Understanding the Overlap Between IBS, SIBO, and Reflux

Have you been struggling with symptoms of IBS and GERD or acid reflux?

Are you confused on what to do and what the cause of your symptoms are?

This guide will walk you through some of the causes of GERD and if there is a link with IBS.

We will also explore some clinical case studies in alleviating symptoms of GERD and the link with IBS and Small Intestinal Bacterial Overgrowth.

With a proper understanding of IBS and GERD you may be able to relieve symtoms and decide on best treatment options.

What is IBS?

IBS is a functional gastrointestinal disorder characterized by symptoms such as abdominal pain, bloating, gas, and altered bowel habits (diarrhea, constipation, or both).

The exact cause of IBS remains unclear. According to the NHS, IBS is thought to result from a combination of factors such as abnormal gut motility (food moving too quickly or too slowly through the digestive tract), a history of gastroenteritis, increased gut sensitivity, stress, and a family history of the condition.

What is GERD and Acid Reflux?

GERD, on the other hand, occurs when stomach acid frequently flows back into the esophagus, leading to symptoms like heartburn, regurgitation, and chest discomfort. This backflow, or acid reflux, can irritate the esophageal lining and is often due to a weakened lower esophageal sphincter (LES).

What are the traditional causes of GERD?

According to clinical guidelines, GERD is considered a chronic condition and can lead to complications like esophagitis (inflammation of the esophagus) or Barrett’s esophagus if left untreated.

The traditional root causes of GERD are said to include:

• a weak lower esophageal sphincter- LES
  The LES is a ring of muscle located at the bottom of the esophagus. Its job is to open briefly to allow food into the stomach, and then close tightly to keep stomach contents from coming back up. When this muscle becomes weak or relaxes inappropriately (known as transient LES relaxations), acid and partially digested food can reflux into the esophagus, causing heartburn and irritation. Factors that can weaken the LES include stress, obesity, pregnancy, hiatal hernia, and certain medications.
  
  
  
• poor stomach motility
  
  Normally, your stomach should break down food and move it into the small intestine at a steady pace. But in some people, this process becomes sluggish—a condition known as delayed gastric emptying. When this happens, food and acid sit in the stomach for too long, increasing pressure and the chance of reflux.
  
  
• Certain foods and drinks can either relax the LES or increase acid production, making reflux symptoms worse.
  
  Common triggers include:
  • Caffeine
  • Alcohol
  • Chocolate
  • Spicy or fatty foods
  • Tomatoes and citrus fruits
  • Carbonated drinks
  • Overeating or eating late at night can also increase pressure on the stomach, leading to reflux.
    
    
    
• Imbalances in Stomach Acid
  
  While GERD is often treated with acid-suppressing medications, such as omeprazole not all reflux is caused by too much acid. In some cases, low stomach acid (hypochlorhydria) can actually contribute to reflux.
  
  Without enough acid to properly digest food, the stomach contents may linger too long and ferment, producing gas and pressure that pushes contents upward.
  
  
  
  
  
  

Does IBS Cause GERD?

Current evidence does not conclusively show that IBS causes GERD.

However IBS and GERD frequently occur together

A review of research found that people with IBS are 4 times more likely to develop GERD than people without IBS (Frontiers in Genetics, 2024).

So, what’s going on? Researchers believe that IBS and GERD share a few common triggers:

• An overly sensitive gut – visceral Hypersensitivity: Both conditions may involve an increased sensitivity of the gastrointestinal tract, leading to heightened perception of pain and discomfort.
  
  
• Abnormal movement of food through the digestive tract- Gastrointestinal Motility Disorders: Abnormal movement of the digestive tract muscles can contribute to symptoms in both IBS and GERD.
  
  
• Stress and anxiety and depression are common in individuals with IBS and GERD, potentially exacerbating symptoms through the gut-brain axis.
  
  
• Certain foods (like caffeine, alcohol, and high-fat meals) can trigger symptoms in both conditions.
  
  
  

They don’t directly cause each other, but they can show up as part of the same gut imbalance.

Does SIBO cause GERD and acid reflux?

If you have been looking for answers to why you have developed GERD, Sibo may be the hidden driver reflux and GERD symptoms.

What is SIBO?

SIBO, or Small Intestinal Bacterial Overgrowth, is a condition where bacteria that normally belong in the large intestine start multiplying in the small intestine, where they don’t belong. This can interfere with normal digestion and nutrient absorption, and lead to a wide range of symptoms. Many studies suggest that 60–80% of people with IBS may actually have SIBO.

Common signs of SIBO include:

Bloating (especially after eating)
Cramping and abdominal pain
Diarrhea, constipation, or a mix of both
Gas, belching, or nausea
Food intolerances (especially to fermentable carbs like garlic, onion, and legumes)

SIBO is often triggered by anything that slows gut motility or disrupts the gut microbiome—such as food poisoning, long-term use of proton pump inhibitors (PPIs), low stomach acid, stress, or previous surgeries.

My Clinical Observation: SIBO and GERD in Practice

I have increasingly observed a strong link between SIBO and GERD in the patients I see.

In addition to chronic acid reflux, heartburn, and regurgitation symptoms many patients have also shown signs of SIBO.

These patients often report:

• Persistent bloating and abdominal distension
• Excessive belching or gas
• Worsening of reflux after meals, even on conventional GERD treatments

What they have told me is that conventional acid-suppressing medications alone do not resolve these symptoms.

Often they have tried Omeprazole or Lansoprazole to no avail.

My Experience in Practice

I often run simple breath tests to check for Small Intestinal Bacterial Overgrowth (SIBO) or Intestinal Methanogen Overgrowth (IMO). In many cases, the results come back positive.

For these clients, I usually recommend a low FODMAP diet combined with targeted herbal antimicrobials. In some cases, a short course of antibiotics like rifaximin may be needed.

The results? Many clients notice a big improvement in their symptoms, including:

• Less bloating
• Fewer reflux episodes
• Feeling lighter and more comfortable after eating

Because of this, I now routinely check for SIBO in anyone with stubborn reflux, especially when it comes with bloating, excess gas, and poor response to standard acid-reducing medications.

Why does SIBO Cause GERD?

Although GERD is commonly linked to excess stomach acid, research increasingly shows that SIBO may play a major role in driving reflux symptoms—especially when bloating, belching, or upper abdominal pressure are involved.

Here’s why:

Fermentation causes gas: When you eat carbohydrates like bread, pasta, cakes, the excess bacteria in the small intestine ferment these carbohydrates, creating gas.

This gas increases pressure in the abdomen, pushing stomach contents upwards and triggering acid reflux.

LES Dysfunction: Pressure from gas can also cause the lower esophageal sphincter (LES) to relax at the wrong time, allowing acid to escape.


SIBO slows down digestion. SIBO is linked to slow gastric emptying, which can cause food and acid to sit in the stomach longer—raising the risk of reflux.


Inflammation and Sensitivity: SIBO may cause gut inflammation and increase sensitivity to even mild reflux episodes.

In short, SIBO can create the perfect environment for GERD to develop or worsen—particularly in people who don’t respond well to acid blockers.

How can I test for SIBO?

Small intestinal bacterial overgrowth is diagnosed using a Hydrogen and Methane breath test.

Can Treating SIBO Improve GERD?

If you’ve tried reflux diets, cut out trigger foods, and still find yourself relying on antacids or PPIs, it might be time to consider what’s happening deeper in the gut.

Small Intestinal Bacterial Overgrowth (SIBO) is increasingly recognised as a hidden contributor to persistent reflux—especially in people who also experience bloating, belching, and upper abdominal discomfort.

A 2025 study published in Diseases of the Esophagus explored this connection by evaluating patients with laryngopharyngeal reflux (LPR)—a form of silent reflux—and confirmed SIBO or intestinal methanogen overgrowth (IMO). After undergoing treatment with targeted antimicrobials and motility support, the results were striking:

• Reflux symptoms significantly decreased
• 95% of patients reduced or discontinued PPI use
• None required surgical intervention
• Quality of life scores improved across the board

These findings underscore an important message: when reflux is driven by bacterial overgrowth and impaired motility, simply reducing stomach acid may not be enough. In these cases, addressing the root cause—by restoring microbial balance and supporting gut function—can offer more lasting, meaningful relief.

If you suffer from reflux alongside symptoms like gas, bloating, or unpredictable digestion, testing for SIBO may be a smart next step in uncovering what’s really behind your symptoms.

Research Linking SIBO and GERD

1. Association Between SIBO and GERD

A 2025 study published in the Journal of Inflammation Research found a significant association between SIBO and GERD. Among 394 patients studied, those with positive methane breath tests (indicative of IMO) had a higher prevalence of GERD. The study concluded that GERD is an independent risk factor for SIBO, and patients with both conditions exhibited distinct gut microbiota profiles, notably an abundance of Bacteroides uniformis. PubMed

2. SIBO’s Role in Refractory GERD Symptoms

Research has indicated that SIBO may contribute to persistent GERD symptoms, especially in patients unresponsive to proton pump inhibitors (PPIs). A study found that 60.6% of patients referred for antireflux surgery had intestinal dysbiosis, with 39.4% testing positive for SIBO. These patients were more likely to report bloating and belching, suggesting that SIBO may exacerbate GERD symptoms. PubMed

3. Impact of SIBO Treatment on GERD Symptoms

A retrospective cohort study conducted between 2018 and 2023 evaluated the effects of treating SIBO and intestinal methanogen overgrowth (IMO) on laryngopharyngeal reflux (LPR) symptoms. The study reported significant improvements in GERD-related quality of life scores and a reduction in reflux symptom index scores post-treatment. Notably, 95% of patients reduced or discontinued PPI use, and none required surgical interventions. PubMed

4. Mechanisms Linking SIBO to GERD

The fermentation of carbohydrates by excess bacteria in SIBO produces gas, leading to increased intra-abdominal pressure. This pressure can cause transient relaxations of the lower esophageal sphincter, facilitating acid reflux. Additionally, the gas may lead to belching, which can aerosolize gastric contents into the esophagus and throat, contributing to LPR symptoms. RefluxUK

Can you test for IBS, SIBO and GERD?

There’s no single test that diagnoses IBS, GERD, and SIBO together. Instead, diagnosis is made by combining clinical symptoms, a detailed health history, and targeted testing to rule out other causes.

Here’s how each is typically assessed:

• IBS is diagnosed using the Rome IV criteria, based on symptoms like abdominal pain, bloating, and changes in bowel movements for at least 3 months.
  
• GERD is usually diagnosed based on symptoms (like heartburn and regurgitation) and response to acid-suppressing medications. In more complex cases, endoscopy or 24-hour pH monitoring may be used.
  
• SIBO is diagnosed using a lactulose or glucose breath test, which measures gas production (hydrogen and methane) after consuming a sugar solution.
  

Additional tests such as stool analysis, food intolerance testing can provide further insights, especially if you have severe digestive symptoms.

Treatment Strategies for IBS, GERD and SIBO

If you are dealing with both IBS and GERD—and especially if SIBO is involved—a multi-targeted approach works best. Here’s how functional medicine typically addresses the overlap:

1. Diet & Lifestyle

• Low-FODMAP diet to reduce bacterial fermentation and bloating.
• Avoid known reflux triggers like caffeine, alcohol, spicy and fatty foods, chocolate, and late-night meals.
• Smaller, more frequent meals support better digestion and reduce pressure on the stomach.
• Elevate the head of the bed if nighttime reflux is an issue.
  
  

2. Gut Support & Supplementation

• Antimicrobials (like rifaximin or herbal alternatives) for confirmed SIBO.
• Prokinetics (natural such as ginger or prescription) to improve gut motility and prevent relapse.
• Digestive enzymes to support breakdown of food and ease pressure in the upper GI tract.
• Alginate therapy (e.g., Gaviscon Advance) to create a physical barrier against reflux.
• Use PPIs cautiously—short-term only, and always with a long-term gut health strategy in place.
  
  

3. Gut-Brain & Nervous System Support

• Stress management is critical. Chronic stress can affect both gut motility and reflux.
• Gut-directed therapies such as CBT, gut-focused hypnotherapy, or vagus nerve support (like breathing exercises or cold exposure) can dramatically improve symptoms.

Summary and Key Takeaways:

• Does IBS cause GERD? No, IBS does not directly cause GERD, but they often occur together and share common triggers like gut sensitivity, poor motility, and stress.
• IBS and GERD are strongly linked. Studies show up to 79% of people with IBS also experience GERD symptoms.
• SIBO may be a hidden factor. Many people with IBS and reflux also test positive for SIBO (or IMO), which can contribute to both bloating and acid reflux.
• Treating SIBO often helps. Addressing bacterial overgrowth with diet, targeted supplements, or antibiotics has helped many of my clients reduce both IBS and reflux symptoms.
• You can feel better. Testing and personalised support can help get to the root cause and bring long-term relief.

If you’re struggling with ongoing IBS and reflux symptoms, talk to a functional medicine practitioner about whether SIBO testing and treatment might help you too.

A Functional Medicine Perspective

From a functional medicine standpoint, GERD, IBS, and SIBO aren’t just isolated conditions—they’re often symptoms of a deeper imbalance within the digestive system. Rather than focusing solely on symptom suppression (like acid blockers or laxatives), the goal is to identify and address the root causes of dysfunction.

This may involve:

• Testing for sibo, microbial imbalances, gut inflammation, or food sensitivities
• Supporting the gut-brain axis, including vagus nerve tone and stress resilience
• Restoring gut motility with lifestyle tools, prokinetics, and nervous system regulation
• Rebalancing the microbiome through targeted antimicrobials, diet, and probiotics

Working with a healthcare provider can help tailor a  tests, dietary advice and a tailored supplement regimen to your specific needs for optimal results.

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References

1. Chey WD, Kurlander J, Eswaran S. Irritable bowel syndrome: a clinical review. JAMA. 2015;313(9):949-958. doi:10.1001/jama.2015.0954
2. El-Serag HB, Olden K, Bjorkman D. Overlap of IBS and GERD: diagnostic and therapeutic implications. Gastroenterology. 2001;121(4):1108-1117.
3. Quigley EM, Fried M, Gwee KA, et al. World Gastroenterology Organisation global guidelines IBS: a global perspective. J Clin Gastroenterol. 2016;50(9):704-713.
4. Ghoshal UC, Ghoshal U, Das K, et al. Small intestinal bacterial overgrowth and IBS: a prospective study in a tertiary care center in India. Neurogastroenterol Motil. 2012;24(11):1042-e547. doi:10.1111/j.1365-2982.2012.01966.x
5. Rezaie A, Buresi M, Lembo A, et al. Hydrogen and methane-based breath testing in GI disorders: the North American consensus. Am J Gastroenterol. 2017;112(5):775-784. doi:10.1038/ajg.2017.46
6. Pimentel M, Lembo A, Chey WD, et al. Rifaximin therapy for patients with IBS without constipation. N Engl J Med. 2011;364(1):22-32. doi:10.1056/NEJMoa1004409
7. Pimentel M, Mathur R, Chang C. Gas and the microbiome. Curr Gastroenterol Rep. 2020;22(2):8. doi:10.1007/s11894-020-0746-x
8. Frontiers in Genetics. Mendelian randomization analysis of the causal relationship between IBS and GERD. 2024.
9. Rezaie A, Pimentel M. The role of methane-producing organisms (methanogens) in digestive diseases. Nat Rev Gastroenterol Hepatol. 2016;13(12):692-702. doi:10.1038/nrgastro.2016.155

Author – Victoria Tyler BSc Hons MBANT

Victoria Tyler owns and runs two busy clinics : Nutrition and Vitality and the IBS and Gut Disorder Clinic.

Nutrition and Vitality, along with the IBS and Gut Disorder Clinic, were founded with the goal of helping patients alleviate IBS symptoms by uncovering and addressing the root causes of their digestive issues.

As a Registered Nutritional Therapist, Victoria holds a BSc (Hons) in Nutritional Therapy and has trained with the Institute of Functional Medicine. She is also accredited by BANT and CNHC.

Before transitioning into health, Victoria earned a degree in Economics and an MBA, working with corporations including Canon and Vodafone. However, her own health challenges led her to pursue a career in Nutritional Therapy.

With a passion for learning, Victoria is committed to staying at the forefront of Functional Medicine. She helps patients manage IBS and other digestive disorders, including SIBO, Candida, and IBD, by identifying and addressing their root causes.

Victoria strongly believes that every symptom has an underlying cause, and there is always a solution to every health condition. To learn more, or to see patient reviews, visit Victoria’s profile on Google.

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