E2 ModeratePreliminaryPEM unclearCase-ControlPeer-reviewedMachine draft
Increased d-lactic Acid intestinal bacteria in patients with chronic fatigue syndrome.
Sheedy, John R, Wettenhall, Richard E H, Scanlon, Denis et al. · In vivo (Athens, Greece) · 2009
Quick Summary
This study found that people with ME/CFS have higher levels of specific bacteria in their gut that produce a substance called D-lactic acid. These bacteria were found in much larger quantities in stool samples from ME/CFS patients compared to healthy people. The researchers suggest this excess D-lactic acid might help explain why some ME/CFS patients experience brain fog and cognitive problems.
Why It Matters
This research offers a potential biological explanation for the neurological and cognitive symptoms that affect many ME/CFS patients, suggesting a modifiable factor (gut microbiota composition) that could inform future interventions. Understanding whether D-lactic acid accumulation contributes to symptom severity could lead to targeted dietary or antimicrobial treatment strategies for a subset of patients.
Observed Findings
- Enterococcus spp. viable count in CFS patients: 3.5 × 10⁷ cfu/L vs. 5.0 × 10⁶ cfu/L in controls (7-fold increase, p<0.01).
- Streptococcus spp. viable count in CFS patients: 9.8 × 10⁷ cfu/L vs. 8.9 × 10⁴ cfu/L in controls (>1000-fold increase, p<0.01).
- Enterococcus faecalis and Streptococcus sanguinis produced significantly more D-lactic acid from labeled glucose than E. coli (p<0.01).
- Significant increase of Gram-positive facultative anaerobic fecal microorganisms in CFS cohort compared to controls (p<0.01).
Inferred Conclusions
- Intestinal colonization with D-lactic acid producing bacteria (Enterococcus and Streptococcus species) is elevated in ME/CFS patients and may link to neurocognitive dysfunction symptoms.
- D-lactic acidosis could explain both the neurological impairment and mitochondrial dysfunction observed in some ME/CFS patients.
- Dysbiosis characterized by elevated Gram-positive facultative anaerobic bacteria may represent a treatable pathophysiological feature in a subgroup of ME/CFS patients.
Remaining Questions
- Is the dysbiosis a primary cause of ME/CFS or a secondary consequence of infection, antibiotic use, diet, or reduced activity?
- Do D-lactic acid levels in blood or cerebrospinal fluid correlate with symptom severity or cognitive impairment in ME/CFS patients?
What This Study Does Not Prove
This study demonstrates association, not causation—it does not prove that elevated D-lactic acid bacteria cause ME/CFS symptoms or dysfunction. It cannot determine whether the altered microbiota is a primary driver of disease or a secondary consequence of ME/CFS or its associated lifestyle factors. The study does not establish whether reducing these bacteria would improve patient symptoms.
Tags
Symptom:Cognitive DysfunctionFatigue
Biomarker:MetabolomicsBlood Biomarker
Method Flag:Weak Case DefinitionExploratory Only
Metadata
- PMID
- 19567398
- Review status
- Machine draft
- Evidence level
- Single-study or moderate support from human research
- 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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