Studies have found the odds of small intestinal bacterial overgrowth (SIBO) are about 3.7 times higher in people diagnosed with irritable bowel syndrome than in healthy controls. In diarrhea-predominant IBS, roughly one in three patients turn out to have it.
SIBO is an imbalance in the microbes of the small intestine, according to the Cleveland Clinic. Unlike IBS, it can be verified with a test and treated with antibiotics.
The National Library of Medicine's StatPearls reference lists watery diarrhea, bloating, abdominal pain and gas as the four most common clinical manifestations. All four are also textbook IBS symptoms, which is why the two are routinely confused.
The malabsorption cluster near the bottom of the list below is what most often separates SIBO from IBS in a doctor's office.
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Eight signs worth watching for
1. Bloating and abdominal distension. Bacteria that do not belong in the small intestine ferment carbohydrates and release hydrogen and methane, according to a peer-reviewed SIBO review. The result is a swollen belly that often worsens after meals.
2. Excess gas and belching. The same fermentation drives audible flatulence, one of the classic presentations noted in the StatPearls reference.
3. Abdominal pain or cramping. Discomfort in the middle or lower abdomen is common and mirrors IBS almost exactly.
4. Chronic watery diarrhea. Bacterial byproducts pull water into the bowel and inflame the intestinal lining. It is one of the four most-cited SIBO symptoms in the medical literature.
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5. Nausea and loss of appetite. Both appear on the Cleveland Clinic's symptom list and often surface when the small-intestine lining is inflamed.
6. Fatty, foul-smelling stools. Overgrown bacteria break down bile salts before the intestine can absorb fat, producing what clinicians call steatorrhea.
7. Unintended weight loss. When fat and calories pass through unabsorbed, weight can fall without any change in diet. Weight loss and malnutrition together set SIBO apart from typical IBS.
8. Fatigue, weakness and tingling. Bacteria consume vitamin B12 before the body can, which the StatPearls reference links to weakness, unsteady movement and pins-and-needles sensations. Deficiencies in vitamins A, D, E, iron and calcium can follow.
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What raises the risk
Prior abdominal surgery, diabetes and slow gut motility all raise the risk. So does long-term use of proton pump inhibitors, the acid-suppressing drugs sold under names such as omeprazole and esomeprazole. One review found the odds of SIBO climbed roughly 70 percent after extended proton pump inhibitor use.
Advanced age, scleroderma, Crohn's disease and immunodeficiency disorders also predispose to bacterial overgrowth, per StatPearls.
When to see a doctor
These signs alone cannot self-diagnose SIBO. The standard first step is a carbohydrate breath test, which measures the hydrogen and methane produced by gut bacteria after a sugary drink. A hydrogen rise of more than 20 parts per million within 90 minutes is considered positive, per the peer-reviewed review.
Anyone with persistent gut symptoms alongside unexplained weight loss, tingling or fatigue should ask a gastroenterologist about a breath test rather than assuming an IBS diagnosis explains everything.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.