RED-S: Recognizing Relative Energy Deficiency in Sport in Female and Male Athletes
Relative Energy Deficiency in Sport, commonly known as RED-S, describes a cluster of health and performance problems that can develop when an athlete's energy intake does not match the energy demands of training. In 2023, the International Olympic Committee (IOC) published an updated consensus statement on RED-S in the British Journal of Sports Medicine, led by Dr. Margo Mountjoy and an international panel of sports medicine experts. The update reflects more than 170 new research studies published since the previous 2018 statement.
What drives RED-S?
At the core of RED-S is low energy availability (LEA) — a mismatch between the energy an athlete eats and the energy left over for normal body functions once exercise costs are subtracted. When this gap persists, the body starts conserving energy by scaling back processes such as bone formation, reproductive hormone production, and immune function. The 2023 statement also highlights that low carbohydrate availability specifically, not just total energy, can independently contribute to the syndrome.
Who is at risk?
RED-S was first described mainly in female endurance and aesthetic-sport athletes, but the updated consensus is explicit: male athletes are also affected, sometimes with less obvious symptoms because they usually lack an equivalent to the menstrual cycle as a visible warning sign. Athletes in weight-class sports, endurance sports, and sports that emphasize leanness or a particular body shape appear to carry higher risk, at any competitive level from youth to elite.
Warning signs to watch for
- Unexplained drop in training performance or slower recovery
- Frequent illness, injuries, or stress fractures
- Irregular or absent menstrual cycles in female athletes
- Persistent fatigue, low mood, irritability, or difficulty concentrating
- Preoccupation with food, body weight, or body image
- Unintentional changes in weight or difficulty maintaining weight
Health and performance consequences
Left unaddressed, RED-S can affect bone density (raising fracture risk), hormonal balance, cardiovascular health, immune function, and mental health. On the performance side, the consensus statement links RED-S to reduced training adaptation, impaired decision-making, decreased endurance and strength, and greater injury risk — the opposite of what athletes are training for.
What the consensus recommends
The 2023 statement introduces an updated screening and management tool, the REDs Clinical Assessment Tool version 2 (CAT2), designed for use by qualified clinicians to assess risk and severity. It calls for a multidisciplinary approach involving physicians, sports dietitians, and mental health professionals, alongside prevention efforts from coaches and sports organizations.
This article is for general education only and is not a substitute for professional medical advice. If you or an athlete you know shows possible signs of RED-S, please consult a physician or a qualified sports dietitian for a proper evaluation — do not attempt to self-diagnose or self-treat.
Source: British Journal of Sports Medicine (BJSM) — 2023 IOC Consensus Statement (Mountjoy et al.)
