In those with abnormal glucose levels, the combined group of PreDM and T2DM (n = 74), the HbA1c levels 2 years after surgery correlated inversely to baseline BMI (r = − 0.27, p = 0.028) and positively to preoperative age (r = 0.43, p < 0.001), preoperative HbA1c (r = 0.37, p = 0.001) and to IGFBP-1 (r = 0.25, p = 0.038) but not to preoperative glucose, IGF-I (SD), lipids, adiponectin, insulin levels or HOMA-IR. Here, IGF1 is linked to type 2 diabetes mellitus.