Background: Institutionalized older adults often experience cognitive and functional decline and altered body composition (BC), making nutritional assessment difficult. Bioelectrical impedance analysis (BIA) offers a simple and non-invasive method to evaluate BC; classic and specific bioelectrical impedance vector analysis do not require predictive models or assumptions about hydration status. Objective: This study aimed to evaluate the utility of BIA, classic bioelectrical impedance vector analysis (BIVA), and specific BIVA (BIVA-Sp) in detecting nutritional and other related disorders in institutionalized psychogeriatric patients. Methods: A cross-sectional study was conducted in 95 institutionalized older adults (52 men, 43 women; mean age: 80 years). Clinical and functional data, including frailty, dependency, handgrip strength, and anthropometry, were collected. BC was assessed using BIA. Nutritional diagnoses included malnutrition (GLIM criteria), sarcopenia (EWGSOP2), adiposity, and sarcopenic obesity (SOGLI criteria). Mean impedance vectors and 95% confidence ellipses were generated for BIVA and BIVA-Sp. Individual vectors were compared with reference data from healthy older adults. Statistical analyses compared clinical variables and impedance vector distributions between groups. Results: Classic BIVA differentiated patients with sarcopenia and sarcopenic obesity, while BIVA-Sp identified vector shifts associated with adiposity and sarcopenic obesity. Neither BIVA nor BIVA-Sp discriminated patients based on body mass index or malnutrition status. Conclusions: The application of BIVA in institutionalized psychogeriatric patients allows for easier, faster, and more effective detection of changes in BC and hydration status compared with conventional methods. This enables individualized monitoring and facilitates interventions that may reduce complications, functional decline, and hospitalizations, thereby improving their quality of life.
