Though it is not surprising to me as a Japanese, Japanese diet was proven to be effective to improve life expectancy, according to a survey with a large sample size.
Approximately 80,000 participants were followed for 15 years in this study. People who adhered to Japanese guidelines of the daily meal had a lowered mortality rate, mainly thanks to infrequent cerebrovascular disease.
International Business Times: Japanese diet plan associated with longer life expectancy: What are the guidelines?
I have not looked through the reports, but this result is trustworthy. The onset of cerebrovascular diseases is deeply connected to the daily meal. People who have much salt are likely to encounter a stroke.
In addition, high level of blood cholesterol is relevant to vascular diseases. Taking excessive fat can increase the risk of hyperlipidemia, even though there are arguments about it recently. On the other hand, low-carbonate diet, whom many people believe as the most effective way to reduce the body weight, deteriorate the long-term risk of vascular diseases, according to recent studies.
My past entry: You can eat high cholesterol food
Traditional Japanese cuisine is relatively saccharide-dominant. They include low fat and protein. People take protein from fish rather than meat. Not a lot of white sugar are frequently used. Also, they taste less rich than Western cuisine. All of these factors may contribute to the health.
However, the fact Japanese have the best life expectancy in the world is not completely attributable to Japanese diet. Rather, the influence of diet is limited, in my opinion. Good hygiene environment, national health insurance covering all Japanese, and low crime rate are also contributing.
Nonetheless, I recommend you to take Japanese cuisine if you are obese. In my experience, American and British diet have excessive calorie, fat, and sugar.