Microbiome science

Dysbiosis

Also called: microbial imbalance, gut dysbiosis

Dysbiosis means an imbalance in the gut microbiome. Most often it refers to lower diversity, a loss of beneficial species, or an overgrowth of unhelpful ones. The term is used in research and clinical writing, but there is no agreed clinical threshold. Many gut conditions are associated with dysbiosis, but cause and effect are still being worked out.

Why the term is hard to pin down

There is no single definition of dysbiosis that all researchers agree on. The British Society of Gastroenterology and the International Scientific Association for Probiotics and Prebiotics (ISAPP) both note that dysbiosis is best thought of as a description rather than a diagnosis. It captures the observation that a microbiome looks different from a typical healthy one, but the boundary between healthy variation and pathological imbalance is blurry.

What dysbiosis usually looks like

  • Lower microbial diversity than expected for someone of similar age and lifestyle.
  • Loss of keystone beneficial species, especially Faecalibacterium prausnitzii and Akkermansia muciniphila, which produce anti-inflammatory compounds.
  • Overgrowth of pro-inflammatory species, often within Proteobacteria.
  • Reduced production of short-chain fatty acids like butyrate, which fuel the colon lining.

Common triggers

  • Antibiotics. A single course can shift composition for months. Repeated courses change baseline diversity for years.
  • Ultra-processed diets low in fibre and high in emulsifiers and certain sweeteners.
  • Chronic stress, which alters gut motility and local immune signalling.
  • Long-term proton pump inhibitor use, which reduces stomach acid and changes which bacteria can travel through to the colon.
  • Medical interventions like chemotherapy, gut surgery, or repeated bowel preparation.

Conditions linked with dysbiosis

Associations exist between dysbiosis and IBS, IBD, colorectal cancer, type 2 diabetes, obesity, atopic conditions like eczema and asthma, and some mental-health conditions. The relationship is bidirectional in most cases. Disease changes the microbiome; the microbiome influences disease. Research has not yet established that correcting dysbiosis cures any of these conditions, but it does help with symptoms in many people.

How to spot it without a stool test

There is no symptom that is specific to dysbiosis. Common patterns include daily bloating, irregular bowel movements, food cravings (especially for sugar), low energy that does not respond to sleep, and frequent minor illness. None of these are diagnostic on their own. Three or four together, alongside known triggers, suggest the gut is worth attention.

Common questions

Can a stool test diagnose dysbiosis?
Stool sequencing tests show what's in your microbiome but cannot tell you with certainty that you have dysbiosis or what to do about it. Results vary day to day with diet. Most clinicians treat consumer microbiome tests as informational rather than diagnostic.
How long does it take to fix dysbiosis?
Composition starts shifting within 24 to 48 hours of dietary change. Lasting shifts take 8 to 12 weeks. Markers like bowel regularity and bloating often improve in the first month, while skin and mood can lag by 4 to 6 weeks behind digestion.
Is dysbiosis the same as SIBO?
No. Dysbiosis describes an imbalance in the colonic microbiome. SIBO refers specifically to bacterial overgrowth in the small intestine, where bacteria are not meant to live in high numbers. The two can co-exist.
Do antibiotics always cause dysbiosis?
Yes, in the short term. A single seven-day course typically reduces diversity for two to four weeks before recovery begins. Some species do not return without active intervention. Repeat courses are the bigger concern. Saccharomyces boulardii during and after antibiotics has the best evidence for reducing the disruption.

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