Since the serendipitous finding that type 2 diabetes is improved through Roux-en-Y gastric bypass (RYGB) more than three decades ago, multicenter trials have revealed that gastric bypass is the most effective method to treat type 2 diabetes mellitus in obese patients. However, the mechanisms underlying the rapid resolution of serum glucose levels after bariatric surgery remain unclear, and a pharmacological agent that can mimic this effect has not yet been identified. 18F-fluoro-2-deoxyglucose (FDG) PET/CT in post-gastrectomy patients shows changes in intestinal glycolysis, which are associated with a reduction in serum glucose level and weight loss. Furthermore, we clinically observed that small intestine glycolysis migrates, as revealed by repeated PET/CT scans performed on the same day. Based on these findings, we hypothesized that serum glucose may be excreted into the small intestine, which might contribute to the rapid improvement of glucose homeostasis after bariatric surgery. To test this hypothesis, we first evaluated whether serum glucose is excreted into the intestinal lumen after RYGB in an obese, diabetic rat model. We then targeted areas of increased glycolysis in the intestine and evaluated the activated signaling pathways in comparison with areas of low glycolysis and sham-operated intestine. Lastly, we mimicked the glucose-excretion effect of RYGB by pharmaceutical administration of target protein, which was found to be overexpressed after RYGB. We confirmed the contribution of GLUT expression and sequestration in the small intestine by locally administering a GLUT inhibitor. In addition, we evaluated whether this effect could be observed in post-RYGB human specimens as well as in a small cohort of clinical post-gastrectomy diabetic patients and investigated the association between improvement in the HbA1c level and FDG uptake in the small intestine.