Low energy availability, such as that associated with undernutrition and obesity, disturbs female reproductive function, and some central and peripheral factors are known to affect these changes; for example, the upregulation of hypothalamic appetite-regulatory factors, such as orexin and neuropeptide-Y (NPY), suppresses gonadotrophin-releasing hormone (GnRH) secretion. Here, NPY is linked to obesity due to melanocortin 4 receptor deficiency.