In an earlier study, based on the experimental evidence, it has been hypothesized that metformin shifts gut microbiota composition through the enrichment of Akkermansia muciniphila [52], the mucin-degrading bacterium which has also been shown to be inversely correlated with the onset of inflammation, altered adipose tissue metabolism and metabolic disorders during obesity in mice [53]. The gene discussed is MUC5AC; the disease is obesity due to melanocortin 4 receptor deficiency.