Moreover, the decrease of fasting insulin was not statistically significant in simple obesity, but in T2DM with obesity, and heterogeneity still existed (MD, − 2.92; 95% CI, − 4.49- -0.74; P = 0.006; I2 = 83%) (Fig. 5b, c). The gene discussed is INS; the disease is type 2 diabetes mellitus.