BACKGROUND/AIMS This study examined sex differences in the effect of changes in body mass index (BMI) on the development of gastric cancer (GC) in South Korea.

METHODS Using data from the National Health Insurance Service-Health Screening Cohort, a retrospective cohort study involving 333,169 Koreans with a median follow-up of 12 years was conducted. BMI was categorized into five groups (<18.5, 18.5-22.9, 23.0-24.9 [reference], 25.0-29.9, and ≥30.0 kg/m²) and the risk of developing GC was evaluated according to changes in BMI by calculating the hazard ratio (HR) using Cox proportional hazard regression.

RESULTS Among males, BMI ≥30.0 kg/m² was associated with a 1.27-fold higher overall risk of developing GC (95% confidence interval [CI], 1.02 to 1.57), but not in females. For non-cardia GC, a U-shaped association between BMI and risk of developing GC was observed in males, although statistical significance was observed only for BMI 18.5-22.9 kg/m². Additionally, an increase in BMI to 23.0-24.9 kg/m² was associated with a decreased non-cardia GC risk among males. In females, the largest waist circumference category was significantly associated with an increased risk of developing overall GC (HR, 1.37; 95% CI, 1.07 to 1.74).

CONCLUSIONS This study demonstrated that maintaining a BMI in the range of 23.0-24.9 kg/m² is optimal for minimizing the risk of non-cardia GC, particularly in males. In females, visceral obesity, represented by a large waist circumference as a proxy, was associated with an increased risk of developing GC.