SAN FRANCISCO – People who had obesity surgery got drunk after just one glass of red wine, researchers reported in a small study that was inspired by an episode on “The Oprah Winfrey Show.”

“A lot of people think they can have one glass of wine and be OK,” said Dr. John Morton, assistant professor of surgery at Stanford University Medical Center, who is the study’s lead author. “The concern here is they really can’t.”

Morton has performed more than 1,000 gastric bypass, or stomach stapling, surgeries. He said he routinely warns his patients about drinking alcohol, but it wasn’t until Winfrey discussed the issue on her show last October that the public really took notice. He said questions poured in.

“I didn’t find a whole lot in the literature, so that prompted the study,” he said.

The research team gave 36 men and women – 19 who had obesity surgery and 17 who did not – five ounces of red wine each to drink in 15 minutes. Using a breathalyzer, their alcohol levels were measured every five minutes until it returned to zero.

More than 70 percent of the surgery patients hit a blood-alcohol level of 0.08 percent, which qualifies as legally intoxicated in California, and two reached levels above 0.15, Morton said.

By contrast, most of the control group had levels below 0.05 percent, the study reported.

Researchers also found that obesity patients took longer to sober up.

After matching the control group with the patient group for age, gender and weight, they found the patients took 108 minutes on average to return to a zero blood-alcohol level versus 72 minutes for the control group.

Morton said the obesity surgery patients don’t produce as much of an enzyme that breaks down alcohol because their stomachs are smaller. Also, the alcohol passes to their small intestine faster, speeding up absorption, he said.

The findings, which were presented recently at a meeting of bariatric surgeons, highlight an important warning for obesity patients: “Never have more than a couple of glasses in a single sitting, and don’t drive afterward,” Morton said.

Meg Semrau, a nurse coordinator of Stanford’s bariatric program who had gastric bypass surgery herself more than three years ago, said she noticed her tolerance for alcohol was lower after surgery.

“I literally feel it within a couple of sips now,” she said. “Flushing in the face, a kind of disequilibrium.”

While some experts took issue with the study’s size and methodology, they said it basically confirmed what they had suspected for some time: People who have gastric bypass surgery are more sensitive to alcohol.

Dr. Madelyn Fernstrom, director of the weight management center at the University of Pittsburgh Medical Center, said Morton’s results support alcohol warnings normally given to gastric bypass patients.

However, she called drinking five ounces of wine in 15 minutes an “artificial” test. No one – let alone bariatric surgery patients – would be advised to drink that amount of alcohol so quickly, she said.

In fact, Fernstrom said patients are discouraged from drinking alcohol because it is a “waste of calories.”

“Alcohol is not part of a healthful diet for gastric bypass surgery patients,” she said. “If this is a pleasant part of life to certain people on special occasions, it must be monitored and discussed with their surgeon.”