Luteinizing Hormone Pulsatility Is Disrupted at a Threshold of Energy Availability in Regularly Menstruating Women
The 30 kcal/kg LBM/day experiment
Participants
n=29 regularly menstruating, habitually sedentary young women of normal body composition.
Protocol
5 days in the early follicular phase; two randomized trials per subject separated by at least 2 months
Supervised exercise expending 15 kcal/kg lean body mass (LBM) per day at 70% of aerobic capacity
Clinical dietary product set energy availability at 45 kcal/kg LBM/day (balanced) and at either 10, 20 or 30 kcal/kg LBM/day
Blood sampled daily, then every 10 min for 24 h; assayed for LH, FSH, estradiol, glucose, β-hydroxybutyrate, insulin, cortisol, GH, IGF-I, IGFBP-1, IGFBP-3, leptin and T3
Key Results
LH pulsatility was unaffected at 30 kcal/kg LBM/day (P > 0.3)
Below 30 kcal/kg LBM/day, LH pulse frequency decreased and pulse amplitude increased (all P < 0.04) — a threshold, not a linear dose-response
The disruption was more extreme in women with short luteal phases (P < 0.01)
The pattern of LH disruption most closely resembled the responses of glucose, β-hydroxybutyrate, GH and cortisol, and differed from the other metabolic hormones
The abstract reports no bone-marker outcome and states no result for T3 or IGF-I direction
Mechanism
Authors' interpretation: LH pulsatility is disrupted only below a threshold of energy availability "deep into negative energy balance"; the metabolic signals that tracked it (glucose, ketones, GH, cortisol) are candidates for the mediating mechanism
Inference, not tested here: chronic disruption of LH pulsatility is the route to menstrual dysfunction and, downstream, bone loss — those outcomes were not measured in this 5-day experiment
Practical Application
In 29 sedentary young women, 5 days at 30 kcal/kg LBM/day left LH pulsatility intact, while 20 and 10 kcal/kg LBM/day disrupted it (lower pulse frequency, higher amplitude) — the origin of the 30 kcal/kg FFM/day "floor" used in REDs work. An athlete whose intake minus training expenditure sits well below that per kg of lean mass for consecutive days is in the range where this experiment saw the reproductive axis falter.
Not from this paper; the base's own practice: periodize fuelling with training load — rest days are not automatic "eat less" days, because repair still needs substrate.
The threshold was measured in sedentary women over 5 days; how it transfers to trained athletes, to men and to chronic exposure is inference (see REF-341 for the 2023 consensus framing of LEA as a continuum with individual moderators).
Limitations
Female-only, habitually sedentary, young; not athletes
Short-duration (5-day) exposure; long-term dynamics extrapolated
Only 10, 20, 30 and 45 kcal/kg LBM/day tested — the threshold sits somewhere between 20 and 30
Controlled-lab feeding and exercise ≠ free-living athletes
How this entry was checked and changed
Why this level
regraded 2026-09-27 from A: controlled experimental study, n=29, each subject in two conditions
Content correction 2026-09-27
"EA reduction from 45 to 30 kcal/kg FFM/day produces detectable suppression of LH pulsatility" -> the abstract says LH pulsatility was UNAFFECTED at 30 and disrupted only below it (20 and 10); direction corrected.
"Changes bone turnover markers", "reduces T3 and IGF-1" -> not reported in this abstract; removed. Title reworded to the paper's actual finding.
Tier "4-5 Elite" -> Tier 0 (habitually sedentary women). Level A -> B+ (controlled experiment, n=29). Added n=29 and the protocol details from the abstract.
2026-09-28: added Journal line from the Europe PMC record (DOI 10.1210/jc.2002-020369, PMID 12519869).