Despite the relatively consistent finding that Conscientiousness, Agreeableness and low Neuroticism are associated with the practice of health-promoting behaviors, the reasons for these linkages are not well understood. This prospective study addressed this gap by taking a self-regulation resource perspective on why these traits relate to health-promoting behaviors by examining the role of higher positive relative to negative state affect. Students completed baseline (N = 330), and two week follow-up (N = 195) surveys. Bootstrapping analyses of the indirect effects of each of the three traits on Time 2 health behaviors were significant in the expected directions, with Kappa squares ranging from .11 to .13. In the full longitudinal analyses controlling for Time 1 health behaviors, the indirect effects of Conscientiousness and Agreeableness through affect balance on Time 2 health behaviors were positive and significant, whereas the indirect effects through Neuroticism were negative and significant after accounting for the Time 1 practice of health behaviors. These findings provide a process-oriented understanding of how Big Five traits are linked to health-promoting behaviors and extend previous research supporting a self-regulation resource perspective on personality and health behaviors.