<h3>Background & Aims</h3> The histopathology of nonalcoholic fatty liver disease (NAFLD) is similar to that of alcoholic liver disease. Colonic bacteria are a source of many metabolic products, including ethanol and other volatile organic compounds (VOC) that may have toxic effects on the human host after intestinal absorption and delivery to the liver via the portal vein. Recent data suggest that the composition of the gut microbiota in obese human beings is different from that of healthy-weight individuals. The aim of this study was to compare the colonic microbiome and VOC metabolome of obese NAFLD patients (n = 30) with healthy controls (n = 30). <h3>Methods</h3> Multitag pyrosequencing was used to characterize the fecal microbiota. Fecal VOC profiles were measured by gas chromatography–mass spectrometry. <h3>Results</h3> There were statistically significant differences in liver biochemistry and metabolic parameters in NAFLD. Deep sequencing of the fecal microbiome revealed over-representation of Lactobacillus species and selected members of phylum Firmicutes (Lachnospiraceae; genera, <i>Dorea</i>, <i>Robinsoniella</i>, and <i>Roseburia</i>) in NAFLD patients, which was statistically significant. One member of phylum Firmicutes was under-represented significantly in the fecal microbiome of NAFLD patients (Ruminococcaceae; genus, <i>Oscillibacter</i>). Fecal VOC profiles of the 2 patient groups were different, with a significant increase in fecal ester compounds observed in NAFLD patients. <h3>Conclusions</h3> A significant increase in fecal ester VOC is associated with compositional shifts in the microbiome of obese NAFLD patients. These novel bacterial metabolomic and metagenomic factors are implicated in the etiology and complications of obesity.

Fecal Microbiome and Volatile Organic Compound Metabolome in Obese Humans With Nonalcoholic Fatty Liver Disease