While many Asian countries undergo dietary transitions, little is known about Japan’s dietary pattern changes and their impact on nutritional intake. We aimed to examine 17-year trends in dietary patterns and nutrient intakes in Japan.

Principal component analysis was used to derive dietary patterns. The nutrient intake of subjects with principal component scores in the highest quartiles of each dietary pattern was assessed using the NRF9·3, which is a scale that evaluates the entire diet in terms of nutrient density.

Japan.

We used data from the National Survey 2003–2019 (67 066 women, 55 133 men).

Two common dietary patterns were identified in both sexes: the ‘Japanese style’ and the ‘bread and dairy’ pattern. Additionally, two other patterns: ‘meat and oil’ and ‘noodles’, were pronounced in men. Over the 17 years, the scores of the ‘Japanese style’ pattern decreased while the ‘meat and oil’ and the ‘bread and dairy’ patterns increased. The nutrition assessment result showed that the highest quartiles of the ‘Japanese style’ pattern had higher NRF scores (women: 716·0, men: 670·5) (P < 0·001), whereas those of the ‘bread and dairy’ pattern had a lower score (636·9 in women, 661·2 in men) (P < 0·001).

Trend analysis in this study suggests the ongoing Westernisation of diet in Japan. A decreasing trend of the dietary pattern with the most preferable nutrient profile (i.e. the ‘Japanese style’) might indicate a potential decrease in beneficial nutrient intake and, thus, a deterioration of the nutritional status of the Japanese population.