Overview

Small intestinal bacterial overgrowth (SIBO) is a condition in which excess bacteria accumulate in the small intestine, where they can interfere with normal digestion and nutrient absorption. This imbalance often leads to symptoms such as bloating, gas, abdominal discomfort, and changes in bowel habits. Because symptoms overlap with other digestive disorders, proper evaluation is important to confirm the diagnosis and guide targeted, individualized treatment.

What Is SIBO?

Small intestinal bacterial overgrowth (SIBO) is a digestive condition in which an excessive number of bacteria are present in the small intestine. These bacteria often normally found in the colon can interfere with digestion and nutrient absorption. SIBO commonly causes symptoms such as bloating, gas, abdominal discomfort, diarrhea, and changes in bowel habits. In some cases, it may also contribute to inflammation of the small intestine.

SIBO develops when the digestive system’s normal protective mechanisms are disrupted. These include adequate stomach acid, coordinated intestinal movement, healthy digestive anatomy, and proper separation between the small and large intestines. Antibiotic use can also contribute, as it may alter the normal balance of gut bacteria and, in some cases, allow certain bacteria to overgrow. When one or more of these defenses is affected, bacteria may accumulate in the small intestine and lead to digestive symptoms.

What Are The Symptoms Of SIBO?

Diarrhea, bloating, abdominal pain, gas, and distension are the most common symptoms of SIBO. However, no single symptom can be specifically attributed to SIBO, as symptoms often overlap with irritable bowel syndrome (IBS), functional diarrhea, functional dyspepsia, and functional bloating. Additional symptoms may include nausea, flatulence, abdominal cramping, and constipation. Some patients report fatigue and poor concentration. Early satiety, postprandial discomfort, and belching have also been described in association with SIBO.

Constipation is often linked to a specific pattern seen on breath testing called methane production. Methane is made by certain microorganisms in the gut that are different from typical bacteria. When methane levels are higher, the intestines tend to move more slowly, which can lead to constipation. People with this methane pattern are more likely to experience constipation than those who do not produce methane.

Symptom presentation varies widely depending on underlying risk factors and the extent of bacterial overgrowth. Because SIBO symptoms are non-specific and frequently masquerade as other diagnoses, proper evaluation and testing are essential for accurate diagnosis and targeted treatment.

What Are The Risk Factors For SIBO?

Certain conditions and factors can increase the risk of developing small intestinal bacterial overgrowth (SIBO) by disrupting normal digestion or gut movement. These may include:

• Prior or frequent antibiotic use, which can alter the normal balance of gut bacteria
• Reduced stomach acid, including from long-term use of acid-suppressing medications
• Slowed intestinal movement, which can occur with conditions such as diabetes, celiac disease, or certain connective tissue or nerve disorders
• Inflammatory bowel disease (IBD), particularly Crohn’s disease, especially in people with prior intestinal surgery or narrowing
• Chronic digestive symptoms, such as ongoing diarrhea or bloating
• Chronic alcohol use, which may affect gut motility and the intestinal lining
• Structural or surgical changes in the digestive tract that allow bacteria to collect rather than move through normally

Not everyone with these risk factors develops SIBO, but their presence can increase susceptibility and help guide evaluation.

SIBO and Irritable Bowel Syndrome (IBS)

The symptoms of small intestinal bacterial overgrowth (SIBO) often overlap with those of irritable bowel syndrome (IBS), including bloating, gas, abdominal discomfort, and changes in bowel habits. Because these symptoms are similar, the two conditions cannot be reliably distinguished based on symptoms alone.

Research suggests that SIBO is more common in people with IBS than in those without digestive symptoms. Certain features seen in some patients with IBS such as altered gut movement or chronic diarrhea may increase the risk of developing SIBO. However, SIBO is not the cause of IBS in everyone, and not all people with IBS will have abnormal SIBO testing or benefit from SIBO directed treatment.

For this reason, careful evaluation, appropriate testing, and individualized treatment are important to determine whether SIBO may be contributing to symptoms and to guide the most effective care.

How Is SIBO Diagnosed?

Small intestinal bacterial overgrowth (SIBO) is most commonly evaluated using a noninvasive breath test. During testing, breath samples are collected over time after drinking a sugar solution. Certain microorganisms in the gut produce gases that can be detected in the breath, helping identify patterns that may be contributing to symptoms.

In addition to traditional test tube based testing, a reusable, at home medical-grade breath testing device, the MedAIRE2®, is also available at our practice. These tools allow for structured, clinician-guided breath testing outside of the office and can be reused for subsequent follow up as needed. As with all breath testing, proper preparation and medical interpretation are essential, and results must always be considered in the context of symptoms and medical history.

Types of Intestinal Bacterial Overgrowth

Breath testing may identify different gas patterns, which can help explain symptoms:

• Hydrogen-predominant SIBO: More commonly associated with diarrhea, bloating, and looser stools
• Methane-predominant overgrowth (also called intestinal methanogen overgrowth, or IMO): More often linked to constipation and slower digestion
• Mixed gas overgrowth: Involves both hydrogen and methane and may cause mixed or alternating bowel symptoms

Not everyone with digestive symptoms will have abnormal breath testing, and not all abnormal results require treatment. Testing is used to support individualized evaluation and care, rather than as a diagnosis on its own.

How Is Small Intestinal Bacterial Overgrowth Treated?

Treatment of small intestinal bacterial overgrowth (SIBO) is individualized and guided by a clear overall objective: relieving symptoms and improving digestive function and quality of life. Care focuses on reducing excess bacterial overgrowth, addressing underlying factors that predisposed to the imbalance, and supporting overall digestive and nutritional health.

Antibiotics are the primary treatment used to reduce excess bacteria and are often effective in improving symptoms such as bloating, gas, abdominal discomfort, and changes in bowel habits. The choice of medication and length of treatment are tailored to each patient based on symptom pattern, and breath test findings. In some cases, additional or repeat treatment may be appropriate.

Because SIBO can recur, identifying and addressing contributing factors is an important part of care. This may include reviewing current medications, managing related medical conditions, and developing a longer-term strategy to reduce symptom recurrence.

The success of treatment is measured by how patients feel and function, not by normalizing test numbers alone. Care is guided by clinical improvement and individualized goals.

Diet and SIBO

Dietary modifications may help manage symptoms by reducing fermentation within the small intestine and minimizing gas production. Common dietary approaches include:

• Low-FODMAP diet, which limits fermentable carbohydrates known to increase bloating and gas
• Reducing excess sugars and refined carbohydrates, which may promote bacterial overgrowth
• Structured meal spacing, which may support normal intestinal cleansing waves and motility

Dietary interventions should be individualized and are ideally guided by a nutrition specialist experienced in gastrointestinal disorders. Long-term overly restrictive diets are generally discouraged.

Early evaluation by a gastroenterologist experienced in the treatment of SIBO can help ensure an accurate diagnosis and guide targeted, effective treatment.