Although the rate of alcohol abuse climbed only 2 percentage points a fter the procedures, this translates into more than 2,000 new cases of abuse every year in the United States, according to the findings, which were presented at the annual meeting of the American Society for Metabolic and Bariatric Surgery in San Diego.

They were also published online in the Journal of the American Medical Association.

For the study, Wendy King of the University of Pittsburgh and colleagues followed nearly 2,000 patients who had undergone a weight-loss procedure, including gastric bypass surgery and gastric banding, in which a silicone band is placed around the top portion of the stomach to restrict food intake.

People in the study answered questions about their drinking habits before surgery and again one and/or two years later. The team then rated the alcohol use on a scale developed by the World Health Organization to measure alcohol use disorders.

Before surgery, 7.6 percent of the patients had drinking problems, but two years after surgery, it had increased to 9.6 percent.

Patients described having more symptoms of dependence - such as needing a drink in the morning or failing to meet normal expectations - and more alcohol-related harms, such as black-outs, feelings of guilt or injuring someone.

More than half of the 167 patients who had developed drinking problems after surgery had not abused alcohol prior to their operations, suggesting the surgery played a role.

Alcohol issues were particularly common in those who had gastric bypass, known as Roux-en-Y, and in younger men.

CAUSES UNCLEAR

King said it is not clear why people would develop drinking problems after weight-loss surgery, but it may be that these patients are more sensitive to the effects of alcohol after having the size of their stomach reduced.

King said there is no reason to believe the procedures would replace one addiction for another.

"This idea of addiction transfer has been popular in the general media, but there is no empirical evidence to back it up," King said in an interview, adding that binge eating before surgery was not linked to later drinking problems in her study.

"This is something that we need to really pay attention to," said Dr. Robin Blackstone, president of the American Society for Metabolic and Bariatric Surgery, who was not involved with the research.

She said alcohol sensitivity is known to increase after gastric bypass because acid in the stomach usually makes some alcohol molecules less potent before they are absorbed.

Blackstone said the findings should not deter very obese people from having gastric bypass.

Surgery is considered the gold-standard treatment for morbid obesity, which plagues about 15 million Americans and is linked to a host of health problems, including diabetes and heart disease.

"People who get weight-loss surgery are getting it because they are really unhealthy," Blackstone said. "I think (this study) needs to be taken into account in terms of procedure choice, but the big picture of metabolic surgery is really about obesity."

More than 220,000 Americans had some type of weight-loss surgery in 2009, at a price of about $20,000 per patient, according to the American Society for Metabolic and Bariatric Surgery. Reuters