This study followed girls from age 9 to 18 and found that those who were heavier as children stayed heavier as teens, gaining more fat than muscle, especially after puberty and in Black girls.

This study examined longitudinal changes in waist-to-height ratio and components of body mass index (BMI) among young and adolescent girls of black and white race/ethnicity. Girls were recruited at age 9 years through the National Heart, Lung, and Blood Institute Growth and Health Study (NGHS) and were followed annually over 10 years. Girls were grouped into low (<20(th) percentile), middle, and high (>80(th) percentile) BMI on the basis of race-specific BMI percentile rankings at age 9, and low, middle, and high waist-to-height ratio, on the basis of waist-to-height ratio at age 11. BMI was partitioned into fat mass index (FM) and fat-free mass index (FMI). Girls accrued fat mass at a greater rate than fat-free mass, and the ratio of fat mass to fat-free mass increased from ages 9 through 18. There was a significant increase in this ratio after age at peak height velocity. Participants with elevated BMI and waist-to-height ratios at age 18 tended to have been elevated at ages 9 and 11, respectively. There were strong correlations between BMI at age 9 with several outcomes at age 18: BMI (.76) and FMI (.72), weaker but significant with FFMI (.37), and ratio of fat mass to fat-free mass (.53). In addition, there was significant tracking of elevated BMI from ages 9 through 18. In girls, higher BMI levels during childhood lead to greater waist-to-height ratios and greater than expected changes in BMI by age 18, with disproportionate increases in fat mass. These changes are especially evident in adolescent girls of black race/ethnicity and after the pubertal growth spurt.