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Background Malnutrition and disability in Activities of Daily Living (ADL) are significant health concerns among the older adults. The Geriatric Nutritional Risk Index (GNRI) is a validated nutritional assessment tool; however, the mechanisms linking it to ADL disability, particularly in rural settings, remain incompletely understood. This study investigated the associations between GNRI and Basic ADL (BADL), Instrumental ADL (IADL), and overall ADL disability, and assessed the potential mediating roles of biomarkers related to inflammation, metabolism, obesity, and insulin resistance. Methods This cross-sectional study (2016–2018) included 4,399 community-dwelling adults aged ≥60 years from Donglan County, Guangxi, China. BADL and IADL were assessed using the Chinese-adapted versions of the Physical Self-Maintenance Scale (PSMS) and the Lawton Instrumental Activities of Daily Living Scale, respectively. GNRI was calculated and categorized as normal (98) or low (≤98). Biomarkers included the Systemic Inflammation Response Index (SIRI), Aggregate Index of Systemic Inflammation (AISI), Metabolic Score for Insulin Resistance (METS-IR), A Body Shape Index (ABSI), and Triglyceride-Glucose Index (TyG). Associations were examined using multivariable logistic and generalized linear models. Restricted cubic splines explored nonlinearity, and mediation analyses quantified indirect effects. Subgroup and sensitivity analyses were conducted. Statistical analyses were performed using IBM SPSS Statistics (version 26.0) and Zstats (version 1.0). Results In fully adjusted models, low GNRI was associated with higher odds of BADL (OR = 2.10, 95% CI: 1.56–2.83), IADL (OR = 1.69, 95% CI: 1.34–2.12), and ADL (OR = 2.18, 95% CI: 1.60–2.97) disability. GNRI was negatively associated with ABSI ( β = −0.0017, p 0.001), which was positively associated with all three disability types (ORs: 1.45–2.00). RCS analyses indicated nonlinear relationships for GNRI. ABSI significantly mediated 24.39 to 31.07% of the associations between GNRI and disability. The GNRI-disability association was significantly stronger in participants with anemia (P for interaction 0.001). Sensitivity analyses confirmed the robustness of these findings. Conclusion Lower GNRI is independently associated with increased risks of BADL, IADL, and ADL disability in the rural Chinese older adult population. ABSI mediates a substantial portion of these associations, suggesting that malnutrition may influence functional disability partly through adverse body shape changes, such as central obesity. These findings highlight the potential value of integrated nutritional and body composition management, especially for anemic older adults. From a public health perspective, routine screening for nutritional risk using GNRI, combined with central obesity assessment, should be considered in rural primary care settings. Future longitudinal studies and intervention trials are needed to establish causality and evaluate the effectiveness of targeted nutritional and body composition interventions in preventing or delaying ADL disability.
Liang et al. (2026) studied this question.