Background and aims: Post prandial hypoglycemia (PPHG) is a common complication after bariatric surgery (BS); however, there are not studies investigating the role of PPHG before BS on outcomes. The goal of our study was to evaluate how PPHG before BS impacts body mass index (BMI), blood pressure and glycometabolic profile. Materials and methods: One-hundred fourteen non diabetic patients affected by severe obesity, waiting for BS, were evaluated before and after BS with a regular follow-up. Before surgery, on the basis of a 5-h Oral Glucose Tolerance Test (OGTT) the population was divided in two groups based on the presence of PPHG (PPHGg), or not (No-PPHGg). Oral Glucose Insulin Sensitivity (OGIS) and Fatty Liver Index (FLI) were used to estimate insulin sensitivity and hepatic steatosis, respectively. Results: Before BS: of 114 patients, 23 patients had PPHG (20%); no significant differences were found for sex, age or BMI between PPHGg and No-PPHGg. Furthermore, there were no differences in blood pressure, HbA1c, cholesterol profile and triglycerides. On the contrary, PPHGg showed a significantly higher OGIS (421±83 vs 374±62 ml/min1/m2, p=0.003) and a lower FLI (87±17 vs 94±9, p=0.016). The area under the curve of insulin (AUCi 0-120 min) during OGTT, was significantly higher in PPHGg than in No-PPHGg (p=0.030). Accordingly, plasma glucose at 120 min was significantly lower in PPHGg (p<0,001). 2-y after BS: all clinical variables improved in both groups, with a significant reduction in serum triglycerides (-8.7±3.3 vs +10±7.3, p=0.02) and HbA1c in No-PPHGg (No-PPHGg -0.41±0.39, PPHGg -0.27±032%; p=0.036). Furthermore, weight loss was inferior in PPHGg than No-PPHGg, with a significant ∆BMI (11.8±5.7 No-PPHGg vs 15±4.4 kg/m2, p<0.004). OGIS increased (p<0.001) without difference between groups (p int=0.32), while FLI improved mostly in No-PPHGg (p=0.049). PPHGg generally developed PPHG after BS as well. Conclusion: Our study shows that a high percentage of patients affected by severe obesity develops PPHG before BS. PPHG is associated with an increased insulin sensitivity and decreased hepatic steatosis index. However, PPHG before surgery negatively impacts weight loss and metabolic parameters after surgery.