When Steve Jobs underwent surgery for pancreatic cancer in 2004 (nine months after learning of the cancer and seeking "alternative treatments"), he received a "pylorus preserving pancreaticoduodenectomy," or mini-Whipple procedure, which removed the malignant tumor and gall bladder but preserved part of the pancreas which was then attached to his stomach and intestine. If you aren't already more than a little grossed out by the picture above from Johns Hopkins depicting the reconfiguration of organs, you can watch a video of the same procedure (on a different patient). Which goes a long way in explaining why he's lost weight.
A German study comparing the long-term effects of two variations of the Whipple procedure on 104 patients found an increase in diabetes and various degrees of gastric acid reflux, stomach ulcers, oily bowel movements, intolerance toward larger meals and aversion to certain foods.
It also lends credence to rumors Jobs is on a special diet, one that seeks to avoid or mitigate these symptoms. According to studies, 80 to 90 percent of patients who survive the surgery live at least ten years. Which means that barring some unfortunate complication, Jobs will probably be announcing products at keynotes through 2014.