The Effects of Relative Energy Deficiency in Sport (RED-S) on Endocrine, Bone, and Metabolic Health and Athletic Performance: A Narrative Review

Background: Relative Energy Deficiency in Sport (RED-S) is a syndrome caused by low energy availability that impairs multiple aspects of athletes’ health and performance. It affects both female and male athletes and may lead to endocrine, bone, and metabolic disturbances, as well as impaired recovery and increased injury risk. Aim: To review the effects of Relative Energy Deficiency in Sport (RED-S) on athletes’ endocrine, bone, and metabolic health, as well as on athletic performance and injury risk. Material and methods: A narrative review of studies published between 2016 and 2025 was conducted using PubMed, Scopus, and Web of Science to evaluate the effects of LEA and RED-S on endocrine, bone, metabolic, and performance-related outcomes in athletes Results: RED-S was consistently associated with endocrine and metabolic disturbances, impaired bone health, and a higher risk of bone stress injuries. Evidence for adverse effects on recovery, training adaptation, and performance was also identified, although these findings were more heterogeneous. Conclusions: RED-S is a multisystem condition that can compromise athletes’ endocrine, bone, and metabolic health, with the strongest evidence relating to skeletal health and bone stress injury risk. Early recognition and correction of low energy availability are essential to protect both health and athletic performance.