RED-S Syndrome and Bone Health in Athletes: A UK Evidence Guide

What is RED-S syndrome?

RED-S — Relative Energy Deficiency in Sport — is the International Olympic Committee's term for a syndrome in which low energy availability impairs multiple body systems, including bone, hormones, metabolism and immunity. "Low energy availability" (LEA) simply means the dietary energy left over after exercise is too low to support normal physiological function — an athlete is out-training what they eat.

The concept broadened the older female athlete triad — low energy availability, menstrual dysfunction and low bone mineral density — to recognise that the same energy shortfall harms male and para athletes too, not only women Deutsche Zeitschrift für Sportmedizin, 2020. The IOC's RED-S framework, first set out in 2014, was updated in 2023 to describe LEA as sitting on a spectrum — from an adaptable, low-level deficit to a problematic one that drives ill health Wu Tsai Human Performance Alliance summarising British Journal of Sports Medicine 2023;57:1073-1097, 2023.

Does RED-S affect male athletes or only women?

It affects both — that recognition was the whole point of moving from the "female athlete triad" to RED-S. Because the female triad was framed around menstrual disruption, it left male athletes out of the picture even though the same underlying energy shortfall affects them Sports Medicine (Springer), 2024.

In men the signals are often quieter. Rather than a missed period, the clues may be suppressed sex hormones, recurrent bone stress injuries, persistent fatigue and underperformance — which is one reason RED-S in male athletes is frequently missed Physiological Research, 2025.

How does RED-S affect bone health and stress-fracture risk?

When energy availability stays low, bone is one of the first systems to suffer — turnover shifts toward breakdown over formation, gradually lowering bone density and raising stress-fracture risk. Prolonged LEA changes the hormonal environment bone depends on — lower oestrogen, IGF-1 and leptin alongside higher cortisol — which impairs bone metabolism and lowers BMD Z-scores, particularly in endurance and aesthetic athletes Physiological Research, 2025.

At the tissue level this looks like a catabolic state: in a retrospective analysis of elite athletes, those with REDs showed reduced bone-formation markers (osteocalcin and P1NP) alongside raised resorption, together with significantly lower lumbar-spine and total-hip Z-scores than athletes without REDs Journal of Cachexia, Sarcopenia and Muscle (Wiley), 2025. In that same study, 70% of athletes with REDs had sustained stress fractures, versus 25% of those without Journal of Cachexia, Sarcopenia and Muscle (Wiley), 2025. The link between low BMD and higher stress-fracture incidence is well recognised, classically in endurance runners and ballet dancers Physiological Research, 2025, and amenorrhoeic athletes carry a greater stress-fracture burden still, with BMD falling as more menstrual cycles are missed StatPearls Publishing / NCBI Bookshelf, 2023.

Left unaddressed over years, the same process that lowers an athlete's BMD in their twenties can set the stage for osteoporosis later in life — which is why catching it early matters.

Which athletes are most at risk of RED-S?

Risk is highest wherever energy demands are large or leanness is prized. Three groups stand out across the literature:

• Endurance sports — distance running above all, where high energy expenditure meets a lean-is-fast culture Physiological Research, 2025.
• Aesthetic and leanness sports — gymnastics, figure skating and ballet/dance, where appearance and low body mass are rewarded Nutrients (MDPI), 2024.
• Weight-category and "weigh-in" sports — rowing and combat sports, where making weight can drive short-term energy restriction Deutsche Zeitschrift für Sportmedizin, 2020.

The judged and endurance sports are consistently flagged as carrying the greatest bone risk within the female-triad framework too StatPearls Publishing / NCBI Bookshelf, 2023.

What are the warning signs of RED-S?

The clearest early flags are menstrual disturbance in women, recurrent stress injuries, unexplained fatigue and a stalling of performance. A UK narrative review lists amenorrhoea lasting more than three months, recurrent stress fractures, fatigue and reduced performance among the clinical signs that should prompt a closer look Deutsche Zeitschrift für Sportmedizin, 2020.

Two traps are worth naming. First, in men these signs are subtler — there's no missed period to flag the problem, and research links low energy availability to reduced bone density in male athletes too Sports Medicine (Springer), 2024. Second, athletes often read fatigue and underperformance as needing more training, which deepens the very energy deficit driving the problem. Building bone-loading strength work into a programme — the kind covered in our guide to the best exercises for bone health — supports the skeleton, but it cannot substitute for eating enough.

How is bone health assessed in RED-S?

In the research and clinical literature, bone density in athletes is measured with a DXA scan and reported as Z-scores, with reassessment usually every 6–12 months in those affected. Z-scores (which compare an athlete against age- and sex-matched peers) are used rather than the T-scores applied to older adults, and repeat DXA every 6 to 12 months is the standard monitoring interval in RED-S management Deutsche Zeitschrift für Sportmedizin, 2020. DXA is likewise the assessment method named in the female-triad guidance these frameworks grew out of StatPearls Publishing / NCBI Bookshelf, 2023.

Because RED-S monitoring means repeating a scan every 6 to 12 months, the case for a radiation-free option is strong. Our own bone health assessment uses REMS (Radiofrequency Echographic Multi Spectrometry), an ultrasound-based, radiation-free method — which makes repeat scanning across a season more comfortable to justify than X-ray-based DXA. (Note: the RED-S studies above evaluate DXA specifically; REMS is offered here as SMB's own modality, not something these particular papers assessed.)

How is RED-S managed?

Management doesn't treat the bone loss in isolation — the priority is restoring energy availability, delivered by a multidisciplinary team. The fix is to close the gap between energy taken in and energy burned, through better fuelling and, where needed, adjusted training load — not to reach first for a bone medication Nutrients (MDPI), 2024.

As a rough population-level guide, LEA is described as occurring below around 30 kcal per kg of fat-free mass per day, with an optimal target nearer 45 kcal/kg FFM/day — though these are general reference points, not individual diagnostic cut-offs Nutrients (MDPI), 2024. Delivery is a team effort: typically a sports physician, a dietitian, a physiotherapist and a psychologist working together, with bone density reassessed periodically to confirm recovery Deutsche Zeitschrift für Sportmedizin, 2020.

If you're an athlete, coach or parent who recognises these signs, a baseline bone assessment gives you a number to track against as fuelling and training are corrected. You can book a radiation-free bone health assessment to establish that baseline.

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This article is part of our screening technology series.