We examined explanatory pathways for the association between spatial access to fast food outlets and body weight in 5,076 European adults (18+). The total effect of spatial access to fast food outlets on self-reported weight status was examined using regression analyses accounting for clustering at the neighborhood level. Perceived availability and usage of fast food outlets, and fast food consumption, were considered as potential mediators and age, gender, socioeconomic status, and urban region as potential moderators. Spatial access to fast food outlets was not significantly related to weight status. Spatial access to fast food outlets was associated with perceptions about and usage of fast food outlets, and this was in turn associated with greater reported fast food consumption and unhealthier weight status. We found limited evidence for mediation effects and no evidence for effect modification.