Endocrine markers of semistarvation in healthy lean men in a multistressor environment

Summary

Cohort study following 50 healthy lean US Army Ranger candidates through the eight-week Ranger course — a known multistressor combat-leadership selection involving sustained caloric deficit (roughly 1000 kcal/day below maintenance), sleep restriction (3.6 hours/night), and high physical demand. The authors documented body composition and endocrine markers across the eight-week course. Body fat fell from a starting mean of approximately 14% to a nadir of approximately 6%. Total testosterone, free testosterone, IGF-1, and T3 fell sharply over the course; testosterone reached roughly 10% of baseline values by the end-course measurement. The paper establishes the endocrine signature of sustained caloric deficit in already-lean men: when fat reserves drop below approximately 6%, the male reproductive and growth axes collapse.