LEP and obesity due to melanocortin 4 receptor deficiency: On the other hand, it has been suggested that lower obesity rates among highlanders as compared to lowlanders can also be explained by direct effects of living at high-altitude on human physiology (e.g., loss of appetite due to increased leptin concentrations [55] and increased thermogenesis due to cold temperatures that increase thyroid hormone [56] and catecholamine levels [57]).