To estimate the consumption of ultra-processed foods and determine its association with dietary quality among middle-aged Japanese adults.

Cross-sectional study using data from the Saitama Prefecture Health and Nutrition Survey 2011. Dietary intake was assessed using one- or two-day dietary records. Sociodemographic and lifestyle factors were obtained via self-administered questionnaire. Food items were classified according to the NOVA system into four groups: unprocessed or minimally processed foods; processed culinary ingredients; processed foods; and ultra-processed foods. The dietary share of each NOVA food group and their subgroups was calculated in relation to total energy intake, and the average dietary content of key nutrients was determined across tertiles of the dietary energy share of ultra-processed foods (low, middle and high intake).

Saitama Prefecture in Japan.

Community-dwelling adults aged 30–59 years (256 men, 361 women).

Consumption of unprocessed or minimally processed foods, processed culinary ingredients, processed foods and ultra-processed foods contributed 44·9 (se 0·8) %, 5·5 (se 0·2) %, 11·3 (se 0·4) % and 38·2 (se 0·9) % of total daily energy intake, respectively. A positive and statistically significant linear trend was found between the dietary share of ultra-processed foods (tertiles) and the dietary content of total and saturated fat, while an inverse relationship was observed for protein, vitamin K, vitamin B6, dietary fibre, magnesium, phosphorus and iron.

Our findings show that higher consumption of ultra-processed foods was associated with decreased dietary quality among Japanese adults.