Glossary · Dysbiosis and disease
Dysbiosis
In one sentence
Dysbiosis is a change in the composition or function of the microbiota away from what is considered compatible with health: loss of diversity, loss of beneficial microbes or overgrowth of others.
Also known as: gut dysbiosis · intestinal dysbiosis · microbial imbalance
What is dysbiosis?
Dysbiosis describes a microbiota that has moved away from eubiosis. Three patterns are usually described, and they can occur together:
- Loss of diversity: fewer species, or a community dominated by a handful of groups.
- Loss of beneficial organisms, such as butyrate-producing bacteria.
- Expansion of potentially harmful organisms, such as pathobionts or opportunistic pathogens.
It can affect the gut, mouth, skin or vagina. In the small intestine, excess bacteria are investigated specifically as SIBO.
Causes and associations
Well-documented drivers include antibiotics, abrupt dietary changes (particularly diets low in dietary fibre), gastrointestinal infections and certain medicines. Studies have associated dysbiosis with inflammatory bowel disease, irritable bowel syndrome, obesity and type 2 diabetes, and with processes such as low-grade inflammation and increased intestinal permeability.
These associations need careful reading. In many cases it is not known whether dysbiosis is a cause, a consequence of the disease or its treatment, or both.
A contested concept
The term is useful but imprecise. In a 2016 commentary in Nature Microbiology, “Dysbiosis is not an answer”, Olesen and Alm argued that the notion of microbial “balance” is used without a concrete definition. The 2024 Gut review on what defines a healthy gut microbiome makes a similar point. In practice, when a report mentions dysbiosis, it is worth asking which parameter is altered and against what reference.
How it is studied
Dysbiosis is investigated by analysing the DNA in a stool sample with next-generation sequencing. Reports typically include diversity, the relative abundance of the main groups, any pathogens detected and, depending on the test, dysbiosis indices or functional profiles. Complementary tests such as faecal calprotectin help establish whether there is associated gut inflammation.
Example
A GP sees a patient with bloating and altered bowel habit since a prolonged course of antibiotics. Having excluded red-flag features, he requests a microbiota analysis. The report shows reduced diversity and few butyrate producers, with no pathogens. He reads it as a pattern consistent with post-antibiotic dysbiosis and plans follow-up according to how the symptoms evolve.
Dysbiosis at Xenogene
Xenogene’s Gut Microbiota test is designed to detect alterations such as dysbiosis, overgrowth, infections and changes in microbiota function, using Nanopore NGS sequencing of a stool sample. It is requested on prescription, and interpretation rests with the professional who orders the test.
Frequently asked questions
Is dysbiosis a disease?
It is not a diagnosis in itself but a description of an imbalance in the microbiota. It can accompany various conditions or appear temporarily, for instance after antibiotics. Its relevance is judged by the healthcare professional in the clinical context.
What are the symptoms of gut dysbiosis?
It has been linked with bloating, wind and changes in bowel habit, but these symptoms are non-specific and have many other possible causes. Dysbiosis cannot be confirmed on symptoms alone.
How long does it take for the gut to recover from dysbiosis?
It depends on the cause and the person. After a course of antibiotics, many people regain much of their original composition within weeks to months, although some groups may take longer. Follow-up is decided by the professional managing the case.
Related terms
- Microbiota
The microbiota is the community of living microorganisms (bacteria, archaea, fungi, protozoa) that inhabits a specific site of the body, such as the gut, mouth, skin or vagina.
- Eubiosis
Eubiosis is the state in which the microbiota is stable, diverse and compatible with the host's health. It is the opposite of dysbiosis, although neither term has an agreed operational definition.
- Intestinal permeability
Intestinal permeability is how easily substances in the gut lumen cross the intestinal lining into the bloodstream. It is a normal, regulated property; increased permeability is associated with several diseases.
- SIBO
SIBO (small intestinal bacterial overgrowth) is the presence of excessive numbers of bacteria in the small intestine, accompanied by digestive symptoms such as bloating, wind, abdominal pain or diarrhoea.
- Low-grade inflammation
Low-grade inflammation is a mild, persistent, systemic inflammatory activation with no acute infection or injury to explain it. It is detected through modest rises in markers such as high-sensitivity CRP.
Educational content for healthcare professionals and the general public. It does not replace assessment by a healthcare professional: ordering and interpreting any test is the responsibility of the requesting clinician.
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