All about Relative energy deficiency in Sport (Red-s)


Relative energy deficiency in sport (Red-s), formerly known as the “Female Athlete Triad”, describes low energy availability affecting both male and female athletes of all ages and levels. The syndrome results in impaired physiological function – metabolic rate, menstrual function, bone health, immunity, protein synthesis and cardiovascular health, caused by an imbalance in dietary energy intake and energy expenditure required for daily living, growth and sporting activities.

Development of Red-S from the Female Athlete Triad

In 2005, the Female Athlete Triad was described as the combination of disordered eating and irregular menstrual cycles, eventually leading to a decrease in endogenous oestrogen and other hormones, resulting in low bone mineral density. Following progress in scientific understanding, it was redefined in 2007 as a clinical entity that refers to the relationship between energy availability, menstrual function and bone health. At this time, there was also an understanding that an athlete could be on a continuous spectrum, ranging from a healthy athlete with optimal energy availability, regular menses and health bones, to the opposite end, characterised by amenorrhoea, low energy availability and osteoporosis.

After 2007, scientific and clinical evidence displayed that the aetiological factor underpinning the triad was energy deficiency relative to balance between dietary energy intake and expenditure required to support homeostasis, health and daily physical activities; not just a triad of three entities – energy availability, menstrual function and bone health. It also became evident that the “female athlete triad” also affects men and it was hence more suitably renamed to Relative Energy Deficiency in Sports (Red-s).

Groups most affected

Red-s in males is significantly less prevalent than in females and among females athletes, Red-s tends to occur among the same at risk sports; particularly weight sensitive sports in which leanness/ weight plays a role in performance, appearance or requirement to meet a competition weight category (figure skating, gymnastics, dance and long distance running). Perfectionism is also often seen as desirable in successful sports people, which is something that can further drive disordered eating.

Calculating energy deficiency

Below is the equation to calculate ones energy availability and hence energy deficiency. However, in reality it is very tedious and difficult to measure this accurately, as it requires detailed analysis and is prone to inaccuracies.

Energy availability = Energy intake – energy cost of exercise relative to fat free mass

Energy balance = 45kcal/kg FFM/ day

Energy availability below the energy balance results when there is a reduction in energy intake OR increased exercise load without adjustment to the other. Low energy availability has been shown to disrupt an array of hormonal, metabolic and functional characteristics in the body. Additionally, external psychological stress and inadequate sleep can further contribute to this, prompting the body to go into energy saving mode, dampening hormonal pathways. Cumulative low energy availability will build up, ultimately impairing one’s health significantly.

Though disordered eating is a cause for a large proportion of low energy availability cases, it can also occur without psychological overlay by accident, when poor management programs are used to quickly reduce body mass.

Effects of RED-s

There are numerous short and long term effects of RED-s, which compromise an athlete’s health and athletic performance. Primary physiological and medical complications involve altered levels of metabolic hormones and substrates, affecting the cardiovascular, gastrointestinal, endocrine, reproductive, skeletal, renal and central nervous systems, which can ultimately result in osteoporosis and increased risk of heart disease in the future.

Menstrual Cycle

Low energy availability leads to suppression of reproductive hormones, which affects the menstrual cycle and can have further effects on fertility.

Primary amenorrhea – the lack of the first menstrual cycle by age 15. Studies have shown that this is prevalent in 7% of collegiate athletes and 22% in cheerleading, diving and gymnastics

Secondary amenorrhea – an absence of three consecutive cycles after one's first menstrual cycle. Studies have shown this to be as high as 69% in dancers and 65% in long-distance runners

Functional Hypothalamic Amenorrhea (common type of secondary amenorrhea)– results in a reduction in energy availability, which can affect the hypothalamic hormone gonadotropin, disrupting Luteinising hormone levels and subsequently altering the menstrual cycle

Bone health Males and females build bone mass in their adolescent years, with peak bone mass occurring at around 19 years in women and 20.5 years in men. Low energy availability leads to the disruption of bone mass formation, which can lead to one never reaching their peak bone mass and hence starting at a lower level of bone mineral density, which subsequently declines for the rest of one’s life. Weaker bones later in life can have devastating consequences, such as hip fractures and joint injuries.

Oestrogen increases the uptake of calcium into the blood and deposition into bone, while progesterone facilitates the actions of oestrogen. Progesterone and oestrogen imbalances because of low energy availability and disruption to the menstrual cycle hence produce negative changes in bone density and health due to a decrease in IgF-1 and bone marker levels, which may be irreversible. Amenorrhea can also decrease estrogen, weakening bones and leading to stress fractures.

Athletic performance

Energy deficiency can lead an athlete to be more susceptible to viral illnesses and injuries, hindering their ability to train. Importantly, it can also reduce their responsiveness to training and their performance ability. Should athletes practise extreme weight control methods such as fasting, vomiting, diuretic and laxative abuse, their health and athletic performance can be adversely affected from dehydration, electrolyte imbalances and gastrointestinal problems. Diuretics and diet pills used may also be under prohibited substances for athletic use, which can prevent athletes from participating in competitions.

Treatment strategies

The most straightforward treatment strategy for Red-S is to increase energy intake and reduce exercise. However, for it to be treated, healthcare professionals need to first recognise and identify Red-s in a clinical setting (this can often be done when athletes present with amenorrhea and increased injuries due to poor bone health), to advise athletes on a treatment plan.

Oral contraceptives

Female athletes who suffer from amenorrhea may be advised that taking an oral contraceptive pill will address their symptoms. However, in reality this may only mask low energy availability and menstrual disturbance, without truly providing one with adequate bone protection. Hormone replacement therapy provides superior bone protection compared to the oral contraceptive pill.

Bone health

Though full recovery may not be feasible, bone health should still aim to be optimised by increasing energy intake, to restore the energy and oestrogen dependant mechanisms of bone loss. Additionally, an athlete should aim to include 1500 mg/ day of calcium through dietary sources or supplementation to further support this growth.

Efforts in the UK to combat RED-S

  • specialist NHS RED-S clinic in London that receives support from the National Institute of Dance Medicine and Science (NIDMS)

  • #TrainBrave has been established in an effort to increase awareness of RED-S and combat myths that encourage high risk behaviours amongst athletes, such as “lighter is faster”

  • websites such as Health4performance have been created to raise awareness of RED-s and provide the public with information and support


To reach your full potential as an athlete, one needs to be healthy both physically and mentally and this can only arise with sufficient energy and nutrition, which should ideally be tailored according to one's age, gender and sporting requirements. Furthermore, it's important to remember that Red-s can impact one’s long-term health and it is thus of the utmost important to take nutrition seriously when training at a high level.






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