What Is RED-S? Symptoms, Causes, and Recovery Explained

What is RED-S? Relative Energy Deficiency in Sport happens when you're not eating enough to support both your training and your body's basic functions. It's not just "overtraining" or "burnout", it's a systemic problem that affects hormones, metabolism, bone density, mood, immunity, and performance. And it doesn't just happen to elite athletes or women.

RED-S occurs when energy intake is too low relative to exercise expenditure, leaving insufficient fuel for the body to maintain normal physiological function. The result is a cascade of symptoms that many athletes dismiss as "just part of hard training", but chronic fatigue, feeling cold all the time, irritability, lost periods, frequent injuries, and stalled performance aren't badges of honor. They're warning signs.

How RED-S differs from the Female Athlete Triad: The older "triad" model focused on three connected problems in female athletes: disordered eating, amenorrhea (lost periods), and low bone density. RED-S expanded this framework in 2014 to recognize that under-fueling affects all body systems—and all genders. Men can and do develop RED-S, though it often goes undiagnosed because the warning signs (like hormonal disruption) are less visible than a missed period.

Early warning signs of RED-S: declining performance despite consistent training, frequent illness or injuries that won't heal, loss of menstrual period (in women) or low libido (in men), feeling cold when others are comfortable, mood changes including irritability, depression, or anxiety, obsessive thoughts about food or body composition, and stress fractures or unexplained bone injuries. Many athletes experience these symptoms for months or years before connecting them to under-fueling.

What the research says: A 2024 paper asked "Does RED-S Exist?", not to dismiss the condition, but to push for clearer diagnostic criteria and better research. The science is still evolving, but the clinical reality is clear: athletes who chronically under-fuel experience measurable hormonal, metabolic, and bone density changes that resolve when energy availability improves.

Why athletes fall through the cracks: Diet culture celebrates restriction. Endurance sports often reward lighter bodies in the short term. Coaches and even medical providers may miss the signs, especially in male athletes or those who don't "look" underweight. And many athletes genuinely don't realize they're under-eating, high training loads make it easy to fall into energy deficit without intentional restriction.

What recovery actually requires: Eating enough is non-negotiable—and "enough" is usually more than athletes expect. Recovery also means reducing training load, sometimes significantly, to allow the body to repair. This isn't a quick fix; hormonal and metabolic recovery can take months to years depending on severity. Working with professionals who understand RED-S—sports dietitians, endocrinologists familiar with athletes, therapists if disordered eating is involved—makes a meaningful difference.

Being tired, cold, and cranky isn't "just part of training." Losing your period isn't a sign you're finally lean enough. Getting injured every season isn't bad luck. These are symptoms, and they're telling you something. Whether you're chasing PRs or just trying to feel good in your body again, the answer is almost always the same: eat more, rest more, and stop treating your basic needs as obstacles to performance.

References:

Mountjoy, M., Ackerman, K. E., Bailey, D. M., Burke, L. M., Constantini, N., Hackney, A. C., … Verhagen, E. (2023). International Olympic Committee’s (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine, 57(17), 1073–1097. https://doi.org/10.1136/bjsports-2023-106994

Stellingwerff, T., Mountjoy, M., McCluskey, W. T. P., Ackerman, K. E., Verhagen, E., Heikura, I. A., … et al. (2023). Review of the scientific rationale, development and validation of the International Olympic Committee Relative Energy Deficiency in Sport Clinical Assessment Tool: V.2 (IOC REDs CAT2). British Journal of Sports Medicine. https://doi.org/10.1136/bjsports-2023-106914

Jeukendrup, A. E., Areta, J. L., Van Genechten, L., Langan-Evans, C., Pedlar, C. R., Rodas, G., … Walsh, N. P. (2024). Does relative energy deficiency in sport (REDs) syndrome exist? Sports Medicine, 54, 2793–2816. https://doi.org/10.1007/s40279-024-02108-y

Areta, J. L., Jeukendrup, A. E., Van Genechten, L., Langan-Evans, C., Pedlar, C. R., Rodas, G., … Walsh, N. P. (2025). Limited empirical support for relative energy deficiency in sport (REDs) syndrome. Sports Medicine, 55(8), 2051–2055. https://doi.org/10.1007/s40279-025-02220-7

Ackerman, K. E., Palacios, C., Lambert, M. I., & others. (2023). Methodology for studying Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine, 57(17), 1136–1144. https://bjsm.bmj.com/content/bjsports/57/17/1136.full.pdf