Doctors do not yet know how likely patients' bones are to thin enough to break in the years after surgery. But one of the first attempts to tell suggests they might have twice the average person's risk, and be even more likely to break a hand or foot.

Simply popping today's doses of calcium supplements may not be enough.

Here's the irony: Obesity actually is considered protective against bone-weakening osteoporosis, possibly the only positive thing you'll ever hear a doctor say about too much fat.

More than 1.2 million US patients have undergone the surgery in the past decade, 220,000 in the last year alone, according to the American Society for Metabolic and Bariatric Surgery.

There is little data on how patients fare many years later; large National Institutes of Health studies, on both adults and teens, are under way.

But doctors have long noted that the radical weight loss can speed bone turnover until the breakdown of old bone outpaces the formation of new bone. Silverberg cites recent studies showing that a year after gastric bypass, adults' hip density drops as much as 10 per cent, raising concern about a common fracture site of old age. -- AP