Inclusion Criteria:  History:  over the age of 18, normal pubertal development stable weight for previous three months, normal body mass index (BMI between 18.5-25) regular menstrual cycles  Physical examination:  • systolic BP < 140 mm Hg, diastolic < 90 mm Hg  Laboratory studies: (per MGH reference ranges)  normal hemoglobin hemoglobin A1C < 6.5% BUN, creatinine not elevated AST, ALT < 3x upper limit of normal  Exclusion Criteria:  active illicit drug use, history of a medication reaction requiring emergency medical care, difficulty with blood draws. history of chronic disease, except well controlled thyroid disease, recent use of prescription medications which interfere with metabolism or reproduction (recent = within 5 half-lives of the drug). Use of levothyroxine or seasonal allergy medications is acceptable, history of diabetes in a first degree relative, use of contraceptive pills, patches or vaginal rings within last 4 weeks. hyperlipidemia by fasting lipid panel positive serum pregnancy test (for all women)