E2 ModeratePreliminaryPEM not requiredCase-ControlPeer-reviewedReviewed
Standard · 3 min
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.
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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Would selective reduction of these bacteria (via diet, probiotics, or antimicrobials) improve symptom outcomes in affected patients?
What percentage of the total ME/CFS population has this specific dysbiotic pattern, and are there other distinct microbiota profiles in other patient subgroups?