Dietary patterns and emotion dysregulation in borderline personality disorder and eating disorders as a shared mechanism underlying symptom severity.

Borderline personality disorder (BPD) and eating disorders (EDs) are often comorbid and share a core feature of emotion dysregulation (EDys). While diet has been linked to mental health, its relationship with EDys and symptom severity in these groups remains understudied. This study investigated dietary intake in BPD, EDs, and their comorbidity, and examined whether EDys mediates the relationship between diet and symptom severity. Female inpatients with BPD (n = 40), ED (n = 22), and BPD with comorbid ED (BPD + ED; n = 37), along with healthy controls (HCs; n = 37) completed Food Frequency Questionnaire (FFQ-6), Emotion Dysregulation Scale (EDS), and clinical self-report measures. Dietary patterns differed between groups. Clinical groups consumed sources of omega-3 polyunsaturated fatty acids and Mediterranean diet (MD) foods less frequently than HCs. EDys fully mediated the link between dietary patterns and symptom severity in most models. The mediation was partial when omega-3 intake predicted ED severity in the ED group. Women with BPD and BPD + ED showed poorer diet quality, especially regarding omega-3 and MD-aligned foods. EDys mediated the association between low-quality diet and symptom severity, suggesting a transdiagnostic mechanism. Nutritional interventions may positively influence emotion regulation, thereby reducing the risk of developing and maintaining symptoms of BPD and EDs.