High-quality diets have been found to be beneficial in preventing long-term weight gain. However, concurrent changes in diet quality and body weight over time have rarely been reported. We examined the association between 10-year changes in diet quality and body weight in the Multiethnic Cohort Study. Analyses included 53 977 African Americans, Native Hawaiians, Japanese Americans, Latinos and Whites, who completed both baseline (1993–1996, 45–69 years) and 10-year follow-up (2003–2008) surveys including a FFQ and had no history of heart disease or cancer. Using multivariable regression, weight changes were regressed on changes in four diet quality indexes, Healthy Eating Index-2015, Alternative Healthy Eating Index-2010, alternate Mediterranean Diet and Dietary Approaches to Stop Hypertension scores. Mean weight change over 10 years was 1·2 (sd 6·8) kg in men and 1·5 (sd 7·2) kg in women. Compared with stable diet quality (< 0·5 sd change), the greatest increase (≥ 1 sd increase) in the diet scores was associated with less weight gain (by 0·55–1·17 kg in men and 0·62–1·31 kg in women). Smaller weight gain with improvement in diet quality was found in most subgroups by race/ethnicity, baseline age and baseline BMI. The inverse association was stronger in younger age and higher BMI groups. Ten-year improvement in diet quality was associated with a smaller weight gain, which varied by race/ethnicity and baseline age and BMI. Our findings suggest that maintaining a high-quality diet and improving diet quality over time may prevent excessive weight gain.

FFQ comprising food items, intake frequency categories and portion sizes have been used in large-scale observational studies to assess long-term dietary exposure. Although gender is an important influence on food choice and portion size, gender differences are not often analysed during FFQ development. This study investigated whether gender differences were considered sufficiently when developing FFQ, which affects the results of validation studies. A PubMed search using combinations of ‘FFQ’, ‘Food Frequency Questionnaire’, ‘Validation’ and ‘Validity’ identified 246 validation studies available in English, published between January 1983 and May 2014, which included healthy male and female adults. The development process of the 196 FFQ used in the 246 validation studies was examined. Of these, twenty-one FFQ (10·7 %) considered gender during item selection or portion size determination, and were therefore classified as gender specific (GS), but 175 (89·3 %) did not consider gender, and were classified as ‘not gender specific (NGS)’. When the ratios between intake levels obtained using the FFQ and a reference method for energy and seven nutrients were compared between the GS group and the NGS group, more significant differences were observed in women than in men (four v. one nutrient). Intake of three nutrients was significantly underestimated in both sexes in the GS group. In the NGS group, nutrient intakes were significantly overestimated more often in women than in men (four v. one). These results indicate that not considering gender in FFQ development causes greater inaccuracy in dietary intake assessment in women than in men. Results of nutritional epidemiological studies should be re-evaluated for their validity, especially if the studies used NGS-FFQ.

During the past decades, a rapid nutritional transition has been observed along with economic growth in the Republic of Korea. Since this dramatic change in diet has been frequently associated with cancer and other non-communicable diseases, dietary monitoring is essential to understand the association. Benefiting from pre-existing standardised dietary methodologies, the present study aimed to evaluate the feasibility and describe the development of a Korean version of the international computerised 24 h dietary recall method (GloboDiet software) and its complementary tools, developed at the International Agency for Research on Cancer (IARC), WHO. Following established international Standard Operating Procedures and guidelines, about seventy common and country-specific databases on foods, recipes, dietary supplements, quantification methods and coefficients were customised and translated. The main results of the present study highlight the specific adaptations made to adapt the GloboDiet software for research and dietary surveillance in Korea. New (sub-) subgroups were added into the existing common food classification, and new descriptors were added to the facets to classify and describe specific Korean foods. Quantification methods were critically evaluated and adapted considering the foods and food packages available in the Korean market. Furthermore, a picture book of foods/dishes was prepared including new pictures and food portion sizes relevant to Korean diet. The development of the Korean version of GloboDiet demonstrated that it was possible to adapt the IARC-WHO international dietary tool to an Asian context without compromising its concept of standardisation and software structure. It, thus, confirms that this international dietary methodology, used so far only in Europe, is flexible and robust enough to be customised for other regions worldwide.

In the present study, we examined the associations of total carbohydrate intake, dietary glycaemic load (DGL) and white rice intake with metabolic syndrome risk factors by sex in Korean adolescents. For the present cross-sectional study, data from the Fourth Korea National Health and Nutrition Examination Survey (2007–9) were used. A total of 2209 adolescents (n 1164 boys and n 1045 girls) aged 10–18 years with complete anthropometric, biochemical and dietary intake data were included in the study. Dietary intake data were obtained using the 24 h recall method, and total carbohydrate intake, DGL and white rice intake were divided into quartiles by sex. The metabolic syndrome and its risk factors were defined using the International Diabetes Federation criteria for children and adolescents. Fasting insulin levels and insulin resistance were included as the metabolic syndrome risk factors. All statistical analyses considered the complex sampling design effect and appropriate sampling weights. Multivariate linear regression analysis was used to estimate means with their standard errors of the mean for the metabolic syndrome risk factors across the quartiles of total carbohydrate intake, DGL and white rice intake. While high DGL was significantly associated with increased fasting glucose levels in boys, high total carbohydrate intake, DGL and white rice intake were consistently associated with reduced HDL-cholesterol levels in girls. High white rice intake was significantly associated with an increased risk of insulin resistance and the metabolic syndrome in girls but not in boys. Optimising dietary carbohydrate intake with respect to the source or amount is fundamental to preventing and managing metabolic diseases in Asian adolescents.

Sources of variation in nutrient intake have been examined for Western diets, but little is known about the sources of variation and their differences by age and sex among Koreans. We examined sources of variation in nutrient intake and calculated the number of days needed to estimate usual intake using 12 d of dietary records (DR). To this end, four 3 d DR including two weekdays and one weekend day were collected throughout four seasons of 1 year from 178 male and 236 female adults aged 20–65 years residing in Seoul, Korea. The sources of variation were estimated using the random-effects model, and the variation ratio (within-individual:between-individual) was calculated to determine a desirable number of days. Variations attributable to the day of the week, recording sequence and seasonality were generally small, although the degree of variation differed by sex and age (20–45 years and 46–65 years). The correlation coefficient between the true intake and the observed intake (r) increased with additional DR days, reaching 0·7 at 3–4 d and 0·8 at 6–7 d. However, the degree of increase became attenuated with additional days: r increased by 13·0–26·9 % from 2 to 4 d, by 6·5–16·4 % from 4 to 7 d and by 4·0–11·6 % from 7 to 12 d for energy and fifteen nutrients. In conclusion, the present study suggests that the day of the week, recording sequence and seasonality minimally contribute to the variation in nutrient intake. To measure Korean usual dietary intake using open-ended dietary instruments, 3–4 d may be needed to achieve modest precision (r>0·7) and 6–7 d for high precision (r>0·8).

We used a database approach in developing a dish-based, semi-quantitative FFQ for Korean diet and cancer research. Cancer-related dietary factors (CRDF) recognised in the scientific community and dietary intake data from the 2001 Korean National Health and Nutrition Examination Survey and the 2002 Korean National Nutrition Survey by Season were used. The list of dishes (n 993) was those reported to be consumed by individuals over 30 years of age during all four seasons. The resulting 112-dish list was selected using contribution analyses and variability analyses to detect between-person variation for CRDF and non-CRDF nutrients. Variations of each dish were grouped into one dish for the final list of 112 dishes, which were then linked to the nutrient database. The final 112 dish items consisted of nine Korean staple dishes, including rice and noodles, twenty-five soups and stews, fifty-four side dishes, nine beverages, nine fruit dishes and six alcoholic beverages. The percentage coverages of energy, protein, fat, carbohydrate and alcohol intake in the selected 112 dishes were 82·4, 76·4, 68·9, 86·0 and 99·8 %, respectively. Dietary exposure to cancer-related Korean dietary factors can be assessed by this new dish-based, semi-quantitative FFQ. This new instrument can calculate the intake of CRDF along with non-CRDF nutrient intake for cancer research.

Little is known about the bioavailability of isoflavones in children. Previous studies have shown that children excrete more isoflavone in urine compared with adults. Thus we examined the relationship between usual dietary isoflavone intake and the urinary excretion of isoflavonoids in Korean girls of pubertal age. Twelve girls each were selected from the lowest and the highest quartiles of isoflavone intake among 252 Korean girls aged 8–11 years. Age, BMI and sexual maturation stage were matched between the two groups. Dietary intakes for 3 d by diet record and overnight urine samples were collected at baseline and at 6 and 12 months. Total and individual isoflavone (daidzein, genistein and glycitein) intakes were calculated from diet records. The parent isoflavone compounds (daidzein, genistein and glycitein) and their metabolites (equol, O-desmethylangolensin (O-DMA), dihydrodaidzein and dihydrogenistein) present in the urine samples were analysed using liquid chromatography–MS. Intake levels of total and individual isoflavone compounds were significantly higher in the high isoflavone (HI) group than the levels in the low isoflavone (LI) group (P < 0·05). Urinary excretion of all isoflavone parent compounds was significantly higher in the HI group than in the LI group (P < 0·0001). Among isoflavone metabolites, only O-DMA and total metabolites were significantly different (P < 0·05). Total isoflavone intake was highly correlated with the urinary excretion of total parent compounds (r 0·68; P < 0·01), parent compounds plus their metabolites (r 0·66–0·69; P < 0·01) and total isoflavonoids (r 0·72; P < 0·0001). In conclusion, overnight urinary excretion of total isoflavonoids is a reliable biomarker of usual isoflavone intake in Korean girls of pubertal age.

We investigated the adverse effect of phytate on mineral absorption and the effect of dietary phytate and age on the relationship between faecal phytate and faecal mineral excretion. Fourteen young women (aged 19–24 years) and fourteen elderly women (64–75 years) were studied for two metabolic periods (MP). In MP1, the subjects consumed a controlled high-phytate (HP) diet for 10 d; in MP2, they were on a low-phytate (LP) diet for 10 d. In each period, diet samples and complete faecal samples for 5 d were collected to analyse phytate and mineral contents. Mineral concentrations in diet and faeces were measured by inductively coupled plasma–atomic emission spectrometry. Linear regression analysis was used to examine the associations between faecal phytate and mineral excretion. The degradation rate of dietary phytate was about 77 % for young women, which was significantly lower than that of elderly women (86 %) (P < 0·05). Faecal phytate excretion was positively correlated with mineral excretion (Ca, P, Fe and Zn) in both the HP and LP diet groups in young women (P < 0·05). The linear relationship tended to be greater during the LP diet period compared with the HP diet period in young women. However, no association was found between phytate excretion and mineral excretion in elderly women. In summary, undegraded dietary phytate (10–20 %) had a negative effect on mineral absorption in young women, and the relationship between faecal phytate and mineral excretion was affected by both dietary phytate and age.

The purpose of this study was to investigate the association between dietary patterns and sexual maturation among Korean children. A cross-sectional study was conducted in 422 boys and 365 girls aged 9–12 years living in Seoul, Korea. Three-day food records were obtained, and pubertal stages were determined with a questionnaire using Tanner stages. Body fat was measured by bioelectrical impedance analysis, and bone mass content at the right calcaneus was measured by portable dual-emission X-ray absorptiometry. Exploratory factor analysis with a Varimax rotation was applied to identify dietary patterns using twenty-four food groups. Four distinct dietary patterns – ‘rice and Kimchi’, ‘shellfish and processed meat’, ‘pizza and drinks’ and ‘milk and cereal’ – were obtained. Twenty-six per cent (24% stage 2, 2% stage 3) of boys had genital development, and 79% (63% stage 2, 16% stage 3) of girls showed breast development. In boys, genital development was weakly positively associated with ‘shellfish and processed meat’ dietary factor scores (odds ratio 1·65, CI 0·95, 2·89, pfor trend 0·07) after adjusting for confounders. In girls, breast development was significantly positively associated with the factor score of ‘shellfish and processed meat’ (odds ratio 1·88, CI 1·08, 3·26, p for trend 0·05). These results suggest that dietary patterns were related to body composition and sexual maturation among the Korean children. Further investigations are needed to identify components of the foods consumed in high amounts in these patterns and how they are related to sexual maturation.

Korea has experienced exceptionally rapid economic developments. Even though the country has managed to maintain aspects of its traditional diet, dietary habits are changing, especially among adolescents. This study was carried out to identify prevailing dietary patterns among Korean adolescents and to compare the nutrient intakes and dietary behaviours between the patterns. A 3 d diet record, collected from 671 Korean adolescents aged 12–14 years in Seoul, Korea, was assessed. By cluster analysis, subjects were classified into a modified (69·9 %) and a traditional (30·1 %) dietary pattern group. The modified group consumed more bread, noodles, cookies and pizza/hamburgers compared with the traditional group, which consumed mainly rice and kimchi (fermented cabbage). The modified group had significantly higher intakes of all nutrients. It had a higher total daily energy intake (7719 kJ), a higher daily energy intake from fat (29·8 %) and a higher cholesterol intake (326 mg/d), compared with the traditional group (6686 kJ, 24·8 % and 244 mg/d, respectively). The modified group was more likely to consume fast foods, fried foods and carbonated beverages even though they consumed more fresh fruits and milk, while the traditional group was more likely to have a rice-based diet and not to skip breakfast. These results suggest that monitoring dietary behaviours of adolescents, especially in a society experiencing a nutrition transition, is necessary in order to identify both negative and positive changes in respect of risk factors for nutrition-related chronic diseases as well as for undernutrition.