Relative Energy Deficiency in Sport (RED-S)
Introduction[edit | edit source]
Relative Energy Deficiency in Sport (REDS) (the updated model of the female athlete triad) was defined by the International Olympic Committee in 2014 as: ‘impaired physiological functioning caused by relative energy deficiency, and includes but is not limited to impairments on metabolic rate, menstrual function, bone health, immunity, protein synthesis, and cardiovascular health’
This term has replaced the female athlete triad, which is the interrelationship between menstrual dysfunction, low energy availability and reduced bone mineral density . This is because it is now evident that this syndrome impacts both female and male individuals experiencing low energy availability, and that the effects of the low energy availability extend far further than menstrual function and bone health.
Glossary[edit | edit source]
- Amenorrhea - An abnormal absence of menstruation
- Dysmenorrhea - Painful menstruation, typically involving abdominal cramps
- The Female Athlete Triad – The interrelationship of menstrual cycle dysfunction, reduced energy availability and reduced bone mineral density
- Hypomenorrhea – Abnormally light menstrual bleeding
- Menarche – ‘The occurrence of the first menstrual period in the female adolescent’ 
- Menorrhagia – Heavy menstrual blood loss
- Menstrual cycle - The process of ovulation and menstruation
- Menstruation - The process of discharging blood and other material from the lining of the uterus at intervals of about one lunar month from puberty to the menopause, except during pregnancy
- Oligomenorrhea - Menstrual cycle length of greater than 45 days
- Osteopenia - A medical condition in which the protein and mineral content of bone is reduced, but less severely than in osteoporosis
- Relative Energy Deficiency in Sport (REDS) - This is impaired physiological function including, but not limited to impairment of: metabolic rate; menstrual function; bone health; immunity; protein synthesis; and cardiovascular health, caused by energy deficiency
Low Energy Availability (LEA)[edit | edit source]
LEA underpins REDS, and is the instance in which there is a chronic mismatch between nutritional intake and energy expenditure, thus leaving insufficient energy available for essential physiological functions . As a result, physiological functions are down-regulated in order to preserve energy for more essential functions and for movement, thus leading to detrimental health and performance implications for the athlete.
LEA may be intentional, with the athlete intentionally restricting their dietary intake, or unintentional, in which the athlete's nutrition simply does not meet the demand of their training load . Whether the LEA is intentional or unintentional, there remain the same significant implications to the health and performance of the athlete, but it is essential to recognise which form of LEA an athlete may be suffering, as management for each differs.
- Intentional LEA - the athlete is intentionally restricting their dietary intake to control body weight and/or body composition .This is more commonly seen in sports in which their is a weight category such as light-weight boxing and rowing due to the additional external pressure and emphasis on aesthetics or appearance .
- Management - management is complex because relationship with food and psychology must be addressed. This requires a multidisciplinary team approach with medical, dietary and mental health support
- Unintentional LEA - the athlete is not meeting the demands of their sport, commonly during periods with increased training volume or when engaging in sports with high energy expenditure 
- Management - this is easier to manage, and it may be sufficient to simply educate the patient on the nutritional demands of their training load
Epidemiology of REDS[edit | edit source]
The prevalence of REDS is not well documented due to the inherent methodological difficulties in diagnosing true low energy availability. A narrative review conducted in 2020 found prevalence varies between sports, and ranges in the literature between 22-58% in the female population. There is significant difficulty in estimating LEA due to the wide variety of methods used to estimate LEA, and therefore comparing data across studies proves challenging.
Additionally, the understanding of REDS and its symptoms are poorly known by athletes and coaches, and therefore it is also not commonly recognised. A further review identified that fewer than 50% of physicians, coaches, physiotherapists and athletic trainers could identify the triad components (Low energy availability +/- disordered eating, menstrual dysfunction, low bone mineral density). As a result, fewer cases will be recognised, diagnosed, and therefore highlighted as suffering from REDS.
Health and Performance Implications of REDS[edit | edit source]
Health implications are multi-system, affecting the endocrine, metabolic, skeletal, cardiovascular and immune systems; and in women, the menstrual cycle is disrupted. Not infrequently are also significant ramifications on the psychological state of the individual, given the prevalence of disordered eating in this population.
- Endocrine health- LEA disrupts the hypothalamic-pituitary-gonodal axis, and has subsequent implications on thyroid function. These hormonal changes occur as a response to LEA, thus attempting to conserve energy for more important functions .
- Menstrual function - Stress and low energy availability cause suppression of the hypothalamic–pituitary–axis (HPA) and subsequent reduction in the volume of GnRH secreted from the hypothalamus. As a result, the menstrual cycle is disrupted, in a condition called hypothalamic amenorrhea.The degree to which the HPG axis is affected, directly dictates the severity of menstrual dysfunction. For example, oligomenorrhea may develop into amenorrhea with further disuprtion to the HPA axis and reductions to GnRH, LH and FSH levels.
- Prevalence of amenorrhea - the prevalence of amenorrhea has been estimated to be between 2.6% and 4.4% by Bachmann and Kemmann (1982), and Pettersson et al., (1973), respectively. Similarly, a third study found that in a population of pre- menopausal women, 4% had experienced secondary amenorrhea (Miller and Klibanski, 1999). More recently, in a systematic review, the prevalence of amenorrhea in a sporting population was reported to be 27.7% , and is therefore far higher than in the general female population.
- Bone Health - LEA causes a chronic state of hypoestrogenism, which in turn causes down-regulation of osteoclast activity . As a result of the suppression of osteoclasts, normal bone remodelling is not initiated, and therefore bone mineral density is reduced . With less robust bone health, there is an increased prevalence of stress injuries and stress responses in individuals suffering with LEA.
- Metabolic implications - Resting metabolic rate is reduced in order to conserve energy
- Cardiovascular implications - Individuals with LEA/REDS are found to have lower heart rates and systolic blood pressure, and atherosclerosis has been found to be associated with hypoestrogenism
- Gastrointestinal impact - the influence of LEA on gastrointestinal function is important, as these symptoms resulting from LEA are commonly used in screening tools (as detailed below). Individuals suffering from LEA may experience: altered sphincter function and constipation
- Immunological - LEA is commonly associated with increased bouts of illness, most commonly upper respiratory symptoms, but also inclusive of symptoms relating to the gastrointestinal tract 
- Psychological - In the population of individuals with REDS, there is an increased prevalence of eating disorders and disordered eating. This has significant implications for psychological well-being, by potentially exacerbating low self-esteem, anxiety and depression. The aforementioned drive for thinness seen in athletes competing in weight categories is associated with higher depressive traits and worsened ability to manage stress , and higher social insecurity.
Performance implications are significant and are the result of the negative influences on training adaptations, coordination, endurance performance, muscle strength, worsened concentration, irritability, impaired judgement, and the increased risk of injury.
- Muscular strength and endurance - Adaptations associated with LEA are known to negatively influence muscular adaptations in both endurance and strength and power athletes. Endurance athletes, because of a negative impact on mitochondrial protein synthesis and strength, and power athletes, because of a negative impact on muscle protein synthesis. 
- Neuromuscular performance and reaction times are reduced 
Red Flags for REDS[edit | edit source]
- Recent weight loss
- Restrictive eating and body dysmorphia
- Stress fractures
- Overuse injuries
- Recurrent illnesses
- Cardiac abnormalities
Screening Tools[edit | edit source]
- REDS CAT - Relative Energy Deficiency in Sport (REDS) Clinical Assessment Tool (CAT) https://bjsm.bmj.com/content/bjsports/49/7/421.full.pdf 
- Can assess males and female athletes at risk of REDS
- Is a more functional model using a traffic light system
- Assess both risk of REDS and guides return to play decisions
- LEAF-Q - Low Energy Availability in Females Questionnaire http://www.diva-portal.org/smash/get/diva2:1303041/FULLTEXT02.pdf 
- For female athletes only
- High Sensitivity (78%) and specificity (90%)
- Covers injury history, gastrointestinal function and menstrual function
Diagnosis of REDS is challenging as it is a diagnosis of exclusion, but the above screening tools provide a good framework to go off, and allow the flagging of certain athletes.
For confirmation of diagnosis, a sports (female specific) endocrinologist provides great insight and will consider a whole host of blood work to rule out other potential causes of this menstrual dysfunction and worsened health and performance.
Common Investigations and Findings for those with REDS/FHA[edit | edit source]
- LH (low)
- FSH (low)
- Oestradiol (low)
- Thyroid hormones
- TSH (low)
- T3 (low)
- Additional assessments
- Pituitary profile
- Pelvic ultrasound
- DEXA scan to quantify BMD
REDS in Male Athletes[edit | edit source]
As mentioned, there has been a move away from the female athlete triad towards relative energy deficiency in sport, as it is known to affect both female and male athletes, although the physiological effects of the condition inevitably differ.
In male athletes, the mechanism is the same: low energy availability (intentional or unintentional) leads to a host of health and performance consequences . In male athletes it is predominantly characterised by low testosterone levels, thus impacting both the health and performance of the athlete.
REDS in Specific Sports[edit | edit source]
The higher prevalence of REDS has been documented in combat sports, in rowers and in jockeys all of which have weight categorisations, and therefore an increased emphasis on the weight of the athlete and drive for thinness pre-competition.
REDS is prevalent in male cyclists, and the negative association between risk level and peak power has been identified . A sport-specific screening tool (SEAQ-1) has been created to help with the identification of those at risk and the diagnosis of individuals experiencing REDS. This is particularly important in cyclists, given the lack of impact and weight-bearing activity their sport requires, thus increasing the risk of reduced BMD.
For further information on REDS in Male Athletes, a second Physiopedia page has been created: The Male Athlete Triad
Management[edit | edit source]
Non-pharmacologic – When a patient is diagnosed with REDS, the following management strategies should be implemented: education; optimising energy availability; modification of exercise and nutrition; supplementation of vitamin D and calcium; and CBT. An MDT approach should be adopted, including mental health support. Sport participation may be used as leverage. High-impact should be avoided due to the increased risk of developing a stress response, and therefore exercise should consist of resistance training and low-impact weight bearing exercise in order to optimise BMD
Pharmacologic – oral contraceptive is not recommended as it creates false menstruation or a ‘pseudo-period’ in female athletes. The use of recombinant parathyroid hormones and its role in improving bone mineral density is currently under review .
The role of physiotherapists in management of REDS: As holistic practitioners, physiotherapists are well-placed to identify and treat the multimodal causes of physical impairment. They can assess, modify and monitor an individual's activity levels during recovery, prescribe an appropriate training schedule for the athlete, and work as part of the multidisciplinary team to develop treatment goals for the patient.
Conclusion[edit | edit source]
Regular screening for REDS is essential for holistic, patient-centred care, as there are significant health implications (both physical and psychological) and performance implications resulting from this condition. It is important that clinicians consider REDS not only in sporting populations, but in any individual at risk from a chronic mismatch between energy input and expenditure (both male and female).
Author and Affiliations[edit | edit source]
References[edit | edit source]
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