Trends and inequalities in obesity and thinness among Chinese older adults based on CLHLS

China's aging population faces dual nutritional challenges as socioeconomic shifts reshape health outcomes. Between 2008 and 2018, obesity prevalence (BMI ≥ 28 kg/m²) surged from 2.6% to 7.8%, while thinness (BMI < 16.5 kg/m²) declined from 14.2% to 6.6%. Urban areas consistently reported higher obesity rates, peaking at a 3.2% urban-rural gap in 2014, whereas rural regions had greater thinness prevalence, with the largest disparity (-3.6%) in 2008. Socioeconomic disparities intensified: by 2018, the most advantaged region (T3) exhibited 4.7% higher obesity and 5.0% lower thinness rates than the most disadvantaged region (T1). Notably, provincial-level analyses revealed urban-rural obesity gaps narrowed by 2018, with rural men in mid-level SES region (T2) surpassing urban counterparts, while urban women maintained higher obesity rates. Thinness remained concentrated in rural women, though urban areas in T1 showed unexpected reversals. Economic growth correlated strongly with rising obesity in men and declining thinness in women. Projections suggest obesity will shift toward rural areas as Gross Domestic Product (GDP) grows, while thinness may resurge among urban women. These trends highlight China's accelerating nutrition transition and widening inequities. Policymakers must address divergent needs: curbing rural obesity while safeguarding vulnerable urban women from thinness.