Understanding the Relative Energy Deficiency in Sports Syndrome: A Silent Threat to Athletic Performance and Health
An article written by Sophie Herzog, Øyvind Sandbakk, Trond Nystad and Rune Talsnes
Achieving peak performance in sport is associated with rigorous training, mental toughness, and disciplined nutrition. However, this pursuit can sometimes lead athletes down a dangerous path where the line between optimal performance and health risks becomes blurred. One of the most critical yet under-recognized dangers is under fueling, low energy availability and the development of the Relative Energy Deficiency in Sport (REDs) syndrome[i].
REDs goes beyond what was previously referred to as the Female Athlete Triad[ii], and can affect both male and female athletes who – knowingly or unknowingly – deprive their bodies of the necessary energy required for optimal for health and performance. This blog post delves into what REDs is, how it develops, its health and performance consequences, and most importantly, how to recognize and address it before more severe and long-term health consequences occur.
1. What is REDs?
REDs, or Relative Energy Deficiency in Sport, refers to a condition where athletes experience problematic low energy availability (LEA) – a chronically inadequate energy intake relative to their exercise energy expenditure, which can manifest into various negative health and performance consequences[i], including osteoporosis, stress fractures, menstrual dysfunction (women), and reduced testosterone (men). While some athletes may experience short-term performance gains in a state of LEA, it is important to know that this is not a sustainable or long-term gain. Long-term consequences can severely impact both health and performance, emphasizing the importance of careful, sustainable approaches to body composition and power-to-weight ratio. Intentional efforts to optimize body composition should always prioritize health, avoid disordered eating behaviors, as both conscious restriction and inadvertent under-fueling can lead to REDs.
Definitions from the 2023 IOC consensus statement on REDs[i]:
Energy availability
Energy availability is the dietary energy left over and available for optimum function of body systems after accounting for the energy expended during exercise. Energy availability is expressed as kcal per kg of fat-free mass per day and is defined in the scientific literature in the form of a mathematical formula:
𝐸𝑛𝑒𝑟𝑔𝑦 𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑖𝑙𝑖𝑡𝑦 (𝐸𝐴) = (𝐷𝑖𝑒𝑡𝑎𝑟𝑦 𝑒𝑛𝑒𝑟𝑔𝑦 𝑖𝑛𝑡𝑎𝑘𝑒 (𝐸𝐼) −𝐸𝑥𝑒𝑟𝑐𝑖𝑠𝑒 𝐸𝑛𝑒𝑟𝑔𝑦 𝐸𝑥𝑝𝑒𝑛𝑑𝑖𝑡𝑢𝑟𝑒 (𝐸𝐸𝐸)) / (𝐹𝑎𝑡 𝑓𝑟𝑒𝑒 𝑀𝑎𝑠𝑠 (𝐹𝐹𝑀) )
Low energy availability (LEA)
LEA is any mismatch between dietary energy intake and energy expended during exercise that leaves the body’s total energy needs unmet. That is, there is inadequate energy to support the functions required by the body to maintain optimal health and performance. LEA occurs as a continuum between scenarios in which effects are benign (adaptable LEA) and others in which there are substantial and potentially long-term health and performance consequences (problematic LEA).
Adaptable LEA is exposure to a reduction in energy availability that is associated with mild and quickly reversible changes in biomarkers of various body systems. Adaptable LEA exemplifies the remarkable flexibility of human physiology – how the body can adapt by distributing energy to where it is needed most. In some cases, the scenario that underpins the reduction in energy availability (e.g., optimization of body weight/composition or scheduled period of intensified training or competition) is even associated with acute health or performance benefits (e.g., increased power-to-weight ratio). Adaptable LEA is typically a short-term experience with minimal (or no) impact on athletes’ long-term health, well-being or performance. However, moderating factors such as characteristics of individual athletes (e.g., gender, age, sex), their environment or behavior, may alter (amplify or attenuate) the different outcomes associated with LEA.
Problematic LEA represents a long-term exposure to LEA that is associated with greater and more severe disruption of various body systems, often presenting with various signs and/or symptoms (indicators) representing a maladaptive response. The characteristics of problematic LEA exposure (e.g., duration, magnitude, frequency) may again vary based on different moderating factors that can amplify or attenuate the impact on health, well-being and performance.
Relative Energy Deficiency in Sport (REDs)
A syndrome of impaired physiological and/or psychological functioning experienced by both male and female athletes that is caused by exposure to problematic (prolonged and/or severe) LEA. The detrimental outcomes include - but are not limited to - impairments in energy metabolism, reproductive function, musculoskeletal health, immunity, glycogen synthesis and cardiovascular and haematological health, which can all individually and synergistically lead to detrimental health and performance consequences.
REDs is particularly prevalent in sports that demand high training volumes and correspondingly have high energy expenditures and/or in sports that emphasise a high power-to-weight ratio and promote excessive leanness. This includes endurance sports (e.g., cycling, running, rowing, cross-country skiing) as well as aesthetic (e.g., gymnastics, ballet, dance), weight-class (e.g., rowing, boxing) and weight-carrying (e.g., climbing, ski jumping) disciplines, where a lean physique is often perceived as an advantage for performance. Studies present a wide range in the reported prevalence of LEA/REDs, ranging from 23-80% in female and 15-70% in male athletes across a variety of sports. This wide range likely appears due to the lack of a definitive standardized diagnosis, insufficient accuracy of research methodologies, such as inaccurate EA measurements and a lack of biomarkers or indicators that make it possible to distinguish between adaptable and problematic LEA (and hence REDs) which consequently can lead to mistaken use of terminology.
2. The Root Causes of REDs and its Link to Allostatic Load
In some situations, practices linked to adaptable LEA, like adjusting body composition or increasing training and competition loads associated with high exercise energy expenditure, can be safely incorporated into an athlete's yearly training plan. This is possible when experts guide the process, the athlete is physically and mentally mature, healthy and prepared, recovery periods are integrated in the plan, and health markers are monitored closely[iii]. However, LEA exposures can occur along a continuum from adaptable to problematic without discrete boundaries. Currently, the only way to diagnose problematic LEA or REDs is to study symptom presentation and assess risk factors[iv], and we lack a clear-cut distinction when adaptable LEA becomes “problematic” and hence REDs – as the most recent IOC consensus statement has specified that REDs is a “collection of symptoms that are caused only by problematic LEA[i].
However, while the focus of REDs is often on energy intake, it is important to avoid narrowing down the scope too much. As the recent 2024 paper by Jeukendrup et al. emphasizes, the REDs model is built upon the idea that (problematic) LEA is the primary cause of REDs symptoms. However, empirical evidence supporting this is not sufficient and it is acknowledged that REDs symptoms can be caused by multiple factors, which makes it hard to pinpoint LEA as the single culprit[iv]. In the latest consensus statement of the IOC[i], additional moderating factors, such as gender, age or sex, are mentioned which may help explain the varying outcomes of LEA exposures. Altogether, it is highly likely that in almost all cases the causes for complex syndromes such as REDs – but also unexplained underperformance – are multi-factorial. Interestingly though, the neuroendocrine pathways that respond to various challenges athletes face, such as exercise load, competition, sleep disruption, and travel, all involve the hypothalamic-pituitary-adrenal (HPA) axis and hence it could be simply the combined accumulated stress, also called allostatic load[v],[vi] that causes pathology over time through wear and tear on one or many systems in the body[iv].
Allostasis is the body’s response to a challenge and changes the body’s set points. An example for an allostatic response is for instance a reduction of the resting metabolic rate in response to energy deficiency. The allostatic model explains how a single stressor, or a combination of different stressors, can lead to an increased allostatic load. Over time, this added strain wears down bodily systems, potentially leading to disease if not addressed. In this regard, it is important to note that there are clear similarities between the disease states described in allostasis research and the wide range of symptoms associated with REDs. It may not always be about LEA in isolation, as factors such as poor mental health, sleep issues or stress – whether they are the originating cause, or a result of LEA – are eventually all “energy thieves” and can contribute to relative energy deficiency.
Many different scenarios and often many factors can contribute to the detrimental outcome of REDs. Figure 1 illustrates eight different categories of factors that can contribute to symptoms of REDs – independent or in combination with LEA[iv]:
Figure 1: Athletes may experience symptoms due to many interacting factors – but potentially beyond just low energy availability (LEA). Jeukendrup et al., suggested eight categories to capture these factors, including stress from relationships, competition, self-image, psychiatric disorders, trauma, behavioral factors like training, nutrition, sleep, and even lingering infections or nutritional deficiencies (e.g., iron). These various challenges can increase allostatic load – the body's stress response – leading to wear and tear over time, with the brain and the neuro-endocrine system playing a central role. Figure from Jeukendrup et al.[iv]
While we appreciate a holistic athlete health approach, we also acknowledge the continuously evolving model of REDs and believe that athletes benefit from education about its concept, symptoms and long-term consequences.
In the 2023 IOC consensus statement, where LEA has been identified as the major underlying etiology of REDs, an improved understanding of (1) the combined effect of low carbohydrate availability (LCA) and LEA in the development of REDs; (2) the overlap in symptoms between REDs and overtraining syndrome (OTS); and (3) how REDs relates to mental health was emphasized:
Studies show that low carbohydrate intakes often accompany LEA, amplifying the negative effects on health outcomes related to REDs such as bone health, immunity and iron metabolism. But even in the absence of LEA, LCA can impair bone formation, increase bone resorption and elevate inflammation markers like IL-6[vii],[viii],[ix].
REDs and OTS share similar symptoms related to the HPA axis and have no single validated diagnostic biomarker – making it challenging to disentangle them or distinguish between the two[x]. Often, “overtrained” athletes show indications of LEA and LCA due to increased training loads but fail to compensate this increase with adequate energy intake and thus they may show REDs outcomes rather than OTS. Consequently, and although challenging, an OTS diagnosis always requires exclusion of LEA or LCA first.
Mental health issues like anxiety or depression but also early life adversity can pose a higher risk of developing syndromes like REDs[xi]. Furthermore, disordered eating (DE) or eating disorders (ED) are more common in athletes and are considered an important risk factor for developing REDs and can create a dangerous cycle of under-eating and over-training[xii].
3. Recognizing the Signs and Symptoms of REDs and Eating Disorders
The current conceptual health and performance models (Figure 2) illustrate the wide range of body systems affected by REDs – although these outcomes can vary in severity and significance from athlete to athlete and occur over different timeframes i,[xiii].
REDs can impair numerous bodily functions, such as energy metabolism, reproductive function, bone health, immune function, cardiovascular health, mental health and eventually also performance (see inside wheels in Figure 2). Due to the whole-organism impact, there is a large range of possible signs and symptoms (indicators) that athletes suffering from REDs can experience.
Figure 2: The REDs Health and Performance Conceptual Models. These Models, although illustrated separately effectively show considerable overlap. Figure taken from Burke et al. [xiii].
In the process of educating around REDs, it is important to distinguish between signs and symptoms, which are in common language often used interchangeably. Signs are what we can observe through testing (e.g., changes in hormone levels or bone mineral density). Symptoms are what athletes can feel and report (e.g., pain, fatigue, missed periods) or what coaches and athlete stakeholders can observe. While a list of all possible symptoms is perhaps too long for practical purposes and may not cover all outcomes, it is important for athletes and coaches to develop an awareness and understanding which symptoms they may be able to feel or see early on and what to be wary of, especially as athletic performance on its own is usually not a good early indicator to warn athletes or coaches that something is going awry[xiv].
The IOC consensus statement provides a long list of common symptoms that athletes may display, recognizing that “each of these outcomes can [also] occur in the absence of LEA” and therefore, it is essential to rule out or consider other possible underlying causes when assessing and diagnosing the severity or risk of REDs, as outlined in the Clinical Assessment Tool and differential diagnoses in the 2023 IOC statement.
In the list below you can find a non-exhaustive list of signs and symptoms:
Physical Indications:
The symptoms of REDs can be subtle and often go unnoticed until the condition has significantly progressed. Some athletes also might maintain a stable body mass or even have a higher body fat percentage despite eating very little, potentially due to a reduction in resting metabolic rate (RMR) – an inherent human adaptive response to energy restriction[xv]. Common physiological signs and symptoms are wide-ranging but include:
Chronic fatigue
Impaired reproductive function: anovulatory, irregular or absent menstrual cycles in women[1], decreased libido (both men and women) and reduced testosterone and morning erections in men
Impaired bone health: loss of bone mineral density leading to more frequent injuries like stress fractures
Impaired gastrointestinal function: abdominal pain, cramps, bloating, “carb intolerance”
Impaired metabolism: hypothyroidism[2], low resting metabolic rate, increased cortisol, reduced leptin
Impaired haematological status: low iron status and reduced iron absorption, lower haemoglobin mass, reduced response to altitude training
Impaired cardiovascular function: ECG abnormalities, hypotension, reduced blood flow
Behavioural Indications:
Athletes with a long-term REDs condition often show decreased performance, reduced ability to recover between training sessions or competitions and more frequent injury or illness. Furthermore, problematic LEA outcomes might show impaired neurocognitive function, such as reduced reaction time, memory, decision-making and cognitive flexibility. Some athletes might also exhibit disordered eating behaviors such as obsessively counting calories, skipping meals, or avoiding certain food groups entirely. They may also engage in excessive training beyond what is prescribed by their coaches, driven by the belief that more training and a lower weight will lead to better performance, regardless of their declining energy levels.
Psychological Symptoms:
Low energy availability, whether it’s short-, medium- or long-term, has been linked to significant mood issues in athletes, including feelings of anxiety, anger, confusion, mental fatigue, tension and decreased motivation[xvi]. It has also been associated with sleep problems, long-term depressive symptoms and the development of eating disorders, which almost always includes a preoccupation with body weight and appearance. Athletes may also show signs of body dysmorphia, where they perceive themselves as overweight despite being at or below a healthy weight.
4. Diagnosing REDs
The current REDs clinical assessment consists of a three-step process: It starts with 1) using REDs screening questionnaires or clinical interviews, which are easy and inexpensive ways to identify athletes who might be at risk, though they are subjective and not highly sensitive. 2) In a second step, one can use the IOC REDs CAT2 tool[xvii], which assesses primary and secondary risk indicators (like biomarkers, bone density and injury history, see Table 1). This tool categorizes athletes into risk levels: green (low risk), yellow (moderate), orange (high) or red (severe) and provides guidelines for their participation in sports based on their risk level. In step 3), a doctor with expertise in REDs makes the formal diagnosis. This should always involve a team of specialists (e.g., nutritionist, psychologist, doctor) and include questionnaires, physical assessments and lab tests to rule out other conditions.
5. Breaking the Cycle: Prevention and Treatment
Educational efforts must go beyond warning about the dangers of problematic LEA, REDs, eating disorders and disordered eating. Athletes (and coaches) should be educated about the energetic demands of their athletic lifestyle but also made aware that non-training stressors can influence energy requirements. In fact, coping with any stressful situation implies allostatic responses and hence has an energetic cost[xviii]. Consequently, it is important to educate athletes on how to optimally manage their nutritional intake in and around their training and recovery process. This includes practical knowledge on food choices, macronutrient distribution, meal planning, and proper timing of nutrition or ergogenic aids relative to training sessions. Furthermore, athletes should be encouraged to understand the impact of different environments (e.g., altitude, heat, cold) and the metabolic demands associated with it. Altogether, knowledge of the physics of their sport can help athletes to understand and rationalize the importance of the needed energy intakes for optimal performance.
However, we must recognize that there are currently no simple and easy-to-execute methods for assessing energy availability in free-living athletes. The time, effort and education required for athletes to accurately record food intake, combined with the potential for errors in measuring energy intake, exercise energy expenditure, fat-free mass or resting metabolic rates make providing precise guidance for athletes highly challenging. Additionally, athletes may experience widely varying physiological responses to LEA, such as hormonal changes or impacts on different bodily systems, and there is still much we don’t understand about how individuals react to various forms of energy deficiency, including factors like low-carb diets or calorie restriction, which may depend on moderating factors such as sex, age, and genetics.
It is highly valuable for athletes and coaches to familiarize themselves with potential REDs symptoms. However – and importantly – signs and symptoms of REDs can also have underlying health issues unrelated to LEA. As a result, a comprehensive approach is crucial in distinguishing between REDs and other potential conditions. Early identification of REDs symptoms through screening tools, individual health interviews, and objective biomarkers remains a valuable strategy for prevention by catching issues before they lead to long-term consequences.
While efforts to educate athletes and their support systems are growing, there is still a need for more research and the development of specific REDs education programs tailored to both athletes and key personnel. These programs should be further explored and validated to ensure lasting impact in preventing REDs. Additionally, athletes who have experienced REDs and share their stories can help to highlight the serious health and performance consequences of the condition and foster greater awareness.
Seeking Professional Help:
If an athlete or members of the athlete support team suspect a REDs outcome, it is essential to seek help from professionals who understand the condition. This includes sports dietitians who can assess and correct energy imbalances, endocrinologists who can monitor hormone levels, and mental health professionals who can address the psychological aspects and assess or exclude mental disorders (e.g., eating disorder) Team-based approaches, bringing together professionals in sports medicine, nutrition, psychology and sports science, with the added involvement of coaches and family, are recommended. This ensures a holistic strategy for the athlete’s recovery, where treatment goals prioritize safe participation in sports while undergoing long-term care and monitoring. It is also important to evaluate whether it is safe for an athlete to continue training and competing during their treatment. With more specialized REDs clinics emerging, athletes can receive comprehensive, coordinated care that supports their recovery from different angles.
Nutrition and Training Adjustments:
To break the cycle of REDs, athletes need to ensure they are restoring optimal energy availability. This might involve changes to their diet such as increasing portion sizes, adding snacks between meals, reducing fiber intake, increasing energy density, and making sure appropriate contributions of macronutrients and micronutrients are provided. Additionally, adjusting training loads during periods of recovery can help to achieve a sustained and optimal energy availability.
Mental Health Support:
Addressing the psychological components of REDs is just as important as managing physical symptoms. Athletes should have access to counseling services that can help them develop a healthier relationship with food, body image, and training. In some cases, cognitive behavioral therapy (CBT) can be particularly effective in treating the underlying issues related to eating disorders and REDs.
6. Conclusion
The pursuit of athletic excellence should never come at the expense of health, and, in fact, maintaining good health underlies a successful long-term performance development. Understanding and addressing LEA and REDs is essential, not only for long-term performance development, but also for safeguarding the well-being of athletes. By fostering an environment that prioritizes both physical and mental health, we can help athletes achieve their goals in a sustainable and healthy manner.
It is crucial for athletes to listen to their bodies and seek help if they notice abnormal symptoms, pointing in the direction of REDs. However, it is also important that athletes are served by an unbiased approach that places health at the center and leaving open all possible explanations for their symptoms – also beyond REDs.
Coaches, teammates, and families should be vigilant and supportive, encouraging a balanced approach to training and nutrition. Together, we can create a sports culture that values health as much as it does performance, ensuring that athletes can enjoy long, successful, and healthy careers. If you or someone you know is struggling with performance issues linked to REDs or other suspected factors, don’t hesitate to reach out. At MYRA, we’re here to help create an individual support system tailored to your needs.
Footnotes
[1] Note that menstrual cycle status and endogenous sex hormone levels cannot be accurately assessed in athletes who are taking sex hormone-altering medications (eg, hormone-based contraceptives)
[2] Note that thyroid hormone status indicators cannot be accurately assessed in athletes who are taking thyroid medications
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