High malnutrition risk burden in the oldest-old in integrated medical and long-term care institutions for older adults: a cross-sectional study

Objective This study aimed to assess the burden of malnutrition risk among the oldest-old admitted to integrated medical and long-term care institutions for older adults in Chengdu, Sichuan, China, and to evaluate factors associated with malnutrition risk. Methods This cross-sectional study included 220 adults aged ≥80 years admitted to three integrated medical and long-term care institutions for older adults between July 2024 and June 2025. Nutritional risk status was assessed using the Mini Nutritional Assessment–Short Form (MNA-SF). Demographic, anthropometric, dietary, laboratory, comorbidity, and functional data were collected. Multivariable logistic regression was used to identify factors associated with malnutrition risk. Restricted cubic splines were used to characterize the shape of the association between BMI and nutritional risk. Because BMI contributes to the MNA-SF score, models including BMI were interpreted as exploratory. Results The mean age was 87.46 ± 3.96 years, and 65.5% were women. Overall, 52.7% (95% CI: 46.1–59.4%) had MNA-SF scores in the malnourished range, 44.1% (95% CI: 37.5–50.7%) were at risk of malnutrition, and only 3.2% had a normal nutritional status. In exploratory models that included BMI, higher BMI was associated with lower odds of MNA-SF-defined malnutrition, whether modeled continuously (OR = 0.676, 95% CI: 0.591–0.773), by conventional BMI categories (OR = 0.227, 95% CI: 0.125–0.411), or by older-adult BMI categories (OR = 0.129, 95% CI: 0.062–0.269; all p < 0.001). A liquid or semi-liquid diet was associated with higher odds of malnutrition in models with and without BMI (ORs ranging from 2.092 to 2.487, all p < 0.05). Conclusion Malnutrition risk was highly prevalent among the oldest-old in integrated medical and long-term care institutions for older adults. Routine MNA-SF screening at admission, attention to residents receiving texture-modified diets, and confirmation of the BMI association in independent cohorts may support early nutritional intervention in this vulnerable population.