What is RED-S and Why is it Important to Talk About?

What is RED-S? 

Relative energy deficiency in sport (RED-S) describes a condition in which low energy availability leads to impaired physiological function.¹ In simpler terms, RED-S exists when there is not enough energy available to fuel the normal functions of the human body. As a result, general health deteriorates and sporting performance weakens.²  

RED-S has been adapted from the ‘female athlete triad’, a model depicting a link between low energy availability, menstrual dysfunction and poor bone health.³ The triad however only took into account female athletes and failed to recognise the many other physiological systems that could be affected by having low energy availability.⁴ In 2014 the American College of Sports Medicine changed the triad to RED-S, emphasising that it is not exclusive to females, and that the complexity of the condition is much greater than once assumed.⁴  

In 2018, the International Olympic Committee released a consensus statement outlining the wide range of physiological systems that could be negatively impacted by living in a low energy state.¹ The list includes metabolism, menstrual function, bone health, the immune system, protein synthesis and cardiovascular health.¹ It is clear that if these systems are weakened, sporting performance will suboptimal, and more importantly, general health is at risk of long-term complications.³

This article is going to investigate what could potentially cause athletes to develop low energy status, and discuss what some of the health complications may be.  

What does energy availability mean? 

First it is important to clarify what is meant by ‘energy availability’. The term refers to the amount of energy that metabolically active tissue has to maintain normal function.¹ High energy availability means that cells in the body have enough energy to do their job, with excess so that weight gain might occur.⁵ On the other hand, low energy availability means that there is not enough energy for the cells of the body to function normally, so adaptations have to be made in order for survival.⁵

Energy availability can be calculated. It is equal to energy intake (amount of energy we consume through our diet) minus energy expenditure (the energy we use during our daily activity), divided by the weight of a person’s fat free mass (FFM), because this is the metabolically active tissue that utilises energy.¹ A value of about 45kcal per kilogram of FFM per day is viewed as being healthy.⁵ Both males and females showing values under 30kcal/kg FFM/day are classified as having low energy availability.⁵

Why might athletes be in a low energy state? 

Energy intake, or the calories we get from our diet, is the most prominent factor that determines energy status. Due to the intense lifestyle associated with being an athlete, there are many extra factors that could cause them to develop disordered eating.¹ These could include pressure to lose weight, coach behaviour, compulsive exercise or overtraining.^1,5,6

The IOC consensus statement suggests that the prevalence of disordered eating in adult female athletes is 20%, and 8% in males.¹ It has been noted that the prevalence may be higher among athletes competing in sports where low body mass is a performance or aesthetic advantage, such as endurance events like cycling or running.² For example, Heikura et al. reported that 31% of female and 25% of male elite middle- and long-distance runners were classified as having clinical low energy availability.⁷

Torstveit et al.⁶ suggests that exercise dependence may also be associated with being in a low energy state. Participants who demonstrated excessive exercise behaviour and a reliance on physical activity were more likely to have a negative energy balance.⁶ 

What are the health and performance consequences of low energy availability?  

When the body is in a state of low energy, adaptations have to be made in order to reduce energy expenditure.⁵ To do this, physiological processes all over the body are down-regulated, having negative effects on many different systems.² Some processes that are disrupted include metabolism (metabolic rate is lowered to conserve energy), protein synthesis (which can be reduced when energy availability is below 30kcal/kg FFM/day) and cardiovascular health.¹ Most often discussed is menstrual dysfunction and poor bone health, both which will be discussed in greater detail.  

Menstrual Dysfunction: 

Reproduction is not necessary for the individual’s survival, therefore menstrual dysfunction can often occur in an attempt to reduce energy output. This may be observed in the form of secondary amenorrhoea (loss of periods), or in more subtle forms such as irregularity, light bleeding or spotting.¹ 

It is understood that in a low energy state, luteinising hormone release is disrupted which has knock on effects that disturb the menstrual cycle.¹ This condition is known as functional hypothalamic amenorrhoea (FHA). FHA has been associated with several health concerns including low bone mineral density, infertility, and decreased neuromuscular performance.⁵

The prevalence of menstrual dysfunction in athletes is concerning. Melin et al.⁵ suggest that it could be as high as 60% of elite middle- and long-distance runners and 40% of track and field athletes.

Bone Health: 

In both male and female athletes, bone health is of particular concern when discussing low energy availability. It has been established that low energy availability can increase the risk of poor bone health; a problem that could potentially be irreversible.¹ Bone strength is reduced and and the risk of injury through stress fractures and osteoporosis is significantly elevated.⁸

Particularly in non-weight bearing sports such as cycling where there is less loading on the bone, there are large concerns that this could be detrimental to health. For example Keav et al.⁹ reports that male cyclists who were identified as having low energy availability also had lower levels of testosterone. This hormone is required for bone mineralisation, the process that makes bone rigid and able to withstand pressure.⁹

The longer an athlete remains in a low energy state, the more likely they are to experience these negative effects that could be extremely damaging to health and performance.²

Why is it important to discuss?  

Raising awareness of RED-S is a vital step in order to educate all types of athletes and coaches about the importance of sufficiently fuelling the body. Improving education about this topic would be beneficial not just to identify but support those individuals currently suffering.  

Particularly in sports that equate a lower body mass to being better, a change of attitude may be useful to understand that by significantly restricting the amount of fuel that the body receives, a very complex set of physiological issues could arise. If maintained for a long period of time, long lasting consequences may be career ending and detrimental to health.  

References

1. Mountjoy M, Sundgot-Borgen J, Burke L, et al. The IOC consensus statement: beyond the Female Athlete Triad–Relative Energy Deficiency in Sport (RED-S). Br J Sports Med. 2014;48(7):491‐497. doi:10.1136/bjsports-2014-093502
2. Keay N, Rankin A. Infographic. Relative energy deficiency in sport: an infographic guide. Br J Sports Med. 2019;53(20):1307‐1309. doi:10.1136/bjsports-2018-100354
3. Statuta SM, Asif IM, Drezner JA. Relative energy deficiency in sport (RED-S). Br J Sports Med. 2017;51(21):1570‐1571. doi:10.1136/bjsports-2017-097700
4. Marcason W. Female Athlete Triad or Relative Energy Deficiency in Sports (RED-S): Is There a Difference?. J Acad Nutr Diet. 2016;116(4):744. doi:10.1016/j.jand.2016.01.021
5. Melin AK, Heikura IA, Tenforde A, Mountjoy M. Energy Availability in Athletics: Health, Performance, and Physique. Int J Sport Nutr Exerc Metab. 2019;29(2):152‐164. doi:10.1123/ijsnem.2018-0201
6. Torstveit MK, Fahrenholtz IL, Lichtenstein MB, Stenqvist TB, Melin AK. Exercise dependence, eating disorder symptoms and biomarkers of Relative Energy Deficiency in Sports (RED-S) among male endurance athletes. BMJ Open Sport Exerc Med. 2019;5(1):e000439. Published 2019 Jan 10. doi:10.1136/bmjsem-2018-000439
7. Heikura IA, Uusitalo ALT, Stellingwerff T, Bergland D, Mero AA, Burke LM. Low Energy Availability Is Difficult to Assess but Outcomes Have Large Impact on Bone Injury Rates in Elite Distance Athletes. Int J Sport Nutr Exerc Metab. 2018;28(4):403‐411. doi:10.1123/ijsnem.2017-0313
8. Papageorgiou M, Dolan E, Elliott-Sale KJ, Sale C. Reduced energy availability: implications for bone health in physically active populations. Eur J Nutr. 2018;57(3):847‐859. doi:10.1007/s00394-017-1498-8
9. Keay N, Francis G, Hind K. Low energy availability assessed by a sport-specific questionnaire and clinical interview indicative of bone health, endocrine profile and cycling performance in competitive male cyclists. BMJ Open Sport Exerc Med. 2018;4(1):e000424. Published 2018 Oct 4. doi:10.1136/bmjsem-2018-000424

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