Body Mass Index and Waist-to-Height Changes During Teen Years in Girls Are Influenced by Childhood Body Mass Index

Purpose: 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. Methods: 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). Results: 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. Conclusions: 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. (C) 2010 Society for Adolescent Medicine. All rights reserved.