Trajectories of Fat Mass Index, Fat Free–Mass Index, and Waist Circumference in Children: Project HeartBeat!
Background
Body composition and fat distribution change dramatically during adolescence. Data based on longitudinal studies to describe these changes are limited. The aim of this study was to describe age-related changes in fat free–mass index (FFMI) and fat mass index (FMI), which are components of BMI, and waist circumference (WC) in participants of Project HeartBeat!, a longitudinal study of children.
Methods
Anthropometric measurements and body composition data were obtained in a mixed longitudinal study of 678 children (49.1% female, 20.1% black), initially aged 8, 11, and 14 years, every 4 months for 4 years (1991–1995). Trajectories of change from ages 8 to 18 years were measured for FFMI, FMI, and WC. Because of the small number of observations for black participants, trajectories for this group were limited to ages 8.5–15 years.
Results
Body mass index, FFMI, and WC increased steadily with age for all race–gender cohorts. However, in nonblack girls, FFMI remained constant after about age 16 years. For black boys and girls, FFMI was similar at age 8.5 years but increased more steeply for black boys by age 15 years. In girls, FMI showed an upward trend until shortly after age 14 years, when it remained constant. In boys, FMI increased between age 8 years and age 10 years, and then decreased.
Conclusions
The extent to which each component of BMI contributes to the changes in BMI depends on the gender, race, and age of the individual. Healthcare providers need to be aware that children who show upward deviation of BMI or BMI percentiles may have increases in their lean body mass rather than in adiposity.
aMedical School, University of Texas Health Science Center, Houston, Texas
bSchool of Public Health, University of Texas Health Science Center, Houston, Texas
cDivision for Heart Disease and Stroke Prevention, CDC, Atlanta, Georgia
dAdolescent Medicine, Department of Pediatrics, University of Utah, Salt Lake City, Utah
Address correspondence and reprint requests to: Mona A. Eissa, MD, PhD, Associate Professor of Pediatrics and Adolescent Medicine, Department of Pediatrics, The University of Texas Medical School, 6431 Fannin MSB #3.146A, Houston TX 77030
ABSTRACT