SIRT1 and obesity due to melanocortin 4 receptor deficiency: According to other scientific articles, calorie restriction increases SIRT1 concentrations [38] while in contrast overweight and obesity is associated with SIRT1 down-regulation [39,40], which might have been the reason in our experiment for the lower than usual SIRT1 expression in case of the Wistar rats that produced significant weight gain during the study.