Scientists examine possible link between bacteria, obesity.

Byline: Laura Beil

DALLAS _ When two Australian scientists won a Nobel Prize this month for discovering that a bacterium causes ulcers, the judges praised the men for keeping faith in an idea dismissed by the scientific mainstream as crazy.

True to Helicobacter pylori's unconventional past, some scientists are now exploring another theory just as radical: that wiping out those bacteria with antibiotics, thus curing all those ulcers, could unintentionally make people fat.

Populations throughout the modern world have been revamping their internal ecosystems through improved hygiene and six decades of antibiotics. The resulting decline of H. pylori or some microbe nestled alongside it, the theory goes, may be a force behind the epidemic of obesity.

"It's speculative, but intriguing," said Dr. Martin Blaser of New York University School of Medicine. Blaser began his research more than 20 years ago with the belief that H. pylori was a stomach-wrecking nuisance. Yet the more he has studied it, the more he has come to think that causing disease is not H. pylori's day job.

Scientists believe that the bacterium, though declining in developed nations, has inhabited the human stomach for more than 60,000 years. It is usually passed from person to person, and doesn't make its home in any other animal. "The evidence of its…