Piggyback off Doug's post.

It seemed like a coincidence at first. The patient, suffering from mysterious attacks of low blood sugar so severe that she sometimes passed out, also happened to have had weight-loss surgery a few years before. But her doctors doubted that the surgery had anything to do with her blood sugar problem.

"But then we had another case, and then another," said Dr. F. John Service, an endocrinologist at the Mayo Clinic in Rochester, Minn. "It just went on from there."

Before long, Dr. Service had five more patients like the first. All had had weight-loss surgery, followed months or years later by sporadic attacks of low blood sugar - hypoglycemia. The levels would plummet from one to three hours after a meal, sometimes low enough to affect the brain.

The first patient blacked out while driving and had a car accident, and others suffered from spells of confusion or tunnel vision.

In all six, tests revealed that the pancreas had gone into overdrive, its cells multiplying furiously and churning out enormous amounts of the hormone insulin, which drove their blood sugar perilously low.

Though the attacks did not occur every day, they were so severe that all six patients chose to undergo major surgery, having more than half the pancreas cut out in hopes of bringing insulin and blood sugar levels back to normal.

"They had no quality of life," Dr. Service said. "We operate only when they say: 'I've had it. I can't live like this anymore.' We don't do this cavalierly."

In a report last week in The New England Journal of Medicine, Dr. Service and his colleagues suggested that the pancreas disorder might be a previously unrecognized side effect of the most popular weight-loss operation, the gastric bypass. In an interview, he said that although the problem seemed uncommon, gastric bypass patients should be followed carefully and checked for it if they repeatedly have symptoms of hypoglycemia after eating.

More than 140,000 Americans had weight-loss surgery last year, mostly gastric bypass. The operation involves stapling the stomach shut so that only a tiny pouch is left to hold a few tablespoons of food, and then connecting the pouch to the small intestine at a point lower than the one where the stomach usually empties into it.

Patients usually lose about a third of their body weight and generally keep most of it off. For many people who are extremely obese, the operation is the only thing that works.

Researchers said Dr. Service's report might help explain a great but puzzling benefit of gastric bypass: it often cures diabetes, so soon after surgery that weight loss cannot account for the improvement.

Rather, by rearranging the small intestine, the surgery seems to make the gut produce increased amounts of hormones that stimulate cell growth in the pancreas.

It is not clear how often extreme cases of pancreas stimulation occur after gastric bypass, but at a recent medical conference Dr. Service asked a room full of endocrinologists how many had seen patients like his who were suffering from hypoglycemia, and, he said, "I think three dozen to four dozen hands went up."

Dr. David Flum, a surgeon who performs gastric bypasses at the University of Washington, said he and other surgeons he knew had also encountered patients with hypoglycemia, but none had needed pancreas surgery.

"We don't think it's a big deal," Dr. Flum said.

Despite their experiences, none of Dr. Service's six patients regretted having weight-loss surgery.

"All of these folks had great benefit regarding weight loss from gastric bypass," he said.

Dr. David E. *******s, an endocrinologist from the University of Washington and the author of an editorial that accompanied Dr. Service's report, wrote that the complication was rare and "hardly represents a public health crisis."

On the contrary, he suggested that the hyperactive pancreas in Dr. Service's patients was an extreme case of "a phenomenon that would probably benefit the vast majority of obese patients with diabetes."