Endometriosis and SIBO: Why Gut Symptoms Can Be Hard To Untangle
If you have endometriosis, persistent digestive symptoms such as bloating, abdominal pain, constipation, diarrhea, nausea, or painful bowel movements can leave you wondering whether they come from the disease itself, a separate digestive condition, or both. These symptoms are frequently reported, but determining what is causing them is not always straightforward [1][3][4].
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For patients, the relationship between endometriosis and gastrointestinal symptoms can be both complicated and frustrating. The disease can directly affect the bowel through lesions on or within bowel tissue, but digestive symptoms are also common without direct bowel involvement [3][4]. People with endometriosis are considerably more likely to have irritable bowel syndrome (IBS), which can cause many of the same symptoms [8]. Newer research suggests that microbial overgrowth, including small intestinal bacterial overgrowth (SIBO) and intestinal methanogen overgrowth (IMO), may be another often overlooked part of the picture [15].
For those whose digestive symptoms remain unexplained or persist even while their endometriosis is being treated, understanding these overlapping conditions can open the door to additional answers.
Table of Contents
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Endometriosis Affects More Than the Reproductive System
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Why Endometriosis and IBS Overlap So Often
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Could SIBO or IMO Be Part of the Picture?
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Why Might Endometriosis and Microbial Overgrowth Be Connected?
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What Breath Testing Can Tell You
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What About IBS-Smart?
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​Getting Clearer Answers About Persistent Gut Symptoms
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Frequently Asked Questions
Endometriosis Affects More Than the Reproductive System
Endometriosis is a chronic inflammatory condition in which tissue similar to the lining of the uterus grows outside the uterus, most commonly within the pelvis [1][4]. The World Health Organization (WHO) estimates that it affects about 10 percent of reproductive-age women worldwide, or roughly 190 million people [1].
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Its most well-recognized symptoms include pelvic pain, painful periods, pain during sex, and infertility. Gastrointestinal complaints are also common. The WHO includes abdominal bloating, nausea, and problems affecting bowel movements among the recognized features of endometriosis [1].
Sometimes there is a clear anatomical explanation. Deep endometriosis (also known as deep infiltrating endometriosis) can extend into the bowel and most often affects the rectum or sigmoid colon. This type of direct intestinal involvement is estimated to occur in 8 to 12 percent of women with endometriosis [2].
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However, digestive symptoms are not limited to those patients whose endometriosis has infiltrated the bowel. In a study of 116 women, overall gastrointestinal symptom scores and most individual symptom complaints were similar across all groups: those with superficial endometriosis, deep endometriosis without bowel involvement, and deep endometriosis involving the rectum. Cyclic pain during bowel movements and cyclic constipation were more common when the rectum was involved, but both symptoms also occurred frequently in the other groups [3].
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A separate study comparing 109 patients with endometriosis and 65 controls found that those with endometriosis experienced more severe abdominal pain, constipation, bloating, flatulence, bowel urgency, and incomplete evacuation. Most of these symptoms showed little relationship to the location of the endometriosis lesions [23].
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Several mechanisms may help explain this disconnect. Cyclic inflammation may irritate the digestive tract, while increased visceral sensitivity may make intestinal pressure or stretching feel more painful [3][4]. In research on the severe bloating commonly referred to as “endo belly,” people with endometriosis also showed a reduced pain threshold when the intestinal wall was stretched [4]. These mechanisms may be part of the explanation, but they do not tell the whole story. Endometriosis also frequently overlaps with IBS, and emerging evidence suggests that microbial overgrowth may contribute to digestive symptoms in some patients [8][15].
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In the sections that follow, we’ll look more closely at these overlapping conditions, how they may add to the digestive burden of endometriosis, and how testing can help clarify what may be contributing to your symptoms.
Why Endometriosis and IBS Overlap So Often
IBS commonly causes recurrent abdominal pain, bloating, and changes in bowel movements, including diarrhea, constipation, or a mix of both [5]. Because these symptoms are also common in endometriosis, it can be difficult to determine whether IBS is contributing to them [1][3][4]. A 2023 clinical review for gastroenterologists noted that many patients with endometriosis initially seek care from gastroenterologists or primary care clinicians because their gastrointestinal symptoms resemble those of IBS and other digestive disorders [6].
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That symptom overlap can be especially consequential because endometriosis has historically taken years to identify. The American College of Obstetricians and Gynecologists (ACOG) has noted that patients wait four to eleven years, on average, from the onset of symptoms to diagnosis. To help shorten that path, its updated 2026 guidance supports making a presumptive clinical diagnosis through symptom assessment, supplemented by a physical examination when appropriate. This allows treatment to begin without waiting for surgical confirmation [7].
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But symptom overlap is only part of the relationship. IBS is genuinely more common among people with endometriosis. A 2022 systematic review and meta-analysis involving more than 96,000 participants found that people with endometriosis had approximately three times the odds of having IBS compared with controls. Across six of the included studies that reported prevalence, about 23 percent of women with endometriosis met the criteria for IBS [8]. Earlier meta-analyses found associations in the same general range, adding weight to the evidence that the two conditions frequently coexist [9][10].
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Genetics may also help explain why the conditions often occur together. A 2023 study found that endometriosis and IBS share some genetic risk factors, including some connected to inflammation and the way the body regulates estrogen [11].
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For patients and providers, that means endometriosis and IBS should not always be viewed as competing explanations. Both conditions can occur in the same person and may contribute different pieces to the same puzzle [8][11].
Could SIBO or IMO Be Part of the Picture?
The evidence connecting endometriosis with SIBO and IMO is newer, but the emerging findings are notable.
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SIBO occurs when excessive numbers of bacteria are present in the small intestine [12]. IMO occurs when methane-producing microorganisms called methanogens become overly abundant in the digestive tract [13]. Although the conditions are related, they tend to be associated with different digestive symptoms. SIBO commonly causes bloating, abdominal discomfort, and diarrhea, while methane-associated IMO is particularly associated with constipation [12][13][14].
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These differences can also be seen in the gases measured during breath testing. In a 2026 nationwide study of three-gas breath testing led by researchers at the Medically Associated Science and Technology (MAST) Program at Cedars-Sinai, higher hydrogen levels were associated with more severe diarrhea, while higher methane levels were associated with constipation [14].
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The possible connection with endometriosis came into sharper focus in 2025, when researchers compared 148 women with endometriosis against 148 women without the condition [15]. The endometriosis group was selected based on MRI findings or histologic assessment and matched by exact age to women without endometriosis.
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All 296 participants came from the same larger group of 1,027 women who had already undergone breath testing to evaluate SIBO or IMO. The control group was therefore also drawn from a population being evaluated for microbial overgrowth, not from the general population [15].
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Within this breath-tested population, SIBO or IMO was detected in 91.9 percent of the endometriosis group compared with 83.1 percent of the control group. The difference was statistically significant. Hydrogen-positive SIBO was also associated with a higher risk of diarrhea, while IMO was associated with a higher risk of acid reflux [15].
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Those high percentages require some context. Because every participant had already undergone breath testing, the 91.9 percent figure should not be interpreted as the prevalence of microbial overgrowth among all women with endometriosis. Instead, it indicates that among the women in this breath-tested population, SIBO or IMO was significantly more common in those with endometriosis [15].
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While the study does not establish that endometriosis causes microbial overgrowth, it adds evidence that the conditions may be associated. For patients experiencing persistent digestive symptoms alongside endometriosis, the findings suggest it may be worthwhile to evaluate whether SIBO and IMO could be possible contributors.
Why Might Endometriosis and Microbial Overgrowth Be Connected?
So why would endometriosis have anything to do with microbial overgrowth or the gut microbiome? One possible link involves gut motility and the speed of intestinal transit.
Motility is the coordinated muscle activity that moves food, waste, and microorganisms through the digestive tract. Intestinal transit refers to how long that movement takes. This system does more than keep bowel movements regular. It also helps maintain a healthy microbial balance. The colon naturally contains far more bacteria than the small intestine, and normal motility helps preserve that distribution. Between meals, recurring waves of contractions sweep residual material and bacteria through the small intestine and toward the colon [16].
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The same 2025 study found altered intestinal transit in 85.8 percent of women with endometriosis compared with 71 percent of controls. Constipation was also significantly more common in the endometriosis group, occurring in 67.8 percent compared with 44.7 percent of controls [15].
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These findings matter because slower or poorly coordinated motility can make the small intestine’s clearing process less effective. Bacteria then have more opportunity to remain and multiply in an area where they are normally present in much smaller numbers. This is why slower intestinal transit is a recognized factor associated with the development of SIBO [16].
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Endometriosis is already associated with gastrointestinal effects that extend beyond direct bowel infiltration, including inflammation, altered bowel function, and visceral hypersensitivity [3][4]. Changes in bowel function could therefore make the small intestine less efficient at clearing bacteria. The existing evidence does not prove that this is how SIBO develops in people with endometriosis, but it gives researchers a biologically plausible pathway to investigate.
What Breath Testing Can Tell You
Endometriosis, IBS, and microbial overgrowth can cause many of the same symptoms, so symptoms alone may not reveal what’s going on inside you. Tracking your bowel habits, bloating, abdominal pain, meals, medications, menstrual cycles, and responses to treatment can help uncover patterns. And breath testing can add some real, objective data.
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During a breath test, a patient drinks a solution containing a carbohydrate such as glucose or lactulose and provides breath samples at set intervals. Microorganisms in the digestive tract break down the carbohydrate and produce gases. Those gases can enter the bloodstream, travel to the lungs, and be measured in exhaled breath [13].
Traditional breath tests measure hydrogen and methane. The Trio-Smart 3-Gas Breath Test measures hydrogen and methane, plus hydrogen sulfide, the gas associated with Intestinal Sulfide Overproduction (ISO). Higher hydrogen sulfide levels have been linked to more severe diarrhea, urgency, and abdominal pain, as well as a greater abundance of hydrogen sulfide-producing organisms in the gut [14][17][18].
For someone with persistent bloating, gas, constipation, diarrhea, or a combination of multiple gut symptoms, breath testing can provide valuable information about whether one of these microbial patterns may be contributing to their symptoms [12][13][15].
What About IBS-Smart?
IBS remains an important consideration, particularly when someone with endometriosis experiences chronic diarrhea or mixed bowel habits. The conditions can coexist, so persistent digestive symptoms should not automatically be attributed to endometriosis alone [8][11].
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For some people, IBS begins after bacterial gastroenteritis, commonly called food poisoning. This is known as post-infectious IBS (PI-IBS). It involves new, ongoing or recurring abdominal pain and changes in bowel habits that continue after the original infection has cleared. Symptoms can persist for months or years, so the connection to a past illness may no longer be obvious by the time someone seeks care [22].
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Researchers have identified an immune response that may help explain why these symptoms persist. During the infection, certain bacteria release a toxin called CdtB. The immune system responds by producing antibodies against the toxin. Because CdtB resembles vinculin, a protein involved in normal gut function, the immune response may also produce antibodies against vinculin [19][22].
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IBS-Smart is a blood test that measures these two antibodies, anti-CdtB and anti-vinculin, to look for evidence of the PI-IBS pathway [19][21]. In the original validation study, both antibodies were significantly elevated in patients with diarrhea-predominant IBS compared with patients with inflammatory bowel disease, celiac disease, and healthy controls [19].
A later study found that antibody positivity was highest in diarrhea-predominant IBS (IBS-D), followed by IBS with mixed bowel habits (IBS-M). Positivity was substantially lower in constipation-predominant IBS (IBS-C) and healthy controls. IBS-Smart is therefore intended for patients with IBS-D or IBS-M, not IBS-C [20][21].
Getting Clearer Answers About Persistent Gut Symptoms
Endometriosis can explain many digestive symptoms, but it is not always the only contributor. IBS and microbial overgrowth can occur alongside the condition, adding another layer to an already complicated symptom picture.
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Trio-Smart and IBS-Smart answer different questions. Trio-Smart measures microbial gas patterns associated with SIBO, IMO, and ISO. IBS-Smart measures immune markers associated with post-infectious IBS. Used alongside a patient’s history and clinical evaluation, these tests can help clarify what may be contributing to persistent digestive symptoms [18][21].
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If you have endometriosis and ongoing bloating, abdominal pain, constipation, or diarrhea, talk with your healthcare provider about whether breath testing or testing for post-infectious IBS may be appropriate. You can also take our short quiz or visit triosmartbreath.com and ibssmart.com to learn more.
Frequently Asked Questions
Can endometriosis cause digestive problems?
Yes. Bloating, nausea, constipation, diarrhea, abdominal pain, and painful bowel movements are commonly reported in people with endometriosis [1][3][4]. Some symptoms may result from lesions involving the bowel, but digestive complaints also occur without direct bowel involvement [3]. IBS and microbial overgrowth may also contribute, so tracking symptom patterns and discussing appropriate evaluation or testing with your healthcare provider can help clarify what may be causing them [8][15].
Can endometriosis cause bloating?
Yes. Bloating and visible abdominal distension are commonly reported in people with endometriosis, with severe episodes sometimes referred to as “endo belly.” Increased sensitivity to stretching of the intestinal wall may contribute [4]. Bloating can also result from a coexisting digestive condition such as IBS or SIBO, so persistent symptoms may warrant further evaluation [8][15].
Can endometriosis cause constipation?
Yes. Constipation is reported more frequently in women with endometriosis than in controls and can occur with or without direct bowel involvement [3][15]. IBS-C and methane-associated IMO are other possible contributors when constipation is persistent [5][13][14].
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Can endometriosis cause diarrhea?
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Yes. Diarrhea is among the gastrointestinal symptoms reported with endometriosis and may fluctuate with the menstrual cycle in some patients [4]. Chronic diarrhea is also associated with IBS-D and with elevated hydrogen or hydrogen sulfide patterns on breath testing [5][14].
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Is endo belly the same as SIBO?
No. Endo belly refers to pronounced abdominal bloating and distension associated with endometriosis [4]. SIBO is a condition involving excessive bacteria in the small intestine [12]. The two can produce similar symptoms, which is one reason further evaluation may be useful when bloating persists.
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Is there a connection between endometriosis and SIBO?
Yes, there is evidence of an association. A 2025 case-control study found SIBO or IMO in 91.9 percent of women with endometriosis compared with 83.1 percent of age-matched controls within a population undergoing breath testing [15].
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Are IBS and endometriosis related?
Yes. A large systematic review and meta-analysis found that people with endometriosis had approximately three times the odds of IBS compared with controls. Across the prevalence studies included in the analysis, approximately 23 percent of women with endometriosis had IBS [8].
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Can you have endometriosis, IBS, and SIBO at the same time?
Yes. Endometriosis, IBS, and SIBO are distinct conditions, and none excludes the presence of the others. Research documents a substantial overlap between endometriosis and IBS and has now also identified an association between endometriosis and SIBO/IMO in a breath-tested population [8][15].
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Can breath testing help if I have endometriosis?
Breath testing is not intended to diagnose or test for endometriosis, but it can provide objective information about microbial gas patterns associated with SIBO and IMO, as well as hydrogen sulfide patterns associated with ISO [13][14]. For someone with endometriosis and persistent gastrointestinal symptoms, it can help determine whether microbial overgrowth should be considered alongside the endometriosis itself [15].
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Should I get a SIBO breath test if I have endometriosis?
If you have endometriosis along with persistent or unexplained bloating, gas, constipation, diarrhea, or abdominal discomfort, breath testing is an option worth discussing with your healthcare provider. The 2025 endometriosis study specifically concluded that microbial overgrowth deserves greater attention in the care of patients with endometriosis [15].
References
[1] World Health Organization. Endometriosis. Fact sheet. Updated October 15, 2025. https://www.who.int/news-room/fact-sheets/detail/endometriosis
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[2] Abrão MS, Petraglia F, Falcone T, Keckstein J, Osuga Y, Chapron C. Deep endometriosis infiltrating the recto-sigmoid: critical factors to consider before management. Human Reproduction Update. 2015;21(3):329–339. doi:10.1093/humupd/dmv003.
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[5] National Institute of Diabetes and Digestive and Kidney Diseases. Symptoms & Causes of Irritable Bowel Syndrome. https://www.niddk.nih.gov/health-information/digestive-diseases/irritable-bowel-syndrome/symptoms-causes
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[16] Efremova I, Maslennikov R, Poluektova E, et al. Epidemiology of small intestinal bacterial overgrowth. World Journal of Gastroenterology. 2023;29(22):3400–3421. doi:10.3748/wjg.v29.i22.3400.
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[18] Trio-Smart. Breath Testing 101 for Better Gut Health. Trio-Smart/Gemelli Biotech. https://www.triosmartbreath.com/breathtesting
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[19] 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. doi:10.1371/journal.pone.0126438.
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[21] IBS-Smart. IBS-Smart Blood Test. Gemelli Biotech. https://www.ibssmart.com/ibs-smart-blood-test
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[22] Klem F, Wadhwa A, Prokop LJ, et al. Prevalence, risk factors, and outcomes of irritable bowel syndrome after infectious enteritis: a systematic review and meta-analysis. Gastroenterology. 2017;152(5):1042–1054.e1. doi:10.1053/j.gastro.2016.12.039.
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[23] Ek M, Roth B, Ekström P, et al. Gastrointestinal symptoms among endometriosis patients: a case-cohort study. BMC Women’s Health. 2015;15:59. doi:10.1186/s12905-015-0213-2.