INS and obesity due to melanocortin 4 receptor deficiency: This speculation is supported by gnotobiotic mouse model, whereby noteworthy elevations in body fat, fasting glucose and insulin levels, and development of insulin resistance that mimic physiological alterations in obesity patients, have been observed in GF mice post-colonization with a single saccharolytic gut bacterial species (Bacteroides thetaiotaomicron) and with gut microbiota from obese mice respectively (Backhed et al., 2004; Turnbaugh et al., 2006).