In this article, we present paradoxical findings from a formative evaluation research project that explores how preadolescent girls understand and feel about their bodies after participating in “Girls on the Run of Los Angeles County”(GOTR LA), a girl-serving positive youth development program. Findings from pre/post test data (n=138) show that girls’ body image improved after participation in GOTR LA, yet many girls also reported the dominant thin ideal and the importance of not being fat as key characteristics of strong and healthy bodies. Ethnographic data suggest that institutional, organizational, and interactional factors contribute to these findings. Institutionalized fat-negative discourses translate into subtle messages regarding health and the body through organizational communications and through interactions between volunteer coaches and participants in ways that solidify dominant conceptions of the feminine body despite explicit programmatic intentions to challenge them. Theoretically, we draw from feminist cultural studies’ work on the gendered body to expand the dominant focus on institutionalized obsessions with thinness through the critical analysis of fat and anti fat bias. On an applied level, our discussion of unintended program outcomes reveals the complexities in organizational interventions designed to influence girls’ body image.