Objective: Insulin resistance and other metabolic problems are frequently linked to obesity, which is a significant global public health issue. For people with severe obesity, bariatric surgery is regarded as one of the best therapy options for attaining substantial and long-lasting weight loss. The purpose of this study was to compare body composition measures and preoperative and postoperative triglyceride-glucose index (TGI) levels in individuals having bariatric surgery.

Material and Method: Ninety-nine patients who were admitted to Samsun Training and Research Hospital\'s Internal Medicine outpatient clinic and satisfied the inclusion criteria were included in this study. Prior to bariatric surgery, preoperative measures were taken, and six months following the procedure, postoperative measurements were taken. Fasting blood glucose, LDL and HDL cholesterol, triglycerides, HbA1c, body-mass index (BMI), fat and fat-free mass, muscle mass, mineral content, protein level, and TGI were evaluated. Appropriate parametric and nonparametric statistical tests were applied according to data distribution.

Results: Comparative analysis revealed statistically significant differences between preoperative and postoperative measurements for all parameters except protein level. The mean TGI decreased from 2.05±0.13 preoperatively to 1.96±0.10 postoperatively. Similarly, the mean BMI decreased from 40.9±8.2 to 29.3±5.7. Significant reductions were also observed in fat mass, muscle mass, and fat-free mass in the postoperative period.

Conclusion: Bariatric surgery significantly improves TGI and body composition parameters in patients with severe obesity, supporting its beneficial effects on metabolic health and insulin resistance. Further long-term studies with larger sample sizes are needed to confirm the durability of these effects.