Stability of Adolescent Body Mass Index during Three Years of Follow-up

ObjectiveA 4-year longitudinal study was conducted to determine the prevalence of overweight, detect shifts in body mass index (BMI) distribution, and determine which adolescents were at risk for pathologic weight gain.Study designBMI was analyzed in 1746 adolescents in years 1 (2001-2002) through 4 (2004-2005) of a school-based study. Changes in BMI-Z according to baseline BMI category were examined with general linear modeling.ResultsIn year 1, the prevalence of at risk for overweight (BMI = 85th-95th percentile) and overweight (BMI ≥ 95th percentile) was 19.1% and 18.1%, respectively. Between years 1 and 4, the cohort exhibited no increase in the prevalence of at risk for overweight (19.1% versus 17.2%) or overweight (18.2% versus 18.8%; P > .5). The mean BMI Z-score (BMI-Z) for the cohort was identical in years 1 and 4 (0.66 ± 1.0 Z-score units). Although the overall cohort exhibited stability in BMI-Z, individuals at the lowest categories of BMI-Z (year 1 BMI Z-score <0) exhibited significant increases in BMI Z-score by year 4 (P < .01), with lean girls gaining more than lean boys (P for difference <.007).ConclusionThe study cohort exhibited stability in adiposity during 3 years of follow-up. However, lean adolescents, particularly girls, experienced significant increases in BMI-Z, beyond that expected for age- and sex-related growth.