The present study describes findings in relation to perceived body size and ‘desire for thinness’ by age and residential areas (‘metropolitan areas’, ‘large cities’, ‘small cities’ and ‘towns’) among young Japanese women. Data on 1731 non-pregnant, non-lactating women aged 15–39 years from the 1998 National Nutrition Survey of Japan were used. Current body size was evaluated by BMI percentiles (lean, < 5th; underweight, 5th ≤  BMI < 25th; normal, 25th ≤  BMI <  75th; overweight, 75th ≤ BMI < 95th; obese, ≥ 95th), calculated for 5-year age groups. Perceived body size was obtained by self-report. We defined ‘overestimation’ as non-overweight, non-obese women who perceived themselves as being ‘overweight’ or ‘obese’. Desired body size was evaluated by applying the desired BMI to these cut-off points. Of all the women, 48·4 % perceived themselves as being ‘overweight’ or ‘obese’, and 43·7 % desired a ‘lean’ or ‘underweight’ body size. Adjusted for the current BMI, the OR for ‘overestimation’ calculated by a logistic regression model was significantly elevated in the 15–19-year age group (OR 2·79; 95 % CI 1·76, 4·43), compared with the 25–29-year age group. The OR for ‘desire for thinness’ was significantly high in the 35–39-year age group (OR 2·74; 95 % CI 1·93, 3·89) and the 15–19-year age group (OR 2·26; 95 % CI 1·57, 3·24). Women living in metropolitan areas had higher OR for ‘desire for thinness’ (but not for ‘overestimation’) than did women in towns (OR 1·47; 95 % CI 1·05, 2·07). The findings suggest the nature of excessive weight concerns of young women in Japan; thus efforts to control such health-risk behaviours at a national level are urgent.

Foot-to-foot bioelectrical impedance analysis (BIA) is simple and non-invasive, making it particularly suitable for use in children. There is insufficient evidence of the validity of foot-to-foot BIA compared with dual-energy X-ray absorptiometry (DEXA) as the criterion method in healthy young children. Our objective was to assess the validity of foot-to-foot BIA against DEXA in a large cohort of healthy young children. Body composition was measured by foot-to-foot BIA and DEXA in 203 children (mean age 8·9 (sd 0·3) years). Bland–Altman and simple linear regression analyses were used to determine agreement between methods. BIA overestimated fat-free mass by a mean of 2·4 % in boys and 5·7 % in girls, while fat mass was underestimated by 6·5 % in boys and 10·3 % in girls. The percentage fat recorded by BIA was, accordingly, also lower than by DEXA (boys 4·8 %; girls 12·8 %). In boys, however, there were correlations between the size of the difference between methods and the size of the measure under consideration such that in smaller boys fat-free mass was underestimated (r − 0·57; P < 0·001) while fat mass and percentage fat were overestimated (r 0·74 for fat mass; r 0·69 for percentage fat; both P < 0·001) with the reverse in bigger boys. Mean differences between techniques were greater in the girls than in the boys but in boys only, the direction of the differences was dependent upon the size of the child. Therefore, BIA may be useful for large-scale studies but is not interchangeable with DEXA and should be interpreted with caution in individuals.