Objective: In men and male monkeys, a short-term fast has been reported to have a major effect on the reproductive axis. In this study we investigated the effects of a short-term fast (72 hours) on female reproductive hormone secretion and menstrual function.
Design: The study consisted of an admission day (control), three successive fasting days (fast 1, 2 and 3) and a refeeding day (post fast).
Patients: Eight normal cycling women, ages 21-35, within 10% of ideal body weight, were fasted for 72 hours during the follicular phase of their menstrual cycle.
Measurements: On the admission day, the last day of the fast and the day of refeeding, blood samples were collected at 10-minute intervals from 0800 to 2000 h for determination of the LH pulse pattern. Daily determinations of immuno LH, FSH, oestradiol (E) and progesterone (P) were performed throughout the menstrual cycle in which the fast occurred.
Results: Throughout the fasting days, the consistently low serum levels of glucose and insulin confirmed that all the subjects were fasting. However, in spite of profound metabolic changes and a significant loss of weight, the short-term fast did not have discernible effects upon the reproductive hormones studied. Basal mean LH concentrations did not show any significant variation throughout the study period. The mean +/- SEM number of LH pulses was 13.4 +/- 1.5/12 h on the control day, 12.4 +/- 1.2/12 h (NS) on the third day of fasting and 11.0 +/- 1.5/12 h (NS) the day of refeeding. Each woman maintained a physiological pattern of LH, FSH, E and P throughout the menstrual cycle including the LH surge; ultrasound evidence of normal growth of a dominant follicle; and cycle length consistent with previous cycles.
Conclusions: Our results indicate that in spite of profound metabolic changes, a 72-hour fast during the follicular phase does not affect the menstrual cycle of normal cycling women. It appears that the female reproductive axis during this phase of the cycle is more resistant to an acute caloric deprivation than that of men or male monkeys.