Evidence for a causal role of low energy availability in the induction of menstrual cycle disturbances during strenuous exercise training.
Level 5 - mechanism / opinion, no new human data
Animal research model (non-human primates)
PubMed 11701675 · doi:10.1210/jcem.86.11.8024
What was done
A longitudinal study evaluated whether low energy availability causes exercise-induced reproductive dysfunction in eight adult female cynomolgus monkeys (Macaca fascicularis). The monkeys underwent progressive running training up to 12.3 ± 0.9 km/day over 7 to 24 months with constant food intake until amenorrhea developed (absence of menses for ≥100 days with suppressed LH, FSH, estradiol, and progesterone). Four of the eight amenorrheic monkeys were then given supplemental calories (138–181% of baseline intake) while maintaining their daily exercise volume. Hormone levels, time to ovulatory recovery, and plasma T3 concentrations were tracked.
What was found
All four supplemented monkeys restored ovulatory cycles and elevated reproductive hormone levels while continuing strenuous daily running. Circulating gonadotropins recovered within 12 to 57 days from the start of supplemental feeding. The rate of reproductive recovery correlated strongly with the amount of supplemental energy consumed (r = -0.97, P < 0.05). Plasma T3 decreased by 27% during amenorrhea induction and increased by 18% during reversal (P < 0.05).
Why it matters
This study provides direct experimental evidence that exercise-induced amenorrhea is driven by an energy deficit rather than the mechanical or physiological stress of exercise alone. It demonstrates that ovulatory function can recover through increased caloric intake without reducing training volume.
Limits
The study was conducted in a non-human primate model with a very small sample size (n = 8 total, n = 4 re-fed). The abstract does not report the trajectory or comparator data for the four monkeys that did not receive supplemental calories.
Cited by
- supports Exercise-induced amenorrhea in female athletes is caused by an overall shortage of available energy budget rather than intrinsic ovarian pathology.