Leptin is a hormone secreted by fat cells under normal conditions and acts in the brain to decrease appetite and increase energy use. Leptin levels usually go down with fasting. This study will evaluate the secretion of an investigational agent called leptin in lean and overweight individuals while fasting and investigate the potential role of leptin as a regulator of immune function and mediator of the neuroendocrine response to food deprivation in humans. Data derived from these studies will provide insights into the mechanisms underlying altered hormone levels and immune function in malnutrition and obesity and thus may provide the basis for future therapeutic interventions for obesity.

Comparison: fed state vs. fasting state vs. fasting + leptin state

Accepts Healthy Volunteers

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 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, eating disorder
• on medications known to affect the hormones to be measured (glucocorticoids, anti-seizure medications, thyroid hormones
• a known history of anaphylaxis or anaphylactoid-like reactions, or a known hypersensitivity to E. Coli derived proteins