Association Between Body Mass Index and Overall Survival in Patients With Colorectal Cancer in Taiwan

<h3>Background/Aim:</h3> Colorectal cancer (CRC) represents an increasing global health burden. Evidence suggests that body mass index (BMI) may influence survival in CRC; however, large-scale data from Asian populations and sex-specific differences remain limited. We investigated the association between BMI and overall survival among patients with CRC in Taiwan. <h3>Patients and Methods:</h3> We conducted a nationwide cohort study using the Taiwan Cancer Registry linked with National Health Insurance claims for patients with CRC diagnosed between 2011 and 2020. A total of 96,500 patients were categorized as underweight (&lt;18.50 kg/m²), normal weight (18.50-23.99 kg/m²), overweight (24.00-26.99 kg/m²), or obese (≥27.00 kg/m²). <h3>Results:</h3> During follow-up to December 2021, 37,728 deaths occurred. Compared with normal BMI, underweight status was associated with higher mortality [adjusted hazard ratio (aHR)=1.61, 95% confidence interval (CI)=1.55-1.67], whereas overweight (aHR=0.80, 95%CI=0.78-0.82) and obesity (aHR=0.77, 95%CI=0.75-0.80) were associated with reduced mortality risk. Sex-stratified analyses demonstrated consistent trends across both sexes: underweight status significantly increased mortality in men (aHR=1.70, 95%CI=1.63-1.79) and women (aHR=1.52, 95%CI=1.45-1.60), whereas overweight and obesity remained protective factors for both sexes (all <i>p</i>&lt;0.05). <h3>Conclusion:</h3> These findings exhibit a significant association between BMI and mortality in patients with CRC. Underweight status confers increased mortality, while overweight or obesity is associated with improved survival in both men and women.