Sex Steroid Responses to Energy Deficits in Elite Male Soldiers

Long term energy deficits can result in impaired sex steroid hormones, health, and performance in elite athletes, yet the effect of multiple bouts of energy deficits combined with operational stressors on sex steroid hormones during extended military training are less established. The Army Ranger Course (RTC) is a 61+ day leadership training with considerable physiological and psychological stress due to high physical activity volume coupled with sleep and energy deficits. This research assesses the hypothesis that male testosterone and estradiol concentrations would decrease across RTC while in energy deficits. Methods: Male Soldiers (n=26; 25±4 yrs; 82.5±9.1 kg) provided blood samples and measured body composition (dual-energy x-ray absorptiometry) at the start of RTC (F0) and immediately following each of the three field training exercises: general (F1, 4d), mountains (F2, 5d), swamp (F3, 10d). Total testosterone (T, ng/ml), estradiol (E2, pg/ml), sex hormone binding globulin (SHBG, nmol/L), and albumin (ALB, g/dL) were measured in serum and free testosterone (freeT, ng/ml) calculations used T, SHBG and ALB values. Total energy expenditure (TEE, Kcal/d; doubly labeled water), energy intake (EI, Kcal/d; ration food wrappers) and energy balance (EB, Kcal/d; EI-TEE) were measured during each exercise. Linear mixed models adjusted for age, body mass, and/or time of day assessed differences in hormones, body composition, and EB from F0 to F1, F2, and F3. Results: Soldiers experienced an average daily EB of -1550±772 (F1), -1890±1040 (F2), and -1210±1050 (F3) kcal/d. Fat mass and fat free mass decreased in each exercise compared to F0 (p<0.001). T decreased at F1 (Δ [95% CI]; -1.1 [-2.0, -0.3] and F2 (-1.4 [-2.0, -0.8]) compared to F0 (p<0.01) but was similar to F0 at F3. FreeT remained lower (F1: -38.2 [-55.0, -21.5]; F2:-36.4 [-48.1, -24.8]; F3: -23.4 [-41.4, -5.3]; p<0.02) whereas SHGB remained higher (F1: 23.3 [19.1, 27.5]; F2: 14.0 [9.7, 18.3]; F3: 12.4 [8.1, 16.7]; p<.001) than F0 across all exercises and ALB only decreased during F3 (-0.2 [-0.3, -0.1]; p<0.02). E2 decreased at F2 (-5.4 [-9.8, -1.0]; p=0.02) compared to F0. Similar trends were seen in EB and T changes from F1-3, but these changes were not significantly associated with each other. Conclusion: These findings indicate male T and E2 concentrations, but not SHBG or freeT, can be comparable to baseline levels despite an energy deficit. Interestingly, the recovery of T and E2 levels were noted during the exercise with the least severe energy deficit yet longest duration. However, the lack of association between changes in energy deficit and hormones highlights the need to further investigate the influence of severity and duration of energy deficits along with additional stressors unique to military training environments on sex steroid hormones. Funded by USAMRDC; author views not representative of the Army/DoD. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.