Does Relative Energy Deficiency in Sport (REDs) Syndrome Exist?

Abstract

Relative energy deficiency in sport (REDs) is a widely adopted model, originally proposed by an International Olympic Committee (IOC) expert panel in 2014 and recently updated in an IOC 2023 consensus statement. The model describes how low energy availability (LEA) causes a wide range of deleterious health and performance outcomes in athletes. With increasing frequency, sports practitioners are diagnosing athletes with "REDs," or "REDs syndrome," based largely upon symptom presentation. The purpose of this review is not to "debunk" REDs but to challenge dogmas and encourage rigorous scientific processes. We critically discuss the REDs concept and existing empirical evidence available to support the model. The consensus (IOC 2023) is that energy availability, which is at the core of REDs syndrome, is impossible to measure accurately enough in the field, and therefore, the only way to diagnose an athlete with REDs appears to be by studying symptom presentation and risk factors. However, the symptoms are rather generic, and the causes likely multifactorial. Here we discuss that (1) it is very difficult to isolate the effects of LEA from other potential causes of the same symptoms (in the laboratory but even more so in the field); (2) the model is grounded in the idea that one factor causes symptoms rather than a combination of factors adding up to the etiology. For example, the model does not allow for high allostatic load (psychophysiological "wear and tear") to explain the symptoms; (3) the REDs diagnosis is by definition biased because one is trying to prove that the correct diagnosis is REDs, by excluding other potential causes (referred to as differential diagnosis, although a differential diagnosis is supposed to find the cause, not demonstrate that it is a pre-determined cause); (4) observational/cross-sectional studies have typically been short duration (< 7 days) and do not address the long term "problematic LEA," as described in the IOC 2023 consensus statement; and (5) the evidence is not as convincing as it is sometimes believed to be (i.e., many practitioners believe REDs is well established). Very few studies can demonstrate causality between LEA and symptoms, most studies demonstrate associations and there is a worrying number of (narrative) reviews on the topic, relative to original research. Here we suggest that the athlete is best served by an unbiased approach that places health at the center, leaving open all possible explanations for the presented symptoms. Practitioners could use a checklist that addresses eight categories of potential causes and involve the relevant experts if and when needed. The Athlete Health and Readiness Checklist (AHaRC) we introduce here simply consists of tools that have already been developed by various expert/consensus statements to monitor and troubleshoot aspects of athlete health and performance issues. Isolating the purported effects of LEA from the myriad of other potential causes of REDs symptoms is experimentally challenging. This renders the REDs model somewhat immune to falsification and we may never definitively answer the question, "does REDs syndrome exist?" From a practical point of view, it is not necessary to isolate LEA as a cause because all potential areas of health and performance improvement should be identified and tackled.

Fig. 1

Comparison of the current REDs model that centers around LEA as the only cause of symptoms (Left: with permission [4]) and the more holistic approach we are presenting in this paper

Fig. 2

The general adaptation syndrome (GAS) (A), allostatic load model (B), and the pathway (C) that connects various stressors with symptoms and pathology. Effective coping to any stressful situation depends on the person’s cognitive appraisal of the stressful event (perceived stress), and the subsequent type of behavioral coping strategy used [167]. The GAS model (A) described how a stress response causes function (represented by the blue line) to decrease initially (phase 1). Adaptation occurs and this helps to resist the continued stress (phase 2). After a while this cannot be sustained anymore and exhaustion occurs (phase 3). The GAS model also explained the role of common neuroendocrine pathways for various challenges (sympathetic nervous systems and HPA axis) (C). The GAS model was further developed into the allostatic model (B) [169, 171]. Allostasis is a response to challenges whereby the setpoint will change. The most well studied allostatic responses to a range of challenges involve the sympathetic nervous systems and HPA axis (C). Activation of these systems, independent of the source of stress, releases catecholamines from nerve endings and adrenal medulla and leads to corticotropin secretion from the pituitary gland. Corticotropin, in turn, will stimulate the release of cortisol from the adrenal cortex and this will exert its effect through binding to glucocorticoid receptors in various target tissues, which can be up or downregulated. This is a fast and effective response. If this response is not immediately turned off, over time this increases the “allostatic load.” Allostatic load or eventually overload will affect many body systems causing wear and tear [169, 171]. Four situations are associated with allostatic load (panels B1–4; the red line represents problematic responses and the green line normal responses). The first and most obvious is frequently repeated stress (B1). A second situation would be inadequate adaptation to repeated stressors of the same type (B2). This can also result in prolonged exposure to stress hormones. The third would be a situation where there is an inability to shut off the stress response after termination of the stress (B3). An example of this is exercise training that induces allostatic load in the form of elevated sympathetic and HPA-axis activity, which may result in weight loss, amenorrhea, and even AN [182]. In the fourth type of allostatic load, there could be an inadequate response by one system and this could trigger a compensatory increase in another (B4). For example, if cortisol secretion fails to increase in response to stress, secretion of inflammatory cytokines (which are counter-regulated by cortisol) increases [183]. A range of challenges that an athlete faces (training load, competition stress, poor nutrition, poor sleep) can increase allostatic load, which can trigger a range of symptoms and clinical conditions

Fig. 3

Common symptoms and clinical conditions in athletes that are similar to REDs may be caused by many factors independent of—or in combination with—LEA. Eight categories of factors that can contribute to these symptoms are shown (in no order preference). In many situations several factors, potentially from several categories, may play a role in the development of REDs symptoms in athletes. Many different types of challenges can independently or in combination increase allostatic load and over time this can cause wear and tear on the body and ultimately result in symptoms and pathology. The common pathways are the HPA axis and central nervous system (CNS). The brain plays a central role and psychiatric disorders, trauma, and abuse, as well as major life events, play an important role by modifying neuro-endocrine reactivity to stress. Life/environmental factors that can cause stress related to relationships, competition or self-image, to name just a few. There are also many important behavioral factors, most notably for athletes, including their training, their nutrition and sleep. Lingering infections can also affect allostatic load, but could also have direct effects on a number of symptoms. This is the case for several other factors as well; for example, iron deficiencies or other nutritional deficiencies can have direct effects, causing REDs symptoms

Fig. 4

Athlete Health and Readiness Checklist (AHaRC) providing a multidimensional decision tree to maintain athletes’ health and performance. The AHaRC will act as a guide for practitioners working with athletes, to implement regular checks, identifying possible tools and the most relevant professionals to consult. There are eight categories (no order of preference), all important to check. Some need frequent checks (daily or weekly) others more periodically (suggested frequency: D = daily, W = weekly, M = monthly, AH = ad hoc, OI = on indication). The list here is not exhaustive but should be a good starting point for those responsible for athlete health. For each component in the checklist, the recommended tools and possible actions are supported by expert/consensus recommendations. Profile of mood states (POMS); recovery stress questionnaire for athletes (RESTQ-S), and daily analyses of life demands of athletes (DALDA). (1) Training/exercise [–206], (2) life/environmental [207], (3) mental health [208], (4) disordered eating/eating disorders [208, 210], (5) nutrition [211], (6) sleep [213], (7) infection/illness [216], and (8) undiagnosed clinical condition [214, 217]