BackgroundAlthough our previous study using a food frequency questionnaire simulated nutritional characteristics of the traditional Japanese diet, this issue has not been sufficiently evaluated. This study was conducted to examine the relationship between the traditional Japanese diet and nutrient density (ND).MethodsA cross-sectional study employing the dietary record method was conducted among 2221 community-dwelling Japanese adults (40-88years) living in Aichi Prefecture, Japan, in 2006-2008. Based on previous studies, a 9-component Japanese Diet Index (JDI) and a 12-component modified JDI (mJDI(12)) were defined. To develop a new weighted index, a multiple linear regression model was used to select food components which were significantly associated with an ND score (integrated by 11 nutrient components) from the mJDI(12) and weight them. Correlation analyses were performed between JDI, mJDI(12), the new weighted JDI score and the ND score and its 11 nutrient components. The findings were validated with data from 2008 to 2010 by assessing the associations between the JDIs scores and the ND score.ResultsScores of the JDI and mJDI(12) were positively correlated with the ND score (corresponding Spearman's rho [95% confidence interval; CI], 0.34 [0.31, 0.38] and 0.44 [0.41, 0.48], respectively; P<0.05 for both). Among the mJDI(12), 9 food components (rice, fish and shellfish, green and yellow vegetables, seaweed, green tea, beef and pork, soybeans and soybean foods, fruit, and mushrooms) significantly associated with the ND score. All of these 9 components were weighted and a new weighted JDI (wJDI(9)) was developed. The wJDI(9) score was also positively correlated with the ND score (Spearman's rho [95% CI]=0.61 [0.58, 0.64]; P<0.05). However, scores for all 3 indices were positively correlated with sodium intake. The wJDI(9) score obtained using dietary record data from 2008 to 2010 was also positively correlated with the ND score (Spearman's rho [95% CI]=0.61 [0.58, 0.64]; P<0.05).Conclusions-Adhering to a traditional Japanese diet as defined by the JDI was associated with good ND. Furthermore, the modified indices (mJDI(12) and wJDI(9)) had a higher performance for ND. However, all of the indices were correlated with high sodium intake.