Few prevention programs have been developed and empirically evaluated to address eating disorder (ED) and muscle dysmorphia (MD) symptoms in men. Furthermore, new strategies for the broad implementation of available programs are needed. We investigated the acceptability and efficacy of a dissonance-based (DB) intervention for Brazilian undergraduate men with body dissatisfaction to target risk and protective factors for ED and MD symptoms (the Body Project: More Than Muscles) after an online training for facilitators.