What is SIBO? Symptoms, Causes, Testing and Treatment

The bacteria in your colon and gastrointestinal tract play a vital role in your health. Studies have shown the importance of microbiome within digestion, immune system function, nutrient absorption, metabolism, mental health and more. However, overgrowth of specific types of bacteria in certain areas of your body can lead to dysfunction and symptoms. 

SIBO, or small intestinal bacterial overgrowth is excessive amounts of bacteria in the small intestine, causing gastrointestinal symptoms. It is normal and healthy to have bacteria in your small intestine, but too many bacteria and the wrong kind of bacteria can upset your digestive system. These bacteria in your small intestine ferment carbohydrates, producing gas that can lead to bloating, distension and gastrointestinal symptoms. 

Causes of SIBO

SIBO is multifactorial and is the result of an imbalance of the chemical and mechanical functions of the small intestine. The motility of the small intestine ensures bacteria continues to move down the gastrointestinal tract. Chemical functions of the small intestine including gastric acid secretion, digestive enzyme activity and bile production limit bacterial colonization in the small intestine. Conditions that disrupt normal small intestinal motility, create anatomic abnormalities, reduce gastric acid secretion, or impaired immune defenses may result in SIBO. 

Impaired motility of the small intestine may be a result of neuropathy, medications such as opioids, and anticholinergics, autoimmune conditions, or stress. Chronic stress activates the sympathetic nervous system, which may disrupt gastrointestinal motility, leading to decreased bacterial clearance from the small intestine. 

SIBO Symptoms

SIBO can present with a range of gastrointestinal and systemic symptoms. Common symptoms include:

Bloating and abdominal distension

Excessive gas (hydrogen- or methane-dominant, depending on the bacteria type)

Diarrhea or constipation (methane-dominant SIBO is more associated with constipation)

Abdominal pain or cramping

Nausea

Fatigue and brain fog

Nutrient deficiencies (e.g., B12, iron, fat-soluble vitamins) due to malabsorptionList Item

Causes and Risk Factors 

SIBO is multifactorial—it often arises from disrupted motility or protective mechanisms in the gut.

Impaired intestinal motility: Disorders like irritable bowel syndrome (IBS), diabetes-induced neuropathy, or chronic stress can slow the migrating motor complex, allowing bacteria to stagnate in the small intestine.

Medications: Opioids, proton pump inhibitors (PPIs), and anticholinergics can impair gastric acid secretion or motility.

Anatomical abnormalities: Scar tissue, diverticula, or surgical changes (such as in gastric bypass) may create pockets for bacteria to grow.

Immune dysfunction: Impaired immune defenses or autoimmune conditions may increase susceptibility.

Low stomach acid: Acid normally helps sterilize incoming food. Reduced secretion (from medications, aging, or chronic illness) creates a favorable environment for bacterial growth.List Item

Testing for SIBO

The hydrogen and methane breath test is the most commonly used diagnostic tool. Patients ingest a sugar solution (glucose or lactulose), and breath samples are measured at intervals.

Hydrogen rise: Suggests hydrogen-producing bacteria.

Methane rise: Suggests methanogen overgrowth, more linked to constipation.

Treatment Options

Antibiotic Therapy

Rifaximin is the most studied antibiotic for hydrogen-dominant SIBO and is recommended by the American Gastroenterological Association (Quigly et al., 2020).

Studies show symptom improvement rates range from 40–70%, though recurrence is common.

Dietary Interventions

Low-FODMAP diet: Restricts fermentable carbohydrates, reducing gas and bloating.

Specific Carbohydrate Diet (SCD): Limits complex carbs that can feed bacteria.

These diets are not curative but may reduce symptoms and support gut healing.

Probiotics

Evidence is mixed, but some studies suggest specific strains (e.g., Lactobacillus plantarum, Saccharomyces boulardii) may help reduce symptoms and recurrence (Zhong et al., 2017).

Probiotics are best considered on a case-by-case basis, ideally under provider guidance.

Nutritional Support

Supplementing B12, iron, and fat-soluble vitamins if deficiencies are identified.

Monitoring for weight loss or malnutrition is key in long-standing SIBO cases

Prevention and Recurrence Management

Since relapse rates are high (up to 45% within 9 months), prevention is an important part of care (Pimental, 2020). Strategies include:

Addressing root causes: Correct motility issues, review medications, and manage stress.

Regular monitoring: Retesting if symptoms return, especially in patients with chronic conditions.

SIBO is a complex condition that can significantly impact digestive health and overall well-being. While testing and treatment options are available, recurrence is common, making long-term prevention and management essential. A comprehensive approach—addressing underlying causes, optimizing nutrition, and supporting gut function—offers the best chance at lasting relief. If you suspect you may have SIBO, working with a knowledgeable healthcare provider is key to developing a personalized treatment and prevention plan.

References

Pimentel, M., Saad, R. J., Rao, S. S. C., & Mayer, E. A. (2020). AGA clinical practice update on small intestinal bacterial overgrowth. Gastroenterology, 159(5), 1526–1532.

Quigley, E. M. M., Murray, J. A., & Pimentel, M. (2020). AGA Clinical Practice Update on Small Intestinal Bacterial Overgrowth: Expert review. Gastroenterology, 159(4), 1526–1532. https://doi.org/10.1053/j.gastro.2020.07.025

Zhong, C., Qu, C., Wang, B., & Liang, S. (2017). Effects of probiotics in patients with small intestinal bacterial overgrowth: A systematic review and meta-analysis. Journal of Clinical Gastroenterology, 51(4), 300–311.

About the Author:

Rachel Grosklags is a registered nurse and integrative health specialist at Lutanen Health. She leads digital health and coaching programs that connect advanced care with wearable technology and lifestyle medicine. Rachel is board certified in nursing, trained in nutrition and mindful movement, and currently pursuing her Family Nurse Practitioner degree. Her approach blends science, empathy, and innovation to help patients achieve lasting wellness.

Rachel Grosklags RN

October 16, 2025