Long COVID and the gut: when your stomach won't settle after COVID
Diarrhoea, bloating and IBS after a COVID infection: what cohort studies show, what viral remnants in the gut might mean and which treatments have been tested so far.
How solid is the research? Trust score 2 of 5:Plausible
Large cohorts show that gut symptoms and IBS occur more often after COVID, although the figures vary. Viral remnants in gut tissue and an altered gut flora have been found; whether they cause the symptoms is open. For treatment there is so far a single larger positive trial with a synbiotic; most other approaches are untested or have failed in trials.
Cause or consequence? Root cause 3 of 5:Cause and consequence
Symptoms often remain after an infection. The infection starts things off, but the consequences can then carry on by themselves.
Healthy state
The coronavirus SARS-CoV-2 does not only attack the airways; it can also multiply in the gut lining. That is why many people have diarrhoea, nausea or abdominal pain in the acute phase. In a Stanford study, viral RNA was found in the stool of about half of those infected in the first week.
For most people this settles within days to a few weeks. The lining renews itself, the immune system tidies up, and the Microbiome, gut microbiota The community of all microbes in the gut, mainly bacteria, plus viruses, fungi and archaea. Most live in the colon. More in the chapter “Building microbial diversity” finds its balance again. In a Hong Kong cohort, the gut flora of people who recovered fully looked like that of people without COVID again after six months.
The World Health Organization speaks of a post-COVID-19 condition when, about three months after infection, symptoms are present that last at least two months and cannot be explained otherwise. Fatigue, shortness of breath and concentration problems are common; gut symptoms can be part of it.
Disrupted state: causes and effects
In a US cohort of more than 150,000 people after COVID and millions of controls, new gut disorders occurred more often in the year after infection: reflux, functional dyspepsia, functional bowel disorders, pancreatitis, liver and gallbladder problems. The risk rose with the severity of the acute illness, but was also present after cases not needing hospital care.
As after other gut infections, Irritable bowel syndrome Recurring abdominal pain linked to bowel movements, without tests finding another cause. Today it is understood as a disorder of gut–brain interaction. More in the chapter “The gut-brain axis” can develop (see IBS after infection). In an Italian study of hospitalised patients, 3.2 percent had new IBS one year after COVID, compared with 0.5 percent without COVID. Meta-analysis An analysis that combines the results of several studies. It is only as good as the studies it includes. arrive at about 12 percent but disagree on whether this is more than after other infections. Anxiety and depression clearly raised the risk.
A much-discussed lead is viral remnants in the gut. In 14 people without symptoms, researchers still found viral RNA and protein in small-bowel biopsies in half of them four months after infection. In Innsbruck, among 46 people with Inflammatory bowel disease Umbrella term for Crohn’s disease and ulcerative colitis: long-term, relapsing inflammation of the gut that needs medical treatment. More in the chapter “Immune system and inflammation”, seven months after mild COVID 32 had viral RNA and 24 had viral protein in the lining; post-COVID symptoms were mainly found in those with such remnants. No replicating virus could be cultured. A follow-up after two years reports that remnants and symptoms disappeared again.
Viral RNA can also persist in stool for a long time: in the Stanford study in 12.7 percent after four months and 3.8 percent after seven months, when nothing was detectable in the throat any more. Those with RNA in their stool more often had abdominal pain, nausea and vomiting. Whether such remnants cause symptoms or are simply left over is not clear.
The gut flora changes too. In the Hong Kong cohort, people with post-COVID had fewer Butyrate A short-chain fatty acid and the main energy source for the cells of the colon wall. It strengthens the barrier and dampens inflammation. More in the chapter “Butyrate and other short-chain fatty acids” producers such as Faecalibacterium prausnitzii and Bifidobacterium pseudocatenulatum and more Ruminococcus gnavus after six months. That is an association, not proof of a cause.
Where uncertainty reigns, expensive offers flourish: blood washing, infusion series, long courses of antibiotics or antivirals, special stool tests with a treatment plan. In a double-blind trial, plasma exchange did no better than a sham treatment, and a 15-day course of the antiviral nirmatrelvir/ritonavir did not improve symptoms.
Where it comes from and where it leads
The same symptoms can have different roots. This map shows what may be involved in this problem and what may follow from it.
Possible causes. . Possible consequences. Vagus nerve, POTS & connective tissue, Heartburn, Sensitive stomach, Brain fog & fatigue, IBS after infection, Gastroparesis, Digestive chain, SIBO, Weak cleaning wave, Pelvic floor, Food fear, Acid blockers (PPI), Abdominal pain, Bloating, Diarrhoea, Weak digestion, Methane & H₂S, Leaky barrier, Low DAO, Histamine, Intolerance, Nutrient deficiency, Constipation, Mouth & gums, Low variety, Opportunists, Allergies
- Possible causes
- This problem
- Possible consequences
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Connections, not certainty: a link means “can”, not “must”. What applies to you is best clarified in a talk with your doctor.
What often helps
Lifestyle
Diet, exercise, sleep, social contact and dealing with stress.
- Approach it like IBS after infection Symptoms after COVID resemble those after other gut infections. What is proven for IBS is a sensible starting point: regular meals, soluble fibre such as psyllium husk, and if needed a time-limited low FODMAP phase with support. Studies specifically after COVID are lacking. Promising How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [1]
- Pace your energy If you crash for days after exertion, it is better to take on activity in small portions with breaks rather than pushing through, and to discuss this with your doctor. This advice is based on clinical experience, not on a study checked here. Plausible How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.
- Eat varied food instead of doing cures There is no tested diet for rebuilding the gut flora after COVID. Plant variety, fibre as tolerated and fermented foods are the general basics. Strict elimination diets without reason tend to do harm because they reduce diversity. Plausible How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.
Natural supplements
Supplements do not replace a medical check-up. Discuss dosage and interactions with your doctor or pharmacist.
- Synbiotic: a first positive trial In a double-blind trial of 463 people in Hong Kong, a mix of bacteria and fibre (SIM01) taken for six months improved fatigue, memory and concentration problems, gut symptoms and general unwellness more often than placebo. The product was developed by the research group itself, independent confirmation is lacking, and the results cannot be transferred to other products. Plausible How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [2]
Medical treatments
Information, not a treatment recommendation. Decide together with a doctor. Approval and availability differ from country to country.
- Rule out other causes New gut symptoms after COVID are not automatically long COVID; the studies also show more reflux, gallbladder and pancreas problems. With weight loss, blood in the stool, fever, night-time symptoms, yellowing of the skin or new symptoms after 50, have it checked by a doctor, as well as coeliac disease, thyroid and inflammation markers. Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [3][1]
- Beware of expensive protocols Blood washing, infusion series, long courses of antibiotics or antivirals and special stool tests with treatment plans are not proven for long COVID. Plasma exchange and an antiviral brought no benefit in controlled trials. A post-COVID clinic or taking part in a trial is a better choice where available. Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [4][5]
- Psychological support as one building block Anxiety and depression clearly raised the risk of IBS after COVID. Gut-directed psychological therapy has good evidence in IBS, even though it has not been tested specifically after COVID. This does not mean the symptoms are imagined. Promising How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [6][7]
From the community: what people report
Experiences and tips from people with the same problems that come up again and again, but for which there are no meaningful studies yet. They are explicitly not evidence.
Rebuilding the gut after antibiotics
Many report that their gut collapsed after courses of antibiotics and that they spent months rebuilding it with probiotics, fibre and products for the gut barrier. Some say this clearly improved their complaints; others report the opposite and complain of intolerance to certain lactic acid bacteria. The relationship between antibiotics and rebuilding the gut is discussed inconsistently in the forums.
Histamine and mast cells as an explanation
Many people report that their gut problems went together with excess histamine and mast cell activation, visible in flushing, nausea and reactions to many foods. A combination of a low-histamine diet, antihistamines and mast cell stabilizers is frequently described, with mixed success. Some see the gut as a consequence here, not as the trigger.
Viral remnants in the gut as a core thesis
Many report the conviction that long Covid is sustained by viruses or viral remnants remaining in the gut, and from this they derive measures such as fasting, certain supplements or "antiviral" approaches. This interpretation is passed on as a self-model and rests on individual research hints; evidence for therapeutic benefit is lacking. Prolonged fasting can be dangerous for weakened people.
Personal reports can mislead: what helps many people may be a placebo, and what helps one may harm another. Treat them as ideas to raise with your doctor or pharmacist – not as instructions.
In the mood for something completely different? Another one, at random
How we rate the evidence
- Trust score 5 of 5:Established
- Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies.
- Trust score 4 of 5:Well supported
- Several randomised studies in humans with largely consistent results.
- Trust score 3 of 5:Promising
- Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies.
- Trust score 2 of 5:Plausible
- Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms.
- Trust score 1 of 5:Experimental
- Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.
Sources
- Lacy et al. 2021: ACG clinical guideline on irritable bowel syndrome (American Journal of Gastroenterology)
- Lau et al. 2024: Synbiotic SIM01 for post-acute COVID-19 syndrome, RECOVERY trial, randomised and placebo-controlled (Lancet Infectious Diseases)
- Xu et al. 2023: Gastrointestinal disorders in the year after COVID-19, US veterans cohort (Nature Communications)
- España-Cueto et al. 2025: Plasma exchange for post-COVID, double-blind against sham (Nature Communications)
- Geng et al. 2024: Nirmatrelvir/ritonavir for post-COVID, STOP-PASC trial (JAMA Internal Medicine)
- Wang et al. 2024: Incidence and risk factors of IBS after COVID-19, meta-analysis (European Journal of Gastroenterology & Hepatology)
- Black et al. 2020: Psychological therapies for IBS, network meta-analysis of 41 trials (Gut)
- Natarajan et al. 2022: GI symptoms and viral RNA in stool up to ten months after COVID-19 (Med)
- Liu et al. 2022: Gut microbiota over time in post-acute COVID-19 syndrome, prospective Hong Kong cohort (Gut)
- Soriano et al. 2022: WHO definition of post-COVID-19 condition, Delphi consensus (Lancet Infectious Diseases)
- Marasco et al. 2022: IBS after COVID-19, prospective GI-COVID19 cohort (Gut)
- Marasco et al. 2023: Functional dyspepsia and IBS after COVID-19, meta-analysis (Alimentary Pharmacology & Therapeutics)
- Gaebler et al. 2021: Antibody evolution after COVID-19, with viral remnants in small-bowel biopsies (Nature)
- Zollner et al. 2022: Viral antigens in gut mucosa in post-COVID and IBD (Gastroenterology)
- Zollner et al. 2024: Clearance of viral antigens and post-COVID symptoms after two years in IBD, short report (Gastroenterology)
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