UC San Diego

Background: This dissertation explored three hierarchical levels of the

Behavioral Ecological Model (BEM) related to childhood obesity by addressing the following aims: (1) explore the relationships between preadolescents’ body

composition (i.e., fat and lean mass) and bone mass/density; (2) explore the

relationships between preadolescents’ engagement in physical activity and sedentary behavior with their body composition; and (3) perform a systematic review evaluating the relationships between parental household rules, child/adolescent sleep, other obesity-related behaviors, and weight status/body composition.

Methods: For Aims 1 and 2, analysis of the validity baseline data collected

between 2009 and 2014 for the Healthy Smiles Trial was performed (N = 44). For Aim 3, a systematic review of the literature was performed using PubMed (Medline) and Google Scholar databases. After screening abstracts and articles for inclusion, studies included in the review (N = 48) were evaluated and study fidelity was scored.

Results: In 8- to 14-year-old boys and girls, DXA-derived body composition

was related to bone mass. Bivariate analyses showed lean mass measures were positively associated with total body less head (TBLH) and AP Spine (L1L4) bone mineral content (BMC)/density (BMD); however, after controlling for age, gender, height, weight, and pubertal status, the relationships were insignificant. Partial correlations controlling for age, gender, height, weight, and pubertal status showed fat mass index (FMI) was significantly negatively associated with TBLH BMC and L1L4 BMC (p < 0.01), and android fat mass was negatively associated with TBLH BMD (p < 0.05). In 8- to 14-year-old boys and girls, after controlling for age, gender, height, weight, leg length, and pubertal status, partial correlations showed moderate, vigorous, and MVPA were positively associated with DXA-derived lean mass measures and

negatively associated with DXA-derived fat mass measures (p < 0.05). There were no relationships between DXA-derived body composition and light PA, total PA, or sedentary time. Finally, systematic review results showed: (1) higher fidelity studies demonstrated expected relationships between parental household rules and associated obesity-related behaviors (e.g., TV watching rules associated with decreased TV time); (2) parental household rules demonstrated an inconsistent relationship with child weight status/body composition; (3) sleep duration was consistently inversely associated with child weight status, irrespective of study fidelity; (4) parental household rules may be related to sleep duration, and sleep duration may mediate the relationship between rules/child behaviors and child weight status, but more research

is needed. Several limitations in the literature were identified.

Conclusions: In summary, body composition is an important physiological

component and should be evaluated in addition to BMI, as lean and fat mass may have different yet important relationships with variables pertinent to childhood obesity related research. Both physical activity and sedentary behavior should continue to be concurrently evaluated, as they are not simply opposite ends of the same spectrum. Furthermore, future studies should confirm that intensity of PA may be more important with regard to child body composition and weight status, so more effective evidence based recommendations for preventing and reducing childhood obesity can be established. Finally, parental household rules may influence child obesity-related behaviors; however, more research is needed to determine their relationship with child weight status/body composition. Systematic review results call for more multi-level, dynamic, robust studies to determine more effectual means for combating childhood obesity.