BACKGROUND/OBJECTIVES: Depressive mood is prevalent in geriatric patients who undergo rehabilitation. Malnutrition, which frequently coexists in this demographic group, likely affects mental health status significantly. This study examined the association between malnutrition and depressive mood at discharge in geriatric patients who were undergoing rehabilitation and identified the mediating roles of specific malnutrition components in this association. SUBJECTS/METHODS: This prospective cohort study comprised 189 geriatric rehabilitation patients. Malnutrition was determined using the Global Leadership Initiative on Malnutrition (GLIM) criteria, and depressive mood was assessed using the Geriatric Depression Scale-15 (GDS-15). The potential mediation of the GLIM components in the relationship between malnutrition and depressive mood was evaluated using causal mediation analysis. RESULTS: Malnutrition was positively associated with increased GDS-15 scores at both admission (p = 0.007) and discharge (p <
0.001). The severity of malnutrition corresponded with increased odds of depressive mood at discharge (moderate malnutrition: odds ratio [OR] 3.84, 95% confidence interval [CI] 1.48-9.94, p = 0.005
severe malnutrition: OR 5.11, 95% CI 1.52-15.17, p = 0.003). Notably, both muscle mass reduction (OR 1.51, 95% CI 1.01-2.27, p = 0.042) and disease burden (OR 1.37, 95% CI 1.00-1.89, p = 0.047) were identified as mediators in the association between malnutrition and depressive mood at discharge. CONCLUSIONS: Nutritional status significantly influenced the mental health of geriatric rehabilitation patients, with muscle mass reduction and disease burden mediating this relationship. These findings emphasize the importance of a multidimensional geriatric rehabilitation approach that includes nutritional interventions.