Rising trends in body mass index and obesity prevalence among young Thai men: a 16-year analysis of new military conscript data (2009–2024)

This serial cross-sectional study evaluated trends in mean body mass index (BMI) and obesity prevalence among young Thai men from 2009 to 2024. We defined obesity using both Asia–Pacific (BMI ≥ 25 kg/m 2 ) and World Health Organization (WHO) (BMI ≥ 30 kg/m 2 ) cutoffs and identified associated factors. The analysis included 54,622 men with a mean age of 21.2 years. Over the 16 years, age-adjusted mean BMI significantly increased from 21.7 kg/m 2 (2009) to 22.5 kg/m 2 (2024) ( P -trend < 0.001). Using the Asia–Pacific cutoff, age-adjusted obesity prevalence rose from 12.5% (95% confidence interval [CI]: 11.0–13.9) to 22.6% (95% CI 21.0–24.1) ( P -trend < 0.001), with the most substantial increases in the central (13.4% to 31.8%) and northern regions (14.7% to 26.2%). According to the WHO cutoff, prevalence increased from 2.2% (95% CI 1.6–2.8) to 6.2% (95% CI 5.3–7.1) ( P -trend < 0.001), with similar trends observed across all regions. Factors associated with the increase in obesity prevalence (BMI ≥ 25 kg/m 2 ) included older age, indoor occupation, and residence in the northern, central, or northeastern regions. Regular exercise was identified as a protective factor against obesity. We highlighted that obesity poses a significant health risk in this population.