You're tired. You are tired of feeling bloated, tired of not knowing what's causing that constant discomfort, and tired of trying new diets only to see little or no improvement. Sound familiar?
If you've been stuck in this cycle of gastrointestinal turmoil, you've likely come across two terms: SIBO (aka Small Intestinal Bacterial Overgrowth) and IBS (Irritable Bowel Syndrome). They're often confused with one another, and it's easy to see why: both conditions involve gut issues, and the symptoms can feel like a constant guessing game.
So, how can you tell if it's SIBO or IBS that's wreaking havoc in your gut?
In this blog post, we'll dive into the differences and similarities between these two conditions—SIBO vs IBS—so you can better understand your symptoms, seek the right diagnosis, and find the treatment that finally brings relief. We'll also look into why IBS often gets criticized as a "catch-all" label and how you can advocate for a better understanding of your gut health.
What is SIBO?
Small Intestinal Bacterial Overgrowth (SIBO) is a condition in which an excessive amount or abnormal type of bacteria are present in the small intestine, where their numbers should be relatively low compared to the large intestine.
See, your small intestine isn’t meant to host a large number of bacteria—that’s more the colon’s job. Your colon is the place where you can find the gut microbiome (a community of trillions of microorganisms).
In SIBO, bacteria that should stay in the large intestine migrate up into the small intestine, causing interference with normal digestion and absorption of food by fermenting carbohydrates and fibers and creating gases (methane, hydrogen, hydrogen sulfide).
How does it feel to live with SIBO?
Imagine having too many guests at a dinner party: there’s no room to breathe, everyone’s stepping on each other’s toes, and nothing works as it should.
This overcrowding leads to the fermentation of your food in the wrong part of the gut, resulting in:
- Chronic bloating that tends to get worse as the day goes by,
- Changed bowel movements involving constipation and/or diarrhea or alternating bowel movements,
- Abdominal pain,
- Nausea,
- Burping,
- Fatigue,
- Brain fog,
- Muscle or joint pain,
- Skin issues (acne, rosacea, eczema)
- Unexplained weight loss or weight gain,
But it can also impact other areas of the body. (1)
Interestingly, SIBO often follows another gut-altering event, like food poisoning or surgery, which disrupts the balance of your gut bacteria. Fibers and probiotics—usually gut heroes—can worsen the condition by providing extra fuel for the overgrown bacteria to feast on.
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What is IBS?
Did you know that more than 60 million people have Irritable Bowel Syndrome (IBS), and 70% of them are women? (2)
IBS is a bit more elusive. It’s a functional GI condition defined by a collection of chronic gut symptoms, but there’s no clear-cut cause, making it somewhat of a medical mystery.
IBS is commonly diagnosed based on a specific set of criteria known as the Rome IV Criteria, which include recurrent symptoms like abdominal pain, bloating, constipation, diarrhea, or a combination of both, for at least three months. (3)
How does it feel to have IBS?
Imagine being in a car with a faulty GPS—some days, you might end up at your destination, but other days, you’re stuck in traffic or stranded on a dead-end street. IBS feels like that: the gut’s regular motility goes haywire, leading to unpredictable and uncomfortable outcomes.
The brain-gut connection plays a big role in IBS, with stress and heightened sensory responses making symptoms worse. (4)
IBS is categorized by the following categories:
- IBS with predominant constipation (IBS-C)
- IBS with predominant diarrhea (IBS-D)
- IBS with mixed bowel habits (IBS-M)
SIBO vs IBS: similarities and differences
At first glance, SIBO and IBS seem similar —both share many of the same symptoms, which can make it difficult to tell them apart.
However, a closer look reveals important distinctions in the underlying mechanisms, as well as how the symptoms manifest.
Symptom overlap
When comparing SIBO vs IBS, the overlap in symptoms is undeniable.
Both conditions can cause:
- Bloating
- Abdominal pain, cramping
- Constipation and/or diarrhea
- Fatigue
- Food intolerances
However, the way these symptoms manifest differs between the two conditions.
For example, in SIBO, there are a few tell signs, like bloating, which tends to worsen as the day progresses, and meals rich in fiber or taking probiotics can exacerbate the discomfort.
In contrast, bloating in IBS can happen at any time, and fiber is often recommended as a helpful addition.
Main differences
Causes:
While multiple factors influence both SIBO and IBS, SIBO is specifically characterized by bacterial overgrowth in the small intestine, where these microbes shouldn't be present in large numbers. This overgrowth leads to the fermentation of undigested food, which causes gas, bloating, and discomfort.
However, the underlying reasons for SIBO can also be many things, from impaired gut motility through infections to structural problems.
IBS, on the other hand, is more ambiguous. In contrast, IBS is more of a functional gastrointestinal disorder—it involves issues with how the gut functions rather than an actual bacterial overgrowth in a specific area.
IBS can be driven by many causes, such as gut-brain axis dysfunction, hypersensitivity of the gut, altered motility, and even imbalances in the gut microbiome (known as dysbiosis), without necessarily involving bacterial overgrowth in the small intestine.
However, it is important to mention that studies show up to 80% of IBS cases may, in fact, be related to SIBO. (5)
This suggests that, in many cases, SIBO might be an underlying cause of IBS symptoms. However, it's important to remember that not all IBS cases are caused by SIBO.
Diagnosis:
SIBO is commonly diagnosed using a lactulose or glucose breath test (link to breath test blog), which measures the gases (hydrogen, methane, and, in some cases, hydrogen sulfide) produced by bacteria or archaea in your small intestine. A positive test result confirms not just SIBO but it helps determine the level of overgrowth and the type of SIBO.
IBS, on the other hand, is often diagnosed by exclusion after ruling out other conditions, which can be frustrating for many patients. The Rome IV Criteria help guide the diagnosis, and patients are typically diagnosed based on symptoms that have been present for at least three months. IBS may also require stool tests or colonoscopies to rule out conditions like inflammatory bowel disease or celiac disease.
However, there is also a diagnostic test for certain people with IBS. The IBS-Smart test is available on the market to diagnose IBS with predominant diarrhea (IBS-D) and mixed symptoms (IBS-M).
This blood testing looks for anti-CdtB and anti-vinculin antibodies, the markers of a food poisoning event. These antibodies can attack the gut's nerves and impair the gut's cleaning wave. (6)
Nutrient absorption:
SIBO can interfere with nutrient absorption, leading to deficiencies in vitamins and minerals (especially deficiency in fat-soluble vitamins such as Vitamin A, D, and E, and also negatively impacting vitamin B12 and iron levels) (7).
In contrast, nutrient absorption in IBS is generally normal unless it's combined with another condition like celiac disease.
Probiotic response:
Another major difference is how each condition responds to probiotics and dietary fibers. Probiotics, often touted as a gut health remedy, may worsen symptoms of SIBO. This is because the overgrown bacteria feed on these probiotics, leading to more gas and bloating.
In contrast, many people with IBS can benefit from the right probiotics or fiber supplements.
Let’s look at the treatment options: SIBO vs IBS
The treatment plans for SIBO vs IBS vary significantly, largely because the causes of each condition are so different.
Treating SIBO
Treatment for SIBO primarily focuses on reducing bacterial overgrowth and addressing underlying causes like gut motility issues.
The main strategies include:
- Antibiotics or antimicrobials: Common treatments include rifaximin, often combined with another antibiotic (in case of methane and hydrogen sulfide gas), or herbal antimicrobials that target bacterial overgrowth in the small intestine. (1)
- Dietary changes: Many people with SIBO find relief through a certain SIBO diet, such as the low-FODMAP diet, SIBO Bi-phasic, or the low fermentation diet, which restrict the types of carbohydrates that can fuel bacterial overgrowth.
- Prokinetics: These are medications or supplements that help improve gut motility and prevent bacteria from lingering in the small intestine.
- Post-treatment care: Relapse is fairly common with SIBO, unfortunately. Studies show that about 45% of patients experience recurrence after antibiotic treatment (8), so long-term care might involve dietary and lifestyle changes and addressing the root causes.
Read the complete guide on how to heal your gut from SIBO with a natural approach.
Treating IBS
Treatment for IBS is often more varied and personalized since its exact cause isn’t clear-cut.
Options include:
- Dietary adjustments: The low-FODMAP diet is also commonly recommended for IBS, showing great symptom relief of bloating, gas, and pain (9), while some patients find relief by eliminating specific trigger foods like dairy or gluten.
- Medications: Depending on whether you have IBS with constipation (IBS-C) or IBS with diarrhea (IBS-D), doctors may prescribe medications like laxatives, anti-diarrheal, or antispasmodics to manage symptoms.
- Psychological approaches: Since stress and anxiety can exacerbate IBS, therapies like cognitive behavioral therapy (CBT) or gut-directed hypnotherapy (like Nerva) have shown promise in helping manage symptoms.
- Probiotics: While probiotics can sometimes aggravate SIBO, they’re often beneficial for IBS patients in supporting healthy gut bacteria balance.
Why is IBS criticized as a label?
One of the biggest frustrations with an IBS diagnosis is that it can feel like a "wastebasket diagnosis"—a label given when doctors can't figure out exactly what's wrong.
In fact, some researchers believe that IBS is often misdiagnosed when in reality, patients may have an underlying condition like SIBO or even mild inflammatory bowel disease.
This misdiagnosis can lead to a frustrating cycle of trying different diets, medications, and supplements without ever addressing the root cause.
Conclusion on SIBO vs IBS
The road to understanding your gut health is rarely straightforward.
When it comes to SIBO vs IBS, knowing the key differences between these two conditions is essential in navigating your symptoms and finding a treatment plan that works.
While SIBO involves an overgrowth of bacteria that can be tested for and treated directly, IBS is a broader, more complex condition that often requires a multi-faceted approach, including diet, stress management, lifestyle changes, and sometimes medication.
If you’ve been diagnosed with IBS but feel like your treatment isn’t working, consider asking your doctor about SIBO testing.
Understanding the true source of your symptoms is the first step to reclaiming your gut health—and your life.
This post is only for informational purposes and is not meant to diagnose, treat, or cure any disease. I recommend always consulting your healthcare practitioner before trying any treatment or dietary changes.
- Achufusi, T. G. O., Sharma, A., Zamora, E. A., & Manocha, D. (2020). Small Intestinal Bacterial Overgrowth: Comprehensive Review of Diagnosis, Prevention, and Treatment Methods. Cureus, 12(6), e8860. https://doi.org/10.7759/cureus.8860
- Saito, Y. A., Schoenfeld, P., & Locke, G. R., 3rd (2002). The epidemiology of irritable bowel syndrome in North America: a systematic review. The American journal of gastroenterology, 97(8), 1910–1915. https://doi.org/10.1111/j.1572-0241.2002.05913.x
- Lacy, B. E., & Patel, N. K. (2017). Rome Criteria and a Diagnostic Approach to Irritable Bowel Syndrome. Journal of clinical medicine, 6(11), 99. https://doi.org/10.3390/jcm6110099
- Ancona, A., Petito, C., Iavarone, I., Petito, V., Galasso, L., Leonetti, A., Turchini, L., Belella, D., Ferrarrese, D., Addolorato, G., Armuzzi, A., Gasbarrini, A., & Scaldaferri, F. (2021). The gut-brain axis in irritable bowel syndrome and inflammatory bowel disease. Digestive and liver disease : official journal of the Italian Society of Gastroenterology and the Italian Association for the Study of the Liver, 53(3), 298–305. https://doi.org/10.1016/j.dld.2020.11.026
- Ghoshal, U. C., & Srivastava, D. (2014). Irritable bowel syndrome and small intestinal bacterial overgrowth: meaningful association or unnecessary hype. World journal of gastroenterology, 20(10), 2482–2491. https://doi.org/10.3748/wjg.v20.i10.2482
- Rezaie, A., Park, S. C., Morales, W., Marsh, E., Lembo, A., Kim, J. H., Weitsman, S., Chua, K. S., Barlow, G. M., & Pimentel, M. (2017). Assessment of Anti-vinculin and Anti-cytolethal Distending Toxin B Antibodies in Subtypes of Irritable Bowel Syndrome. Digestive diseases and sciences, 62(6), 1480–1485. https://doi.org/10.1007/s10620-017-4585-z
- Wielgosz-Grochowska JP, Domanski N, Drywień ME. Identification of SIBO Subtypes along with Nutritional Status and Diet as Key Elements of SIBO Therapy. International Journal of Molecular Sciences. 2024; 25(13):7341. https://doi.org/10.3390/ijms25137341
- Sorathia SJ, Chippa V, Rivas JM. Small Intestinal Bacterial Overgrowth. [Updated 2023 Apr 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK546634/
- Nanayakkara, W. S., Skidmore, P. M., O'Brien, L., Wilkinson, T. J., & Gearry, R. B. (2016). Efficacy of the low FODMAP diet for treating irritable bowel syndrome: the evidence to date. Clinical and experimental gastroenterology, 9, 131–142. https://doi.org/10.2147/CEG.S86798
Alexandra is a Functional Medicine Certified Health Coach & Holistic Nutritionist specializing in IBS, SIBO, and Gut Health. She helps her clients identify the root causes of their chronic gut issues with functional testing, supporting their bodies holistically and implementing the necessary lifestyle changes long-term to regain control of their bodies and enjoy food freedom. Book your FREE SIBO Assessment call now >>>