INS and obesity due to melanocortin 4 receptor deficiency: For example, the Firmicutes genus (dominant in people living with obesity) significantly decreased in people after MBS, associating with significant weight loss, improved insulin sensitivity, and widespread systemic inflammation, while the Akkermansia genus (reduced in mice with obesity and T2D) increased after MBS, showing reduced fat mass, increased thermogenesis, and induction of systemic GLP-1 secretion in mice [87].