E1 ReplicatedPreliminaryPEM unclearRCTPeer-reviewedMachine draft
A randomized, double-blind, placebo-controlled pilot study of a probiotic in emotional symptoms of chronic fatigue syndrome.
Rao, A Venket, Bested, Alison C, Beaulne, Tracey M et al. · Gut pathogens · 2009 · DOI
Quick Summary
This study tested whether a specific probiotic bacteria could help reduce anxiety in ME/CFS patients. Thirty-nine patients took either the probiotic or a placebo daily for two months. The researchers found that patients taking the probiotic had lower anxiety scores compared to those taking placebo, and their gut bacteria levels changed in expected ways.
Why It Matters
Anxiety affects many ME/CFS patients and current treatment options are limited. This study provides preliminary evidence that modifying gut bacteria through probiotics may offer a non-pharmacological approach to reducing emotional symptoms, opening a new avenue for symptom management in ME/CFS.
Observed Findings
- Significant increase in Lactobacillus counts in the probiotic group compared to placebo
- Significant increase in Bifidobacteria counts in the probiotic group compared to placebo
- Significant decrease in anxiety symptom scores in the probiotic group versus placebo (p=0.01)
- No significant change reported in depression scores (Beck Depression Inventory results not detailed)
- 39 CFS patients completed the two-month intervention with stool and symptom data collected at baseline and endpoint
Inferred Conclusions
- Lactobacillus casei strain Shirota supplementation alters the composition of gut microbiota in CFS patients in the expected direction
- Changes in gut microbiota composition may be associated with reduction in anxiety symptoms
- The gut-brain axis, potentially mediated by intestinal microbes, may play a role in emotional symptom regulation in CFS patients
Remaining Questions
- What is the durability of anxiety symptom improvement after the probiotic intervention ends?
- Which specific bacterial metabolites or signaling pathways are responsible for the anxiety reduction?
What This Study Does Not Prove
This pilot study does not prove that probiotics are an effective treatment for ME/CFS—the small sample size and short duration limit generalizability. It also does not establish the causal mechanism by which the bacteria reduce anxiety, nor does it clarify whether the observed effect would persist beyond two months or which CFS patients might benefit most.
Tags
Symptom:Fatigue
Biomarker:Blood Biomarker
Method Flag:PEM Not DefinedWeak Case DefinitionSmall SampleExploratory Only
Metadata
- DOI
- 10.1186/1757-4749-1-6
- PMID
- 19338686
- Review status
- Machine draft
- Evidence level
- Replicated human evidence from multiple independent studies
- Last updated
- 8 April 2026
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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