Gastric bypass surgery shrinks the stomach's size and attaches it to a lower portion of the intestine. That limits food intake and the body's ability to absorb calories. Researchers believe it also changes how the body digests and metabolizes alcohol.
Researchers asked nearly 2,000 women and men who had various kinds of obesity surgery at 10 centers nationwide about their drinking habits one year before their operations, versus one and two years afterward. Most didn't drink excessively before or after surgery, and increases in drinking didn't occur until two years post-surgery.
Two years after the surgery, almost 11 percent, or 103 of 996 bypass patients, had drinking problems, a 50 percent increase from before surgery.
About 8 percent of U.S. adults abuse alcohol by drinking excessively. The study authors say their results suggest that an additional 2,000 people each year will develop drinking problems because of obesity surgery.
More than 200,000 stomach-reducing surgeries are performed each year.
The benefits of gastric bypass surgery include sometimes reducing diabetes and heart disease risks.
Patients should be screened for alcohol problems before and after surgery and told about the risks, said lead author Wendy King, an assistant professor at the University of Pittsburgh's graduate school of public health.
She noted that obese people are often socially isolated because of their weight, and that drinking often increases when patients have slimmed down and pursue a more active social life.