Background <p>To update previous meta-analyses by evaluating the association between body mass index (BMI) categories (underweight, overweight, and obesity) and gallbladder cancer (GBC) risk, and to compare findings between earlier and more recent studies.</p> Methods <p>A systematic search of PubMed and Web of Science identified 10 observational studies published between January 2017 and May 2025. Studies reporting risk ratios (RRs), hazard ratios, or odds ratios with 95% confidence intervals (CIs) for GBC by BMI category were included. Pooled RRs were calculated using fixed- and random-effects models, and heterogeneity was assessed using I² statistics. Subgroup analyses compared older with newer studies, and men with women.</p> Results <p>Twenty-four studies (14 previous, 11 new) were included. The underweight group showed a a 5% increased possible risk of GBC (fixed-effects RR = 1.05, 95% CI: 0.89–1.24), but there was no clear evidence as statistical significance was not demonstrated. The overweight group was associated with a 19% increased risk (random-effects RR = 1.19, 95% CI: 1.11–1.27), and obesity with a 69% increased risk (random-effects RR = 1.69, 95% CI: 1.51–1.88). Recent studies reported higher RRs for the overweight and obesity groups compared with earlier studies.</p> Conclusions <p>Excess body weight is significantly associated with increased GBC risk, with stronger associations reported in recent studies. Underweight also suggests a possible positive association. These findings emphasize the importance of weight management in GBC prevention strategies.</p> Trial registration <p>Prospero registration ID: CRD420251089832.</p>