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See article vol. 24: 393–401
Lifestyle modifications such as diet change and exercise therapy are recommended as first-line therapy for risk factors for atherosclerotic cardiovascular diseases (ASCVD).
Ancel Keys et al., in their landmark epidemiological study, the Seven Countries Study, which started in 1958.1), reported that a high serum cholesterol level is a risk factor for coronary artery diseases (CAD) and that a high intake of dietary cholesterol and saturated fatty acids leads to a high serum cholesterol level. At that time, the incidence of CAD in Japan was the lowest among the seven countries, indicating that the Japanese diet was cardioprotective. However, there was remarkable economic development in Japan after World War II, and the associated urbanization caused marked changes in the living environment, i.e., westernization of lifestyle, which led to an increase in the obese, dyslipidemic, and diabetic populations. Hypertension also changed from the salt-dependent type to hypertension accompanied by metabolic abnormalities, consequently, with marked changes in the pathology of stroke, i.e., from cerebral bleeding and the lacuna type to atherothrombotic cerebral infarction. Such changes in risk factors for ASCVD have led to an epidemiological transition in Japan. However, to date, the incidence of CAD in Japan remains less than half of that in the U.S..2) In the ERA-JUMP study.3), which was a post-World War II cohort study on Japanese men and white men in the U.S., Sekikawa et al. reported that serum n-3 fatty acid levels were much higher among Japanese than among Americans and that the incidences of both carotid intima media thickness and coronary artery calcification were more reduced among Japanese than among Americans, even though lifetime cholesterol levels and blood pressures were similar between Japanese and Americans. The authors concluded that a high intake of n-3 fatty acids has anti-atherosclerotic effects. In another epidemiological study, JPHC.4), the incidence of total CAD was 1/3 in people who had a very high intake of fish compared with those who had a very low intake. However, other epidemiological studies such as JACC.5) did not observe significant differences in the incidence of CAD between people with a high and those with a low fish intake. A recent RCT conducted in Japan, the Japan EPA Lipid Intervention Study (JELIS).6), found that the incidence of CAD was significantly lower in patients treated with a combination of statin and n-3 fatty acids than those treated with statin alone. The authors of that study concluded that n-3 fatty acid, fish oil, has cardioprotective effects.
There is considerable epidemiological evidence showing the cardioprotective effects of other typical Japanese diets such as soybean and soybean products, folic acid, vitamin B6, and dietary fibers.7).
The Japan Atherosclerosis Society summarized this evidence and recommended “The Japan Diet” with reduced sodium intake in the 2012 edition of the Guidelines for Prevention of Atherosclerotic Cardiovascular Diseases. This evidence, however, focused on one component of “The Japan Diet.” Unfortunately, the number of studies on the whole of “The Japan Diet” including Japanese habits and behavior is insufficient to conduct meta-analysis of studies compared with Mediterranean Diet (MD) and DASH diet. The MD was first presented by Ancel Keys in the 1960s, and it is characterized by a high consumption of monounsaturated fatty acids, fruits, vegetables, whole-grain cereals, and fish. The beneficial effect of the MD with regard to all-cause mortality, CAD, cancer, obesity, and type 2 diabetes has been reported by many epidemiological studies and clinical trials. A healthy DASH diet was developed to lower blood pressure without any medication in research sponsored by the US National Institutes of Health. The first DASH diet study showed that it could lower blood pressure. Since then, numerous studies have shown that the DASH diet reduces the risk of many diseases, including ASCVD. It has been proven to be an effective diet to simultaneously reduce weight and become healthier.
To date, however, there are no studies showing that the whole of “The Japan Diet” is more beneficial than the Western diet. In addition, we do not have a sufficient number of epidemiological studies to allow the meta-analysis of the epidemiological studies of “The Japan Diet” such as MD or DASH diet.8, 9).
In this issue of the journal.10), Maruyama et al. tested a hypothesis that the whole of “The Japan Diet,” which is rich in fish, soybeans and soy products, vegetables, seaweed, mushrooms, and unrefined cereals and contains less quantities of animal fat, meat and poultry with fat, sweets, desserts, snacks, and alcoholic drinks, is cardioprotective. The authors showed that educating people on “The Japan Diet” and encouraging them by e-mails resulted in a decrease in body weight, serum triglyceride and MDA-LDL levels, and blood pressure, suggesting that the whole of “The Japan Diet” is effective for protection from metabolic syndrome, which, currently, is a major risk factor for ASCVD in Japan.
This study is important as a pilot study because it showed the effects of the whole of “The Japan Diet” rather than a component of “The Japan Diet” such as fish and soybeans and the importance of e-mails for the adherence to education.
However, the authors were unable to conclude on the beneficial effect of “The Japan Diet” for preventing ASCVD such a small-scale, short-term, single-arm study as mentioned in the study limitations. To overcome these limitations, it is necessary to conduct an RCT in Japan.