The original study executed between 2002-2004 was an interventional trial in which 20, healthy, normal-weight female subjects were randomized to a four-day fast plus daily subcutaneous injections of leptin or a four day fast plus daily subcutaneous injections of a placebo. The primary endpoints were gonadotropin pulsatility, TSH secretion and thyroid function, and cortisol secretion. The current study is a secondary analysis focussed on the placebo group which underwent a four-day fast. The study is looking at the effects of fasting on gut-derived hormones and inflammatory markers in healthy, normal-weight women. The hypothesis for this secondary analysis was that four days of fasting would augment levels of orexigenic gut-derived hormones and suppress levels of anorexigenic gut-derived horomones, while suppressing secretion of inflammatory cytokines.

Inclusion Criteria:

• female age 18-35
• BMI 20-26.0
• eumenorrheic with normal FSH, TSH, Prolactin
• Hgb > 12 g/dL, normal creatinine
• normal puberty and development
• negative pregnancy test. In addition, subjects agreed not to be sexually active during the course of the inpatient study and to use contraception for a period of 48 hours after discharge from the hospital.

Exclusion Criteria:

• medical or endocrine problems known to affect thyroid, reproductive, GH or cortisol function
• medications known to affect neuroendocrine function
• prior history of eating disorder or significant menstrual irregularities
• subjects who have a known hypersensitivity to E. Coli derived protein.
• subjects with a history of seizure disorder, significant cardiac disease, medication for cardiac disease, or kidney disease
• history of anaphylaxis or anaphylactoid like reactions.