Reference
SIBO Glossary
Plain-language definitions of the medical terms used throughout our guides. Underlined terms in articles link here.
- Archaea
- Single-celled microorganisms that are distinct from bacteria. Methane-producing archaea (methanogens) are responsible for intestinal methanogen overgrowth.
- Bile acid deconjugation
- A chemical change bacteria make to bile acids that stops them from emulsifying fat. It leads to fat malabsorption and deficiencies in vitamins A, D, E and K. Read: SIBO symptoms →
- Biofilm
- A protective slime layer that microbial communities build around themselves. It can shield them from antimicrobial treatment. Read: Biofilm disruption →
- Colony-forming units (CFU)
- A count of live microbes in a sample. SIBO is defined as more than 1,000 CFU per milliliter of small-intestinal fluid (older definitions used 100,000). Read: What is SIBO? →
- Cytolethal distending toxin B (CdtB)
- A toxin released by food-poisoning bacteria such as Campylobacter jejuni, E. coli and Salmonella. Antibodies against it can cross-react with vinculin and damage the gut nerves that run the migrating motor complex. Read: Blood tests →
- Diamine oxidase (DAO)
- An enzyme made by the cells lining the small intestine that breaks down histamine from food. When the lining is damaged, low DAO activity can cause histamine intolerance. Read: Sauerkraut & histamine →
- Dysbiosis
- An imbalance in the makeup or activity of the microbes living in the gut.
- Elemental diet
- A liquid diet of pre-digested nutrients (amino acids, simple sugars and easily absorbed fats). They are absorbed in the upper small intestine, which starves bacteria further down. Read: The elemental diet →
- Enteric nervous system
- The network of nerves embedded in the wall of the digestive tract that controls gut movement and secretions, including the migrating motor complex.
- FODMAPs
- Fermentable oligo-, di- and monosaccharides and polyols: short-chain carbohydrates that are poorly absorbed and quickly fermented by gut microbes. Read: The low-FODMAP diet →
- Gastroparesis
- Delayed emptying of the stomach without a physical blockage, often caused by nerve damage such as in diabetes.
- Hypochlorhydria
- Low stomach acid. It weakens the stomach's first barrier against bacteria. Common causes include long-term acid-reducing medication, H. pylori infection and aging. Read: Root causes →
- Ileocecal valve
- The muscular valve where the small intestine meets the colon. It keeps colonic bacteria from flowing backward into the small intestine.
- Intestinal methanogen overgrowth (IMO)
- Overgrowth of methane-producing archaea, mainly Methanobrevibacter smithii. It is diagnosed by a breath methane level of 10 ppm or more and is linked to constipation. Read: Methane SIBO (IMO) →
- Intestinal sulfide overproduction (ISO)
- Excess hydrogen sulfide made by sulfate-reducing bacteria. It is linked to diarrhea and can only be detected by three-gas breath tests. Read: Breath tests →
- Lactulose
- A synthetic sugar the body cannot digest or absorb. As a breath-test substrate it travels the whole small intestine, which also makes false positives more likely. Read: Breath tests →
- Lipopolysaccharide (LPS)
- A molecule in the outer membrane of Gram-negative bacteria, also called endotoxin. When it crosses the gut barrier it triggers a strong inflammatory response. Read: Leaky gut →
- Methanogens
- Archaea that produce methane from hydrogen and carbon dioxide. Methane slows the movement of the intestines.
- Migrating motor complex (MMC)
- A wave of muscle contractions that sweeps the stomach and small intestine between meals, roughly every 90 to 120 minutes, pushing leftover food and bacteria into the colon. Eating interrupts it. Read: Motility →
- Parts per million (ppm)
- The unit breath-test laboratories use to report the concentration of hydrogen, methane and hydrogen sulfide in a breath sample. Read: Breath test interpreter →
- Post-infectious IBS
- Irritable bowel syndrome that develops after a bout of food poisoning. It is linked to anti-CdtB and anti-vinculin antibodies that impair gut motility. Read: IBS & SIBO →
- Prokinetic
- A medication or supplement that stimulates gut movement. Prokinetics are often used after SIBO treatment to support the migrating motor complex and reduce relapse. Read: Motility →
- Proton pump inhibitor (PPI)
- A class of acid-reducing medication used for reflux, such as omeprazole. Long-term use lowers stomach acid and is associated with a higher risk of SIBO.
- Rifaximin
- An antibiotic that is barely absorbed into the bloodstream, so it acts mainly inside the gut. It is a common prescription treatment for SIBO. Read: Prescription antibiotics →
- Short-chain fatty acids (SCFAs)
- Compounds such as butyrate, acetate and propionate that gut bacteria make by fermenting fiber. They fuel the cells lining the colon and help regulate inflammation. Read: Prebiotics →
- Small intestinal fungal overgrowth (SIFO)
- An excess of fungi, most often Candida species, in the small intestine. Its symptoms resemble SIBO, but breath tests cannot detect it. Read: Candida & SIFO →
- Sulfate-reducing bacteria
- Bacteria such as Desulfovibrio that consume hydrogen and sulfur compounds and produce hydrogen sulfide gas.
- Tight junctions
- Protein seals between neighboring cells of the intestinal lining that control what can pass from the gut into the bloodstream. Read: Leaky gut →
- Vinculin
- A protein found in gut nerve cells. Anti-vinculin antibodies, which can form after food poisoning, are a marker of post-infectious IBS. Read: Blood tests →
- Visceral hypersensitivity
- Heightened sensitivity of the gut's nerves, so that normal amounts of gas or stretching are felt as pain.
- Zonulin
- A protein that loosens the tight junctions between intestinal cells. High levels are associated with increased intestinal permeability. Read: Leaky gut →