Symptoms of Mild SIBO
Mild Small Intestinal Bacterial Overgrowth (SIBO) typically presents with bloating, abdominal discomfort, flatulence, and changes in bowel habits (either diarrhea or constipation), without the severe malabsorption or weight loss seen in advanced cases. 1
Core Gastrointestinal Symptoms
The hallmark symptoms of mild SIBO include:
- Bloating and abdominal distention - This is the most common presenting symptom, often worsening after meals 1, 2
- Abdominal pain or discomfort - Typically diffuse and cramping in nature 3, 2
- Flatulence and excessive gas production - Results from bacterial fermentation of carbohydrates in the small intestine 1
- Diarrhea - More common in hydrogen-producing SIBO 2
- Constipation - Particularly associated with methane-dominant SIBO 4
- Nausea - Can occur but is less specific 5
Distinguishing Mild from Severe SIBO
In mild cases, patients typically do not experience:
- Steatorrhea (fatty stools) - This is reserved for more severe cases with significant malabsorption 2
- Significant weight loss - Mild SIBO does not typically cause the chronic weight loss seen in severe disease 6, 2
- Overt malnutrition - Severe nutritional deficiencies are uncommon in mild presentations 1
The key distinction is that mild SIBO causes functional gastrointestinal symptoms without the profound malabsorption and nutritional consequences that characterize advanced disease. 1, 2
Food-Related Symptoms
- Food intolerances - Patients commonly report worsening symptoms with specific foods, particularly those high in fermentable carbohydrates 5
- Post-prandial symptom exacerbation - Bloating and discomfort typically worsen after eating 1
Laboratory and Nutritional Findings in Mild Cases
Even in mild SIBO, some laboratory abnormalities may be present:
- Elevated folate levels - Can occur due to bacterial production 2
- Vitamin B-12 deficiency - Less common but possible 2
- Normal inflammatory markers - Fecal calprotectin and other inflammatory markers are not elevated in SIBO and should prompt investigation for alternative diagnoses if elevated 7, 2
Important Clinical Caveats
The symptoms of mild SIBO overlap significantly with irritable bowel syndrome (IBS), making clinical distinction challenging without diagnostic testing. 1, 2 The American Gastroenterological Association notes that controversy remains concerning the role of SIBO in the pathogenesis of common functional symptoms regarded as components of IBS. 2
Symptom severity does not always correlate with bacterial load or breath test results. 8 Clinical improvement and quality of life depend considerably on patients' subjective perception of their health, not just objective gas normalization. 8
Patients with underlying risk factors (prior GI surgery, pancreatic exocrine insufficiency, diabetes, motility disorders) are more likely to develop SIBO and may present with these mild symptoms even without severe disease. 1