Increasing Rate of Weight Loss among Schoolchildren, Especially Girls, in Sweden

Abstract Purpose This study compared the rates of relative weight loss (body mass index, BMI) among boys and girls, from age 7 to 18 years, in two birth cohorts to determine changing patterns over time. Methods Samples from two Swedish national birth cohorts, 1973 and 1981 (all children born on the 15th day of every month), with few missing cases (4.5% and 1.6%, respectively), were studied. Data (height and weight) were collected from school health records and analyzed longitudinally. Episodes of more than 5% reduction in BMI for 3530 boys and girls born in 1973 and 3041 boys and girls born in 1981 were analyzed and compared. Results An increased rate in 1981 compared with 1973 of relative weight reduction episodes was found for both boys and girls. The increase for girls was most pronounced, started from a higher rate, and was seen in nearly all body weight categories and in all ages. For boys, the reductions increased for all body weight categories in the age interval 7–9 years; otherwise, the pattern was much more heterogeneous. Body weight and reduction of BMI were highly correlated in both cohorts, as more of the overweight than the thinner children reduced their BMI. For girls, the increase in rate reduction between 1981 and 1973 was highest among the thinnest individuals. Conclusions Both boys and, especially, girls had an increased rate of weight loss in two longitudinal cohorts. Whether healthy or unhealthy behavior is causing the increase needs to be investigated further.