Unraveling the Gut-Alcohol Connection After Bariatric Surgery

Although metabolic and bariatric surgery (MBS) remains the most effective and durable treatment for Class III obesity, an emerging body of research has highlighted a concerning complication: increased risk of alcohol misuse following surgery. A new Cleveland Clinic study now aims to unpack a novel and potentially modifiable mechanism behind this trend.

Led by a transdisciplinary team of investigators, the study will examine how changes in the gut microbiome following surgery influence the brain's reward response to alcohol and potentially affect drinking behaviors. The project is centered on what researchers call the Biome-Reward as Mechanisms for EtOH Use (BREW ME) model.

“This is an area of growing concern and clinical importance,” says psychologist Leslie Heinberg, PhD, lead researcher and Director of Enterprise Weight Management at Cleveland Clinic. “Our goal is to better understand why patients who undergo MBS are more vulnerable to problematic alcohol use, and how changes in the gut microbiome may be a key piece of the puzzle.”

A known risk, but an unclear mechanism

The physiological and behavioral risks associated with alcohol consumption following MBS are well-documented. Patients experience significantly altered alcohol absorption and metabolism due to anatomical and metabolic changes precipitated by the treatment. A single glass of wine, for example, can produce a blood alcohol concentration over the legal limit (>0.08%), and those who have undergone MBS can take twice as long to return to sobriety than their nonsurgical counterparts.

Additionally, alcohol’s high caloric content coupled with its contribution to malnutrition, dehydration, dumping syndrome and increased ulcer risk can make its consumption particularly harmful in this patient population, Dr. Heinberg says. Despite these known risks, studies consistently show that rates of alcohol use disorder increase after surgery, especially in males, younger patients and those who undergo gastric bypass.

What’s less clear is why this happens. While the idea of “addiction transfer” has been proposed, Dr. Heinberg notes that current evidence does not support the concept as a primary explanation. Instead, researchers are now turning their attention to the rewarding effects of alcohol and how these might be biologically enhanced after surgery.

“There is growing recognition of the gut microbiome’s role in modulating brain function and behavior,” she explains. “Through the microbiome-gut-brain axis, changes in the microbial environment can influence neurobiological pathways related to reward, decision-making and potential addiction.”

After MBS, patients undergo significant shifts in gut microbial composition that may enhance the hedonic — or pleasurable — effects of alcohol. These changes may be mediated by shifts in microbial metabolites, inflammation or neurotransmitter production that influence brain reward circuitry.

“Patients who report stronger reward responses to alcohol are more likely to engage in frequent or heavy drinking,” Dr. Heinberg says. “If the microbiome amplifies that reward signal, it could explain the increased vulnerability to alcohol misuse we see after surgery.”

Although this concept is compelling, the existing literature has been limited by methodological constraints, most notably the reliance on self-reported alcohol consumption, which can be inaccurate and subject to bias.

A novel approach

To overcome these limitations, the BREW ME study will deploy a multi-method design that combines advanced microbiome sequencing with ecologically valid, real-time assessments of alcohol reward. Using smartphone-based experience sampling and laboratory-based alcohol reactivity tests, researchers will be able to objectively measure the subjective reward value of alcohol in a real-world context.

Dr. Heinberg says the study will address many of the methodological limitations in the literature (e.g., reliance on self-reported drinking behavior) and will be the first to combine a microbiome and ecologically valid, real-time assessment of the reward value of alcohol in MBS patients.

The research team hopes the potential impact of the BREW ME study will extend beyond academic interest, she notes.

“If we can identify microbial signatures or reward response patterns that predict hazardous drinking, we can improve the early identification of at-risk patients and potentially pave the way for tailored interventions,” Dr. Heinberg says. “Eventually, we may be able to develop microbial or behavioral interventions — probiotics, diet modifications, counseling — based on an individual’s risk profile.”

Such personalized approaches could mark a significant shift in postoperative care, moving from generalized recommendations (e.g., “avoid alcohol”) to targeted strategies designed to reduce risk and optimize long-term outcomes, she explains.

Clinical takeaways

For now, Dr. Heinberg urges physicians to remain vigilant about the potential for problematic alcohol use in patients undergoing MBS. Key strategies include:

• Screening for alcohol use disorder both pre- and postoperatively, especially in high-risk groups (e.g., men, younger patients, gastric bypass recipients)
• Educating patients about the altered pharmacokinetics of alcohol and associated health risks
• Encouraging abstinence or strict limitations on alcohol intake, ideally no more than one standard drink and never before driving

Until more is known, she says cautious management and patient education remain essential.

“We know MBS is life-changing,” Dr. Heinberg adds. “Our responsibility now is to ensure those changes are positive and lasting — and that includes addressing risks that don’t show up on a scale.”