Christopher Velez, MD, on SIBO

Dr Velez discusses his presentation on the who, what, and when to treat issues around small intestinal bacterial overgrowth.

Christopher Velez, MD, is program director for the Advanced Fellowship in Neuroastroenterology and Motility Disorders at Mass General Brigham and a staff member of the MGH Center for Neurointestinal Health in Boston, Massachusetts.

CLINICAL PRACTICE SUMMARY

• Diagnosis & At-Risk Populations: Small intestinal bacterial overgrowth (SIBO) reflects excess bacterial colonization in the small intestine. Risk groups include patients on acid suppression therapy, those with pancreatic insufficiency, ileocecal resections, cystic fibrosis, scleroderma, or motility disorders such as gastroparesis.
• Testing & Treatment Considerations: Breath testing for hydrogen and methane remains the standard diagnostic tool but can yield false positives or negatives. Some patients are treated empirically with nonabsorbed antibiotics, most commonly rifaximin.
• Clinical Management & Patient Engagement: It is important to distinguish structural-risk SIBO from secondary bacterial overgrowth in conditions like IBS or delayed transit. For the latter, treating the underlying motility disorder may be more appropriate than antibiotic therapy. Clinicians should ensure shared decision-making and avoid unnecessary antibiotic use to prevent microbiome disruption.

TRANSCRIPT:

Hello, my name is Christopher Velez. I am the program director for the Advanced Fellowship and Neuroastroenterology and Motility Disorders at Mass General Brigham, and I work for the MGH Center for Neurointestinal Health. So here at this ACG 2025 conference in Phoenix, I have given a lecture on the topic of small intestinal bacterial overgrowth—the who, the what, and the when to treat small intestinal bacterial overgrowth. You may hear me referring to it as SIBO. It is a very tricky disease and a lot of people have it. It has caught the popular imagination, particularly in social media platforms. It's important to understand who does have it and who doesn't have it.

So small intestinal bacterial overgrowth reflects the overpopulation, the abundance of bacterial organisms in the small intestine that are not allowing for appropriate health to happen. I think it's important to understand, at least from the perspective of the microbiome and overall health, that you actually need a good, healthy community of bacteria in your GI tract, what we call the gut microbiome. They help to produce nutrients of bacteria, they help to keep other diseases at bay. And sometimes things like antibiotics or diets that aren't rich in fiber or in healthy fats can sometimes lead to changes in the way that the gut microbiome exists in our bodies.

So a lot of controversy exists surrounding the diagnosis and the treatment of it. And oftentimes I find in medicine, a lot of times people tend to have ideas of purity on each extreme of a debate without recognizing that the majority of reality lives somewhere in the middle, somewhere in those shades of gray. So what I would say when it comes to small intestinal bacterial overgrowth, I really think about two different types of patient populations when I'm thinking about who to test and who to treat.

So there are some people who are taking acid suppressing medications, who have deficiencies in pancreatic function, who have resections of a portion of the bowel called the ileocecal area or the ileocecal valve, which is a connection between the small intestine and the colon.

And people have issues of motility where things are moving too slowly throughout the GI tract, such as gastroparesis or in scleroderma, and people like this who have a structural reason. People with CF also being another example of people who may have small intestinal bacterial overgrowth. People like this I think are at risk for having small intestinal bacterial overgrowth, and they're the ideal people to test and to treat for small intestinal bacterial overgrowth. Some people we may treat empirically, meaning that we provide treatment without necessarily offering the diagnostic tests because there are some problems with the diagnostic test. You need to follow particular preparation regimens, not take certain medications, not eat certain foods, and sometimes there can be false positives or false negatives. So sometimes people will give antibiotics that are ideally not absorbed in the rest of the body. Sometimes people will only do breath testing, which is the main way that we assess for small intestinal bacterial overgrowth looking for hydrogen and looking for methane gas.

But there also are other people who, let's say, have irritable bowel syndrome, who may have bacterial overgrowth, and they represent a second type of patient population where I would say that if they have bacterial overgrowth, it's likely a consequence of other disease. So I'd rather treat their other disease if they have gastroparesis or delayed stomach emptying. I want to improve their stomach emptying if they have delays in small intestinal transit. I'm thinking about medications that may improve transit in order to reduce the amount of bacteria. Rifaximin is a commonly accepted antibiotic that we use in the treatment of small intestinal bacterial overgrowth, although sometimes other antibiotics may be needed or there may be some formulary or prior authorization considerations that exist for prescribing rifaximin. So treat symptoms are generally bloating. Sometimes they can have abdominal pain, sometimes people may have nutrient deficiencies that may be associated with their small intestinal bacterial overgrowth.

What I would say is like in many diseases, the patient is the key. Oftentimes, even as a physician, I don't believe someone has small intestinal bacterial overgrowth. It doesn't matter if you describe it as such without getting buy-in from the patient. What I tell my patients sometimes is, I enjoy my visits with you, but I'm seeing you maybe one or two hours a year. You have the other 364 days, 22 hours that you're going to do what you're going to do. So I'd rather have a discussion that both of us leave on the same page to make sure that needs are being met and SIBO. If you think you have SIBO, I would say it's important to talk to your providers about it, your physicians about it. If you're a physician taking care of someone with SIBO even if you don't think they have SIBO, you have to make sure that the patient is heard.

But I also, on the flip side, you don't want to necessarily inappropriately treat someone with antibiotics because antibiotics themselves can cause further disease. So it's really about making sure that you think about the people who are at risk for structural reasons, for having small intestinal bacterial overgrowth versus the other community of people who may have bacterial overgrowth as a consequence of another disease. IBS delays in gastric emptying. You want to treat those abnormalities, and I think if we kind of understood that unique dynamic between those different types of patients, I think there'd be a lot less controversy surrounding SIBO management, both for patients and their physicians.