Clinical Knowledge Hub

SIBO Overview & Pathophysiology

A medical guide to what happens when colonic bacteria colonize the small intestine, impair nutrient absorption, and trigger chronic digestive symptoms.

The > 1,000 CFU/mL Standard

The small intestine is naturally designed to maintain sparse microbial density (< 1,000 CFU/mL) to ensure rapid nutrient absorption without competitive microbial fermentation.

The 3 Distinct Gas Profiles

Overgrowth is grouped by the main gas: hydrogen (linked to diarrhea), methane (IMO, linked to constipation) or hydrogen sulfide (linked to diarrhea).

The 3 Primary Gut Defenses

Stomach acid, the migrating motor complex (the gut's cleaning wave between meals) and the ileocecal valve normally keep bacteria out of the small intestine.

Start here

New to SIBO?

Read these guides first. They link onward to the tests and treatments.

Guide	What it covers
What is SIBO?	Definition, causes, gas types, diagnosis and treatment in one guide
Symptoms	Bloating, diarrhea, constipation, nutrient problems and warning signs
Causes	Slow gut movement, low stomach acid, surgery and other risk factors
Methane SIBO (IMO)	Methane overgrowth and constipation
Hydrogen sulfide SIBO	The least studied gas type and how it is tested
SIBO vs. IBS	How often the two overlap, and what that means

Overview Pillar Guides

Deep-Dive Into SIBO Foundations

Hydrogen Sulfide SIBO: Symptoms, Testing and Treatment

What hydrogen sulfide SIBO is, why standard breath tests miss it, the three-gas test and its 3 ppm cut-off, and how it is treated, based on current research.

Oct 6, 2026 4 min read

Methane SIBO (IMO): Causes, Symptoms, Testing and Treatment

Methane SIBO, now called intestinal methanogen overgrowth (IMO): why it causes constipation, how breath tests diagnose it, and how it is treated.

Oct 6, 2026 3 min read

Candida and SIBO: SIFO, Fungal-Bacterial Interaction & Biofilms

What small intestinal fungal overgrowth (SIFO) is, how Candida relates to SIBO, how SIFO is diagnosed, and what the limited evidence says about treatment.

Sep 20, 2026 5 min read

H. Pylori and SIBO: Low Stomach Acid, Gastritis & Hypochlorhydria

How H. pylori can lower stomach acid and is linked to SIBO and methane overgrowth, how each is tested, and whether treating H. pylori clears SIBO.

Sep 20, 2026 5 min read

IBD and SIBO: Crohn's Disease, Ulcerative Colitis & Structural Risk

How common SIBO is in Crohn's disease and ulcerative colitis, why strictures and surgery raise the risk, how to tell SIBO from a flare, and how it is treated.

Sep 20, 2026 5 min read

SIBO vs. IBS: The Overlap, Post-Infectious Autoimmunity & Rome IV

How SIBO and IBS overlap: how often people with IBS have SIBO, food poisoning and anti-vinculin antibodies, gas types and IBS subtypes, and testing.

Sep 20, 2026 6 min read

SIBO and Leaky Gut: Zonulin, Endotoxemia & Intestinal Permeability

Can SIBO cause leaky gut? What studies of intestinal permeability show, what zonulin is, why leaky gut tests are unreliable, and what helps the gut barrier.

Sep 20, 2026 4 min read

Root Causes of SIBO: Why Does Overgrowth Happen?

What causes SIBO: slow gut movement, low stomach acid, surgery and other conditions, how much each raises the risk, and why finding the cause prevents relapse.

Aug 22, 2026 6 min read

Symptoms of SIBO

The symptoms of SIBO, from bloating and diarrhea to B12 deficiency and brain fog, how they differ by gas type, and which warning signs need a doctor.

Aug 21, 2026 7 min read

What is Small Intestinal Bacterial Overgrowth (SIBO)?

What SIBO is, what causes it, the three gas types, how it is diagnosed and treated, and why it often comes back, based on clinical guidelines and studies.

Aug 20, 2026 13 min read