Diet: Fish Is Key
Study Shows High Omega-3 Levels in Japanese Diet Cuts Heart Disease Rates
By
Salynn Boyles
WebMD Health News
Reviewed By
Brunilda Nazario, MD
July 28, 2008 — It might be called the Japanese paradox.
Men in Japan have similar lifetime cholesterol, blood pressure, and type 2 diabetes rates as men in
the U.S., and they are far more likely to smoke.
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.
High Omega-3 Levels
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.
He adds that the average omega-3 intake in Japan of 1 gram a day is about
eight times higher than the amount the typical American gets.
"We are not a nation that loves fish, and that isn't likely to
change," he says. "But it is increasingly clear that we need to get
more omega-3 into our diets."
Fish oil supplements are one way of doing this. Studies in individuals with heart disease have shown a benefit of
supplemental omega-3 fatty acids. Based on these studies, the American Heart
Association recommends that people with heart disease take 1 gram of EPA plus
DHA daily.
Other good sources of omega-3 include foods such as flaxseed and canola
oils, soybean, tofu, and walnuts. Omega-3 fatty acids are often sold as
capsules but can upset the stomach and should be taken with food.
Harris is working to develop a soybean-based omega-3-enriched oil through a
grant from the company Monsanto.
He believes that many of the foods we eat will soon be fortified with
omega-3 in the same way that they are now fortified with folic acid and other
vitamins.
"Either we get people in the U.S. to start liking oily fish, which
probably isn't going to happen, or we find another way of getting it into our
food," he says.
Fish Eaters Had Less Plaque
The study by Sekikawa and colleagues included 281 Japanese men living in
Japan, an equal number of Japanese men living in the U.S., and 306 white men
who lived in the U.S.
All the men were in their 40s, and all underwent blood testing to determine
serum levels of fatty acids, including omega-3. The men also had two tests for
atherosclerosis — one measuring the thickness of the artery wall in a major
neck artery that sends blood to the brain and the other measuring plaque in
arteries leading to the heart.
While total fatty acid levels were similar in the three groups, blood
omega-3 levels in the Japanese men living in Japan were 45% higher and 80%
higher, respectively, than in Japanese men and white men living in the U.S.
And both measures of artherosclerosis showed less plaque buildup in the
arteries of the Japanese men living in Japan. Atherosclerosis levels were
similar in both Japanese-Americans and in white Americans.
The study appears in the Aug. 5 issue of the Journal of theAmerican
College of Cardiology.
"This indicates that much lower death rates from coronary heart disease
in the Japanese in Japan is very unlikely due to genetic factors," Sekikawa
says.
The 'Omega-3 Hypothesis'
In an editorial accompanying the study, Harris writes that what he calls the
"omega-3 hypothesis" grew from research on the Inuit Eskimos of
Greenland conducted almost four decades ago.
Despite eating a diet low in fruits, vegetables, and complex carbohydrates
and high in fat and cholesterol, the Eskimos had very low rates of heart
disease. Researchers concluded that the reason was the incredibly high levels
of omega-3 in their diets from the consumption of large amounts of fish, whale,
and seal.
But recent studies suggest that heart disease rates among Alaskan Eskimos
are now higher than among whites in the U.S., even though fish consumption in
the population remains high.
"At least part of the problem in Alaska appears to be not a lack of
omega-3 but the introduction of massive amounts of shortenings and other
saturated fats into their Westernizing diet," Harris writes.
He concludes this and other research suggest that the "cardioprotective
punch of the long-chain omega-3 fatty acids may be no match for diets high in
fat, particularly saturated fat."
Cardiologist Robert Eckel, MD, who is a past president of the American Heart
Association, says studies in heart attack patients treated
with very high doses of omega-3 have generally proven disappointing.
Eckel is a professor of medicine at the University of Colorado Denver School
of Medicine.
"We have known for some time that people who eat more fish seem to have
less heart disease," Eckel tells WebMD. "This study supports that, but
more research is needed."
SOURCES: Sekikawa, A. Journal of the American College of Cardiology, Aug. 5,
2008; vol 52: pp 417-424. Akira Sekikawa, MD, PhD, assistant professor of epidemiology, University of
Pittsburgh. William Harris, PhD, director, Metabolism and Nutrition Research Center,
Sanford Research, University of South Dakota. Robert Eckel, MD, professor of medicine, University of Colorado-Denver
School of Medicine; past-president, American Heart Association; professor of
medicine, University of Colorado Denver School of Medicine.
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