Over the past thirty years, the prevalence of obesity among children in the U.S. has tripled. In response to this epidemic, weight management programs have addressed issues of dietary and activity behaviors, through programs aimed at upgrading children's nutritional intake and increasing their physical activity. While obesity increase among children seems to have plateaued over the last few years, the challenge of reducing obesity remains.

This dissertation examined the associations between diet and physical activity behaviors and obesity risk among a diverse sample of 4,414 children (Hispanic = 38%, African American = 36%, White = 26%), who were assessed longitudinally in both 5th and 7th grade. Direct measurements of height and weight were used to calculate body mass index (BMI) and classify participants into obese vs. non-obese. Four dietary and two physical activity behaviors were indexed based on self-report. Household education level indexed socioeconomic status (SES).

In the first portion of the dissertation, as the primary aim, I examined whether physical activity is differentially associated with obesity risk in African American, Hispanic, and White youth and whether such associations are moderated by gender. To this end, main effects of obesity risk were calculated within six racial/ethnic, gender subgroups (3 racial/ethnic x 2 gender), and associations were examined while controlling for socioeconomic differences. As the secondary aim, I examined differences in physical activity across racial/ethnic and gender groups.

In light of unexpected findings (see below) in the first portion of the dissertation, I expanded the focus in the second portion to examine the association between four dietary (fruit, vegetable, fast food, sugar-sweetened beverage intake) and two physical activity (exercise and television viewing) behaviors and obesity risk. As the primary aim, I examined the joint and unique contributions of these behaviors to obesity risk by race/ethnicity and gender at 5th and 7th grade assessments, while controlling for socioeconomic differences. As the secondary aim, I examined differences in behavioral prevalences across racial/ethnic and gender groups.

Overall, the findings of both portions of this dissertation suggest that the proximal determinants of children's weight class, namely diet and physical activity, not only have a differential association with obesity risk among the different racial/ethnic, gender groups examined, but also have an unexpected and largely absent (> 50% of subgroups examined) association with obesity risk. With regard to physical activity, the findings indicate an inverse relationship between physical activity and obesity risk, but in less than half the racial/ethnic, gender subgroups that were examined. In lieu of these sparse and unexpected findings, further research should identify moderating influences on adolescent weight status beyond the presumed "proximal" dietary and activity influences.