Can low energy availability suppress ovulation, and is cholesterol a precursor for ovarian hormones?

Low energy availability is a well-established reversible contributor to reproductive neuroendocrine disruption, whereas cholesterol’s role is fundamental biochemistry but should not be conflated with serum cholesterol measurements.

Clinical and reproductive effects

• In a randomized crossover study of regularly menstruating women, energy availability of 10 or 20 kcal/kg fat-free mass/day, versus 45 kcal/kg fat-free mass/day, reduced LH pulse frequency. This directly indicates altered hypothalamic-pituitary signaling.
• Reduced GnRH pulsatility and downstream LH/FSH signaling can lead to luteal-phase abnormalities, irregular or prolonged cycles, anovulation, and amenorrhea—the clinical spectrum exemplified by functional hypothalamic amenorrhea.
• The clinical effect is not determined by one energy-availability number alone: duration of deficit, exercise exposure, weight change, stress, baseline reproductive status, and individual susceptibility influence whether ovulation is affected. A level around 30 kcal/kg fat-free mass/day did not significantly alter LH pulsatility in the short experimental setting.
• Endocrine Society guidance supports correcting energy imbalance through increased caloric intake and nutritional quality and/or reduced exercise; weight gain is often required to restore hypothalamic-pituitary-ovarian function.

Steroid-hormone mechanism

• Cholesterol is the direct ovarian substrate for steroidogenesis. Following transport to the inner mitochondrial membrane, CYP11A1 converts cholesterol to pregnenolone.
• Pregnenolone is the common precursor for ovarian progesterone, androgens, and estrogens. Theca cells generate androgen intermediates; granulosa cells aromatize these to estrogens, while luteinized granulosa cells synthesize progesterone.
• Cellular cholesterol availability—not total serum cholesterol alone—is biologically relevant. Ovarian cells can obtain cholesterol from LDL/HDL, intracellular cholesteryl-ester stores, and de novo synthesis. In the BioCycle cohort, total cholesterol was slightly higher in anovulatory cycles, without a significant association per 5-mg/dL increment.

Bottom line

• Low energy availability can suppress LH-driven reproductive signaling and disturb ovulation. Cholesterol is indispensable as a steroid-hormone precursor, but low or low-normal circulating total cholesterol alone does not establish impaired ovarian hormone production or ovulation.