The study, published in the Journal of Clinical Endocrinology & Metabolism, found that patients with hypothyroidism had more than double the risk of developing SIBO compared to those with normal thyroid function. The risk was even higher in patients with autoimmune thyroid disease, where the body’s immune system attacks the thyroid gland, but appeared lower in those receiving hormone treatment for the condition.

The findings offer insight into how specific changes in gut bacteria could contribute to disease beyond the gastrointestinal system.

“Studies like this remind us how interconnected the body’s systems are and the important role the microbiome plays in overall health,” said endocrinologist Ruchi Mathur, MD, director of Clinical Research and Clinical Operations for the Medically Associated Science and Technology (MAST) program and the study’s corresponding author.

Mathur sat down with the Cedars-Sinai Newsroom to share key takeaways from the investigation.

What did the study reveal about gut bacteria activity in patients with thyroid disease?

We found that patients with hypothyroidism had different patterns of bacteria in the small intestine compared with those without thyroid disease. In patients with both hypothyroidism and SIBO, we found Klebsiella bacteria dominated rather than the bacterial groups we more commonly see in SIBO. This suggests hypothyroidism may not only increase the risk of SIBO but may also influence the types of bacteria involved.

Could this mean a more severe form of SIBO?

Possibly, more research is needed to confirm this. Previous Cedars-Sinai research has shown that Klebsiella can disrupt the balance and interaction of bacteria in the small intestine more than some other bacterial groups.

How does thyroid hormone treatment affect SIBO risk?

One of the more interesting findings of our study was that patients receiving levothyroxine to treat their thyroid condition appeared to have a lower risk of developing SIBO compared with untreated patients. It is possible that thyroid hormone replacement affects gut motility, which may help reduce bacterial overgrowth in the small intestine. More research is needed, but the finding suggests thyroid treatment may influence digestive health in ways we are only beginning to understand.

Why is it important to study the small intestine directly?

Many microbiome studies rely on stool samples, but the bacteria found in stool can differ significantly from those living in the small intestine. The small intestine plays a central role in digestion, metabolism and hormone function, so studying it directly gives us a much more accurate picture of what may be happening in diseases such as hypothyroidism and SIBO. It also may help researchers identify future therapeutic targets.

What can physicians and patients learn from these new insights?

It is important to recognize the relationship between hypothyroidism and SIBO and address symptoms accordingly. If a patient with hypothyroidism is complaining of gastrointestinal symptoms such as bloating or altered bowel habits, their care team should consider evaluating them for SIBO. Likewise, if a patient presents with bloating, constipation or unexplained gastrointestinal symptoms, thyroid testing may also be appropriate.

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Digestive Disease Week is the largest international gathering of physicians and scientists in the fields of gastroenterology, hepatology, endoscopy and gastrointestinal surgery.

Cedars-Sinai is a nationally recognized leader in gastroenterology and gastrointestinal surgery. Digestive and liver disease experts attending the conference are available to discuss a wide variety of research, including these presentations.

Late-Breaking Trial Shows Progress in Difficult Ulcerative Colitis

Maria T. Abreu, MD, executive director of the F. Widjaja Inflammatory Bowel Disease Institute, will present late-breaking results from a clinical trial evaluating two targeted biologic therapies for ulcerative colitis used together. The study focused on patients whose disease had not responded to multiple advanced treatments and found that the combination led to higher rates of clinical remission and healing of the intestinal lining compared with either drug alone.

“We studied patients whose disease has already proven difficult to treat and found that using two therapies together led to stronger outcomes than either alone, without increasing side effects,” Abreu said.

Irritable Bowel Syndrome (IBS)

Ali Rezaie, MD, medical director of the GI Motility Program, will present research that found palatable elemental diet nutrition replacement reduced abdominal pain and related symptoms in people with irritable bowel syndrome after two weeks.

Zoe Krut, MHDS, a clinical research coordinator with the Center for Outcomes Research and Education at Cedars-Sinai Health Sciences University, will present research from a multicenter randomized trial showing that virtual reality-delivered cognitive behavioral therapy improved symptoms of IBS and was well accepted by patients. Study leader Christopher Almario, MD, MSHPM, assistant professor of Medicine and Health Systems Research, will also be on hand to discuss the research.

Interventional Gastroenterology

Barham K. Abu Dayyeh, MD, MPH, director of Interventional Gastroenterology, will share results of a study in which a less invasive laparoscopic procedure for hiatal hernia-associated GERD (gastroesophageal reflux disease) was used. It achieved results similar to standard surgery, with fewer complications. The abstract has been selected for the “Best of DDW” session held at the end of the meeting, highlighting 6 of the top studies presented.

Abu Dayyeh will also share results of another study in which a novel endoscopic therapy used pulsed electric fields to treat the lining of the small intestine. Results reveal improvements in blood sugar control and weight management for nearly one year in adults with Type 2 diabetes.

Inflammatory Bowel Disease

Talin Haritunians, PhD, a research associate professor of Medicine, will present results of a study that found patients with inflammatory bowel disease (IBD) have distinct genetic variants linked to an increased risk for cardiovascular disease, independent of traditional risk factors.

Allistair Clark, MA, a clinical research data specialist at Cedars-Sinai Health Sciences University, will share results of an investigation that found an AI-powered virtual reality therapy reduced pain and anxiety in patients with inflammatory bowel disease (IBD) in both inpatient and outpatient settings.

Small Intestinal Bacterial Overgrowth (SIBO)

Ruchi Mathur, MD, an endocrinologist, and Gabriela Leite, PhD, a research scientist, will present research linking changes in the small bowel microbiome to Type 2 diabetes. These include strong associations with small intestinal bacterial overgrowth (SIBO) and higher glucose levels. Mathur and Leite are with the Medically Associated Science and Technology (MAST) Program.

Diagnostics: Breath Testing

Mark Pimentel, MD, gastroenterologist, and project scientist Maria Jesus Villanueva-Millan, PhD, of the MAST program, are available to discuss their research t directly comparing breath and small-intestine gases in the same patients, showing that hydrogen sulfide levels reflect those in the small intestine and are linked to specific microbes and diarrhea severity.

Liver Disease

Hyunseok Kim, MD, MPH, PhD, hepatologist and assistant professor, Medicine, will present results of research examining biomarkers that may help predict cirrhosis and liver disease progression in people with alcohol-associated liver disease.

Ju Dong Yang, MD, medical director of the Liver Cancer Program, and clinical research data specialist Osama Khattab, MD, are available to discuss their research showing that transarterial radioembolization (TARE) achieved survival outcomes comparable to ablation in early-stage liver cancer, suggesting it may offer an alternative treatment option for patients.

Media Contact

To schedule an interview with a Cedars-Sinai expert during the conference, please contact Laura Coverson Laura.Coverson@cshs.org or 310-562-1112.

The drugs, known as glucagon-like peptide-1 receptor agonists (GLP-1RAs), are marketed under many brand names. They work by stimulating insulin secretion, slowing down food leaving the stomach, and causing a delay in gastric emptying. As a result, the drugs may help Type 2 diabetes patients manage their blood sugar and help patients with obesity to lose weight.

According to the study, published Oct. 1 in the journal JAMA Network Open, these medications may also lead to problems during upper endoscopies, which involve inserting an endoscope—a long, thin tube with a camera and a light on the end—into a patient’s esophagus, stomach and the beginning of the small intestine under sedation to diagnose diseases and conditions of the digestive system.

Researchers found that patients who regularly took GLP-1RAs were significantly more likely to retain food in their stomachs during the procedure than were patients who did not take the drugs. Food retention can raise the risk of aspiration, a rare but serious complication of surgeries in which stomach contents are introduced into the lungs while a patient is under sedation.  

The researchers found that even though patients in the study, as instructed, stopped taking the GLP-1RAs a week before their upper endoscopies, they were still more likely to retain food than those who did not take these drugs.

"The effects of the GLP-1RA drugs appeared to persist even when patients were asked to stop taking them a week before the procedure," said endocrinologist Ruchi Mathur, MD, professor of Medicine, director of Clinical Research and Clinical Operations for Medically Associated Science and Technology at Cedars-Sinai and the study's corresponding author. She added that although aspiration was not detected in any of the patients, food retention can make aspiration more likely.

A total of 70 individuals taking GLP-1RAs and 139 controls were included in the study.

Results showed that 17% of patients on the drugs who underwent upper endoscopy alone showed food retention, compared with none of the controls. They also observed that patients who underwent both a colonoscopy and an upper endoscopy on the same day, requiring a 24-hour clear liquid and bowel preparation protocol, showed no food retention in either the GLP-1RA group or the controls. "This protective effect against food retention may be due to the preparation typically required for colonoscopies, as opposed to upper endoscopies," Mathur said.

The researchers also found a clear association between GLP-1RA use, which can sometimes produce constipation as a side effect, and unsatisfactory bowel preparation for colonoscopies. Inadequate bowel preparation may contribute to missed lesions, patient dissatisfaction, and cancellation of the procedure.

"Overall, our results support the value of individualizing recommendations for patients and having risk-benefit discussions for patients on these drugs," Mathur said. "Any patients using a GLP-1RA drug should be sure to inform their physicians and anesthesiologists before undergoing gastrointestinal procedures."

Peter Chen, MD, professor of Medicine, the Medallion Chair in Molecular Medicine and interim chair of the Cedars-Sinai Department of Medicine, said, "The rigorous research performed by Dr. Mathur and her team represents an important contribution to our understanding of how these powerful obesity and diabetes medications may impact medical care."

Other Cedars-Sinai authors include Jason Nasser, MD; Ava Hosseini, MPH; Gillian Barlow, PhD; Roma Gianchandani, MD; Ali Rezaie, MD, MSc; and Mark Pimentel, MD.

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