Group-Based Fat Mass Index Trajectories in Boys and Girls from Elementary to High School.

Both boys and girls exhibited three distinct group-based FMI trajectory groups from 5th to 11th grade.

• Boys' sample: n = 320; Girls' sample: n = 389
• FMI was measured at 5th, 6th, 7th, 9th, and 11th grades when children were 10–16 years of age
• Each sex had one group characterized by low FMI and a stable trajectory
• Group-based trajectory analyses were conducted separately by sex

In girls, two of the three FMI trajectory groups increased from ages 10 to 16, while in boys only one trajectory increased and one decreased over time.

• Girls showed two increasing FMI trajectories across the study period
• Boys showed one increasing and one decreasing FMI trajectory in addition to the stable low group
• The pattern of change differed meaningfully between sexes

In girls only, FMI trajectory groups differed by race and parent education level.

• No corresponding demographic differences by race or parent education were found among boys' trajectory groups
• These demographic characteristics were compared between trajectory groups using repeated ANOVAs
• Findings suggest sociodemographic factors may play a role in adiposity trajectories specifically in girls

Boys' FMI trajectory groups differed by moderate-to-vigorous physical activity (MVPA), while girls' trajectory groups differed by diet quality.

• MVPA was measured across 5th, 6th, 7th, 9th, and 11th grades
• Diet quality was also assessed at the same time points
• Group differences in MVPA were found only in boys, and group differences in diet quality were found only in girls
• Repeated ANOVAs were used to compare behavioral characteristics between trajectory groups

Fat mass index (FMI) rather than body mass index (BMI) was used as the measure of adiposity to establish trajectories.

• The authors describe FMI as 'an accurate assessment of adiposity'
• FMI, MVPA, sedentary behavior, and diet quality were all measured at each of the five time points
• The study design was longitudinal, following children transitioning from elementary to high school
• The authors note that group-based trajectories in prior research have 'usually based on body mass index (BMI)'

The study aimed to provide information about when and for whom to target obesity prevention efforts based on trajectory group characteristics.

• The authors state that 'the characteristics of the groups provide valuable information about when and for whom to target obesity prevention efforts'
• The study addresses 'a pressing need to understand developmental patterns of adiposity as well as factors that influence it'
• The longitudinal design spanned from approximately age 10 to age 16