Age- and sex-related trends in body composition among Beijing adults aged 20–60 years: a cross-sectional study

BACKGROUND: Obesity is the most serious global epidemic and body composition is the main indicator to evaluate obesity. This study aimed to investigate the changing trends of body composition by age and gender in Beijing adults aged 20–60 years and explore the distribution of obesity rates in different age groups of both sexes under different evaluation criteria. METHODS: A total of 24,948 adults aged 20–60 years in Beijing, including 10,225 males and 14,192 females, were included, divided into four age groups (20–29, 30–39, 40–49, and ≥ 50 years) with each decade of age as an age group. Body composition indicators (BMI, fat mass, BF%, muscle mass, visceral fat area, and WHR) were measured in all subjects. RESULTS: BMI and total fat mass peaked in males aged 40–49 years (BMI = 25.75 kg/m(2), total fat mass = 17.70 kg). Female BMI, fat mass and BF% all increased significantly with age (p < 0.01). Total muscle peaked in males aged 30–39 years and decreased significantly thereafter (p < 0.0001). Visceral fat area and WHR increased significantly with age in both sexes (p < 0.0001). Age was significantly positively correlated with BMI, BF%, fat mass, WHR, and visceral fat area in both sexes (p < 0.0001), and age was negatively correlated with muscle mass in males (standard β = − 0.14, p < 0.0001) while positive in female (standard β = 0.05, p < 0.0001). Under the BMI criterion, the obesity rate peaked at 27.33% in males at the age of 20–29 years. Under the BF% criterion, the obesity rate peaked at 17.41% in males at the age of 30–39 years, and increased in females with age. The central obesity rate of both sexes increased with age under the criteria of WHR and visceral fat area. CONCLUSION: The results of this study reveal that age- and sex-related patterns of body composition and obesity change among Beijing adults aged 20–60 years may differ across age groups and that such patterns of change should be considered when developing public health strategies. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12889-023-16459-0.