Endocrine and chronobiological effects of fasting in women

Objective: To determine whether fasting in women would suppress GnRH/LH drive in a high- versus low-gonadal steroid milieu. Design: Case-control study. Setting: Academic clinical research center. Patient(s): Eleven eumenorrheic women and eleven women taking combined oral contraceptives. Intervention(s): Seven of the eleven women in each group underwent an acute 72-hour fast. Blood samples were obtained at 15-minute intervals for 24 hours before the fast and during the last 24 hours of fasting. Main Outcome Measure(s): Twenty-four-hour profiles of LH, cortisol, and melatonin were assessed. Ovarian activity was tracked with estradiol and progesterone levels, and metabolic responses were gauged by measuring thyroid hormone and β-hydroxy-butyric acid levels. Result(s): Fasting increaseed β-hydroxy-butyric acid and reduced free thyronine. Fasting in the midfollicular phase had no effect on LH pulsatility or on FSH, estradiol, or subsequent luteal-phase progesterone levels. However, fasting elevated cortisol and resulted in a phase advance in melatonin secretion of 81 minutes in both the midfollicular and luteal phases. Conclusion(s): Fasting in women elicited expected metabolic responses and apparently advanced the central circadian clock without compromising reproductive function.