Background: Asia bears a rapidly increasing cancer burden, driven partly by rising obesity prevalence. Although body mass index (BMI) is widely used to assess obesity, it does not capture fat distribution, which is particularly relevant in Asian populations prone to central adiposity at lower BMI levels. Waist circumference (WC) may therefore provide complementary or superior insight into obesity-related cancer burden. However, no multicountry study has systematically compared BMI- and WC-based population-attributable fractions (PAFs) for cancer in Asia.
 
Objectives: To estimate and compare the population-level cancer burden attributable to obesity using BMI- and WC-based PAFs across 25 Asian countries, and to examine variation by sex, cancer type, region, and smoking status among men.
 
Methods: PAFs for continuous exposure were calculated for obesity–cancer associations, which were selected based on sufficient evidence of the International Agency for Research on Cancer (IARC) or strong evidence of the World Cancer Research Fund/ American Institute for Cancer Research (WCRF/AICR). Dose-response relative risks (RRs) were primarily sourced from WCRF/AICR report where possible, otherwise were retrieved from meta-analyses, pooled analyses of cohort studies, or cohort studies through a systematic PubMed/MEDLINE search. BMI and WC data for 25 Asian countries were obtained from the WHO STEPs database. The number of cancer cases was extracted from GLOBOCAN 2022.
 
Results: Across 25 countries, high BMI and WC accounted for 11.9% (82,694 cases) and 11.4% (79,221 cases) of obesity-related cancer incidence, respectively. BMI-attributable PAFs were slightly higher in men than in women (10.6% vs 9.4%), whereas WC-attributable PAFs were slightly higher in women than in men (13.3% vs 13.1%). Overall, BMI-attributable PAFs exceeded WC-attributable PAFs for most cancer sites by approximately 0.2–8.9 percentage points; however, WC contributed more prominently to oesophageal, gallbladder, pancreatic, breast, ovarian, and prostate cancers, with differences of approximately 2.3–6.6 percentage points. Substantial heterogeneity was observed across countries: BMI-attributable PAFs were highest in Mongolia (both sexes: 20.9%; women: 21.6%; men: 20.2%) and lowest in Timor-Leste (both sexes: 2.9%; women: 3.3%; men: 2.2%). WC-attributable PAFs were highest in Iraq (both sexes: 19.7%; men: 22.0%; women: 11.8%) and lowest in Nepal (both sexes: 4.0%; women: 4.8%; men: 2.9%). Among men, BMI consistently contributed a higher PAF than WC across all smoking groups, while both BMI- and WC-attributable PAFs were highest in former smokers compared with current and never smokers.
 
Conclusions/Implications: Excess adiposity accounts for a substantial proportion of obesity-related cancers across Asia, with broadly comparable population-attributable fractions for BMI and waist circumference at the overall level. However, the relative contribution of BMI and waist circumference varies by cancer site, sex, and country. While BMI remains a practical population-level surveillance metric, incorporating waist circumference may improve cancer prevention strategies for selected cancers, including oesophageal, gallbladder, pancreatic, breast, ovarian, and prostate cancers. Integrated approaches addressing both total and central adiposity are essential to mitigate the growing cancer burden associated with obesity in Asia.