Low Energy Availability and Its Consequences
- The FEMALE ATHLETE TRIAD is the interrelated triad of LOW ENERGY AVAILABILITY (with or without disordered eating), MENSTRUAL DYSFUNCTION (most importantly functional hypothalamic amenorrhoea), and LOW BONE MINERAL DENSITY; each component exists on a spectrum from optimal health to disease, and they are causally linked.
- RELATIVE ENERGY DEFICIENCY IN SPORT (RED-S) is the broader, more recent IOC concept that recognises LOW ENERGY AVAILABILITY as impairing MANY body systems - resting metabolic rate, menstrual/reproductive function, bone health, immunity, cardiovascular and gastrointestinal function, growth and development, and psychological health - as well as impairing PERFORMANCE, and crucially it applies to BOTH SEXES (not only female athletes).
- The CENTRAL DRIVER of both is LOW ENERGY AVAILABILITY (EA), defined as dietary energy intake minus exercise energy expenditure, expressed per kg of FAT-FREE MASS; chronically low EA suppresses the hypothalamic-pituitary-gonadal axis (low GnRH/LH -> low oestrogen, causing functional hypothalamic amenorrhoea) and lowers thyroid/metabolic activity, which together impair bone health.
- The key ORTHOPAEDIC consequence is BONE: low energy availability and low oestrogen reduce bone mineral density and cause BONE STRESS INJURIES and STRESS FRACTURES (and impair healing), so a female athlete presenting with a stress fracture, especially a recurrent one or one in a low-risk site, should be screened for the triad/RED-S, and amenorrhoea plus a stress fracture is a major red flag.
- SCREENING and assessment combine a history of disordered eating/menstrual status/stress fractures with validated questionnaires - the Low Energy Availability in Females Questionnaire (LEAF-Q) and the Low Energy Availability in Males Questionnaire (LEAM-Q) - plus DXA for bone mineral density and, where useful, hormonal/metabolic biomarkers; risk-stratification tools guide return-to-sport decisions.
- MANAGEMENT is MULTIDISCIPLINARY (sports physician, dietitian, psychologist/psychiatrist, and the coach/athlete) and the cornerstone is RESTORING ENERGY AVAILABILITY by increasing energy intake and/or reducing exercise energy expenditure; this restores menstrual function and improves bone health, and the condition is REVERSIBLE when energy balance is restored - alongside treating any disordered eating and optimising bone health (calcium/vitamin D, and oestrogen/therapy where indicated).
- “Female Athlete Triad = LOW ENERGY AVAILABILITY + MENSTRUAL DYSFUNCTION + LOW BMD; central driver = low energy availability (intake minus exercise expenditure per kg fat-free mass).
- “RED-S (IOC) = broader: low EA impairs many systems (metabolism, reproduction, bone, immunity, CVS, GI, psychological) + performance, in BOTH SEXES.
- “Orthopaedic link = bone stress injuries/stress fractures + low BMD (amenorrhoea + stress fracture = red flag). Screen (LEAF-Q/LEAM-Q, DXA); MULTIDISCIPLINARY management restoring energy availability (reversible).
Low energy availability drives menstrual dysfunction and low BMD (the Triad); RED-S broadens this to many systems and both sexes.
A female athlete with a stress fracture (especially recurrent) and amenorrhoea should be screened - restore energy availability (the condition is reversible).
The Triad, RED-S & the Bone Link
The Female Athlete Triad is the interrelated triad of low energy availability (with or without disordered eating), menstrual dysfunction (functional hypothalamic amenorrhoea) and low bone mineral density. RED-S (the IOC term) broadens this to recognise that low energy availability impairs many systems - metabolic rate, reproduction, bone, immunity, cardiovascular and GI function, growth and psychological health - and impairs performance, in both sexes. The central driver is low energy availability (intake minus exercise energy expenditure per kg fat-free mass), which suppresses the hypothalamic-pituitary- gonadal axis (low oestrogen) and metabolic activity, impairing bone. The key orthopaedic consequence is bone stress injuries and stress fractures with low BMD - so a female athlete with a stress fracture (especially recurrent) and amenorrhoea should be screened, and the condition is reversible when energy availability is restored.
| Aspect | Female Athlete Triad | RED-S (IOC) |
|---|---|---|
| Core | Low energy availability + menstrual dysfunction + low BMD | Low energy availability impairing many systems |
| Sex | Female athletes | Both sexes |
| Scope | 3 interrelated components | Multisystem (metabolism, reproduction, bone, immunity, CVS, GI, psychological) + performance |
| Central cause | Low energy availability | Low energy availability |
Screening & Management
- Screen the at-risk athlete: history of disordered eating, menstrual status (amenorrhoea/oligomenorrhoea), and stress fractures; validated questionnaires (LEAF-Q for females, LEAM-Q for males); DXA for bone mineral density; hormonal/metabolic biomarkers where useful.
- Have a low threshold orthopaedically: any female athlete with a bone stress injury/stress fracture - especially recurrent, or amenorrhoeic - should be assessed for the triad/RED-S.
- Restore energy availability (the cornerstone): increase energy intake and/or reduce exercise energy expenditure - this restores menstrual function and improves bone health, and the condition is reversible.
- Multidisciplinary care: sports physician, dietitian, psychologist/psychiatrist (treat disordered eating), with the coach and athlete; optimise bone health (calcium/vitamin D; oestrogen/therapy where indicated).
- Risk-stratified return to sport guides clearance and ongoing participation."
The orthopaedic trap in the Female Athlete Triad / RED-S is to treat the presenting bone stress injury or stress fracture in isolation and miss the underlying low energy availability that caused it - which guarantees recurrence. A female athlete with a stress fracture, particularly a recurrent one, in a low-risk site, or with amenorrhoea, should be screened for the triad with a history of disordered eating and menstrual status, questionnaires and DXA, and managed by restoring energy availability within a multidisciplinary team, not just rested and returned. Because the condition is reversible when energy balance is restored, early recognition and correction of the energy deficit prevent long-term consequences for bone health and fertility; conversely, returning an under-fuelled, amenorrhoeic athlete to full training without addressing the energy deficit is how stress fractures and low bone density recur.
Evidence & Key Studies
Energy availability and low energy availability as the mechanism of RED-S (narrative review)
- Energy availability (EA) is dietary energy remaining after exercise energy expenditure; chronic low EA (LEA) is the underlying mechanism of Relative Energy Deficiency in Sport (RED-S).
- LEA is associated with alterations in thyroid and reproductive hormones, reduced resting metabolic rate, lower bone mineral density and delayed recovery.
- Screening questionnaires (LEAF-Q for females, LEAM-Q for males) help identify at-risk athletes, with hormonal/metabolic biomarkers improving detection.
Reversibility of the Female Athlete Triad when energy balance is restored (case report)
- The Female Athlete Triad and RED-S are associated with low energy availability, causing menstrual dysfunction, impaired bone health and metabolic disturbances.
- A triathlete with critically low energy availability (under 10 kcal/fat-free mass/day), hypothalamic amenorrhoea and low bone density (lumbar Z-score -2.3) recovered menstrual and reproductive function when training reduced and intake improved.
- The case highlights the reversibility of the Female Athlete Triad when energy balance is restored, underscoring the importance of early intervention.
According to PubMed, the definition of energy availability and low energy availability as the mechanism of RED-S (with hormonal, metabolic, bone and recovery consequences) and the LEAF-Q/LEAM-Q screening tools come from the cited Espinar review; the components of the Female Athlete Triad, the link of critically low energy availability with amenorrhoea and low bone density, and the reversibility when energy balance is restored from the cited Gama case report. The triad-versus-RED-S framing, the orthopaedic link to bone stress injuries/stress fractures, the DXA assessment, and the multidisciplinary, energy-availability-restoring management are standard, well- established teaching (aligned with IOC RED-S consensus). (See also our Bone Stress Injuries / Stress Fractures and Osteoporosis topics.)
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A female distance runner presents with a stress fracture and tells you her periods stopped a year ago. What condition are you concerned about?”
“How would you manage the Female Athlete Triad / RED-S?”
Mnemonics & Memory Aids
ENERGY
Hook:ENERGY: low Energy availability, No periods, Eroded bone, RED-S (broader/both sexes), Generalised screen, Yes reversible (restore EA).
Definitions
- Female Athlete Triad: low energy availability + menstrual dysfunction + low BMD
- RED-S (IOC): low EA impairing many systems + performance, both sexes
- Central driver: low energy availability (intake minus exercise expenditure per kg FFM)
Mechanism & link
- Low EA -> suppressed HPG axis (low oestrogen) -> amenorrhoea
- Low oestrogen + metabolic suppression -> low BMD
- Orthopaedic consequence: bone stress injuries / stress fractures
Screening
- History: disordered eating, menstrual status, stress fractures
- LEAF-Q (females) / LEAM-Q (males); DXA for BMD
- Amenorrhoea + stress fracture = major red flag
Management
- Multidisciplinary (sports physician, dietitian, psychologist; athlete + coach)
- Cornerstone: restore energy availability (increase intake / reduce expenditure) - reversible
- Treat disordered eating; optimise bone health; risk-stratified return to sport