When good bacteria live in the wrong place

Understanding SIBO: why it causes bloating, how it is tested, and why it so often comes back

If you feel fine when you wake up but look six months pregnant by dinner, you are not imagining it. Bloating that builds over the day, gas, abdominal discomfort, and bowel habits that swing between loose and sluggish are among the most common complaints I hear in practice. For a meaningful number of these people, the underlying driver is small intestinal bacterial overgrowth, better known as SIBO. Having first written an article about SIBO fully a quarter of a century ago, I am amazed how often this condition is missed by conventional medicine.

SIBO is frequently missed and frequently treated in a way that clears it for a while only to have it return. This article walks through what the science actually supports, where the evidence is thinner than the internet suggests, and how I approach it here.

What SIBO Is

Your colon is home to an enormous and largely helpful population of microbes. Your small intestine, where most digestion and nutrient absorption take place, is meant to hold far fewer. SIBO describes a situation in which bacteria, usually of the type normally found in the colon, accumulate in the small intestine in excessive numbers.

The trouble is location. Those microbes ferment carbohydrates before your body has had the chance to absorb them, producing gas in a part of the gut that is not built to handle it. They can also interfere with bile acids and compete for nutrients. Clinicians now recognize three broad patterns:

• Hydrogen-dominant overgrowth, more often associated with loose stools and urgency.
• Intestinal methanogen overgrowth (IMO), formerly called methane SIBO. The methane producers are archaea rather than bacteria, which is why the name changed. Methane slows intestinal transit and is associated with constipation.
• Hydrogen sulfide overgrowth, a newer category, sometimes linked to diarrhea and a sulfur odor to gas.

Signs It Might Be Worth Investigating

The hallmark is bloating and visible abdominal distension, typically worse after meals and as the day goes on. Other common features include excess gas, belching, abdominal pain, diarrhea or constipation, and a striking intolerance to fiber, beans, onions, garlic, or even probiotics. Because the overgrowth can disrupt absorption, some people develop low vitamin B12, low iron, or shortfalls in the fat-soluble vitamins A, D, E, and K, along with fatigue that is hard to explain.

SIBO overlaps heavily with irritable bowel syndrome. Many people carrying an IBS label have never been evaluated for it.

The Real Question: Why Did It Happen?

SIBO is rarely the root problem. It is usually a sign that one or more of the body’s natural defenses against bacterial overgrowth has broken down. Those defenses include:

• Stomach acid, which sterilizes much of what we swallow.
• Bile and pancreatic enzymes, which have antimicrobial effects of their own.
• The migrating motor complex, a cleansing wave of muscular contraction that sweeps the small intestine between meals and overnight. It is often called the gut’s housekeeper.
• Low thyroid function resulting in slow intestinal transit. Low thyroid activity and SIBO are often connected in a vicious cycle.
• The ileocecal valve, the one-way door between the small intestine and colon.
• Immune defenses in the intestinal lining.

Common contributors therefore include long-term use of acid-suppressing medications (a meta-analysis found proton pump inhibitor use is associated with higher SIBO risk), slowed gut motility from hypothyroidism, diabetes, or opioid medications, and possibly GLP-1s, prior abdominal surgery or adhesions, and aging.

One intriguing line of research connects SIBO to a past bout of food poisoning. Certain bacterial toxins may trigger an autoimmune response that damages the nerves controlling the migrating motor complex. Antibodies to these targets (anti-CdtB and anti-vinculin) have been developed as a blood test, which is available from Vibrant Wellness lab.

How SIBO Is Tested

The most practical test is a breath test. You drink a sugar solution, either lactulose or glucose, and breath samples are collected over two to three hours. Bacteria in the small intestine ferment the sugar early, producing hydrogen or methane that passes into the bloodstream and is exhaled.

Breath testing is useful but imperfect, being prone mostly to false-negative results. Glucose is absorbed early in the small intestine, so it can miss overgrowth further down. Lactulose reaches the colon, so in people with fast transit it can produce a false positive. Results also depend heavily on following the preparation diet and fasting instructions. The more invasive reference standard, culturing fluid aspirated during endoscopy, has its own limitations and is rarely used outside research. For these reasons, I interpret a breath test alongside your symptoms, history, and nutrient status rather than treating a number on a page as the whole story.

Treatment: Three Phases, Not One

 1. Reduce the overgrowth

Several approaches have published support, each with its own strengths and caveats.

Rifaximin, a prescription antibiotic that stays largely within the gut, is the best-studied option. A 2017 meta-analysis found it normalized breath tests in roughly 71 percent of patients. When it is the right fit, I coordinate with your physician, since I do not prescribe medications.

Herbal antimicrobials drew attention after a 2014 study from Johns Hopkins reported that breath tests normalized in 46 percent of patients using herbal protocols, compared with 34 percent using rifaximin. That study was retrospective and from a single center, with no randomization, so it should be read as encouraging and hypothesis-generating rather than proof of equivalence. In practice, botanical options are a reasonable choice for many patients, particularly those who prefer to avoid antibiotics or who have not responded to them. These are the same botanical formulas (Candibactin AR and Candibactin BR) I have used with patients for almost 30 years, long before this study confirmed what I was seeing in practice.

An elemental diet, mBIOTA, a liquid formula of pre-digested nutrients that is absorbed almost entirely in the upper intestine, essentially starves the overgrowth. In a 2004 study, 80 percent of patients had normalized breath tests after 14 days. It is arguably the most effective treatment but is demanding and is contraindicated in some individuals. I reserve it for resistant or recurrent cases.

2. Calm the symptoms

A low-FODMAP diet, which limits the fermentable carbohydrates that bacteria thrive on, can bring meaningful relief. It is important to understand that this approach manages symptoms rather than eliminating the overgrowth, and it is not meant to be followed indefinitely. Long-term restriction can deprive the beneficial bacteria in your colon of the fibers they depend on. The goal is a structured reintroduction to the widest diet you tolerate well. An alternative approach is to take a FODMAP digesting enzyme called FODMATE.

3. Prevent the relapse

This is where conventional care most often falls short. In a 2008 study following patients after antibiotic treatment, SIBO had returned in about 44 percent of them within nine months. Clearing the bacteria without correcting what allowed them to accumulate is a little like mopping the floor without fixing the leak.

Relapse prevention is therefore about the root causes identified earlier. Depending on the individual, that can mean supporting gut motility, spacing meals four or more hours apart without snacking so the migrating motor complex has time to do its job, reviewing acid-suppressing and motility-slowing medications with your prescriber, supporting digestion, and correcting thyroid function, blood sugar regulation, and nutrient deficiencies.

I approach SIBO the way I approach any chronic problem: by asking why it is there. Evaluation typically includes a detailed history and symptom questionnaire, appropriate breath testing, and laboratory assessment of the nutrients SIBO commonly depletes, such as B12, iron, and vitamin D. When the picture calls for it, we also look at thyroid function, blood sugar control, and the broader gut microbiome. Treatment is then sequenced through the three phases above, with relapse prevention built in from the start rather than added as an afterthought.

Ready to Get to the Root of Your Bloating?

If this issue sounds familiar, I would be glad to help you sort out what is driving your symptoms. Call 516-829-1515 or email drdebe@drdebe.com to schedule a consultation.

Dr. Joseph Debé, DC, DACBN, FMCP, CDN, CCSP

Debé Center for Optimal Nutrition and Functional Medicine

265 Sunrise Highway, Suite 41, Rockville Centre, NY 11570

Selected References

1. Pimentel M, Saad RJ, Long MD, Rao SSC. ACG Clinical Guideline: Small Intestinal Bacterial Overgrowth. Am J Gastroenterol. 2020;115(2):165-178.
2. Rezaie A, Buresi M, Lembo A, et al. Hydrogen and methane-based breath testing in gastrointestinal disorders: the North American Consensus. Am J Gastroenterol. 2017;112(5):775-784.
3. Lo WK, Chan WW. Proton pump inhibitor use and the risk of small intestinal bacterial overgrowth: a meta-analysis. Clin Gastroenterol Hepatol. 2013;11(5):483-490.
4. Pimentel M, Morales W, Rezaie A, et al. Development and validation of a biomarker for diarrhea-predominant irritable bowel syndrome in human subjects. PLoS One. 2015;10(5):e0126438.
5. Gatta L, Scarpignato C. Systematic review with meta-analysis: rifaximin is effective and safe for the treatment of small intestine bacterial overgrowth. Aliment Pharmacol Ther. 2017;45(5):604-616.
6. Chedid V, Dhalla S, Clarke JO, et al. Herbal therapy is equivalent to rifaximin for the treatment of small intestinal bacterial overgrowth. Glob Adv Health Med. 2014;3(3):16-24.
7. Pimentel M, Constantino T, Kong Y, et al. A 14-day elemental diet is highly effective in normalizing the lactulose breath test. Dig Dis Sci. 2004;49(1):73-77.
8. Lauritano EC, Gabrielli M, Scarpellini E, et al. Small intestinal bacterial overgrowth recurrence after antibiotic therapy. Am J Gastroenterol. 2008;103(8):2031-2035.