RED-S Syndrome – Relative Energy Deficiency in Sport

The year 1993 marked the initial scientific identification and characterization of a distinct clinical phenomenon termed the "female athlete triad," which predominantly affected young women engaged in high-performance athletics. This condition was characterized by the concurrent presence of three primary disturbances: disordered eating patterns, menstrual dysfunction, and progressive bone mineral density loss culminating in osteoporosis. As physiological research advanced, chronic low energy availability was subsequently incorporated into the symptomatic framework of this syndrome. In 2014, the International Olympic Committee (IOC) introduced a more comprehensive and precise terminology, redefining the phenomenon as *Relative Energy Deficiency in Sport* (RED-S). The underlying etiology of RED-S stems from a sustained mismatch between energy expenditure and intake, which precipitates widespread systemic impairments—affecting both female and male athletes across varying levels of competitive engagement (De Souza et al., 2014).

Low energy availability, alternatively referred to as a caloric deficit relative to elevated metabolic demands, constitutes a physiological state wherein the quantity of calories ingested—whether through dietary sources or supplemental nutrition—proves inadequate when measured against total daily energy expenditure, encompassing both basal metabolic rate and physical activity levels. This condition predominantly affects competitive athletes but is likewise observed among highly active amateurs and individuals with clinically significant underweight, defined by a body mass index (BMI) falling below 17.5 kg/m². Diagnostic confirmation relies on a quantitative threshold: an intake below 30 kilocalories per kilogram of fat-free mass (FFM) is deemed insufficient, whereas the optimal range centers around 45 kilocalories per kilogram of FFM. The health ramifications of sustained energy deficiency are multifaceted, potentially encompassing endocrine dysfunction, compromised immune response, heightened susceptibility to injuries, and long-term declines in physiological performance. Consequently, ongoing supervision by qualified professionals—including sports dietitians and sports medicine physicians—is imperative to mitigate adverse outcomes through personalized nutritional strategies and rigorous physiological monitoring (Melin et al., 2015; International Olympic Committee, 2018).

In individuals with chronic energy deficiency, secondary hypothalamic amenorrhea may develop due to disrupted pulsatile secretion of gonadotropin-releasing hormone (GnRH). This dysregulation results in diminished release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), subsequently leading to reduced estrogen levels and anovulation. Clinical presentations include menstrual irregularities, impaired fertility, or complete cessation of menses (Drosdzol-Cop & Zachurzok, 2020). Diagnosis is particularly challenging in young women, where irregular bleeding patterns are common. Furthermore, hormonal contraceptive use may obscure primary symptoms, significantly complicating the diagnostic process (Gordon et al., 2017).

Inadequate caloric intake triggers a cascade of endocrine disruptions that profoundly compromise skeletal system homeostasis. Diminished levels of critical metabolic regulators—including estradiol, insulin-like growth factor 1, the adipocyte-derived hormone leptin, and the active thyroid metabolite triiodothyronine—are closely associated with progressive bone mineral density loss, impaired bone remodeling mechanisms, and heightened susceptibility to mechanical injuries such as fractures. Notably, while these disturbances predominate in women due to inherent hormonal differences, they are also documented in men, as evidenced by clinical research, including the 2018 meta-analysis conducted by Papageorgiou and colleagues.

Among athletes whose dietary energy intake consistently falls below metabolic demands, a range of cardiovascular abnormalities is frequently documented. These include an unfavorable blood lipid profile, impaired endothelial function within blood vessels, hypotension, and a reduced resting heart rate. In cases of severe or prolonged energy deficiency, more critical conditions may emerge, such as cardiac arrhythmias, bradycardia (abnormally slow heart rate), or valvular dysfunctions (Mountjoy et al., 2018). Individuals with chronically low energy availability also commonly report gastrointestinal disturbances. Persistent symptoms may include constipation, delayed gastric emptying (gastroparesis), and prolonged intestinal transit time, which can compromise nutrient absorption and contribute to digestive discomfort (Norris et al., 2016). Inadequate caloric intake further compromises immune function, rendering affected individuals more susceptible to upper respiratory tract infections, persistent sensations of coldness, sleep disturbances (such as insomnia or fragmented sleep patterns), and recurrent headaches of metabolic origin (Drew et al., 2018). Notably, the relationship between energy deficiency and mental health is bidirectional: chronic caloric restriction may both stem from and exacerbate psychological disorders. Athletes with insufficient energy intake exhibit higher rates of bulimic behaviors, depressive episodes, generalized mood deterioration, reduced stress resilience, and cognitive impairments—including difficulties with focus and short-term memory retention (Mountjoy et al., 2018).

Despite the intuitive assumption that insufficient energy intake adversely affects athletic performance, a substantial number of athletes continue to believe that reduced body mass is the primary determinant of competitive success. Regrettably, this area remains understudied—existing evidence indicates that chronic energy deficiency compromises neuromuscular efficiency, depletes muscle glycogen reserves, and impairs protein synthesis rates. Furthermore, empirical data reveal prolonged reaction times to external stimuli alongside significant disruptions in post-exercise recovery mechanisms (as documented in the 2019 study by A. K. Melin and colleagues). Of particular concern is the compromised structural integrity of bone tissue, which predisposes athletes to a higher incidence of severe injuries and protracted rehabilitation periods (corroborated by the 2017 research conducted by M. K. Drew et al.).

Given the severe health repercussions that may arise from a state of relative energy deficiency in athletes, the timely identification of this condition emerges as a critical priority. Comprehensive screening protocols—encompassing both a meticulously conducted medical interview and a thorough physical assessment—serve as indispensable tools in this regard. Among the red-flag symptoms that warrant immediate attention are an abnormally low body mass index (BMI), rapid and substantial weight loss over a short period, the presence of orthostatic hypotension, the development of lanugo (a fine, downy hair covering the body), hypercarotenemia (manifesting as a yellowish skin discoloration), and indicators suggestive of disordered eating patterns, as outlined by E. Joy et al. in 2014. The interview process must additionally address the patient’s menstrual history, any prior bone fractures, current medication use, familial disease predispositions, and dietary habits. Equally critical is the evaluation of external pressures—particularly from coaches, family members, or teammates—pertaining to body weight or athletic performance metrics. Personality traits such as perfectionism or neuroticism, which may predispose individuals to behaviors resulting in chronic energy deficiency, must also be scrutinized. It is noteworthy that in Poland, systematic screening for RED-S among athletes remains underutilized, a shortcoming potentially attributable to insufficient awareness among healthcare professionals, as highlighted by M. J. De Souza et al. in their 2014 research.

The primary step in the treatment process should involve a gradual increase in total energy intake through dietary modifications or a reduction in physical exertion, thereby restoring the body’s appropriate energy balance. For adults, the target is to achieve a body mass index (BMI) of at least 18.5, whereas in younger patients, the aim is to attain a body weight representing a minimum of 90% of the age-specific reference value. Additionally, integrating clinical dietitians and psychologists into the therapeutic team is crucial, and in justified cases, referral to individually tailored psychotherapy—particularly for those diagnosed with eating disorders—should be considered (Deimel & Dunlap, 2012).

Notwithstanding their long-standing documentation in medical literature, both the athlete triad and Relative Energy Deficiency in Sport (RED-S) syndrome remain peripheral topics within practical sports environments and among coaching professionals responsible for athlete development. This troubling gap in awareness underscores the critical necessity not only to disseminate accurate, evidence-based knowledge regarding these conditions but also to consistently emphasize the paramount importance of balanced nutritional intake—particularly for elite athletes whose physiological systems endure extreme performance demands. An ideal complement to educational initiatives would be the implementation of standardized, periodic diagnostic screenings designed to detect early subclinical manifestations of dysfunction. Such proactive measures would substantially enhance the efficacy of therapeutic interventions while mitigating the risk of long-term health complications associated with these syndromes.