Small Intestinal Bacterial Overgrowth (SIBO)
Information on the causes, symptoms, and treatments of increased bacterial growth in the small intestine.
Symptoms and Causes
Small intestinal bacterial overgrowth, commonly known by its acronym SIBO (Small Intestinal Bacterial Overgrowth), is a condition characterized by an increase in bacteria in the small intestine, specifically microorganisms that are usually resident in the colon.
When a dysbiosis (imbalance) of the intestinal microbiota occurs, the harmony that allows the body to function normally is disrupted. Consequently, in addition to causing uncomfortable symptoms for the patient, it can lead to diseases of varying severity, such as obesity or irritable bowel syndrome.
The prognosis of SIBO is variable and depends on the underlying cause. When detected early and treated appropriately—both for the underlying condition and the bacterial overgrowth—it resolves without complications. Nevertheless, relapses are common, and therapy may need to be adjusted.
Experts note that, although SIBO causes bothersome symptoms that interfere with patients’ quality of life, in most cases it is not a serious condition. Therefore, consulting a physician to improve well-being and identify the underlying cause is advisable, but it should not be a source of excessive concern.
Symptoms
The most characteristic symptoms of SIBO include:
- Abdominal bloating
- Nausea
- Diarrhea
- Occasionally, constipation
- Feeling of fullness after eating
- Loss of appetite
- Unexplained weight loss
- Abdominal pain
- Malnutrition
- Increased gas
Causes
Bacterial overgrowth in the intestine may result from several causes:
- Complications following digestive system surgery, such as procedures for colon cancer or peptic ulcers, gastric bypass, or gastrectomy.
- Diseases that slow digestive motility: diabetes, celiac disease, Crohn’s disease, scleroderma.
- Structural abnormalities in the small intestine or surrounding organs, such as diverticulosis or adhesions.
- Hypochlorhydria: reduced hydrochloric acid in the stomach, which normally acts as a defense barrier by eliminating bacteria.
Risk Factors
Key factors that increase the risk of developing SIBO are closely related to its causes:
- Previous abdominal surgery
- Adhesions resulting from surgical complications
- Structural abnormalities
- Diverticulosis: formation of tissue protrusions in the colon
- Crohn’s disease: chronic inflammatory condition of autoimmune origin
- Scleroderma: accumulation of fibrous tissue that may cause malabsorption
- Intestinal lymphoma: cancer originating in the lymphatic tissue of the digestive tract, especially the stomach and small intestine
- Diabetes
- Injuries to the small intestine
- Previous abdominal radiotherapy
- Medications: prolonged use of antibiotics, opioids, or proton pump inhibitors (PPIs) such as omeprazole
Complications
If SIBO is not properly treated, it may lead to serious complications, including:
- Malabsorption and nutritional deficiencies, usually long-term:
- Vitamin B12 deficiency, which may lead to megaloblastic anemia (bone marrow produces excessively large and poorly functional red blood cells) or nerve damage
- Steatorrhea: fat malabsorption
- Fat-soluble vitamin deficiencies (A, D, E, and K), which may result in osteoporosis or coagulation disorders
- Damage to the intestinal lining: bacteria damage the small intestine wall:
- Enteropathy: inflammation of the intestinal mucosa
- Leaky gut: increased intestinal permeability, allowing part of the food bolus, toxins, or bacteria to enter the bloodstream
- Intestinal pneumatosis cystica: a very rare complication in which excess gas becomes trapped in the intestine as cysts
- Kidney stones due to impaired calcium absorption
- Worsening of pre-existing conditions, such as Crohn’s disease or irritable bowel syndrome
Prevention
Although SIBO cannot always be prevented, maintaining a balanced diet and promoting intestinal transit contribute to good digestive health.
Which Physician Treats SIBO?
SIBO is diagnosed and treated within the specialty of Gastroenterology.
Diagnosis
SIBO can be diagnosed through several tests:
- Hydrogen and methane breath test: commonly known as the breath test. The patient first ingests a sugar preparation. Then, eight breath samples are collected approximately every 30 minutes. A rapid increase in gas levels indicates bacterial overgrowth, as sugars begin fermenting in the small intestine rather than the colon.
- Gastroscopy: an endoscope is inserted through the throat to the small intestine to aspirate a fluid sample for culture. In the laboratory, the sample is analyzed for an excess of bacteria or microorganisms originating from other body sites.
Specialists may also request blood or stool tests to evaluate vitamin deficiencies or fat malabsorption. Imaging studies can detect structural abnormalities, lesions, or intestinal diseases.
Treatment
The primary treatment for SIBO focuses on addressing its underlying cause. This approach not only reduces symptoms but also prevents disease progression:
- Specific antibiotics, probiotics
- Low-FODMAP diet: an acronym for fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols, which are short-chain carbohydrates fermented by gut flora, causing the aforementioned symptoms
To alleviate symptoms caused by bacterial overgrowth, it is recommended to:
- Manage stress as much as possible
- Avoid overweight
- Avoid ultra-processed foods
- Reduce intake of fermentable foods (onion, garlic, dairy, cereals, apple, pear)
- Follow a diet supervised by a nutrition specialist, based on lean meats, fish, eggs, low-fructose fruits, and low-FODMAP vegetables
- Consume natural probiotics without additives, such as yogurt
- Exercise regularly
- Prevent constipation
- Maintain routines: keep a regular schedule for meals and sleep to support normal intestinal motility
- Drink sufficient water to maintain proper hydration
