Time trends in income-related differences in food group intakes: The National Health and Nutrition Survey, Japan in 2010, 2014, and 2018

Background: We aimed to clarify whether differences in food group intake according to household income have changed over the last decade in Japanese people aged 20 years or older. Methods: This cross-sectional study was based on the 2010, 2014, and 2018 National Health and Nutrition Surveys in Japan. Food intake was assessed using a one-day semi-weighed household dietary record. The participants were categorized into three groups based on their income. The mean of each food intake according to the income group was estimated by adjusting for age, occupation, and number of participants from the same household. The significance of the interaction terms between income and survey year was evaluated to assess the change in income-related differences in food intake over time. Results: Cereal intake was lower in the middle-and the highest-income groups than in the lowest-income group, regardless of sex, and the interaction between income and year was insignificant for cereal intake. In the former two surveys, vegetable intake was higher among the highest-income women, while in the 2018 survey, the vegetable intake decreased in the women in the middle-and the highest-income groups. The interaction between income and year was significant for vegetable intake among the women. For other foods, the differences in intake among the income groups did not significantly change over time. Conclusions: The tendency for lower cereal intake in the higher-income groups was consistent over time in both the sexes and the tendency for higher vegetable intake in the highest income women disappeared over time.