Body Mass Index Trajectories and Health-Risk Behaviors

The physical health dangers, as well as social and emotional consequences, of obesity are well established in the literature. Much is also known about the increasing rates of obesity for youth and adults in the United States. Yet, still poorly understood is how individuals fluctuate in terms of their weight or BMI over time and what different weight experiences may mean for later well-being. This dissertation contributes meaningfully to the existing literature on obesity by exploring how body mass index (BMI) trajectories in early life impact psychosocial well-being and behavior later in life. Using data from all four waves of the National Longitudinal Study of Adolescent Health (Add Health), the major research questions of this dissertation are, 1) are there a number of distinctly different BMI trajectories found among American youth as they travel through adolescence and into adulthood? If yes, do these vary significantly by gender?; 2) do socio-demographic characteristics, family background characteristics, and youths' perceptions of interpersonal relationship support predict BMI trajectory membership? If yes, does the association between trajectory membership and these factors differ by gender?; and finally, 3) is there a relationship between adolescent BMI trajectory membership and certain health-risk behaviors, including prescription drug abuse, problematic drinking, and daily cigarette smoking behaviors, during adulthood? If yes, are there conditioning effects of gender? The findings of this dissertation indicate that a four-class model of BMI trajectories generally characterizes the full sample and the sub-sample of girls/women, whereas a three-class model best reflects the boys/men's BMI experiences during adolescence and young adulthood. Among the predictors of individual trajectory membership, it appears that being non-Hispanic Black or Hispanic, attending public schools, reporting lower levels of parental attachment and family income, living in a two-biological parent family and having higher levels of parental availability are all risk factors for youth who experience trajectories elevated in BMI over time. On the other hand, missing values for family income and family education and having higher levels of parental attachment appear to protect youth from entering high BMI trajectories. Also, net of socio-demographic and adolescent/young adult interpersonal relationship characteristics, BMI trajectory membership is significantly associated with health-risk behavioral outcomes, yet only for women. The distal analyses show that experiencing elevated BMI trajectories over the course of early life, specifically being in the Obese to Morbidly Obese and the Obese to High Morbidly Obese classes, is associated with a lower likelihood of engaging in some potentially very harmful health behaviors - prescription drug abuse (for the Obese to Morbidly Obese) and problematic drinking (for the Obese to High Morbidly Obese). Overall, the findings presented in this dissertation add to the emergent knowledge on individual heterogeneity in BMI experiences among adolescents and adults. Future research should strive to uncover some of the paths through which the identified risk factors work to influence weight changes, as well as the odds of engaging in health risk behaviors over time.