As suggested by experimental studies of short-term sleep deprivation, the mechanisms underlying the causal associations between short sleep duration and MetS may include hyperactivation of the hypothalamic–pituitary–adrenal axis and sympathetic nervous system, increased insulin resistance, and a boost of energy-intake behaviors regulated by appetite-regulating hormones (ghrelin, leptin, or endocannabinoids) as well as brain areas responsible for appetite and reward [11–13]. This evidence concerns the gene LEP and metabolic syndrome.