Abstract

Most living organisms have circadian clocks which maintain rhythm in internal cycles of behavior, physiology, and metabolism, allowing them to anticipate the earth's 24-hour rota-tion. In mammals, circadian integration of metabolic systems optimizes energy gathering and usage across the light and dark cycles. Disruption of circadian rhythms may lead to metabolic dysfunctions such as obesity and obesity-related disorders. The molecular and hormonal mechanism behind obesity is mostly related to mRNA expressions in hypothala-mus, and leptin, and melatonin hormone levels. In obesity and related disorders, the chron-obiotic hormone melatonin regulates physiological functions such as energy metabolism, body fat, and reproduction by cross-interacting with leptin. Leptin signals satiety by inhibit-ing Neuropeptide Y/Agouti-Related Peptide (NPY/AgRP genes in hypothalamus and exerts its effects on food intake, body weight, and the reproductive system. In this review, the mo-lecular and hormonal mechanisms behind obesity were discussed.