EPO regulation of metabolism combined with EPO induction by hypoxia-inducible factor (HIF) that gives rise to increased erythropoiesis and hemoglobin at high altitude may account for the reduced incidence of obesity associated with military recruits (about 94% male) in the United States stationed at high altitude [81,82,83,84]. Here, EPO is linked to obesity due to melanocortin 4 receptor deficiency.