Abstract
BACKGROUND: Few comprehensive studies have assessed the long-term trends in physical fitness and nutritional status among Chinese adults, along with the socioeconomic inequalities. This study aimed to bridge this gap by examining the temporal changes and the evolution of socioeconomic disparities in physical fitness and nutritional status among Chinese adults aged 20-59, based on five successive national surveillance surveys. METHODS: We integrated data from five consecutive rounds of National Physical Fitness Surveillance (2000, 2005, 2010, 2014, and 2020) among Chinese adults aged 20-59 years. BMI was categorized into underweight (<18.5 kg/m(2)), overweight (24.0-27.9 kg/m(2)), and obesity (≥28.0 kg/m(2)). Central obesity was defined as a waist circumference ≥90 cm for males and ≥85 cm for females. A composite physical fitness indicator (PFI) was calculated by aggregating the Z-scores of all six components. Provinces were ranked by GDP per capita ($) and stratified into three socioeconomic strata from least (T1) to most developed (T3). Generalized additive models (GAMs), adjusted for age and sex, were employed to assess the associations between nutritional status, PFI, and both per capita GDP and urbanization levels. FINDINGS: A total of 716,790 Chinese adults aged 20-59 were included in the analysis. The PFI score declined from 0.71 in 2000 to -0.84 in 2020, with a particularly sharp annual decline between 2014 and 2020. The underweight prevalence declined from 5.54% in 2000 to 3.51% in 2020, while the prevalence of overweight, obesity, and central obesity increased to 35.84%, 15.05%, and 32.10% in 2020, respectively. After 2005, the urban-rural disparities in physical fitness narrowed, whereas the gap between most and least developed regions widened, with urban and high-SES regions consistently showing better fitness. The prevalence of overweight, obesity, and central obesity in urban and economically developed regions was higher than in less economically developed and rural regions in earlier years, but this pattern reversed over time. The underweight prevalence showed the opposite trend. With increasing GDP per capita, PFI initially rose before declining at higher levels, and it showed a positive correlation with urbanization. Overweight prevalence increased with GDP per capita but slowed at higher levels, while obesity and central obesity exhibited an N-shaped relationship with GDP per capita. Moreover, prevalence of overweight, obesity, and central obesity were positively correlated with urbanization. INTERPRETATION: During the first two decades of the 21st century, China experienced rapid economic growth accompanied by declining physical fitness and rising prevalence of overweight, obesity, and central obesity among adults aged 20-59 years. Inequalities in nutritional status between urban and rural areas and across socioeconomic strata reversed. Less developed and rural regions may face dual challenges of deteriorating physical fitness and the growing burden of overnutrition, which requires urgent attention. The complex interplay between socioeconomic development, urbanization, and physical health further emphasizes the need for health policies tailored to diverse socioeconomic contexts and subpopulations. FUNDING: National Natural Science Foundation of China (72474005, 72122001) and the Peking University Health Science Center-Weifang Joint Research Center for Maternal and Child Health (PKUWF-Y12).