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Why bariatric surgery increases the risk of alcohol problems
Your body absorbs alcohol much more rapidly after bariatric surgery.
“Bariatric surgery can come with a price. Patients have a significantly higher risk of developing alcohol problems than if they did not undergo surgery,” says Magnus Strømmen.
He is a researcher at St. Olavs Hospital's Centre for Obesity Research.
Between one and two per cent of the Norwegian population has undergone bariatric surgery. The two most common procedures are gastric bypass and gastric sleeve.
Remove the patient's protective mechanism
Both procedures reduce how much a person can eat and make them feel full more quickly, partly because of the reduced stomach volume and partly because of hormonal changes.
But the new anatomy also changes what happens when a person drinks alcohol.
“In a normal stomach, a significant part of the alcohol is broken down before it reaches the bloodstream. This is due to an enzyme that is secreted in the lining of the stomach. It's this protective mechanism that we deprive the patient of when we operate on the stomach. In addition, whatever you drink passes into the intestine much faster,” says Strømmen.
The small intestine’s big job is absorption. Since the stomach’s ability to break down alcohol more or less stops, significantly more alcohol passes directly into the bloodstream.
This happens even though the patient drinks the same amount as before the surgery.
You get drunk faster
In a new study, Strømmen and his colleagues had 33 adult patients undergo stress tests with alcohol.
The participants consumed measured amounts of vodka mixed with orange juice before bariatric surgery and again 3, 12, and 36 months after surgery. The researchers then measured their blood alcohol levels after they had consumed the alcohol.
“Our findings show that alcohol uptake almost doubles, both after gastric bypass and gastric sleeve. Perhaps an even more dangerous finding, from a substance-abuse perspective, is that patients reach the maximum blood concentration in only half the time. These effects are lasting, probably lifelong,” says Strømmen.
In other words, patients became intoxicated faster, and to a much greater extent, from the same amount of alcohol. It also took longer for them to sober up.
“The effects were more pronounced for people who had gastric bypass surgery. But that does not mean that the sleeve operation is harmless in terms of subsequent alcohol abuse,” the researcher says.
Bypass had a 69 per cent higher risk than sleeve
In another study, the researchers compared the risk of getting an alcohol abuse diagnosis after the two bariatric surgeries.
The researchers analysed data from the Norwegian Patient Registry linked to the Norwegian Prescription Database for 17,800 patients operated on in the period from 2008 to 2018.
They found that patients who had gastric bypass surgery had a 69 per cent higher risk of being diagnosed with an alcohol-related problem than patients with a gastric sleeve.
Bariatric patients who were given an alcohol-related diagnosis also had a higher mortality rate and used specialist health services more than patients who underwent bariatric surgery and who did not receive an alcohol diagnosis.
“It's important that patients, their relatives, and health personnel – especially in general medicine, substance abuse, and gastro medicine – share this knowledge. These Norwegian studies, based on different data sources and different methodologies, indicate that some of our patients struggle with alcohol problems as a complication from the surgery. Alcohol problems can cost the patient, their relatives, and society a great deal,” says Strømmen.
He often tells patients that they need to practice saying no.
“They will suddenly be in social contexts where friends and surroundings expect you to drink as much as before the operation. But your physiology has changed. That means you need to be more careful than before,” he says.
Risk factors for bariatric surgery must be investigated
Strømmen helped establish the obesity outpatient clinic at St. Olavs Hospital.
Now he wants to be sure that clinics incorporate this new information into their daily practice. Patients must be assessed individually in relation to the risk of alcohol problems.
“We find that many patients have a clear idea of what type of surgery they want when they are referred. And for a long time, this was given very great importance in the decisionmaking. But obesity is not just a single phenotype. Despite having a large body, patients are very different, also in terms of health,” he says.
Some patients may have type 2 diabetes, while others struggle with heartburn. Some may have more extensive obesity and therefore desire greater weight loss.
Strømmen explains that gastric bypass may be the best option for one patient, while other factors may make gastric sleeve the preferred choice.
Researchers now know that the two procedures carry different risks for alcohol-related problems.
"This means we must also investigate the patient’s risk factors for substance abuse before we decide which operation the patient should have. Where patients have several risk factors, gastric sleeve may be a better alternative, but we must also ask whether high-risk patients should be operated on at all,” Strømmen says.
Knowledge encourages caution
He wants patients to receive more specific information before the operation.
“It's important that patients make their decision to undergo surgery on a genuinely informed basis. It's not enough to say that their alcohol uptake will change," says Strømmen.
He believes patients should be educated about the mechanisms behind the increased risk after surgery, particularly how the rapid rise in blood alcohol levels can affect their experience of intoxication.
"This information can, at best, prevent patients from developing alcohol-related problems,” he says.
The patient’s risk factors for substance abuse should be considered before the type of surgery is chosen.
“I think most obesity clinics can get much better at taking an alcohol history. That means having a thorough conversation about the patient’s alcohol habits and any risk factors. We need to get better at asking the right questions, and make a more precise assessment," says Strømmen.
He adds, however, that this also requires transparency from the patients.
"I believe that good patient education can make patients understand why it's important to be honest about these things,” says Strømmen.
Drugs can replace bariatric surgery
In recent years, more effective drugs have been developed against obesity.
Strømmen believes these should be considered for everyone before surgery, but especially for those at increased risk of alcohol abuse.
“The current guidelines state that we should not operate on patients with an active substance abuse problem, and that high-risk patients should abstain from alcohol after surgery. However, the guidelines do not provide any guidelines for how patients should be screened. The lack of specification is a problem because this is information that many clinicians are reluctant to ask for, and which patients may be afraid to share,” he says.
References:
Strømmen et al. Ethanol pharmacokinetics before and after sleeve gastrectomy and Roux-en-Y gastric bypass: a 3 year prospective study (the BAR-TRIAL), International Journal of Obesity, 2026. DOI: 10.1038/s41366-026-02113-3
Strømmen et al. Alcohol use disorders and related morbidity and mortality after sleeve gastrectomy and Roux-en-Y gastric bypass: a nation-wide registry study (the BAR-REGISTER), International Journal of Obesity, 2026. DOI: 10.1038/s41366-026-02123-1
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Read the Norwegian version of this article on forskning.no
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