Running on Empty: Relative Energy Deficiency in a Military Endurance Athlete.

Relative Energy Deficiency in Sports (RED-S) is a clinical syndrome characterized by low caloric intake relative to energy expenditure, resulting in a cascade of endocrine, metabolic, and musculoskeletal consequences. In females, hallmark features include decreased bone mineral density and menstrual dysfunction, though the syndrome affects multiple organ systems in both sexes. We present the case of a 22-year-old active-duty military member who suffered recurrent stress fractures, irregular menstrual cycles, and chronic fatigue that impacted her duty status. She was noted to have a long history of non-intentional calorie restriction and was eventually diagnosed with RED-S. Treatment consisted of a multidisciplinary approach, resulting in objective improvement in bone density and a successful return to full duty status. This case highlights the importance of early diagnosis and appropriate treatment of RED-S among military members to decrease morbidity and prevent limitations to military readiness and career progression.