SIBO (Small Intestinal Bacterial Overgrowth)
Updated: 4 days ago
I've had SIBO twice, so I know how much it can steal the joy out of eating. Here's what SIBO is, why it shows up so often with Lyme and related conditions, and how it's diagnosed, so you can have a better conversation with your doctor.
Short on time or energy? A quick-view graphic with the key points is at the bottom of this post.
SIBO Solutions Post:
WHAT IS SIBO?
- SIBO stands for small intestinal bacterial overgrowth. It means too many bacteria are growing in the small intestine.
- Most of your gut bacteria live in the large intestine. The small intestine usually holds only a few.
- The extra bacteria ferment the food you eat and make gas, which causes many of the symptoms. They can also use up nutrients and irritate the lining of the small intestine, making it harder for your body to absorb what it needs.
- A 2026 review in The Lancet Gastroenterology and Hepatology describes SIBO as something that develops when one or more of the body's natural protections break down, such as stomach acid, digestive enzymes, bile, normal gut movement and the gut's immune defenses.
THE TYPES OF SIBO
Breath tests look for the gases the overgrowth makes: hydrogen, methane or hydrogen sulfide.
HYDROGEN SIBO
- The most common type, according to Dr. Tania Dempsey.
- Often linked to bloating, gas and diarrhea, and to a gut that moves too fast.
METHANE (NOW CALLED IMO)
- Methane-dominant SIBO is now called intestinal methanogen overgrowth (IMO). The methane is made by archaea, tiny organisms that are a different group from bacteria.
- Often linked to constipation and a slow-moving gut. Dr. Dempsey says many practitioners find it harder to treat.
- A 2025 review of 19 studies found people with IMO most often had bloating (78%), belly pain (65%), gas (56%) and constipation (51%). They had more constipation and less diarrhea than people without IMO.
HYDROGEN SULFIDE SIBO
- The newest type, and still being learned about.
- Dr. Dempsey links it to diarrhea, cramping, nausea and bloating, and says it's often mistaken for hydrogen SIBO.
SIFO (SMALL INTESTINAL FUNGAL OVERGROWTH)
- An overgrowth of fungi, like yeast, in the small intestine. Dr. Dempsey says it often shows up alongside SIBO and has similar symptoms, but there's no test for it yet.
- She lists antibiotics, steroids, other immune-lowering medicines and mold toxicity as possible causes.
COMMON SYMPTOMS
- Bloating. For me, it meant randomly looking 6 months pregnant.
- Gas
- Belly pain or cramping
- Diarrhea, constipation, or both
- Nausea
- Heartburn
- Food intolerances
- Fatigue
- Brain fog and memory lapses
- Dehydration
- Low nutrients, such as iron, vitamin B12 and vitamins A, D and E
Dr. Bill Rawls (2020) says that when a belly feels tight as a drum, with lots of cramping, he suspects SIBO.
SIBO and IBS often overlap. A 2026 review of 25 studies found SIBO was much more common in people with IBS than in healthy people.
WHY IT'S SO COMMON WITH LYME
- Dr. Todd Maderis calls SIBO likely the most common gut problem tied to Lyme and other tick-borne infections. He notes an estimated 60 to 70% of people with Lyme have it, and says the rate was as high as 81% in one gut practice that screened its patients for Lyme.
- A 2021 study by Dr. Rahbar and colleagues at a Los Angeles gastroenterology practice (older source, still worth reading) looked at 270 patients with gut symptoms and no other gut disease found. Those with 3 or more gut symptoms had about twice the odds of a positive blood test for a tick-borne infection (Babesia, Ehrlichia, Anaplasma, Bartonella or Borrelia). Food intolerance, indigestion, nausea or vomiting, constipation and heartburn were each linked. SIBO on its own didn't predict a tick-borne infection. The authors say 3 or more gut and/or other symptoms should raise suspicion of one.
- Dr. Richard Horowitz, quoted by Global Lyme Alliance in 2021 (older source, still worth reading), writes that Lyme and co-infections can cause inflammation that leads to gas, bloating, belly pain, constipation, diarrhea or reflux. He notes the gut holds about 80% of the immune system.
- Lyme can affect the nerves of the gut. Dr. Maderis explains it can slow the muscle waves that move food along, sometimes called "Bell's palsy of the gut."
- Dr. Jill Carnahan (2023) explains that tick-borne germs can slow digestion, raise inflammation and upset the balance of gut bacteria, which can sometimes lead to SIBO. Their effect on the gut's nerves can also cause trouble swallowing, slow stomach emptying and constipation.
- Treatment and the infection itself can both shift gut bacteria. Global Lyme Alliance (2021) notes long antibiotic courses carry gut risks like C. diff and yeast. A GLA-funded animal study (in monkeys), shared in 2025, found Lyme itself, not only antibiotics, changed gut bacteria. Global Lyme Alliance (2025) adds that chronic illness and long antibiotic use can upset the gut's balance, leading to bloating, constipation, diarrhea and food sensitivities. LymeDisease.org (2025) explains that an imbalance of gut bacteria can lead to SIBO.
- Dr. Rawls (2020) says antibiotics disrupt gut bacteria but aren't the only driver. Stress, poor sleep and immune problems play a part too.
- Dr. Dempsey often sees SIBO in her patients with Lyme, mast cell activation syndrome (MCAS), dysautonomia and mold toxicity.
- ILADS: a talk at the 2020 ILADS conference listed slow gut movement, an imbalance of gut bacteria and SIBO among the conditions that often show up with chronic Lyme. At its 2023 conference, ILADS gave a full morning session to the microbiome.
MCAS, POTS AND GUT MOVEMENT
- Dr. Dempsey explains the intestines are full of mast cells, so SIBO can be a big trigger and driver of MCAS. She also says low bile flow can be a leading cause of SIBO, especially in MCAS.
- Dr. Leonard Weinstock (2024) did breath tests on 130 patients with MCAS. Most had bloating, belly pain or bowel changes; 30% tested positive for hydrogen and 10% for methane. He counts the gut lining inflammation from overgrowth (and from SIFO) among the triggers that can make the gut's mast cells worse. He suspects lower vagus nerve tone may keep bacteria from being swept out.
- Johns Hopkins researchers (2024) note that people with dysautonomia often have a slow-moving gut, which can set the stage for SIBO.
- A 2026 review of 19 studies and 8,268 POTS patients found that nearly 6 in 10 had gut symptoms, and about 36% had MCAS.
- Dr. Jill Carnahan notes that people with a chronic viral load or tick-borne infection often have trouble with small bowel movement and the vagus nerve.
OTHER CAUSES AND RISK FACTORS
- A slow-moving gut. Dr. Dempsey says SIBO is often the result of this.
- Low stomach acid, especially from acid blockers (PPIs). A 2025 review of 29 studies found about double the odds of SIBO in PPI users, and the risk rose with longer use. Never stop a prescribed acid blocker on your own.
- Antibiotics. A 2024 review notes repeated antibiotics may encourage overgrowth through resistance.
- A bout of food poisoning. Dr. Dempsey says some people find their gut was never quite the same afterward.
- Belly surgery, especially gastric bypass, and conditions that create pockets or narrow spots in the small intestine, such as Crohn's disease or diverticulosis.
- Conditions that slow the small bowel, like diabetes and scleroderma, and immune deficiencies.
- Reflux: a 2025 study of 394 people found reflux was more common in those with SIBO.
- Endometriosis: since my own bloating turned out to be endometriosis and adenomyosis, this caught my eye. A 2025 study found positive SIBO or IMO breath tests in 91.9% of women with endometriosis, compared with 83.1% of women without it. Methane overgrowth and constipation were common.
HOW SIBO IS DIAGNOSED
A doctor may diagnose SIBO from your symptoms and history (a clinical diagnosis), from a breath test, or both.
BREATH TESTS
- Often done at home, on an empty stomach in the morning. You drink a sugar (lactulose or glucose), then breathe into tubes at set times. Dr. Maderis describes collecting breath every 20 minutes for 3 hours.
- Dr. Dempsey finds 3-hour tests more accurate, since some 2-hour tests aren't always long enough to pick up the gases.
- Experts in a 2026 Argentine consensus recommend measuring hydrogen and methane together. Newer three-gas tests add hydrogen sulfide.
- Follow the prep diet closely. The same experts say a high starting hydrogen level may mean the prep diet wasn't followed.
- Lactulose and glucose tests can give different answers. In a 2026 study of 3,004 people (by researchers connected to the company that makes a three-gas test), SIBO showed up more often with lactulose (27%) than with glucose (7.3%). A 2026 review explains glucose tests are more specific, while lactulose tests catch more overgrowth lower in the small intestine.
THE LIMITS OF TESTING
- Breath tests can give false positives and false negatives, partly because they can't show exactly where in the gut the gas is being made.
- Some experts (2025) feel lactulose breath tests have led to SIBO being overdiagnosed, and urge careful use of antibiotics.
- In people with a slow gut, a 2025 letter warns results can be read wrong and SIBO missed.
- The "gold standard" test, a fluid sample taken from the small intestine through a tube, is invasive, rarely used, and still misses most of the bacteria.
- Dr. Carnahan (2023) notes that SIBO can be tricky to diagnose even with a good breath test.
- That's why many doctors look at the whole picture. Dr. Rawls (2020) relies most on symptoms, and Dr. Dempsey says a skilled clinician also weighs your symptoms and history.
- SIBO can also be diagnosed clinically, based on symptoms and history. That's how I was diagnosed both times.
OTHER TESTS TO ASK ABOUT
- Dr. Dempsey always checks nutrient levels in her SIBO patients. Vitamin B12 is the most common deficiency she sees, and vitamins A, D and E are often low too.
- Dr. Maderis notes SIBO can lead to low iron and B12.
SIBO OFTEN COMES BACK
- In an older 2008 study, SIBO came back within 9 months in about 44% of people after rifaximin. Older age, a past appendectomy and long-term PPI use were linked to it coming back (older source, still worth reading).
- A 2025 position paper from Brazil's gastroenterology federation also notes recurrence is common and advises long-term follow-up.
- Dr. Rawls (2020) and Dr. Dempsey both stress finding and treating the root cause, not only the bacteria.
WHEN TO SEE YOUR DOCTOR
See your doctor if you have blood in your stool, are losing weight without trying, or your bloating keeps coming back or won't go away.
MY EXPERIENCE
- I've had SIBO twice. Both times it was a clinical diagnosis, once by my Lyme doctor and once by a gastroenterologist. I could never do the breath test because of the restrictions on what you can take before testing.
- About a year ago, I developed extreme bloating, and specialists suspected my SIBO was back. It turned out to be female related. My Bloating post shares that story.
- What my doctors used for me, and everything that helped, is in my SIBO Solutions post above.
- Feel free to share your experience. I would love more resources!
SOURCES
ILADS 2023 Annual Conference, Boston (program: "The Microbiome" morning session). ILADS, October 2023.
Argentine Consensus on the Clinical Utility of Breath Tests and Small Intestinal Bacterial Overgrowth Management in Patients with Disorders of Gut-Brain Interaction. Revista de Gastroenterología de México, September 2026.
Critical Review: The Past, Present, and Future of Small Intestinal Bacterial Overgrowth (SIBO). JGH Open, May 2026.
Real-world Study of Three-gas Breath Testing Nationwide and the Association With Symptoms. Journal of Clinical Gastroenterology, May-June 2026.
Gastrointestinal Symptoms and Systemic Comorbidities in Patients With POTS. Neurogastroenterology and Motility, April 2026.
Relationship Between Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome and the Efficacy of Rifaximin Intervention: A Systematic Review and Meta-Analysis. Frontiers in Microbiology, March 2026.
Mechanisms and Pathophysiology Leading to Development of Small Intestinal Microbial Dysbiosis. The Lancet Gastroenterology and Hepatology, March 2026.
Bloating. NHS, reviewed January 21, 2026.
Small Intestinal Bacterial Overgrowth and Intestinal Methanogen Overgrowth: Are They Overdiagnosed? Acta Gastroenterológica Latinoamericana, December 2025.
Frequent Errors in the Interpretation of Breath Tests in Patients with Suspected Small Intestinal Bacterial Overgrowth (SIBO). Revista Española de Enfermedades Digestivas, October 2025.
Recovery from Lyme and long COVID begins in the gut. LymeDisease.org (Lonnie Marcum), September 9, 2025.
Healing from the Inside Out: Why Fiber and Probiotics Matter for Lyme Disease Patients. Global Lyme Alliance, August 21, 2025.
New Study Reveals Gut Impact of Lyme Disease. Global Lyme Alliance, August 1, 2025.
The Duration of Proton Pump Inhibitor Therapy and the Risk of Small Intestinal Bacterial Overgrowth: A Systematic Review and Meta-Analysis. Journal of Clinical Medicine, July 2025.
High Prevalence of Small Intestinal Bacterial Overgrowth and Intestinal Methanogen Overgrowth in Endometriosis Patients: A Case-Control Study. International Journal of Gynecology and Obstetrics, July 2025.
Symptom Profile of Patients With Intestinal Methanogen Overgrowth: A Systematic Review and Meta-analysis. Clinical Gastroenterology and Hepatology, June 2025.
Diagnosis and Treatment of Small Intestinal Bacterial Overgrowth: An Official Position Paper from the Brazilian Federation of Gastroenterology. Arquivos de Gastroenterologia, February 2025.
Correlation Between Gastroesophageal Reflux Disease and Small Intestinal Bacterial Overgrowth: Analysis of Intestinal Microbiome and Metabolic Characteristics. Journal of Inflammation Research, January 2025.
The Importance of Food Quality, Gut Motility, and Microbiome in SIBO Development and Treatment. Nutrition, August 2024.
Dr. Leonard Weinstock, interview with Dr. Jill Carnahan on mast cell activation in the gut. March 2024.
Dysautonomia Following Lyme Disease: A Key Component of Post-Treatment Lyme Disease Syndrome? (Johns Hopkins). Frontiers in Neurology, 2024.
Dr. Todd Maderis. Gastrointestinal Symptoms of Lyme Disease. Updated October 24, 2023.
Dr. Jill Carnahan. Small Intestinal Bacterial Overgrowth: Is There a Natural Cure for SIBO? May 2023, updated September 2023.
Dr. Jill Carnahan. Tick-Borne Illnesses and the Gut: A Fascinating Look at Their Link. May 2023, updated September 2023.
Dr. Tania Dempsey. How SIBO Connects to Lyme Disease, Mold Toxicity, Mast Cell Activation, and More. November 2022, updated November 2023.
Small Bowel Bacterial Overgrowth. MedlinePlus Medical Encyclopedia, National Library of Medicine (reviewed April 27, 2026).
Older sources, still worth reading:
Gastrointestinal Issues with Lyme Disease (quoting Dr. Richard Horowitz). Global Lyme Alliance, June 21, 2021 (older source, still worth reading).
Association of Presenting Symptoms With Abnormal Laboratory Values for Vector-Borne Illness: Experience in an Urban Gastroenterology Practice (Rahbar and colleagues). Journal of Patient-Centered Research and Reviews, January 2021 (older source, still worth reading).
Dr. Bill Rawls. Natural SIBO Solutions for Lyme Patients: How to Overcome This Painful Gut Problem. August 2020.
ILADS 2020 Annual Conference, Abstracts ("It Ain't Just One Thing"). ILADS, 2020.
Small Intestinal Bacterial Overgrowth Recurrence After Antibiotic Therapy. American Journal of Gastroenterology, August 2008.
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Disclaimer: Rise Above Lyme makes no claims about any possible benefit of using any product mentioned within this site. Always consult with your doctor before adding anything. The information shared is based on personal experience, years of accumulated researched resources from Lyme Literate doctors and polls conducted within Lyme groups from actual patient experience using these solution ideas.
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