To date, a limited number of studies have examined aspects of food choice values and food literacy in relation to some aspects of dietary behaviours. The aim of this cross-sectional study was to comprehensively examine the associations of food choice values and food literacy with diet quality. In total, 2231 Japanese adults aged 19–80 years completed questionnaires asking about food choice values (accessibility, convenience, health/weight control, tradition, sensory appeal, organic, comfort and safety) and food literacy characterised by nutrition knowledge, cooking skills, food skills and eating behaviours (hunger, food responsiveness, emotional overeating, enjoyment of food, satiety responsiveness, emotional undereating, food fussiness and slowness in eating). As a measure of diet quality, the Healthy Eating Index-2015 (HEI-2015) was calculated using a brief-type diet history questionnaire (BDHQ) or a food combination questionnaire (FCQ). In males, after adjustment for potential confounding factors (including age, BMI and the ratio of reported energy intake to estimated energy requirement), the HEI-2015 derived from BDHQ and that derived from FCQ were associated significantly (P ≤ 0·02) and positively with the food choice values of organic and inversely with food fussiness. In females, the HEI-2015 showed positive associations with the food choice values of health/weight control, nutrition knowledge and cooking skills and an inverse association with food fussiness, irrespective of the dietary assessment questionnaire (P ≤ 0·03). In conclusion, this study suggests that several aspects of food choice values and food literacy were associated with diet quality, and the aspects related differed between males and females.

Despite the increasing market share of commercial complementary foods, their nutritional characteristics and those associated with the price of products are still unknown in Japan. We compared the nutritional characteristics of commercially available complementary foods of different price levels in Japan. Data were obtained from the websites of Japanese brands of infant and young children’s food. Nutrient profiles (unit/100 g), ingredients and food additives were compared between low- and high-priced products by product type. Sixty-three dry meals, 425 soft meals, 187 snacks and sweets, and 60 drinks were analysed. One-fifth of meals and snacks exceeded the CODEX-defined limit (200 mg Na/100 g). Most products lacked content information on nutrients non-mandated to be indicated. High-priced soft meals contained more protein (2·5 v. 1·9 g/100 g) and less Na (0·18 v. 0·46 g/100 g), less frequently used ≥ 1 added sugar (23 % v. 82 %), and less frequently used food additives than low-priced products; however, they had a lower variety of ingredients. The prevalence of products containing ≥ 1 added sugar was higher in low-priced snacks and sweets (91 % v. 77 %) but lower in drinks (48 % v. 84 %) than in their high-priced counterparts. High Na content is a concern among commercial complementary foods in Japan. Nonetheless, the relationship between the price and nutritional profile of these foods differs by product type. High-priced soft meals might be more favourable regarding nutrient content but not the variety of ingredients than low-priced counterparts. These findings elucidate the nutritional characteristics of commercial complementary foods in Japan.

The aim of this cross-sectional study was to examine the relative validity of food and nutrient intakes and overall diet quality scores derived using a newly developed dietary assessment questionnaire (food combination questionnaire, FCQ). Dietary data were collected from 222 Japanese adults (111 for each sex) aged 30–76 years using the online FCQ and then the 4-non-consective-day weighed dietary record (DR). The median of Spearman correlation coefficients for sixteen food groups was 0⋅32 among women and 0⋅38 among men. The median of Pearson correlation coefficients for forty-six nutrients was 0⋅34 among women and 0⋅31 among men. The Pearson correlation coefficient between the total scores of Healthy Eating Index-2015 (HEI-2015) derived from the DR and FCQ was 0⋅37 among women and 0⋅39 among men. The corresponding value for the Nutrient-Rich Food Index 9.3 (NRF9.3) total scores was 0⋅39 among women and 0⋅46 among men. Bland–Altman plots for these diet quality scores showed poor agreement at the individual level, although mean difference was small for the HEI-2015 (but not NRF9.3). Similar results were obtained using the paper version of FCQ, which was answered after conducting the DR, except for somewhat high Pearson correlation coefficients for the total scores of HEI-2015 (0⋅50 among both women and men) and NRF9.3 (0⋅37 among women and 0⋅53 among men). In conclusion, this analysis may lend support to the possible use of the FCQ as a rapid dietary assessment tool in large-scale epidemiologic studies in Japan, but further refinement of this tool should be pursued.

The present study aimed to (1) examine the changes in sleep habits and dietary intake among school-aged children after the school re-opening from a 3-month closure (without school lunch) due to the COVID-19 pandemic, and (2) examine whether the changes differ between those with different temporal patterns of sleep and eating during school closure, namely, ‘Very early’, ‘Early’, ‘Late’ and ‘Very late’. The latter patterns were characterised by later timings of wake up, breakfast and lunch. Questionnaires were answered twice by 4084 children (aged 8–15 years), themselves and/or their parents: first in June 2020 (for assessing lifestyle during school closure) and second, from July 2020 to February 2021 (for assessing lifestyle after school opening). After school re-opening, the participants’ wake-up time became an hour earlier (95 % CI 1⋅0, 1⋅1) and sleep duration got 0⋅94 h shorter (95 % CI 0⋅91, 0⋅97) than during school closure. An increase in dietary intake was observed for thiamine, vitamin B6, potassium, fruits and dairy products, and a decrease was observed for sugars (as foods) and confectioneries and sweetened beverages, despite small effect sizes (Cohen's d: 0⋅20–0⋅30). Significant changes in wake-up time, sleep duration and sweetened beverage intake were observed among children with the latter temporal patterns. Thus, children wake up earlier and sleep for shorter durations after school re-opening than during school closure; however, changes in dietary intake were generally insignificant. Dietary intake among school-aged children in Japan during school closure (without school lunch) might not be worse than that during school days with universal school lunch.

The aim of this study was to examine the relative validity of the online Meal-based Diet History Questionnaire (MDHQ) for assessing the overall diet quality and quality of each meal type (breakfast, lunch, dinner and snacks). In total, 222 Japanese adults (111 for each sex) aged 30–76 years completed the online MDHQ and then the 4-non-consecutive-day weighed dietary record (DR). The diet quality was assessed using the Healthy Eating Index-2015 (HEI-2015) and Nutrient-Rich Food Index 9.3 (NRF9.3). For the HEI-2015, compared with the DR, the MDHQ provided high median values for breakfast (in women only) and dinner and low median values for snacks. There were no significant differences observed for overall diet and lunch. For the NRF9.3, the MDHQ provided higher median values for breakfast and dinner and a lower median value for overall diet than the DR in women, with no significant differences for lunch and snacks. In men, no significant difference was observed, except for overall diet (the MDHQ providing a lower median value). For the HEI-2015, median Spearman correlation coefficient was 0·43, with a range from 0·12 (snacks in women) to 0·68 (breakfast in men). For the NRF9.3, median Spearman correlation coefficient was 0·47, with a range from 0·26 (snacks in men) to 0·65 (breakfast in men). Bland–Altman plots showed wide limits of agreement and, in some cases, proportional bias. In conclusion, the online MDHQ showed an acceptable ability for ranking individuals according to the quality of overall diet, breakfast, lunch and dinner, but not snacks.

Dietary supplements can be used to compensate for an inadequate diet. However, some studies indicate that supplement users consume healthier diets than non-users, although such data are lacking in Japanese children. The aim of the present study was to investigate the food and nutrient intake of dietary supplement users among school-aged children in Japan. A nationwide school dietary survey was conducted at fourteen elementary schools and thirteen junior high schools in twelve prefectures in Japan. Three-day non-consecutive semi-weighed dietary records were obtained on two weekdays and one weekend day. Analysis of covariance was performed to investigate differences in food and nutrient intake from meals consumed at school and outside of school between dietary supplement users and non-users, adjusted for socio-demographic and health-related characteristics. Of the 910 children included in this analysis, 80 (8⋅8 %) reported supplement use. Based on 3-d dietary records, dietary supplement users consumed higher mean amounts of oils and lower amounts of fruits and vegetables than non-users. In school lunches, users consumed significantly higher amounts of oils and lower amounts of protein than non-users. In meals consumed outside of school, dietary supplement users consumed significantly higher amounts of confectioneries and lower amounts of fruits and vegetables, folate, vitamin C and dietary fibre than non-users. Collectively, our findings indicate that dietary supplement users consumed less healthy diets than non-users. Additional studies are warranted to confirm these results and identify factors contributing to poorer dietary habits in supplement users.

A future sustainable dietary pattern for Japanese is yet undefined. This study aimed to explore more sustainable Japanese diets that are nutritious, affordable and with low greenhouse gas emissions (GHGE) and particular emphasis on cultural acceptability. A newly developed data envelopment analysis (DEA) diet model was applied to 4-d dietary record data among 184 healthy Japanese men and 185 women volunteers aged 21–69 years. Alternative diets were calculated as the linear combinations of observed diets. Firstly, for each individual, four modelled diets were calculated that maximised cultural acceptability (i.e. minimise dietary change from observed diet), maximised nutritional quality assessed by the Nutrient-Rich Food Index (NRF), minimised monetary diet costs or minimised diet-related GHGE. The final modelled diet combined all four indicators. In the first four models, the largest improvement was obtained for each targeted indicator separately, while relatively small improvements or unwanted changes were observed for other indicator. When all indicators were aimed to optimise, the NRF score and diet-related GHGE were improved by 8–13 % with the lower monetary cost than observed diets, although the percentage improvement was a bit smaller than the separate models. The final modelled diets demanded increased intakes for whole grains, fruits, milk/cream/yogurt, legumes/nuts, and decreased intakes for red and processed meat, sugar/confectioneries, alcoholic and sweetened beverages, and seasonings in both sexes. In conclusion, more sustainable dietary patterns considering several indicators are possible for Japanese, while total improvement is moderate due to trade-offs between indicators and methodological limitation of DEA diet model.

The relationship of chronotype differences with dietary habits and health-related outcomes among elderly people is not fully understood, although sex and generation differences are observed in human chronotype. Accordingly, we analysed the association of chronotype (as assessed by the midpoint of sleep) with dietary intake and health-related quality of life (HRQoL) in elderly Japanese women. The subjects in this cross-sectional study were 1618 women aged 65 years and older who were grandmothers or acquaintances of dietetics students. The subjects were classified into quintiles with respect to the midpoint of sleep, from the earliest to the latest quintile. HRQoL was assessed by the Japanese version of the short-form 36-item health survey score. Mental health was assessed by the Center for Epidemiologic Studies Depression (CES-D) Scale. Dietary intake was assessed by a brief-type self-administered diet history questionnaire. A later midpoint of sleep was associated with a lower intake of vitamin D and a higher intake of bread and caffeinated drinks. No correlations were observed between chronotype and other nutrient and food intake. The subjects with a late midpoint of sleep (eveningness) showed poor general health perception (GH) and high CES-D scores. Other HRQoL scores did not differ among groups with different midpoints of sleep. In conclusion, chronotype as assessed by the midpoint of sleep is associated with poor GH and depressive tendencies in elderly Japanese women. Additionally, a few associations were found between dietary intake and chronotype in elderly Japanese women.

Intakes of excess Na and insufficient K are two major contributors of heart diseases and stroke development. However, no precise study has previously been carried out on Na and K intakes among Indonesian adults. The present study aimed to estimate the Na and K intakes using two consecutive 24-h urine collections. Participants were community-dwelling adults aged between 20 and 96 years, randomly selected from a pool of resident registration numbers. Of the 506 participants, 479 (240 men and 239 women) completed urine collections. The mean Na excretion was 102·8 and 100·6 mmol/d, while the mean K excretion was 25·0 and 23·4 mmol/d for men and women, respectively. Na and K excretions were higher in participants with a higher BMI. A higher K excretion was associated only with younger age. More than 80 % of the participants consumed more than 5 g/d of salt (the upper limit recommended by the Indonesian government), whereas none of them consumed more than 3510 mg/d of K (the lower limit). The high Na and low K intakes, especially high Na among participants with high BMI, should be considered when future intervention programmes are planned in this country.

FFQ, the primary method of dietary assessment in large-scale nutritional epidemiological studies, preclude an informed evaluation of the timing of dietary intake and meal-specific dietary intake. In this study, we developed the Meal-based Diet History Questionnaire (MDHQ), a self-administered questionnaire designed for estimating food and nutrient intakes for each meal type separately. The development was done based on a 16-d dietary record obtained from 242 Japanese adults. The MDHQ consisted of the three different parts, with a total of 196 items. Part 1 of the MDHQ asks about consumption frequency of generic food groups (n 24) for each meal type: breakfast, morning snack, lunch, afternoon snack, dinner and night snack. Part 2 of the MDHQ asks about relative consumption frequency of sub-food groups within one of the generic food groups which are asked in Part 1. Combining information derived from Parts 1 and 2 enables us to increase the number of foods we can estimate efficiently but within a limited number of questions. Part 3 of the MDHQ asks about general eating behaviours, which are intended to use in a variety of ways during dietary intake calculation. A series of calculation algorithms for food groups, energy and nutrients was also prepared. Given that the MDHQ was empirically developed based on comprehensive information on actual food consumption, this innovative tool may be promising for future epidemiological research on meal patterns and time of day of dietary intake, or chrono-nutrition research. A rigorous evaluation of validity of the MDHQ is warranted.

Epidemiological evidence on the association between eating frequency and overall diet quality does not represent a consistent picture. This cross-sectional study examined the associations of meal frequency and snack frequency with diet quality, using different definitions of meals and snacks. Based on 4-d weighed dietary record data obtained from 639 Japanese adults aged 20–81 years, all eating occasions were divided into meals or snacks based on either the participant-identified or time-of-day definitions. Diet quality was assessed by the Healthy Eating Index-2015 (HEI-2015) and Nutrient-Rich Food Index 9.3 (NRF9.3). One additional meal per d increased the HEI-2015 total score by 3·6 and 1·3 points based on the participant-identified and time-of-day definitions, respectively. A higher meal frequency was also associated with higher values of some of the HEI-2015 component scores (total vegetables, greens and beans, and total protein foods), irrespective of how meals were defined. Additionally, one additional participant-identified snack per d increased the HEI-2015 total score by 0·7 points. The frequency of participant-identified snacks also showed positive associations with some of the HEI-2015 component scores (total fruits, whole fruits, total vegetables, greens and beans, dairy products, and Na). However, the frequency of time-of-day defined snacks was not associated with the total scores of HEI-2015, although there were some associations for its components. Similar findings were obtained when the NRF9.3 was used. In conclusion, higher meal frequency was consistently associated with higher diet quality, while associations between snack frequency and diet quality varied depending on the definition of snacks.