Distal Bypass????
I suggest you contact Michelle Curran, aka Vitalady (vitalady.com). She's a nearly 20 year vet of the distal bypass. I've heard her describe it as" the worse of both worlds" (referring to the proximal RNY and the DS).
The vitamin issues can be TERRIBLE with the distal bypass, as can bowel issues. Plus there are all the potential issues of the stoma/pouch combo. If you seriously need this sort of malabsorption, I strongly urge you to research the DS (duodenal switch). The DS preserves the pylorus and and normal stomach function, which gives a more normal quality of life.