While the relationship between changes in the gut microbiota and energetic homeostasis has mainly been studied in humans with overweight/obesity or in animal models of obesity, in this study, we determined how a WD and repeated FMT from human donors affected phenotype, accumulation of liver FAs, and modifications of the gut microbial community, as well as SCFAs and AAs abundance, in Mtarc2 knockout mice (Mtarc2-KO) compared with background C57BL/6 N mice. The gene discussed is MTARC2; the disease is obesity due to melanocortin 4 receptor deficiency.