Role of Leptin in the Neuroendocrine and Immune Response to Fasting

Inclusion Criteria: * Healthy lean women (with body mass indices \[BMI\] \< 25 kg/m2) * Overweight otherwise healthy men (with BMI \> 27 kg/m2) * Overweight otherwise healthy women (with BMI \> 27 kg/m2). Exclusion Criteria: * A history of any illness that may affect the concentrations of the hormones to be studied, e.g. infectious diseases, renal or hepatic failure, type 1 or type 2 diabetes mellitus, cancer or lymphoma, hypogonadism, malabsorption or malnourishment, hypo- or hyperthyroidism, hypercortisolism, alcoholism or drug abuse, anemia, or eating disorder * On medications known to affect the hormones to be measured (glucocorticoids, anti-seizure medications, and thyroid hormones) * A known history of anaphylaxis or anaphylactoid-like reactions, or a known hypersensitivity to E. coli derived proteins