This study will enroll up to 60 physically active men in a 3-phase randomized, placebo-controlled trial. After completing a 14-day (free-living, phase 1), energy-adequate, diet-acclimation phase (protein, 1.6 g∙kg-1∙d-1; fat 30% total energy intake, with remaining energy derived from carbohydrate), participants will be randomized to one of two experimental groups and undergo a 28-day (live-in, phase 2), 55% energy deficit phase: energy deficit alone (DEF) or energy deficit + exogenous testosterone (DEF+TEST). Recovery (free-living, phase 3) will be assessed after completing phase 2 to determine when body mass has been recovered within ± 2.5% of initial body mass (duration will vary, 42-day maximum for phase 3). This study will delineate the contribution of testosterone declines from the physical and mental demands encountered by Warfighters during military training and combat operations on complex markers of physiological and psychological status, addressing a direct, consistently observed, gap in knowledge.