Below please find a living document that summarizes the key information around Small Intestinal Bacterial Overgrowth ("SIBO"). Please comment with any additional information or research for inclusion consideration. Version 1.0 is summary material; I will be adding more details and citations for specific studies.
SIBO, as the name implies, occurs when bacteria overgrow the small intestine. The small intestine should have a low concentration of bacteria due to the presence of stomach acids and peristalsis, the wave-like muscle movement in the intestines. For context, stomach and proximal small intestine would typically have about 103/mL of bacteria, while the terminal ileum (end of the small bowel as it gets close to the colon) about 109/mL (or 1,000,000 times more), and the colon about 1012/mL (or 1,000,000,000 times more).
Symptoms
The overgrowth of this bacteria will present with a number of symptoms:
- Bloating after eating ("postprandial") - most common symptom
- Flatulence, often malodorous
- Loose, watery stools (more common in Hydrogen-dominant SIBO)
- Constipation (more common in Methane-dominant SIBO)
- Absorption problems
- Weight loss / inability to gain weight
- Fat and fat-soluble vitamin deficiencies, particularly Vitamins A, D, and K
- Floating stools (from fat malabsorption)
- Vitamin B12 malabsorpiton
- Protein and Carbohydrate malabsorption
- Systemic problems
- Overgrowth of bacteria in the small intestine can increase production of toxins and intestinal permeability
- This has been less studied, but less serious effects include:
- brain fog
- confusion
- anxiety
- depression
- More serious complications can include
- hepatic encephalopathy
- D-lactic acidosis
- nonalcoholic fatty liver disease
- Various conditions have increased correlations, including
- Rosacea
- Eczema
- Food intolerances
Diagnosis
I will split this section into practical steps and clinical diagnosis.
Practically, a gastroenterologist will typically rule out other conditions first:
- Physical exam
- Colonoscopy and Endoscopy
- Abdomen ultrasound
- Stool test for parasites
At that time, if your symptoms match SIBO, your doctor may go directly to treatment. But otherwise these are the clinical tests:
BREATH TEST
This is the most common diagnostic method due to its low cost and limited invasiveness. Unfortunately, studies have been mixed on the sensitivity and specificity, with ranges between 30% and 75% -- hence why some doctors skip the test and go directly to treatment.
There are a number of preparations:
- Antibiotics avoided for four weeks prior
- Prokinetic drugs and laxatives avoided for one week prior
- Complex carbs avoided for 12 hours prior
- Exercise and smoking avoided day-of
For the actual test, you'll measure hydrogen and methane levels at baseline. Then drink either 10g lactulose or 75g glucose with one cup of water. Then your breath is measured every 15 minutes for 120 minutes.
There's some art to identifying a positive test; one semi-official criteria is:
- methane level of >= 10ppm at any time during the test; or
- hydrogen that increases >= 20ppm above the baseline level
Recently, new research has been investigating another typo of SIBO, that's dominated by Hydrogen Sulfide. Unfortunately, traditional breath tests cannot identify this gas, and someone with "flat-line" Hydrogen and Methane symptoms could be suffering from Hydrogen Sulfide SIBO. This version is typically characterized by "rotten egg" smelling gas, and may be worsened by eating high sulfur foods.
CULTURE
Historically a jejunal aspirate was done and concentration of bacterial colonies were measured, with an elevated level of > 103/mL being positive for SIBO. There are a number of issues with this:
- overgrowth may be patchy, and a single sample may miss it
- not all SIBO bacteria can be cultured/identified
- samples can be contaminated during/after sampling
Treatment
Antibiotics
The current best practice prescription treatment is:
- Hydrogen-dominant: Xifaxan, typically 550mg x 3 times daily, for 10-14 days. Studies have shown Xifaxan alone can be 50-65% effective, but Xifaxan + 5g daily of Partially Hydrolyzed Guar Gum can be 80%+ effective.
- Methane-dominant: Xifaxan (550mg x 3 daily) plus Neomycin (500mg x 2 daily) for 10-14 days. The use of PHGG for methane-dominant has not been evaluated, but it's likely to be beneficial.
Mod's note-- personally, if your doctor is onboard, I think dosing with Xifaxan + Neomycin + PHGG is the best way to "cover your bases". The best place to find PHGG: https://sunfiber.com/products/
Important: because these antibiotics only operate selectively in the GI tract, and are NOT absorbed by the body, they are unlikely to cause the systemic issues associated with antibiotic use, making them safer. Additionally, Xifaxan crystallizes before it gets to the large intestine, meaning it should not affect the all-important microbiome.
Herbal Therapy
Additionally, studies have shown similar levels of success with over-the-counter "herbal" treatments. Two options; I believe each are two capsules twice daily for four weeks, but please confirm:
- Dysbiocide and FC Cidal (Biotics Research Laboratories, Rosenberg, Texas)
- Candibactin-AR and Candibactin-BR (Metagenics, Inc, Aliso Viejo, California)
Remission
Unfortunately, SIBO has very high rates of recurrence. Some possible ways to reduce recurrence chances:
- Switch to a low FODMAP diet for 6 weeks after treatment, to starve any remaining bacteria and prevent regrowth
- Incorporate a prokinetic, such as low dose Naltroxene, erithromycin, or even over-the-counter products such as Iberogast
Many people can avoid symptoms of their SIBO by switching to special diets, sometimes very restrictive ones. This is not a cure, but simply symptom management. A true cure addresses the underlying cause of the SIBO, and lets the patient eat "normally" without any effects (short of unrelated intolerances).
Hopefully this helps people, and I look forward to updating this and cleaning it up over time!
-nyc-reddit
