Background: Insulin resistance (IR) is a central pathophysiological feature of type 2 diabetes mellitus (T2DM), and its severity is influenced by adiposity. Asian Indians exhibit higher visceral adiposity and metabolic susceptibility even at lower body mass index (BMI). This study aimed to compare insulin resistance between lean and obese Indian adults with T2DM and to identify clinical and biochemical predictors of IR.

Methods: A cross-sectional study was conducted among 110 adults with T2DM, divided into lean (BMI <25 kg/m², n=55) and obese (BMI ≥25 kg/m², n=55) groups. Anthropometric measurements, blood pressure, fasting plasma glucose (FPG), glycated hemoglobin (HbA1c), fasting insulin, and lipid profiles were recorded. Insulin resistance was assessed using the homeostatic model assessment of insulin resistance (HOMA-IR). Correlation and multivariable linear regression analyses were performed to determine predictors of HOMA-IR.

Results: Obese T2DM subjects exhibited significantly higher BMI (29.2 ± 2.8 vs. 22.4 ± 1.4 kg/m², p<0.001), waist circumference (103.5 ± 9.4 vs. 87.2 ± 7.5 cm, p<0.001), and systolic/diastolic blood pressures compared to lean subjects. Fasting insulin (20.4 ± 7.5 vs. 13.2 ± 6.0 µU/mL, p<0.001) and HOMA-IR (7.4 ± 2.3 vs. 4.6 ± 1.7, p<0.001) were significantly higher in obese participants. A greater proportion of obese subjects exhibited HOMA-IR >2.5 (92.7% vs. 72.7%, p=0.005). HOMA-IR correlated positively with BMI (r=0.471), waist circumference (r=0.505), waist–hip ratio (r=0.411), HbA1c (r=0.322), and triglycerides (r=0.378), and inversely with HDL-C (r=−0.209). Multivariable regression identified waist circumference (β=0.12, p=0.002), BMI (β=0.18, p=0.011), triglycerides (β=0.015, p=0.021), and HbA1c (β=0.25, p=0.023) as independent predictors of HOMA-IR.

Conclusion: Obese adults with T2DM exhibit significantly higher insulin resistance than lean counterparts, with central adiposity, BMI, dyslipidemia, and HbA1c as major determinants. These findings underscore the importance of targeting obesity and metabolic risk factors to mitigate insulin resistance and associated complications in Indian T2DM populations.