The Role of the Gut Microbiota in Estrogen Metabolism and Dietary Flax as a Potential Modulator.

Inclusion Criteria: * healthy premenopausal women (20-40 years) * normal to overweight (22-29.9 kg/m2) * normally menstruating (25-35 day cycles) * not have used estrogen-based contraception for \>6 months. * sedentary to moderately active (exercise ≤120 min week-1) * must not be taking phytoestrogenic dietary supplements, or lipid- or glucose- lowering medications. Exclusion Criteria: * smoking * pregnancy or breastfeeding * Hormonal contraceptive use (past 6 mo.) * Women with contraindications to GnRHAG: * History of fragility fracture * Low BMD (i.e., proximal femur or lumbar spine z scores \< -2.0) * Abnormal vaginal bleeding * History of breast cancer or other estrogen-dependent neoplasms * History of venous thromboembolic events * Hypersensitivity to leuprolide acetate or benzyl alcohol (the vehicle for injection of leuprolide acetate) * Evidence for depressive symptoms (Score ≥ 18 on the Beck Depression Inventory, BDI) * Moderate or severe renal impairment defined as a calculated creatinine clearance \<50 mL/min based on the equation of Cockcroft and Gault91 * Chronic hepatobiliary disease, conservatively defined as liver function tests (AST, ALT, alkaline phosphatase, Total Bilirubin) \>1.5 times the upper limit of normal (if such values are obtained on initial screening and thought to be transient in nature, repeated testing will be allowed) * antibiotic or probiotic use within 2 months of sample collection