Small Intestinal Bacterial Overgrowth (SIBO) is a condition characterized by an excessive amount of bacteria in the small intestine, a part of the digestive tract that typically has low bacterial counts compared to the large intestine. This overgrowth commonly leads to increased gas production and a variety of other uncomfortable digestive symptoms. The presence of too many bacteria, or the wrong types, in the small intestine disrupts normal digestion and nutrient absorption.
How SIBO Leads to Gas Production
The primary mechanism by which SIBO causes gas involves the fermentation of carbohydrates by bacteria in the small intestine. Normally, most carbohydrate digestion and absorption occur before food reaches the large intestine, where bacteria are abundant. However, with SIBO, these bacteria are present in higher numbers in the small intestine, where they encounter undigested carbohydrates. As these bacteria consume and break down carbohydrates, they produce various gases as byproducts.
The types of gases produced depend on the specific bacteria or other microorganisms that are overgrown. Common gases include hydrogen, methane, and sometimes hydrogen sulfide. Hydrogen-producing bacteria like E. coli and Klebsiella ferment carbohydrates to release hydrogen gas. Methane is produced by archaea, a different type of microorganism, and is often associated with slower gut motility. Hydrogen sulfide gas, known for its “rotten egg” smell, is produced by specific bacteria such as Fusobacterium and Desulfovibrio species.
Additional Symptoms of SIBO
While gas is a common symptom, SIBO frequently presents with a broader range of digestive and systemic issues. Bloating and abdominal distension are common, resulting from gas buildup within the intestines. Individuals may also experience abdominal pain or cramping. Changes in bowel habits are typical, with some people experiencing diarrhea, others constipation, or an alternation between the two. Hydrogen-dominant SIBO is often linked to diarrhea, while methane-dominant SIBO is associated with constipation due to methane’s effect of slowing intestinal transit.
Other symptoms include nausea, a feeling of uncomfortable fullness after eating, and indigestion. Beyond digestive complaints, SIBO can lead to nutrient deficiencies because the overgrown bacteria consume vitamins and interfere with nutrient absorption. This malabsorption can result in weight loss, fatigue, and deficiencies in vitamins like B12, which can impact the nervous system. SIBO symptoms can mimic those of Irritable Bowel Syndrome (IBS), and a significant percentage of IBS cases are related to SIBO.
Recognizing SIBO and Seeking Care
Recognizing the signs of SIBO and seeking professional medical evaluation is important for proper diagnosis and management. The symptoms of SIBO can overlap with many other gastrointestinal conditions, making self-diagnosis unreliable. A healthcare professional can assess your symptoms and medical history to determine if SIBO testing is appropriate.
The most common and non-invasive diagnostic method for SIBO is a breath test. This test measures the levels of hydrogen and methane gases in your breath after you consume a specific sugar solution, such as glucose or lactulose. A rapid rise in exhaled hydrogen or methane levels within a certain timeframe can indicate bacterial overgrowth in the small intestine. While breath tests are widely available and convenient, their results should be interpreted by a doctor who can consider the clinical context. Medical intervention is necessary for effective treatment, which often involves antibiotics to reduce bacterial overgrowth, along with dietary adjustments and addressing any underlying causes.