This study proposes to test the specific question that a eucaloric, low-fat diet given to women with obesity will result in an increase in reproductive hormones.

This an open-label, multi site study in pre-menopausal women aged 18-40 years old with a history of regular menstrual cycles (25-35 days long) of high BMI. The objective of the study will be to determine the effects of a one month long, eucaloric low-fat diet on reproductive hormone levels in women with a high BMI. The study will occur over 4 menstrual cycle (approximately 4 months). During the study the participants will have a pre-diet cycle where no food will be consumed, an on-diet cycle where the customized low-fat diet will be consumed, and two post diet cycles. First morning voided urine will be collected during all four cycles along with 3 blood draws during the study. Participants will be asked to use a reliable barrier method of birth control or abstain from intercourse during the study.

Inclusion Criteria:

• Normal TSH and prolactin
• Regular menstrual cycles every 25-40 days
• No history of chronic disease affecting hormone production, metabolism or clearance
• No use of reproductive hormones, or medications/supplements known to impact them, within 3 months of enrollment
• Use of a reliable method of contraception (female or male partner sterilization, IUD, abstinence, diaphragm or cervical cap)
• Normal ovarian reserve (AMH of 0.5ng/ml or greater)
• Normal testosterone levels at screening or absence of clinical evidence of hyperandrogenemia (acne, facial hirsutism [defined as Ferriman-Gallwey score>8] or alopecia)

Exclusion Criteria:

• Baseline dietary assessment indicative of 28% or less daily calories from fat
• Inability to comply with the protocol (many meals per week eaten outside of the home, frequent travel)
• Pregnancy or planned pregnancy within next 6 months at time of screening
• HbA1C >6.5%

This study examines female reproductive hormones.