A metabolite study demonstrated that indolepropionate was only detectable in the plasma of conventionally housed mice and not germ-free mice.18 One known function of indolepropionate is its ability to bind and activate Pregnane X receptor (PXR) which leads to improved intestinal barrier function and reduction of enterocyte tumor necrosis factor-α (TNF-α), two features that are abnormal in patients with NAFLD.42 Additionally, indolepropionate has strong correlations with human obesity and fatty liver disease. Here, TNF is linked to fatty liver disease.