What constitutes healthiness of Washoku or Japanese diet?

Japan is a small country geographically located far east of Eurasian continent but has ~126 million people, which was the 11th largest population in the world. Japanese people are proud of their traditional cuisine Washoku, which has been an intangible cultural heritage certified by the United Nations Educational, Scientific, and Cultural Organization in 2013. Before the Covid-19 pandemic in 2020, Japan’s tourism industry thrived for the last decade, as the number of tourists increased from about 10 million in 2013 to over 30 million in 2019 [1]. Together with these enthusiastic visitors excited by Washoku tourism, Japanese government has also been putting a lot of effort into advertising Washoku, emphasizing its healthiness as one of its merits [2, 3]. Authentic Washoku requires Japan’s mild climate with four seasons, quality water originated from mountainous land, and availability of a large variety of fishes and seaweed from the surrounding sea [4].

In this special issue of European Journal of Clinical Nutrition, we listed the health benefits of Japanese diet, first by providing an overview that explained how Japan achieved the world’s highest life expectancy from dietary perspective [5]. Then, we provided four review articles focusing on the health effects of fish and omega-3 polyunsaturated fatty acid [6], seaweed [7], soy [8] and green tea [9], foods, drinks and nutrients that characterize Japanese diet. Interesting findings of three prospective studies followed the reviews. Intake of fermented soy foods such as natto was inversely associated with cardiovascular disease incidence but only in women in the Japan Public Health Center-based prospective Study [10]. Another intriguing new finding is possible enhancement of resistance against influenza by frequent green tea intake [11], which need to be confirmed by future randomized trials. Dietary, i.e., ingredient diversity, which also characterizes Japanese diet [12], was associated with slower hippocampal atrophy, and might give you protection against Alzheimer’s disease in a 2-year follow-up study of the National Institute for Longevity Sciences-Longitudinal Study of Aging [13]. Results of one cross-sectional and one ecological study are also discussed in the present issue. The Japan Multi-Institutional Collaborative Cohort study suggested a SNP related to preference for a Japanese dietary pattern [14]. An ecological study, which utilized Food and Agriculture Organization of the United Nations Statistics Division database, explored intercountry comparisons of traditional Japanese diet score and incidence and mortality of breast cancer [15].

Finally, from social epidemiological perspective, a benefit of school lunch program, which is also considered as an important measure to preserve Washoku culture for future generations [4], was introduced to reduce socioeconomic disparities in diet quality using National Health and Nutrition Survey data [16].

We believe that the collection of these articles focusing on Japanese diet is of interest to our readership as the components are employed in food guidelines of various countries [17, 18]. Also, the benefits of Washoku that consists of a diversity of plant-based ingredients and low amounts of foods from animal sources would not only include human health but a key to environmental sustainability. It is our current responsibility to envision and seek ways to achieve planetary health [19].