RED-S
RED-S is an acronym that stands for Relative Energy Deficiency in Sport. The condition was formerly referred to in the literature as the Female Athlete Triad, which consisted of low energy availability, amenorrhea, and low bone mineral density. The terminology has since changed to be more inclusive of all genders, body types, and the broader range of health consequences associated with low energy availability. According to the International Olympic Committee, RED-S is a condition of low energy availability that can have serious long-term consequences for both health and athletic performance. Simply put, an athlete is not consuming enough energy to meet the demands of exercise, training, and daily life. This can negatively affect multiple body systems, including reproductive health, bone health, immune function, psychological well-being, cardiovascular health, and ultimately athletic performance. There are two primary contributors to RED-S: underfueling and overtraining.
RED-S has also gained increased attention in the media as more athletes have spoken out about the negative aspects of running culture, including weight shaming, which can contribute to RED-s. Inadequate energy intake can lead to both physical injuries and mental health concerns. In females, overtraining and/or underfueling can result in amenorrhea (the absence of a menstrual cycle) or an anovulatory state (the absence of ovulation). These menstrual irregularities can increase the risk of infertility, bone health deterioration, cardiovascular disease, and increased arterial thickness. Low estrogen levels contribute to decreased bone mineral density, which can eventually lead to osteopenia or osteoporosis. In the short term, however, low bone mineral density increases the risk of bone stress reactions or fractures, most commonly affecting the tibia, metatarsals, navicular, and femoral neck. Underfueling is often associated with disordered eating behaviors, including chronic calorie restriction or binge eating, both of which are common among athletes of all genders.
Understanding the causes of RED-S can help coaches, athletic trainers, and healthcare providers identify symptoms earlier and intervene before serious health consequences develop or athletic performance declines. One commonly used screening tool is the Relative Energy Deficiency in Sport Clinical Assessment Tool (RED-S CAT), which helps evaluate individuals suspected of having low energy availability. The RED-S CAT also serves as a guide for physical therapists and coaches when making return-to-play decisions. In addition, coaches and healthcare providers should monitor for signs such as unexplained weight loss, delayed growth or development, recurrent injuries or illnesses, mood changes, menstrual dysfunction, and decreased athletic performance.
Based on the assessment, the RED-S CAT classifies athletes into low-, moderate-, or high-risk categories using a “green, yellow, and red light” system. A red light classification indicates that the athlete is at high risk and should receive evaluation and treatment from a healthcare provider before returning to sport. A yellow light classification indicates moderate risk, meaning the athlete may continue participating with close monitoring and appropriate treatment. A green light classification indicates low risk, allowing the athlete to continue participation without restrictions. A multidisciplinary and interdisciplinary team approach, including the coaching staff, physician, registered dietitian, physical therapist, athletic trainer, and sports physiologist, is the most effective strategy for diagnosing, treating, and monitoring RED-S in order to reduce the risk of long-term health complications. What this means for us, it is important to make sure we are all properly fueling especially if we are increasing training to avoid these health consequences. In addition to monitoring ourselves, it is important to share these risks with others that we run or train with because the lack of education about this topic increases the risk to endurance athletes.
References:
- Mountjoy, M., Sundgot-Borgen, J., Burke, L., Ackerman, K. E., Blauwet, C., Constantini, N., Lebrun, C., Lundy, B., Melin, A., Meyer, N., Sherman, R., Tenforde, A. S., Torstveit, M. K., & Budgett, R. (2018). International Olympic Committee (IOC) Consensus Statement on Relative Energy Deficiency in Sport (RED-S): 2018 Update. International Journal of Sport Nutrition and Exercise Metabolism, 28(4), 316-331. Retrieved May 24, 2026, from https://doi.org/10.1123/
ijsnem.2018-0136 - Todd E, Elliott N, Keay N. Relative energy deficiency in sport (RED-S). Br J Gen Pract. 2022 May 26;72(719):295-297. doi: 10.3399/bjgp22X719777. PMID: 35618459; PMCID: PMC9172228.https://www.
childrenshospital.org/ conditions-treatments/reds - Cabre HE, Moore SR, Smith-Ryan AE, Hackney AC. Relative Energy Deficiency in Sport (RED-S): Scientific, Clinical, and Practical Implications for the Female Athlete. Dtsch Z Sportmed. 2022;73(7):225-234. doi: 10.5960/dzsm.2022.546. Epub 2022 Nov 1. PMID: 36479178; PMCID: PMC9724109.