Relative Energy Deficiency in Sport

Energy availability describes the dietary energy left to support the body once exercise energy expenditure has been subtracted, expressed relative to fat-free mass. When it falls and stays low, the body conserves energy by downregulating functions it can manage without in the short term, and the consequences are systemic rather than confined to one organ.

Current thinking places LEA on a continuum. Brief or mild exposure is adaptable and may cause no harm, whereas prolonged or severe exposure becomes problematic and produces the adverse outcomes that define the syndrome. A single numerical threshold is no longer treated as a reliable dividing line, since individual tolerance varies and moderating factors change how any given exposure plays out.

The effects reach many systems at once. Suppression of the hypothalamic-pituitary axis produces functional hypothalamic amenorrhoea in women and reduced testosterone in men. Bone formation falls while resorption continues, lowering bone mineral density and raising the risk of bone stress injury. Resting metabolic rate may be reduced, and immune, gastrointestinal, haematological, cardiovascular and psychological function may all suffer, with growth and maturation affected in the young athlete. Mental health sits on both sides of this, since psychological problems can precede REDs and drive the restriction, or follow from it. Performance falls through a blunted training response, reduced endurance and strength, and more frequent injury and illness.

REDs rarely announces itself. The athlete attends for something else, usually an injury, and the energy problem sits behind it. Recurrent or slow-healing bone stress injuries are the classic musculoskeletal presentation, alongside unexplained underperformance, persistent fatigue, poor recovery between sessions and frequent minor infections.

The menstrual history is a key part of assessment in female athletes, and oligomenorrhoea, amenorrhoea or delayed menarche should prompt a careful look at energy availability rather than reassurance. In male athletes the clues are subtler, so reduced libido, loss of morning erections, low mood and unexplained fatigue may be all there is. Gastrointestinal symptoms and irritability are common in both. Appearance is unreliable: an athlete with REDs may look entirely well and sit at an unremarkable weight, so a normal body composition must never be used to exclude the diagnosis.

The history carries much of the diagnostic weight, covering training load and its recent progression, eating pattern and any restriction, weight history, menstrual history, injury and illness pattern, mood and sleep. Examination matters too, and includes an assessment of medical stability with basic observations, lying and standing blood pressure and, in the young athlete, growth and pubertal progress. Electrocardiography is performed where the history or examination indicates it.

Screening questionnaires developed for athletes can flag those needing fuller assessment, and the International Olympic Committee (IOC) has published a clinical assessment tool for REDs, which runs from screening, through severity and risk stratification, to physician diagnosis and a treatment plan, stratifying the athlete by a traffic light system that carries training and competition recommendations. These tools support rather than replace clinical judgement.

There is no single validated diagnostic method, so investigations are targeted rather than a fixed panel, and each abnormal finding needs other causes excluded before it is attributed to REDs. In a woman with menstrual disturbance a pregnancy test comes first, followed by follicle stimulating hormone, luteinising hormone, oestradiol, prolactin and thyroid function, since functional hypothalamic amenorrhoea is a diagnosis of exclusion and shows low or inappropriately normal gonadotrophins alongside a low oestradiol. In men, a morning testosterone may be informative. Useful bloods in either sex include a full blood count, ferritin, thyroid function and 25-hydroxyvitamin D. Bone mineral density by dual-energy X-ray absorptiometry is considered where the history suggests bone compromise, and in this age group it is reported by Z-score rather than T-score. A Z-score at or below -2.0 is below the expected range for age, but a weight-bearing athlete should carry higher density than a non-athlete, so a Z-score between -1.0 and -2.0 with secondary risk factors such as hypo-oestrogenism or repeated stress fractures counts as low for an athlete, and bone density alone does not diagnose osteoporosis before the menopause. Magnetic resonance imaging is the investigation of choice for a suspected bone stress injury.

Treatment is easy to state and hard to deliver: close the energy gap. That means increasing energy intake, reducing exercise energy expenditure, or both, planned by a sports dietitian rather than issued as a target in clinic. Where an eating disorder is suspected, referral to a specialist eating disorder service is immediate and without watchful waiting, since the disorder drives the deficit and needs treatment in its own right. Disordered eating that falls short of a diagnosable disorder still needs experienced dietetic and psychological input rather than dietary advice alone.

This is multidisciplinary work involving the SEM clinician, a dietitian and, where indicated, a psychologist, with the coach brought in only where appropriate and with the athlete's consent, since a willingness to adjust the programme often decides whether it works. An athlete who is medically unstable needs urgent medical assessment and may need admission, not load restriction alone. Otherwise training is modified by severity, with load restriction for a high-risk bone stress injury and a reduced or altered programme for others. Return to full training and competition is graded and individualised, decided on health markers rather than on how the athlete is performing.

In women, the return of regular menstrual cycles is a useful clinical marker that energy status is recovering. Combined oral contraceptives should not be prescribed solely to restore menstruation or protect bone, because they do not reliably restore bone and they mask the menstrual signal that tells you whether treatment is working, although they remain appropriate for contraception or another clinical indication. Where amenorrhoea and low bone density persist despite adequate energy restoration, transdermal 17-beta-oestradiol with cyclical progesterone may be considered under specialist guidance, and it is preferred to an oral preparation because oral oestrogen undergoes a hepatic first pass that suppresses insulin-like growth factor 1, blunting the bone benefit. Serum 25-hydroxyvitamin D and calcium intake are assessed and any deficit corrected, alongside rather than instead of energy correction.

Recovery is slow, often many months, and bone density lags further behind. Prevention works better: education for athletes, coaches and parents, sensible load progression, and a culture that treats fuelling as part of training rather than an afterthought.

• •The 2023 IOC consensus statement on relative energy deficiency in sport, in the British Journal of Sports Medicine, updates the terminology from RED-S to REDs, along with the conceptual models and the evidence base.
• •The IOC clinical assessment tool for REDs supports screening, severity and risk stratification, and participation decisions.
• •Health4Performance, the British Association of Sport and Exercise Medicine educational resource, provides UK material for athletes, dancers, coaches, parents and clinicians.
• •Current NICE guidance on eating disorders applies where an eating disorder is identified, with immediate referral to a specialist service.

• •REDs is caused by problematic low energy availability, which may be inadvertent or driven by disordered eating.
• •It affects male and female athletes at all levels and is under-recognised in men.
• •It encompasses and extends the female athlete triad to more body systems and to men.
• •Recurrent bone stress injury and unexplained underperformance are the classic clinic presentations.
• •It is a clinical diagnosis with no single confirmatory test, so exclude other causes for each finding.
• •Treat by correcting the energy deficit with a multidisciplinary team; contraceptives do not restore bone.