Increased Calorie Intake to Reverse Energy Deficiency in Exercising Women: Impact on Bone and Menstrual Cyclicity

Inclusion Criteria for Ovulatory Control Volunteers: * 18-35 years * BMI 16-25 kg/m2 * At least 2 hr/wk of aerobic exercise * Gynecological age \>/= 5 years * Weight stable (+/- 2 kg) last 6 months * History of regular menses for 6 months Inclusion Criteria for Women with Irregular or Absent Menses: * 18-35 years * BMI 16-25 kg/m2 * At least 3 hr/wk of aerobic exercise * Gynecological age \>/= 5 years * Weight stable (+/- 2 kg) last 6 months * No menses within past 3 months or 6 or less menses in last 12 months * Low to normal bone mass (L1-L4 Z score \</=0) Exclusion Criteria for all participants: * Hormonal contraceptives in last 6 months * Smoking currently * Current clinical diagnosis of an eating disorder * Use of medications incompatible with measurement of reproductive or metabolic hormones, including thyroid medications that may interfere with any of the study outcomes. * Dietary habits incompatible with prescribed diet for study * Any metabolic, reproductive or bone disease * Sedentary individuals with less than 120 minutes (2 hrs) of activity per week