ES of post-prandial insulin responses were also significantly lower in both adults with and without T2DM (n = 3 RCTs; ES  – 19.43; 95% CI  – 24.01,  – 14.85; p ≤ 0.0001, I2 = 0%) and (n = 11 RCTs; ES  – 11.26; 95% CI  – 22.11,  – 0.41; p ≤ 0.05, I2 = 90%), respectively. This evidence concerns the gene INS and type 2 diabetes mellitus.