Common models propose that the internalization of societal beauty ideals influences disordered eating behaviors and muscularity-oriented behaviors via body image concerns. However, previous studies addressing these pathways have been mainly cross-sectional and primarily included female samples. We investigated these pathways prospectively in male and female adolescents and young adults, examining two pathways: a 'weight/shape pathway,' linking thin-ideal internalization, weight/shape concern, and restrained eating, and a 'muscularity pathway,' linking athletic-ideal internalization, muscularity concern, and muscularity-oriented behavior. Across three time points, 973 participants from the German general population were assessed. Although the hypothesized pathways could not be supported in their complete temporal sequence, several hypothesized pathways occurred across two time points. Among others, weight/shape concern predicted restrained eating and the athletic ideal played a prominent role in the prediction of muscularity-oriented behavior in both genders.