In relation to cellular metabolism, metformin has been reported to foster SIRT1 activity to maintain proper circadian rhythm of CLOCK and BMAL1 during obesity, since the absence of SIRT1 inhibits function of CLOCK and BMAL1 in an obese phenotype (Caton et al., 2011[25]). Here, CLOCK is linked to obesity due to melanocortin 4 receptor deficiency.