Background/Objectives: Eating disorders, characterized by severe disturbances in eating behavior, are a public health concern, particularly among young women. This longitudinal study aimed to investigate the relationship between disordered eating attitudes and mental health outcomes, including depression, anxiety, and somatization, among individuals with eating disorders. Methods: A total of 471 young German women hospitalized with anorexia nervosa or bulimia nervosa participated in this study. Assessments were conducted at two points over a two-month interval using the Eating Disorder Inventory-2 (EDI-2) and the Patient Health Questionnaire. Regression analyses were performed to determine predictors of depression, anxiety, and somatization. The study controlled for socio-demographic segmentation using Sinus-Milieus, a social classification system, as a covariate. Results: Regression analyses revealed that interpersonal distrust and impulse regulation were significant predictors of subsequent depression. Impulse regulation strongly predicted subsequent anxiety, while both impulse regulation and social insecurity were strong predictors of subsequent somatization. The Neo-Ecological Milieu emerged as the most prevalent socio-demographic group (34.4% of participants). The Sinus-Milieus segmentation, however, did not significantly impact the health outcomes, suggesting consistent mental health issues across socio-demographic groups. Conclusions: This study’s findings underscored the role of disordered eating attitudes in predicting mental health outcomes among young women with eating disorders. Addressing these attitudes in therapeutic settings may help mitigate symptoms of not only the primary condition but also depression, anxiety, and somatization.