SHORT-TERM FASTING AFFECTS LUTEINIZING-HORMONE SECRETORY DYNAMICS BUTNOT REPRODUCTIVE FUNCTION IN NORMAL-WEIGHT SEDENTARY WOMEN

Acute food withdrawal reversibly inhibits the hypothalamic-pituitary-g onadal axis in men and in rhesus monkeys, and it produces defects in L H pulsatility in normal-weight women. However, the clinical effect of short-term nutritional deprivation on the reproductive axis of normall y cycling women has not been evaluated. Thus we studied the effect of a 3-day fast during the midfollicular phase on menstrual cycle length, gonadotropin secretory patterns, follicular development, and ovulatio n. After a baseline ovulatory cycle, 12 women within 15% of ideal body weight were randomized to be fed (n = 7) or fasted (n = 10) on cycle days 7 to 9. Five of the women repeated the study and received the alt ernate diet. Endocrine and metabolic parameters of fasting and reprodu ctive physiology were measured on cycle days 6 to 12. Fasted physiolog y was demonstrated by characteristic alterations in growth hormone, in sulin-like growth factor I, TSH, and T-3 levels. During fed cycles, th e number of LH pulses remained constant on cycle days 6, 9 and 11, whe reas mean LH levels, LH area under the curve, and LH pulse amplitude i ncreased significantly over this time (all P < 0.05). In contrast, fas ted cycles were marked by a significant decrease in the number of LH p ulses on the last day of the fast (cycle day 9, P < 0.05) and by a lac k of increase over time of mean LH values, LH area under the curve, an d LH pulse amplitude. Follicle development, as assessed by daily ultra sound examination and estradiol measurements, was similar in all cycle s and was followed by ovulation in all women; follicular and luteal ph ase lengths of fasted and fed cycles were similar. We conclude that th e alterations in LH secretory dynamics that occur during a S-day fast are not sufficient to perturb follicle development and cycle lengths i n normal-weight sedentary women. The resilience of the reproductive ax is in these healthy women contrasts with the sensitivity of the hypoth alamic-pituitary-gonadal axis to acute nutritional withdrawal in men a nd in monkeys. We speculate that differences in the set point for sens ing fuel availability or in the status of energy balance before the in itiation of food deprivation may account for these species-specific an d sex-specific variabilities.