Research shows Long COVID patients have imbalanced gut bacteria, with fewer beneficial bacteria and more potentially harmful ones, which may contribute to fatigue, digestive problems, and brain fog. According to Gram Research analysis of 62 studies, this bacterial imbalance—called dysbiosis—appears linked to Long COVID symptoms, but treatments targeting the microbiome remain largely untested and unproven.
Scientists are discovering that people with Long COVID often have different bacteria in their gut compared to healthy people. According to Gram Research analysis, a new review of 62 studies found that Long COVID patients tend to have fewer helpful bacteria and more harmful ones. This imbalance, called dysbiosis, might explain why some people experience fatigue, digestive problems, brain fog, and immune system issues after COVID-19. While researchers haven’t proven that fixing the microbiome will cure Long COVID, they’re exploring treatments like probiotics and special diets that might help restore healthy bacteria balance.
Key Statistics
A 2026 scoping review of 62 studies found that Long COVID patients consistently show reduced levels of beneficial bacteria like Faecalibacterium prausnitzii and increased levels of potentially harmful bacteria like Ruminococcus gnavus compared to healthy individuals.
According to research reviewed by Gram, microbiome dysbiosis in Long COVID was most frequently associated with fatigue, gastrointestinal symptoms, brain fog, and immune system dysfunction, though most evidence remains observational rather than from rigorous clinical trials.
A 2026 analysis of microbiome research in Long COVID identified probiotics, prebiotics, dietary changes, and fecal microbiota transplantation as proposed treatments, but found limited direct interventional evidence proving their effectiveness in Long COVID patients.
The Quick Take
- What they studied: Whether changes in gut bacteria (the microbiome) are connected to Long COVID symptoms and whether treatments targeting these bacteria could help patients feel better.
- Who participated: The review analyzed 62 published studies about Long COVID and gut bacteria. Most studies were small and descriptive rather than large clinical trials, so they involved various numbers of patients across different research projects.
- Key finding: Long COVID patients consistently show an imbalance in gut bacteria: they have lower levels of beneficial bacteria like Faecalibacterium prausnitzii and Bifidobacterium adolescentis, and higher levels of potentially harmful bacteria like Ruminococcus gnavus and Clostridium innocuum.
- What it means for you: This research suggests your gut bacteria might play a role in Long COVID symptoms, but it’s still early. Treatments like probiotics or dietary changes might eventually help, but more research is needed before doctors can confidently recommend specific microbiome treatments for Long COVID.
The Research Details
This was a scoping review, which means researchers searched through existing published studies rather than conducting their own experiments. They looked through four major scientific databases (PubMed, Scopus, Web of Science, and Cochrane Library) for all studies published between January 2000 and May 2025 that discussed Long COVID and microbiome changes. They included 62 studies that met their criteria.
The researchers organized information from these studies using a standardized form, looking for patterns about which bacteria were different in Long COVID patients, which symptoms were associated with these bacterial changes, and what treatments were being tested. They then summarized what they found in a narrative format, meaning they described the overall patterns rather than doing statistical calculations across all studies.
This approach is useful for mapping out what we know about a topic when research is still developing, but it doesn’t provide the strongest level of proof because most included studies were small, descriptive, or theoretical rather than rigorous clinical trials.
A scoping review is the right tool for this topic because microbiome research in Long COVID is still new and scattered across many different studies with different methods. By gathering and organizing all available evidence, researchers can identify patterns, highlight gaps in knowledge, and point out which questions need more rigorous testing. This helps guide future research priorities.
The strength of this review is limited by the quality of included studies: most were narrative reviews, conceptual discussions, or small observational studies rather than randomized controlled trials. No large-scale interventional studies testing microbiome treatments for Long COVID were found. The review is current (searching through May 2025) and followed established guidelines (Joanna Briggs Institute methodology), which increases reliability. However, readers should understand this represents early-stage evidence that suggests associations but doesn’t prove causation.
What the Results Show
The review found consistent patterns in gut bacteria composition among Long COVID patients. Specifically, patients showed reduced levels of beneficial bacteria species, particularly Faecalibacterium prausnitzii and Bifidobacterium adolescentis, which normally help maintain gut health and immune function. At the same time, Long COVID patients had increased levels of potentially harmful or inflammatory bacteria, including Ruminococcus gnavus and Clostridium innocuum.
These bacterial imbalances were associated with several Long COVID symptoms. Fatigue—the most common Long COVID complaint—appeared linked to microbiome dysbiosis in multiple studies. Gastrointestinal symptoms like diarrhea, constipation, and abdominal pain were frequently reported alongside bacterial imbalances. Neuropsychiatric symptoms including brain fog, anxiety, and depression also showed associations with altered microbiomes. Additionally, immune system dysregulation (when the immune system doesn’t work properly) was proposed as a mechanism connecting dysbiosis to Long COVID symptoms.
The review identified several proposed mechanisms for how dysbiosis might cause these problems. Beneficial bacteria normally produce compounds that strengthen the gut barrier and regulate immune responses. When these bacteria are depleted, harmful bacteria can cross the gut barrier more easily, triggering inflammation throughout the body. This systemic inflammation could explain fatigue and neurological symptoms.
The review found limited evidence about respiratory and oral microbiomes in Long COVID, suggesting these areas need more research. Several microbiome-targeted interventions were discussed, including probiotics (beneficial bacteria supplements), prebiotics (foods that feed good bacteria), synbiotics (combinations of both), dietary modifications, and fecal microbiota transplantation (FMT, where stool from healthy donors is transferred to patients). However, most of these interventions were only proposed or theoretically discussed rather than rigorously tested in Long COVID patients. The few studies that did test interventions showed preliminary results but lacked the rigorous design needed to prove effectiveness.
This review builds on growing recognition that the microbiome plays important roles in immune function, metabolism, and barrier protection. Previous research has shown microbiome dysbiosis in other post-viral conditions and chronic inflammatory diseases, so finding similar patterns in Long COVID is consistent with existing knowledge. However, this is among the first comprehensive reviews specifically mapping microbiome research in Long COVID, making it a timely synthesis of emerging evidence.
The review’s main limitation is that most included studies were descriptive or observational rather than experimental. This means researchers observed that dysbiosis and symptoms occurred together but couldn’t prove that dysbiosis caused the symptoms. Many studies were small and used different methods, making it hard to compare results. The review found almost no large-scale clinical trials testing whether microbiome treatments actually improve Long COVID symptoms. Additionally, most research focused on gut microbiome; evidence about other microbiomes (respiratory, oral) was sparse. The review cannot determine causality—dysbiosis might cause Long COVID symptoms, result from them, or both might stem from a third factor.
The Bottom Line
Based on current evidence, microbiome-targeted treatments for Long COVID cannot yet be confidently recommended as standard care (low confidence level). However, general gut health practices—eating diverse plant-based foods, staying hydrated, managing stress, and getting adequate sleep—support healthy microbiomes and may be worth discussing with your doctor. If you’re interested in probiotics or dietary changes, consult your healthcare provider first, as individual responses vary and some interventions may interact with medications.
Long COVID patients experiencing fatigue, digestive problems, brain fog, or other persistent symptoms should be aware of this research, as it suggests their microbiome might be involved. Healthcare providers treating Long COVID should consider this emerging evidence when developing treatment plans. Researchers and pharmaceutical companies should prioritize rigorous clinical trials testing microbiome interventions. People without Long COVID don’t need to take action based on this research, though maintaining general gut health is always beneficial.
If microbiome-targeted treatments prove effective, benefits would likely develop gradually over weeks to months as bacterial populations shift, not immediately. Most probiotic studies show changes after 4-12 weeks of consistent use. However, since this research is still preliminary, don’t expect dramatic improvements yet. Realistic expectations involve waiting for more rigorous clinical trials before microbiome treatments become standard Long COVID therapy.
Frequently Asked Questions
What is dysbiosis and how does it relate to Long COVID?
Dysbiosis is an imbalance in gut bacteria where harmful bacteria outnumber helpful ones. Research suggests this imbalance may contribute to Long COVID symptoms like fatigue and brain fog by triggering inflammation and weakening the gut barrier, though causation hasn’t been proven.
Can probiotics help treat Long COVID symptoms?
Probiotics are proposed as a potential Long COVID treatment, but current evidence is limited and mostly theoretical. No large clinical trials have proven probiotics effectively treat Long COVID. Talk to your doctor before starting probiotics, as individual responses vary.
What foods should I eat to improve my gut bacteria if I have Long COVID?
Eat diverse plant-based foods including vegetables, fruits, whole grains, and legumes to feed beneficial bacteria. Fermented foods like yogurt, sauerkraut, and kimchi may also help. Aim for 25-30 grams of fiber daily, but increase gradually to avoid digestive upset.
Is fecal microbiota transplantation being tested for Long COVID?
Fecal microbiota transplantation (FMT) was discussed in Long COVID research as a potential treatment, but the review found almost no rigorous clinical trials testing it specifically for Long COVID. It remains experimental and is not standard care.
How long would it take to see improvements from microbiome treatments?
If microbiome treatments prove effective, changes typically develop over 4-12 weeks as bacterial populations shift. However, since Long COVID microbiome treatments aren’t yet proven, realistic timelines for symptom improvement remain unknown.
Want to Apply This Research?
- Track daily symptoms (fatigue level 1-10, digestive issues yes/no, brain fog severity) alongside dietary intake and any probiotic or prebiotic use. Record this for 8-12 weeks to identify personal patterns between diet, supplements, and symptom changes.
- Start a food diary focusing on fiber intake (aim for 25-30g daily from vegetables, fruits, whole grains) and fermented foods (yogurt, sauerkraut, kimchi) that support healthy bacteria. Use the app to set daily reminders and track which foods correlate with better or worse symptom days.
- Create a weekly symptom score combining fatigue, digestive comfort, and cognitive function. Compare this score to your dietary diversity score (number of different plant foods eaten) and supplement adherence. Over 12 weeks, identify whether increasing plant diversity or adding probiotics correlates with symptom improvement in your individual case.
This article summarizes research on microbiome dysbiosis and Long COVID but does not constitute medical advice. The evidence reviewed is largely preliminary and observational; microbiome-targeted treatments for Long COVID are not yet proven effective or standard care. Do not start probiotics, make major dietary changes, or pursue any Long COVID treatment without consulting your healthcare provider. If you have Long COVID symptoms, work with a qualified physician to develop an individualized treatment plan. This research is evolving, and recommendations may change as new evidence emerges.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.
