The Honest Truth: My experience of Relative Energy Deficiency in Sport (RED-S) by Hannah Knights

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📸 by: @Sakurasportsmedia

What is RED-S?

RED-S stands for ‘Relative Energy Deficiency in Sport’. RED-S is caused when an individual’s dietary energy intake is insufficient to support the energy expenditure required for everyday health and optimal function once the cost of exercise has been considered [1]. In simple terms, energy expenditure > energy intake to a point where physiological function is impaired in the body’s bid to save energy (metabolic rate, menstrual function, bone health, immune system, protein synthesis, cardiovascular health). Psychological consequences can be either precede or be the result of RED-S [2].

Figure 1 [2] shows the potential health consequences of RED-S:

The ‘Female Athlete Triad’ is pictured here as a triangle between low energy availability, menstrual dysfunction (amenorrhoeic/eumenorrheic) and decreased bone mineral density (BMD), perhaps presenting with a stress fracture. However, by 2014, the IOC came to the realisation that the clinical phenomenon was not just a ‘triad’ of three entities, but a syndrome that affects many aspects of physiological function, health, and athletic performance that presents in males as well as females [1]. However, it is a lot easier to spot in females due to the (a/eu)menorrhoeic symptom; a key indicator that your body is not functioning optimally.

Why this topic needs to be discussed:

  • 45% of female athletes show signs of ‘disordered eating’ (DE), potentially 1 in every 2 of your training partners. Even in the absence of DE, female and male endurance athletes are at risk of low BMD.

  • Anywhere between 16-61% suffer from hypothalamic-pituitary disorders.

  • 30% have menstrual disorders in endurance events in an elite category, but it is thought these numbers are higher in college and high school populations where support, education and awareness are not so rife. [3]

Figure 2 shows how RED-S may affect athlete’s performance:

My Story

The best season I ever had was summer 2016, age 18. I ate mounds of nutritious food through the winter in my first year at University and trained hard when my coach told me to, with appropriate and scheduled rest. I was the strongest I had ever been. However, following the taste of England selection and competition at the senior level at the British Championships (Olympic Trials), I started looking for ways to get even quicker. This is the exact moment where I ‘fell off the train’ and unknowingly forced my body into a chronic energy deficit for nearly a year.

There are a variety of reasons for a caloric energy deficit:

  • Over-training (energy expenditure is very high)

  • Unintentional under-fuelling (due to ignorance/lack of awareness on how much you really need to be consuming as a young, growing athlete)

  • Purposeful under-eating (due to subclinical disordered eating tendencies or clinical eating disorders)

For me, it was a unique combination of the above. Following my small taste of success, I started training more (sometimes bashing out two lactic sessions per day; which for anyone who knows 400m training, knows this is not conducive to quick times!); and I became consumed with eating ‘healthily’(orthorexia tendencies)[4]. I was consuming large volumes, but not enough caloric density. This was due to ignorance, following of misleading information and a lack of awareness about how to correctly fuel my body for performance.

The first-time people started to notice I looked a bit too lean was on a warm weather training camp in Easter 2017. After a year of unintentionally restricting my body of the appropriate fuel it needed for the large amounts of training I was doing, my body was exhausted. When the body does not get enough fuel for the demands put onto it, it goes into ‘energy-saving mode’ and starts shutting down your other systems (reproductive, endocrine, metabolic, cardiovascular, immunological, gastrointestinal) that are crucial health.

I experienced the following RED-S symptoms:

  • Decreased performance and training response (I couldn’t train to any intensity and struggled to recover in between sessions)

  • Decreased muscle mass and strength

  • Comprised immune system

  • Felt cold and tired a lot

  • Difficulty engaging and concentrating

  • Underweight/weight loss

  • Loss of regular menstrual cycle (secondary amenorrhea) - **without a period, you don’t produce Oestrogen, an essential hormone for bone health**

Other common symptoms I fortunately did not experience at the time:

  • Decreased Bone Mineral Density (BDM) / stress-related injury. I had a regular cycle from aged 14-18, which luckily formed as a protective shield - **women who have not had their period for 2 continual years prior to the onset of RED-S are at higher risk of this as 25% of your BMD is formed in the first 2 years following menstrual cycle onset and 90% by aged 18; By age 30, a woman reaches her peak bone mass** [1]

  • Mood swings/anxiety/depression

Unfortunately for me, RED-S was only coined as a term in 2014. So, when I was presenting with the symptoms, my GP did not officially diagnose RED-S. Instead, I was put on the contraceptive pill to force my menstrual cycle and provide a synthetic version of Oestrogen and Progesterone, as well as asked, “can you just stop training?”, a seemingly unrealistic suggestion to a young athlete with dreams. Although a justified temporary fix, this was NOT a long-term solution. In an ideal world, I would have been referred on to a sports dietician to help get my natural cycle back by consuming a healthy caloric surplus (whilst slightly and sustainably decreasing my training load – Return to Play Model [2]). I hope now, in 2021, where RED-S is a lot more spoken about, researched and recognised by professionals, younger athletes can avoid ‘falling off the train’ before it is too late. Fast forward to now and I feel strong, educated, and aware. However, it took me years to build back to my full strength and ability, and I still feel the effects now. Just last year I had 3 months off running due to a mystery heart arrhythmia, a possible long-term side effect of RED-S.

When the body is given the appropriate fuel, it is given the opportunity to thrive (for performance, physiological and mental health). Although it is not uncommon for athletes to watch what they eat, consuming too few calories for their activity level can trigger RED-S syndrome. And no, just because I ate a few gelato sundaes whilst on the 2017 training camp, did not automatically mean I was consuming enough caloric density. The body requires fuel for daily bodily functions as well as the extra demands you put on it (considering training intensity, lifestyle, personal physiology). The best advice I can give is to listen to the RED flags your body gives you, enjoy all foods intuitively and seek professional advice where appropriate.

And remember, healthy looks different on everyone - never compare yourself to anyone but yourself.

If you want to learn and understand more about RED-S, or access a helpline, check out the references section below for links to rigorous sources. Also, if you want to learn more specifically about female athlete health, check out the podcast series named ‘Female Athlete Nutrition’ authored by Lindsey Elizabeth Cortes MS RD CSSD (a professional NCAA sports dietician) on Spotify.


[1] Mountjoy, M., Sundgot-Borgen, J., Burke, L., Carter, S., Constantini, N., Lebrun, C., ... & Ljungqvist, A. (2014). The IOC consensus statement: beyond the female athlete triad—relative energy deficiency in sport (RED-S). British journal of sports medicine48 (7), 491-497.

[2] Mountjoy, M., Sundgot-Borgen, J., Burke, L., et al. (2015) RED-S CATTM Relative Energy Deficiency in Sport (RED-S_ Clinical Assessment Tool (CAT); Available at: [Access date: 05/02/20].

[3] Łagowska, K., Kapczuk, K., Friebe, Z., & Bajerska, J. (2014). Effects of dietary intervention in young female athletes with menstrual disorders. Journal of the International Society of Sports Nutrition11 (1), 1-8.

[4] Orthorexia (2018) NEDA website. Available at: [Access date: 06/02/2020].

The Honest Truth: My experience of Relative Energy Deficiency in Sport (RED-S)

Written by Hannah Knights

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