Wang et al. found reduced serum levels of TNF-α and IL-6 to be related to increased abundance of Roseburia and Akkermansia, and the Gram-negative bacterium Prevotella in the feces of Otsuka Long–Evans Tokushima Fatty (OLETF) rats (a genetic animal model of T2DM) treated with metformin and Houttuynia cordata [227]. This evidence concerns the gene TNF and type 2 diabetes mellitus.