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People who undergo gastric bypass surgery for weight loss have more than twice the risk of developing alcoholism, compared with those who have gastric banding surgery, preliminary research finds. This line of inquiry could shed new light on the causes of alcoholism — and how weight loss could prompt some people to switch from food addiction to substance misuse.

The new study, which relied on data from a Swedish health database and was presented at a recent meeting on digestive diseases, examined the records of 12,277 patients who had undergone obesity surgery between 1980 and 2006. They were compared to 122,270 people in the general population, matched for age and gender.

Researchers led by Dr. Magdalena Plecka Ostlund of the Karolinska Institute in Stockholm looked at treatments for psychiatric disorders before and after surgery. They found that obese patients were at greater risk for hospitalization for depression and other mood disorders both before and after surgery, compared with people in the general population. After surgery, the study found, patients’ risk of inpatient alcoholism treatment increased — but more so in a subset of patients. Those who had gastric bypass were 2.3 times more likely to require such care for alcoholism than those who had the banding procedure.

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The difference may lie in the mechanics of each surgery. In gastric bypass — technically known as Roux-en-Y surgery — the surgeon staples off a section of the stomach, rerouting food to bypass most of the stomach and part of the small intestine; this reduces the amount of food people can consume and the amount of calories that the body absorbs. By contrast, in gastric banding, commonly known as Lap-Band surgery, doctors use an inflatable band around the upper stomach to limit the amount of food it can hold — but food still must pass through the entire organ.

The intestines allow alcohol to get into the blood stream much more efficiently. And, generally, drugs that reach the brain faster are more addictive — for example, injected rather than snorted cocaine. So bypass surgery, by rapidly raising blood alcohol concentrations, could increase its addiction potential. Indeed, earlier research shows that after bypass surgery, a single drink can raise blood alcohol levels to the point of legal intoxication.

If the finding is confirmed, it could offer new insight into an old debate over the cause of alcoholism: some researchers think people with alcoholism are generally less sensitive to the effects of alcohol, even before they start drinking. The idea is that because these people’s “hollow legs” allow them to outdrink others, they are more likely to develop alcoholism.

But other researchers say people with alcoholism are more sensitive to alcohol’s rewarding effects, which is why they use it to escape mood problems like depression. The new findings tend to support this side of the argument.

However, says Dr. Nora Volkow, director of the National Institute on Drug Abuse, “I think these [ideas about alcoholism] are not mutually exclusive. Both could be occurring.”

The new findings also add to research suggesting that for some people, alcohol and food are substitute addictions. That is, obese people may use eating to self-medicate their emotional distress the same way many alcoholics use alcohol. William Corbin, an associate professor of psychology at Arizona State University, notes that people with alcohol problems tend to be at lower risk for obesity; conversely, people who are obese have a lower risk of alcohol problems.

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So it makes sense that some obese people, whose surgery no longer allows them to eat as much food as they once did, may end up turning to alcohol. “We’re talking about a really dramatic change in food consumption,” says Corbin. “You’ve taken away this very significant source of reward for this person and they are left with the need to find something to replace that. For those who find alcohol especially rewarding because of fast absorption, you could imagine very quickly developing dependence on alcohol.”

There may also be biological reasons for the effect, says Volkow. One possible explanation involves leptin, a hormone produced by fat tissue that tells your brain when you’re full and satisfied. In obese patients, leptin is unable to transmit its “you’ve had enough” signal to the brain, Volkow says, noting that animal studies have documented that when you block leptin, alcohol tends to lose its rewarding effect.

“Obese people [have] leptin resistance,” says Volkow. “Within 24 hours [of surgery] that’s no longer the case. You’ve removed a factor that has made alcohol less rewarding than in nonobese people, which may have protected them.”

Further, there could be social explanations for why obese people may be at higher risk of alcoholism following surgery. Obese people often remain withdrawn from society, both because of physical limitations and social stigma, Corbin says. But the dramatic weight loss that follows surgery may help bring them out of their shell.

“They might get back into more social activities that might increase access to alcohol and [find themselves in more] situations where alcohol use might occur. For those with increased absorption, that might lead to more rapid alcoholism for both social and neurobiological reasons,” Corbin says.

Because the research has not yet been published in a peer-reviewed journal, it is too early for doctors to draw any conclusions about the potential alcohol-related risk when helping obese patients decide between obesity surgeries. But the findings could affect a great number of patients: gastric bypass is the most commonly used weight-loss surgery in the U.S., and the most successful. A recent study published in the Archives of Surgery found that it nearly doubled the amount of weight lost, compared with Lap-Band surgery — with bypass patients losing 64% of excess weight compared with 36% with the banding procedure. Bypass patients in that study also had better quality of life and greater improvement in diabetes.

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“The risks related to morbid obesity are extremely high,” says Volkow. “The [new findings] need to be investigated further to find out what therapeutic interventions can do to prevent alcoholism [after surgery].”