A possible explanation of why gastric bypass surgery cures diabetes:
After performing the Roux-en-Y bypass in obese, diabetic rats the researchers found that the tissue forming the “Roux” limb (the new passage linking the stomach pouch to the lower gut) seems to grow and expand—an energy intensive process that requires a lot of sugar. The researchers suggest that as the intestinal tissue grows—in girth and absorptive capacity—it harvests glucose from the blood, dropping the sugar level in the blood and essentially curing the diabetes. Once the growth stops the intestine is a larger, energy hungry organ that has to work harder to sustain the increased mass; thus it continuously uses more sugar, which might explain how the effects of the surgery are sustained.
What triggers the growth of this Roux limb? It seems that it’s exposure to the undigested food, which exits the stomach pouch undigested before continuing through the GI tract. Exactly how the Roux-en-Y bypass causes the human intestine to grow in this way still needs much more work to be understood.