Nutritional Status, Fat-Free Mass Index, and Functional Dependency in Older Adults: A Cross-Sectional Path Analysis

This study aimed to investigate the cross-sectional associations among nutritional status, body composition, and functional dependency in older adults and to evaluate whether fat-free mass index (FFMI) statistically contributed to the indirect association between nutritional and functional status using observed-variable path analysis.

This retrospective cross-sectional study included 165 adults aged ≥65 years residing in long-term care centers in Istanbul, Türkiye, of whom 51.5% were women. Nutritional status was assessed using the Mini Nutritional Assessment (MNA), functional status using the Barthel Index, and body composition using multifrequency bioelectrical impedance analysis (InBody S10). Handgrip strength, gait speed, dysphagia, and sarcopenia were also evaluated. Multivariable regression, receiver operating characteristic (ROC), and observed-variable path analyses were performed.

Overall, 44.2% of participants were malnourished, 32.7% were at risk of malnutrition, and 70.3% were functionally dependent. Higher MNA scores (OR=0.66, 95% CI: 0.57-0.77), FFMI (OR=0.84, 95% CI: 0.72-0.98), handgrip strength (OR=0.73, 95% CI: 0.61-0.88), and gait speed (OR=0.64, 95% CI: 0.45-0.91) were associated with lower odds of functional dependency, whereas dysphagia (OR=8.27, 95% CI: 2.23-30.65) and sarcopenia (OR=3.90, 95% CI: 1.43-10.63) were associated with higher odds. The MNA score showed excellent discriminatory ability for functional dependency (AUC=0.894). Path analysis showed a strong positive direct association between MNA and Barthel Index scores (β=0.882, p<0.001) and a small negative indirect association through FFMI (β=-0.023, bootstrap 95% CI: -0.053 to -0.002). The opposing directions of the direct and indirect associations were consistent with a statistical suppression pattern rather than a conventional mediating relationship.

Poor nutritional status, low FFMI, reduced muscle strength, slower gait speed, dysphagia, and sarcopenia were associated with functional dependency in older adults. Although FFMI contributed to the statistical decomposition of the association between nutritional and functional status, the observed indirect association was small and opposite in direction to the direct association. These findings should be interpreted as concurrent cross-sectional relationships rather than evidence of mediation, temporal ordering, or causality. Longitudinal studies are needed to clarify their temporal and clinical significance.