These results may have been, in part, reflective of the imbalance in BMI between the groups in that study, as well as differences in environmental and dietary factors between the two study cohorts. In addition, the lack of classification of patients in each group based
on liver histology may have also affected the results of the study by Zhu et al.29 Lastly, differences in age may have also played a role, as discussed below. There are various theories to support an inverse correlation between Bacteroidetes and steatohepatitis. First, Bacteroidetes carry 45% of the lean metabolic potential in a study comparing the microbiome of lean and obese adults.21 A lower percentage of Bacteroidetes could have affected energy balance by facilitating metabolic dominance of other bacteria
that are more efficient in extracting energy from the diet. Jumpertz et al.11 showed that a 20% increase in fecal Bacteroidetes is associated with a 150 kcal decrease in energy harvest from the diet. A second theory is that an initial hit causes the cell death of Bacteroides leading to LPS release from their cell wall and subsequent endotoxemia.19 The latter leads to the development of NASH.19, 27 It is not clear what would cause the death of these microorganisms. Changes in diet could play a role, as shown by studies in obese subjects, whose baseline lower fecal Bacteroidetes increase when placed on a hypocaloric diet or after bariatric mafosfamide surgery.38, 39 There is literature supporting an increase in intestinal permeability of subjects with IR, such as in obesity40 and diabetes.41 Recently, Zhu et al.29 reported higher serum ethanol levels in children
with NASH, which was thought to be bacterially derived and, hence, potentially also contributing to increased intestinal permeability. In addition, there is scientific evidence linking Trichostatin A cost endotoxemia with states of glucose intolerance, such as NAFLD.41, 42, 43 Animals and humans exposed to low levels of endotoxin develop IR.19, 22 Exploratory analysis from our study also suggested a potential link between the intestinal microbiota and IR by showing a trend toward a negative association between Bacteroidetes and IR when controlling for BMI. This requires further studies. We did not find lower bifidobacteria counts or higher Firmicutes-to-Bacteroidetes ratio in NASH compared to SS and HC. This is in contrast to some of the previously published literature in the field of obesity9, 14, 44 and the recent study by Zhu et al. on children with NASH.29 The inability to show differences in these bacteria may have been due to the sample size; however, the size of our cohort was similar to that of other cross-sectional studies on IM in obesity9, 11, 12, 37 and NAFLD.29 Our results on Firmicutes-to-Bacteroidetes ratio are in line with other smaller projects, which also failed to replicate the findings of Ley et al.