Deci and Ryan (2002) posit the importance of three sources of interpersonal supports--autonomy support, structure, and involvement-- that, when fostered authentically, promote psychological need fulfillment and well-being. Guided by Deci and Ryan's (2002) contentions, the purpose of the study was to examine if enrollment in a weight-loss challenge was associated with (a) greater perceptions of interpersonal supports which (b) translated into greater psychological need fulfillment and subsequent well-being. Participants (` = 34) were commerical fitness facility members enrolled in a weight-loss challenge (nfemale = 28; Mage = 45.12 years; SD = 7.54 years). Using a two-wave design, participants completed self-report instruments at the beginning and end of the weight-loss challenge lasting 12-weeks. Participants reported increased perceptions of interpersonal suppports and psychological need fulfillment in exercise settings (Cohen's d = .31 and .52 respectively). Neglible changes in well-being were noted (Cohen's d = .08). Serial mediation analysis did not support the hypothesized sequence as the serial indirect effect was .001 (95% confidence interval = -.013, .020). Similarly, the indirect effect of interpersonal supports (-.077) and psychological need fulfillment (.016) on well-being were not significant. Overall, the increase in theoretically supported constructs noted in the investigation was enough to sustain, but not increase, well-being. As such, an enhanced understanding of how to increase well-being using exercise-based interventions seems warranted such that individuals can experience the physical and psychological benefits derived from engagement in exercise.