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Martin Šporin and Dorjana Zerbo Šporin

reductions in bone mineral density (Mehta et al., 2018). In 2014, the
International Olympic Committee introduced the broader concept of
Relative Energy Deficiency in Sport (RED-S) to acknowledge that inad-
equate energy availability affects athletes of both sexes (although it is
generally more common in females) and extends beyond reproductive
and skeletal consequences (Mountjoy et al., 2014). High prevalence rates
have been reported among competitive athletes. A systematic review and
meta-analysis found that low energy availability affected 44.2% of female
competitive athletes and 49.4% of male competitive athletes (Gallant et
al., 2024), while the prevalence of RED-S has been estimated at between
22% and 58% across a variety of sports (Logue et al., 2020).

Pathophysiology and Clinical Presentation
RED-S is a clinical syndrome in which low energy availability results
in multisystem physiological dysfunction, affecting, among other sys-
tems, metabolic function, reproductive and menstrual function, skeletal
health, immune function, protein synthesis, and cardiovascular health
(Mountjoy et al., 2014). The hypothalamus and pituitary gland detect the
energy deficit and initiate adaptive neuroendocrine responses. During
periods of low energy availability, fat stores are mobilised and circulat-
ing leptin concentrations decrease accordingly. Reduced leptin signalling
appears to play a central role in this process. Because leptin is downreg-
ulated during LEA, this hormonal alteration may contribute to several
RED-S-related disorders. RED-S is characterised by neuroendocrine dis-
turbances involving the central hypothalamic-pituitary axes, particular-
ly the reproductive, thyroid, adrenal, and somatotropic axes (Angelidi et
al., 2024). Low leptin concentrations are believed to be fully or partially
responsible for the neuroendocrine adaptations associated with starva-
tion, including suppression of reproductive function (Chan & Mantzoros,
2005).
As adipose tissue reserves become progressively depleted, the body
shifts from relying predominantly on lipolysis towards increased protein
catabolism (Angelidi et al., 2024). Female endurance athletes participat-
ing in weight-bearing sports who exhibit signs of low energy availabili-
ty tend to demonstrate reduced bone mineral density, smaller total and
cross-sectional bone area, lower estimated bone strength, and thinner
cortical bone, all of which may increase the risk of bone stress injuries.
In contrast, the effects of low energy availability on bone health in male
athletes remain insufficiently understood (Hutson et al., 2021). Addition-

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