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Gut microbiota and functional diseases of the gastrointestinal tract.

INTRODUCTION
Functional gastrointestinal disorders (FGIDs) are a common group of chronic gastrointestinal (GI) diseases defined by symptom-based diagnostic criteria, which consider chronic or recurrent symptoms of the GI tract in the absence of other organic or biochemical reasons. Recent evidences have been highlighted the role of gut microbiota in the pathophysiology of the FGIDs.


EVIDENCE ACQUISITION
A critical analysis of the existing literature on the role of gut microbiota in FGIDs was performed by evaluating the differences of composition, functions and role of intestinal flora in FGIDs of the upper and lower gastrointestinal tract. Moreover, we focused on recent evidences about gut microbiota and celiac disease (CD), especially in CD patients who are symptomatic despite gluten-free diet (GFD), and who seem to share similar features of FGIDs subjects. In this setting, we conducted an additional PubMed search for guidelines, systematic reviews (SR) and primary studies published after the last search update of the most recent reviews.


EVIDENCE SYNTHESIS
Some data suggest that, in a significant percentage of patients, the microbiota plays an important role in the genesis and maintenance of FGIDs. Probiotic supplementation and antibiotic treatment appear to be of therapeutic value, although the clinical data remain controversial.


CONCLUSIONS
Despite the exciting and growing research on the role of gut microbiota in FGIDs, our knowledge remains fairly limited. Further studies are needed to measure the diversity, function and resistance to antibiotics of the intestinal microbiota in FGIDs.