Bariatric surgeries are a growing field as a treatment choice for morbid obesity (BMI > 35 kg/m2). Most established of these procedures is a Roux-en-Y gastric bypass (RYGB), where duodenum and proximal jejunum is bypassed. Clinical and research evidence shows that shortly (before any significant weight loss) after RYGB, T2DM resolves with improving glucose tolerance. Foregut hypothesis behind bariatric surgeries postulate, that bypassed portions of intestine contain a substance, that acts as an anti-incretin¬, ie. to counteract metabolically favourable incretins. In view of the recent studies, it may be that GIP is really the anti-incretin behind this hypothesis.