When the study of Gorukmez [49] was deleted, the I2 value dropped and no significant association was observed between the combined effects of GSTM1 and GSTT1 polymorphisms and CRC risk in low-quality studies (− − vs. + −: OR = 1.23, 95% CI: 0.58–2.59, I2 = 68.3%). Here, GSTM1 is linked to colorectal carcinoma.