Relative Energy Deficiency in Sport (REDs) is a condition characterized by low energy availability (LEA), which can lead to a range of physiological and endocrine abnormalities. REDs encompasses a spectrum of issues, including neuroendocrine, bone, immune, and hematological effects, and is associated with impaired health, performance, and well-being. LEA is the primary cause of REDs and can affect both males and females, leading to conditions such as menstrual dysfunction, bone stress injuries, and impaired reproductive function. The pathophysiology of REDs involves complex interactions between various hormonal and physiological systems, including the hypothalamic-pituitary-gonadal (HPG), hypothalamic-pituitary-thyroid (HPT), and hypothalamic-pituitary-adrenal (HPA) axes. Leptin, a hormone involved in energy homeostasis, plays a key role in regulating these systems, and its levels are often reduced in individuals with REDs. The activin-follistatin-inhibin (AFI) axis is also implicated in the pathophysiology of REDs. Current treatment approaches for REDs focus on addressing the underlying cause of LEA through nutritional, behavioral, and lifestyle modifications. While leptin replacement therapy is not currently recommended due to limited evidence of its safety and effectiveness, research is ongoing to explore its potential in managing REDs. Additionally, the role of the AFI axis in REDs is being investigated as a potential therapeutic target. The management of REDs requires a multidisciplinary approach, and further research is needed to better understand the underlying mechanisms and develop effective treatments. The definition and recognition of LEA/REDs in athletic and military populations remain areas of ongoing research and debate, with the need for standardized thresholds and diagnostic criteria. Overall, REDs is a complex condition that requires a comprehensive understanding of its pathophysiology and the development of targeted interventions to improve health and performance in affected individuals.Relative Energy Deficiency in Sport (REDs) is a condition characterized by low energy availability (LEA), which can lead to a range of physiological and endocrine abnormalities. REDs encompasses a spectrum of issues, including neuroendocrine, bone, immune, and hematological effects, and is associated with impaired health, performance, and well-being. LEA is the primary cause of REDs and can affect both males and females, leading to conditions such as menstrual dysfunction, bone stress injuries, and impaired reproductive function. The pathophysiology of REDs involves complex interactions between various hormonal and physiological systems, including the hypothalamic-pituitary-gonadal (HPG), hypothalamic-pituitary-thyroid (HPT), and hypothalamic-pituitary-adrenal (HPA) axes. Leptin, a hormone involved in energy homeostasis, plays a key role in regulating these systems, and its levels are often reduced in individuals with REDs. The activin-follistatin-inhibin (AFI) axis is also implicated in the pathophysiology of REDs. Current treatment approaches for REDs focus on addressing the underlying cause of LEA through nutritional, behavioral, and lifestyle modifications. While leptin replacement therapy is not currently recommended due to limited evidence of its safety and effectiveness, research is ongoing to explore its potential in managing REDs. Additionally, the role of the AFI axis in REDs is being investigated as a potential therapeutic target. The management of REDs requires a multidisciplinary approach, and further research is needed to better understand the underlying mechanisms and develop effective treatments. The definition and recognition of LEA/REDs in athletic and military populations remain areas of ongoing research and debate, with the need for standardized thresholds and diagnostic criteria. Overall, REDs is a complex condition that requires a comprehensive understanding of its pathophysiology and the development of targeted interventions to improve health and performance in affected individuals.