Abstract
BACKGROUND: Body mass index (BMI) has been identified as a critical risk factor for frailty. However, studies assessing the impact of dynamic changes in BMI across years on frailty are still limited. The current analysis aimed to explore the association between different BMI change patterns and frailty in a representative American population. METHODS: We analyzed 9,755 adults aged ≥36 years from the United States National Health and Nutrition Examination Survey 2007-2018. Frailty was defined as ≥3 of weakness, low physical activity, exhaustion, slow walking speed, and unintentional weight loss. Latent class analysis derived BMI change patterns. RESULTS: The prevalence of frailty was 11.49%. Clustering analysis identified five distinct BMI change patterns: Maintain normal BMI (mean frailty score 0.82), Gradual increase to overweight (0.80), Rapid increase to overweight (1.14), Increase to obesity (1.31), and Increasing obesity (1.43). Compared to the "Maintain normal BMI" group, the "Rapid increase to overweight"(OR: 1.94, 95%CI: 1.24-3.03), "Increase to obesity"(OR: 2.46, 95%CI: 1.57-3.86), and "Increasing obesity"(OR: 2.96, 95%CI:1.61-4.81) groups had significantly higher frailty risk even with adjustment of sociodemographic, anthropometric, laboratory, and medical history factors, but the "gradual increase to overweight" group showed insignificant increase of frailty risk (OR: 1.03, 95%CI: 0.66-1.60). Furthermore, this association remained robust among several subpopulations. CONCLUSION: Rapid transitions to overweight or obesity and increasing obesity were linked to higher frailty risk compared to maintaining a normal weight. A gradual increase to overweight did not significantly affect frailty risk. Severity and speed of BMI changes are key factors of frailty.