Type 2 diabetes mellitus (T2DM) is a global public health problem often associated with obesity. Bariatric surgery is effective for treating serious obesity, and techniques involving intestinal bypass have metabolic benefits, such as complete and early remission of T2DM. We present a literature review of the possible mechanisms of early normalization of glycemic homeostasis after bariatric surgery, including intestinal gluconeogenesis, increased antidiabetogenic signals from L cells located in the distal small intestine, and impaired secretion of diabetogenic signals in the upper part of the small intestine. Adding to these potential mechanisms, unknown factors that regulate insulin sensitivity may be involved and altered by bariatric surgery. This review discusses the various hypotheses about the mechanisms of glycemic control after bariatric surgery involving intestinal bypass. Further research is essential to better understand these mechanisms and to identify potential new mechanisms that might help in developing less invasive and safer alternatives for the treatment of T2DM and reveal novel pharmaceutical targets for glycemic control.