Some problems never get an answer from routine tests.
Recurrent diarrhoea, bloating, poor digestion — and the endoscopy comes back "no significant abnormality". Course after course of antibiotics; the symptoms settle, and then return within weeks of stopping. Immunity seems to be sliding too: frequent colds, easy fatigue, with no explanation anyone can point to.
These scattered complaints may point in one direction: the gut microbiome.
The human gut hosts trillions of microorganisms. They take part in digestion and absorption, immune regulation and metabolic control, and they hold two-way communication with the central nervous system through the gut–brain axis. When this ecosystem loses its balance, the consequences are not confined to the intestine.
In recent years a treatment called faecal microbiota transplantation (FMT) has moved from the laboratory into the clinic. The idea is simple: transfer gut microbiota from a rigorously screened, healthy donor into the patient, to rebuild the disrupted intestinal ecosystem. The harder question is what it can treat, who it suits, and how strong the evidence is — and that has to be answered in layers, not in one sentence.
1. Three tiers of evidence, which should never be mixed
Guideline-recommended, with the strongest evidence base of any indication. FMT is a standard treatment pathway, not an experiment.
Promising signals, but positioned as an adjunct after specialist assessment — never a replacement for established therapy.
Real and interesting findings, but still clinical research. Not a routine treatment option anywhere yet.
Keeping these three tiers apart is the whole point. Most of the confusion around FMT comes from quoting tier-three findings as if they were tier-one.
2. Recurrent C. difficile infection: where the evidence is strongest
In clinical use, recurrent Clostridioides difficile infection is the indication with the most complete evidence and the highest grade of recommendation.
C. difficile infection usually follows antibiotic use. Antibiotics kill the pathogen — and also destroy the protective normal flora, letting C. difficile multiply and release toxins, causing severe diarrhoea and, in the worst cases, pseudomembranous colitis. The trap is structural: the more antibiotics are used, the more thoroughly the flora is destroyed, and the higher the risk of recurrence — a vicious circle.
The American Gastroenterological Association (AGA)'s 2024 clinical practice guideline on microbiota-based therapies gives an explicit recommendation for FMT in recurrent C. difficile infection. A 2025 systematic review and meta-analysis covering 44 studies and 3,476 patients reported:
The same analysis found that recurrence was significantly less frequent in the FMT group than in the antibiotic group (risk ratio 0.38). For infection that keeps coming back and stops responding to antibiotics, FMT is a standard pathway with a solid evidence base.
3. Inflammatory bowel disease and irritable bowel syndrome: promising, but positioned carefully
Patients with inflammatory bowel disease (ulcerative colitis and Crohn's disease) and irritable bowel syndrome commonly show abnormal microbial composition. That raises a reasonable hypothesis: if the flora is rebuilt, does disease control improve?
The research gives a cautious but positive signal. In a study of 60 patients with irritable bowel syndrome treated with FMT, the response rate three months after transplantation was 80%. In inflammatory bowel disease, FMT is being explored as an adjunct — and its position needs to be stated precisely.
What "adjunct" actually means
FMT does not replace biologics or other established standard treatment. Before it is considered, other causes must be excluded by colonoscopy and infection-related testing. A 2025 review concluded that FMT may have a modulating effect in IBD and IBS, but that more evidence is needed before it becomes routine treatment in either condition.
In practice: a suitable patient may have FMT added to a comprehensive plan after specialist assessment. It is not a universal substitute, and it is certainly not something to arrange independently.
4. Where the research is heading
If the first two tiers answer "what can it treat now", the third answers "what might it treat later". None of the following is standard care.
Metabolic disease. Obesity and type 2 diabetes are closely tied to the microbiome's role in energy regulation and glucose metabolism. Multiple studies are exploring whether microbiome intervention can improve glycaemic control and metabolic markers. A 2025 systematic review assessed probiotics, prebiotics and FMT for glycaemic control in type 2 diabetes and identified FMT as one of the more promising directions.
The gut–brain axis. This is currently one of the most active research fronts in the field:
ADHD in children. A prospective observational study running from April 2024 to May 2025 found that washed microbiota transplantation improved attention deficits and hyperactive symptoms in children with ADHD, along with sleep and gastrointestinal problems.
Parkinson's disease. Evidence is accumulating: an association between FMT and improvement in motor symptoms has been observed in preliminary studies, including randomised placebo-controlled work and a phase 2 trial in drug-naïve patients.
All of this remains at the clinical research stage. Which means that anyone considering microbiome intervention in these areas first has to answer a more basic question: what state is my gut microbiome actually in?
5. Before any transplant, look at the hand you are holding
The logic of FMT is to replace what is missing and rebalance what is disordered. But before deciding whether to transplant — and how — there is a prerequisite step: gut microbiome testing.
An international expert consensus published in The Lancet Gastroenterology & Hepatology in 2025, developed by 69 international experts, concluded that microbiome testing in clinical practice needs to be standardised — with defined indications, validated analytical methods and consistent reporting — so that results can reliably inform clinical decisions. One of its core principles is worth quoting in full: microbiome testing should serve clinical judgement, not replace it.
That is exactly why gut microbiome gene testing is an important prerequisite in any properly run FMT pathway. It helps the clinician establish:
- What kind of imbalance it is, and how severe — not merely that "the flora is off".
- Whether specific pathogens are overgrowing, which changes the whole treatment plan.
- How donor microbiota should be matched for this particular patient.
For people who do not yet meet the criteria for FMT but have lived with digestive trouble for years, testing still has a point: it answers the question "what is actually happening inside my gut?" — which is often the first honest answer they have had.
6. What to take from all of this
Research on the gut microbiome is rewriting a category of digestive problem that medicine used to file under "cause unknown". But scientific rigour requires holding two things at once: what has been established, and what is still being verified.
For the first, FMT has already proved its value in recurrent C. difficile infection. For the second, the answers need more time and more evidence.
If you are living with recurrent gastrointestinal symptoms that routine investigation has not explained, or your general condition has not recovered since prolonged antibiotic treatment, understanding the state of your gut microbiome is a reasonable next step — and a far better starting point than choosing a treatment first and looking for a reason afterwards.
This article is health education for international patients and their families and does not replace an individual consultation, examination or diagnosis. Faecal microbiota transplantation is a specialist procedure requiring screened donors, regulated processing and clinical follow-up; eligibility is determined by a gastroenterologist after full assessment.
About Dr. Ang Jian
Dr. Ang Jian is a gastroenterologist and associate chief physician at SinoUnited Health, and the network's Director of Quality Control. She graduated from Zhejiang University and the University of Melbourne with a doctorate in medicine, holds medical licences in both China and Australia, and has practised gastroenterology in both countries for 28 years. She has worked at the Second Affiliated Hospital of Zhejiang University, Austin Hospital (University of Melbourne) and leading private hospitals in China.
Dr. Ang has performed more than 15,000 endoscopic procedures. Her procedural expertise covers early endoscopic diagnosis of tumours, endoscopic polypectomy, haemostasis, foreign body removal, endoscopic resection of pre-cancerous lesions, and band ligation for oesophageal and internal haemorrhoids. Clinically she has extensive experience in gastro-oesophageal reflux disease, gastritis, functional gastrointestinal disorders, inflammatory bowel disease and chronic liver disease, and her annual procedure and patient volumes have consistently ranked at the top of her institutions. She works to treatment-goal-directed strategies, and to specialist, standardised and individualised management of digestive disease.
Dr. Ang is a master's supervisor at Zhejiang University, has contributed to textbooks for international students and eight-year clinical medicine programmes, and leads teaching in gastroenterology. She has been a visiting scholar at the endoscopy centre of Jichi Medical University in Japan, at UCLA, and at MD Anderson Cancer Center in Houston. She has taken part in projects funded by the National Natural Science Foundation of China, the Zhejiang Provincial Natural Science Foundation, the Zhejiang Department of Science and Technology and Australia's NHMRC Dora Lash medical research programme, and has published in Chinese and international journals. As Director of Quality Control, she oversees SinoUnited's quality and safety system.
About the Digestive Disease Centre
The Digestive Disease Centre is led by Dr. Justin Zhu, a pioneer of endoscopic ultrasound in China, together with senior clinicians and a specialist nursing team. It covers disease of the oesophagus, stomach, small intestine and colorectum, as well as hepatobiliary and pancreatic disease, with particular strengths in endoscopic ultrasound, screening and minimally invasive treatment of pre-cancerous and early cancers of the gastrointestinal tract, long-term chronic disease management in inflammatory bowel disease, functional gastrointestinal disorders, and hepatobiliary and pancreatic disease.
Precise endoscopic diagnosis and minimally invasive therapy are a defining service, supported by high-standard protocols, private consulting environments and structured follow-up planning. See the Digestive Disease Centre.
References
- AGA Clinical Practice Guideline on Fecal Microbiota-Based Therapies for Select Gastrointestinal Diseases. Gastroenterology. 2024;166(3):409–434.
- Effectiveness and safety of fecal microbiota transplantation for recurrent Clostridioides difficile infection in immunocompromised patients. Clinical Gastroenterology and Hepatology. 2025.
- El-Salhy M, et al. Efficacy of faecal microbiota transplantation for patients with irritable bowel syndrome in a randomised, double-blind, placebo-controlled study. Gut. 2020;69(5):859–867.
- Faecal microbiota transplantation in 2025: two steps forward, one step back. Current Gastroenterology Reports. 2026;28:5.
- Shalbaf N, et al. Probiotics, prebiotics, synbiotics and FMT for glycaemic control: a systematic review of clinical efficacy and mechanistic readouts in type 2 diabetes and related dysglycaemia. Metabolism Open. 2025;100419.
- Li B, et al. Efficacy and safety of faecal microbiota transplantation on depressive and anxiety symptoms: a systematic review and meta-analysis. Journal of Affective Disorders. 2026.
- Washed microbiota transplantation improves multisystem symptoms in children with neurodevelopmental disorders (IDDF2026-ABS-0455). Gut. 2026;75(Suppl 2):A493.
- Figura M, et al. Safety and efficacy of faecal microbiota transplantation in alleviating symptoms of Parkinson's disease: a randomised, placebo-controlled, double-blinded study. Annals of Neurology. 2026.
- Zhang R, et al. Gut microbiota modulation via repeated donor faecal transplantation improves motor and gastrointestinal symptoms in drug-naïve Parkinson's disease: a randomised phase 2 trial. Signal Transduction and Targeted Therapy. 2026.
- Porcari S, Mullish BH, Asnicar F, et al. International consensus statement on microbiome testing in clinical practice. The Lancet Gastroenterology & Hepatology. 2025;10(2):154–167.