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Empowering Cyclist with Knowledge about Relative Energy Deficiency in Sport (RED-s)

Updated: Aug 19, 2023

Relative Energy Deficiency in Sport (RED-s), is getting more attention in the press, but there's still a long way to go before athletes, coaches and sporting organizations are all well informed about the syndrome, how to prevent it and what resources are available for athletes who need help. I've put this article together for anyone who wants to learn more about RED-s and will link to some resources throughout. I plan to update this article regularly as new research is published.

Whether you are a professional athlete or a weekend warrior, there’s a chance you’ve heard about RED-s. The syndrome, which can impact bone health, reproductive hormones, immunity and metabolic rate, as well as many more physiological functions, has been making its rounds in the news lately. Professional runner Mary Cain spoke out about her own experience with RED-S and the abusive “win at all costs” system that acted as the catalyst for it. Her story in the New York Times put a much needed highlight on the topic.

For Cain, the constant push to be thinner left her with years of missed periods, five broken bones and deep emotional pain. Indeed, the deep-rooted systemic issues around irresponsible dietary practices, arbitrary weight goals and abuse of power in sporting organizations play a part in perpetuating unhealthy behaviours associated with RED-S in many athletes.

Other stories about RED-S can look quite different from Cain’s and can lead to a spectrum of impacts on athletic performance and mental health. You may be a masters, junior or recreational athlete who puts in hours training while assuming you’re meeting your calorie needs. Maybe you find yourself hitting performance plateaus, getting colds or nagging injuries that won’t resolve in a timely manner, struggling with poor sleep and mood, and even low libido or absence of or skipped periods. If you’re an athlete like this, RED-S can simply be a result of misinformation about how to fuel properly for training or even misplaced dietary behaviours that don’t belong in sport. And since RED-S does not discriminate by sex, age, body size or ability, spreading awareness is critical.

There is still much to learn about RED-S and research is consistently shedding more light on the topic. I plan to update this article as new research arises.

As a sports nutrition/performance coach and scientist who has been supporting athletes for over a decade, my focus has always prioritized athlete physical and mental health. A healthy athlete is a more consistent athlete and a consistent athlete has more opportunities to perform well and enjoy the process of sport. All athletes will inevitably surf waves of success and drop into valleys of adversity. If through it all, you can maintain general health with the help of optimal nutrition while being surrounded by a healthy and encouraging environment, you’ll be able to manage adversity with more mental and physical resilience.

What is RED-S?

RED-S is an extension on The Female Athlete Triad, a medical condition composed of three factors including low energy availability with or without an eating disorder, menstrual dysfunction and low bone density. Both models are underpinned by low energy availability, however RED-S is not limited to females. It is often unintentional, and athletes are often unaware that they have the syndrome.

What’s “energy availability?” It’s the energy (calories) you have left after you subtract the calories you expend during your training from the calories you consume in your diet for the day. If you do not have enough energy left to fuel your body’s physiological functions, you have low energy availability which could lead to RED-S.

RED-S is defined by the International Olympic Committee (IOC) as “impaired physiological functioning caused by relative energy deficiency and includes, but is not limited to, impairments of metabolic rate, menstrual function, bone health, immunity, protein synthesis and cardiovascular health[1].” The underlying factor leading to these impairments is low energy availability (LEA), where an athlete has inadequate energy available to meet basic physiological needs.

Symptoms of RED-s

Before we discuss symptoms related to RED-S, it is important to note that many of these same symptoms could arise from other underlying medical conditions. As an athlete you should always visit with your sports medicine or medical doctor to rule out any potential medical reasons for any symptoms you may be experiencing, including but not limited to menstrual/reproductive disturbances. Having a team of professionals around you who can communicate with one another is ideal.

Symptoms of RED-S include both physical and psychological symptoms to which we can also add behavioural signs. RED-S can be insidious and occur slowly over time and some of the symptoms, such as poor bone health, may go undetected without diagnostic testing unless an athlete experiences a stress fracture or accident which leads to a break or fracture.

The 2018 IOC Consensus Stand notes the following symptoms related to RED-S.

As you can see in the diagram above, the ramifications of RED-S can be far reaching physiologically, however every situation will not necessarily have impacts on all areas of our physical and mental well being. Every athlete will have their own individual experience at different severities. Some professionals in the industry do work with a system of green, yellow and red when assessing athlete risk as well as return to play based on severity.

Symptoms and Behaviours to Watch For

Specific examples that you may find more relatable which fall into the above categories would include but are not limited to:

  • increased moodiness/depression/

  • anxiety

  • loss of or irregular menstruation or failure to begin menstruation by 16

  • loss of or lowered libido

  • inability to maintain consistent training

  • decreased muscular strength, endurance, co ordination

  • increased injury risk or nagging injuries with prolonged recovery

  • decreased immunity, increase in sickness/colds

  • stunted growth

  • low iron

  • decreased bone health: broken bones or stress fractures

  • digestive problems

  • sleep disturbances

  • overall drop off in performance

Some behavioural signs you can watch for include:

  • diet behaviours that do not support performance goals

  • perfectionist behaviours

  • obsessive about “clean eating”

  • trying to stay very lean all season

  • obsessive or compulsive exercise routines beyond what is required for the sport

  • overly critical of one’s appearance and shape

  • refusal to stop exercising when injured despite coach recommendations

It's possible that many of these same symptoms could be related to other underlying medical problems, which is why it is important to work with your sports physician and other professionals who can accurately assess your specific situation.

RED-S Prevalence and Sex Differences

RED-S is relevant to both males and females however prevalence is higher in females which could be explained by a few factors. If you’re reading this as a women, you may know from experience that women face immense pressure from society to meet a certain aesthetic, even beyond the sporting arena, and may restrict nutrition based on aesthetics alone. I believe that men also restrict for reasons of aesthetic and the lack of openness about this likely contributes to our more narrow insight in this area. Having said this the research on men is expanding and it’s possible more men struggle then we currently are aware of.

Females have a very measurable symptom of RED-S, being the loss of or absence of a first period by age 16, also known as secondary or primary amenorrhea, respectively. (Not all women will lose their period and some may take longer than others when they do). It is also possible that as women we may be more willing to discuss symptoms, visit a physician or speak to a coach. Often the culture of sport doesn’t invite men to speak openly about what may be perceived as weaknesses.

Recent evidence has shown that the prevalence in males across many sports is also problematic[4]. Healthy men participating in higher levels of chronic intense endurance training can also experience consequential suppression of reproductive function and report having low libido. Current research suggests men have a higher tolerance to LEA. More research is needed to understand the underlying mechanisms here[5].

More male athletes are also speaking up publicly about disordered eating, particularly cyclists, endurance runners and figure skaters, echoing the evidence that RED-S is prevalent for males athletes. Hopefully these stories along with education, will lead to shifts in the male sporting culture, to the point where men can also express their struggles with body image and how these psychological challenges are impacting their nutritional habits.

Body Image, Eating Disorders or Disordered Eating:

If you’re concerned about body image and thinness you may find yourself intentionally cutting calories or training longer to “burn off calories.” Noteworthy is that research has shown that athletes who meet their energy needs regularly, have better body composition than those in long term deficits.

Athletes meeting energy needs can keep their resting energy expenditure up and maintain their lean body mass [3]. It’s important to remember a loss in ‘scale weight’ can also reflect loss of lean body mass and an increase in body fat, a less ideal body composition. Chronic calorie cutting approaches often backfire, especially in the long run, with consequences beyond body composition. We will cover potential long te ramifications in a follow up article.

RED-S is not limited to athletes with eating disorders, or disordered eating. For example it’s very possible that you may be unaware of the mismatch between your energy expenditure and intake, which is why this education is so key.

Is RED-S Limited To Certain Sports?

The prevalence of RED-S is higher in sports where power to weight or aesthetics tend to be prioritized (gymnastics, ballet, endurance sports, jockeys etc.). Not surprisingly these sports can be the very ones which praise leanness and may have people within the culture who turn a blind eye to athletes who are visually struggling with energy deficiency, especially if they are performing well. It’s important to note that not all athletes with RED-S have a lean appearance. In my own experience I have worked with athletes of all sizes who were not meeting energy needs. Referring to a previously mentioned point, the leaner athlete may actually be the athlete meeting energy needs, while the ones restricting have been shown to store more body fat and have less optimal body compositions as a result. We can’t judge an athlete on their appearance alone.

Endurance cycling poses a high risk for RED-S as there can be an over fixation on power to weight and training often leads to high energy expenditure. It would be easy to assume short distance runners, sprinters, wouldn’t be affected by RED-S however research would prove us wrong [6]. Additionally there is minimal research about RED-S in team sports, so it’s possible we simply don’t know what we don’t know. Again, RED-S does not discriminate, even by sport.

Regardless of the sport, the culture of each sport continues to play an important role. Physique expectations and inappropriate dietary practices continue to drive some of the behaviours associated with RED-S.

How To Eat To Avoid Low Energy Availability (LEA)

There are no validated diagnostic test in the early stages of RED-s. Education is critical to avoid low energy availability, and optimal energy availability (EA) should be emphasized. Optimal energy availability is defined as the energy required to fuel daily exercise plus energy consumed to meet needs of daily living (your resting metabolic rate – RMR). By achieving optimal energy availability, you can achieve optimal metabolic function and health[1[,[2].

The goal is to consume enough calories to cover both your Resting Metabolic Rate (daily needs to run your body) PLUS energy expended during exercise.

The 2018 IOC Consensus Statement on RED-s notes that “In women, energy intake for healthy physiological function has been measured in laboratory settings and is typically 45kcal/kg/FFM per day[1]”. Energy availability below 30kcal/kg/FFM per day—although not absolute—serves as the current guideline for low energy availability. This calculates closely to one’s resting metabolic rate (RMR).

Practical Example: if you’re a 59kg athlete consuming 30kcal per kg of body weight this = 1770 calories, which equates close to the RMR for an athlete this size. (We will discuss later how RMR can change throughout a season).

You should aim for optimal EA for most of the season, while manipulating energy intake in a safe periodized approach, when appropriate, within the season only if deemed necessary (think about a few peak races). Although research is limited in this area of nutrition periodization, we know this approach will limit the time you spends in a state of energy deficiency, and duration is likely an important factor contributing to the negative consequences of RED-s.

How To Measure Energy Availability

To measure energy availability, in kilocalories per kg of fat free mass (FFM), we calculate an athlete’s energy intake (EI) minus exercise energy expenditure (EEE) divided by fat free mass (FFM). EI refers to the food you eat and EEE refers to the energy you expend during exercise. What we are looking to avoid is a mismatch in energy availability, (what’s left over to run your body for the day), based on this calculation.

It’s important to note that this syndrome can occur from mismatches in energy as little as 300 calories per day. (That’s as little as bagel plus one egg or 4 tbsp of hummus and a slice of whole grain bread). Seemingly small calorie mismatches can culminate over time. The positive side of this is that with awareness of this mismatch an athlete can bridge this gap with nutrition and be on their way to recovery.

Practical Examples:

Example 1: An obvious example of an athlete with low energy availability would be a 59kg athlete with 17% body fat (10.3kg) is consuming (EI) 2000 calories per day and expending (EEE) 2000 calories per day. Her FFM is therefor 59kg-10kg = 49kg.

Energy Availability = 2000(EI) – 2000(EEE) ÷ 49kg FFM = 0

In this situation the athlete is left with zero calories for basic physiological needs and has low energy availability. For optimal function, an athlete would still be left with 45kcal per kg FFM to run their body for the day, which in this case would equal 2205 calories.

(*to convert your weight in pounds (lbs) to kg simply divide lbs/2.2 and then calculate your kcal intake based on your FFM).

Example 2: 59kg athlete, 17% body fat (10.3kg) consuming 3500 calories per day, expending 1600.

EA = 3500(EI) – 1600(EEE)/49kg/FFM = 39kcal/kg FFM/day (equal to 1911kcals) which is moderate.

Optimal EA: 45kcal x 49kg/FFM = 2205 calories of EA remaining to meet all physiological needs.

Several circumstances can lead to low energy availability:

  • High energy expenditure through exercise and a failure to meet energy needs based on this.

  • Restricting energy intake through their diet, could be a result of disordered eating or misplaced dieting programs.

  • Food insecurity (low access to food) and insufficient finances in some populations resulting in unmet energy needs.

Other ways you can end up with low energy availability? You can have a low appetite, long training hours can interfere with your regular meal intakes or your life situation which may be extremely busy, can be so distracting that you actually forget to eat. Some athletes may need to cut back on training in order to regain health, which is an important consideration.

Any of these scenarios can happen to any of us on a given day, yet it is important to realize this doesn’t mean that we instantly have RED-S.

Research has shown how difficult it is to pinpoint an exact threshold on the low end of calorie intake where objective measures and impaired health are seen, including menstrual disturbances and hormonal disruptions[2]. Evidence has associated a calorie intake of less than 30kcal per kg of FFM per day with disturbances in physiological systems, particularly in women. In men it is possible that this low end is below 30kcal per kg of FFM per day, however more research is needed in this area. Although more literature is needed, this can be used as a guiding principle, while keeping in mind, different responses can occur among athletes and even change within a season.

RED-s Diagnosis and Challenges

  • Questionnaires

  • Hormonal status – secondary indicators

  • Birth Control Pill

  • Resting Metabolic Rate (RMR)

  • Food journaling

  • Compounding food specific factors

  • Energy expenditure

  • Coach athlete relationship

There is no definitive diagnosis for RED-S or validated test in early stages. The process of determining if you have the syndrome is multifaceted. The goal is to understand both the big picture of what has been going on leading into this moment and what’s going on now as far as nutrition and training. While elite athletes may have access to lab equipment and medical teams for testing, there are other options for the amateur athlete. A medical team should be involved and blood testing will be important. Some information is better than zero information. Read on to learn more about investigative steps you can take.

Specific questionnaires such as the Low Energy Availability in Females Questionnaire (LEAF-Q) can be very insightful. The LEAF-Q questionnaire, as one piece of information, has proven to be quite effective in recent research. Currently a questionnaire for males is being developed, the Low Energy Availability in Males Questionnaire (LEAM-Q).

Blood testing for secondary indicators such as hormonal status is definitely important and can be done through your medical doctor,/sports medicine doctor. Ideally they are knowledgeable about RED-s. Talk to them about what’s happening and why you are concerned and what you're feeling.

Taking note of performance measures such as inconsistency, lasting fatigue, mood disturbances, and injuries, as well as signs of disturbances in reproductive hormones; skipping menstrual cycles or losing them all together; are all important factors to take into consideration.

If you are on the birth control pill, it is important to understand that while it may appear you are having a natural period monthly, the period you have while on hormone based birth control pills are referred to as a ‘withdrawal bleed’. Therefor it is possible to have the syndrome while still appearing to have a monthly ‘period’. Again, consultation with your medical doctor to investigate hormone levels is one of the most important steps you can take in this process of investigation. It's also important to rule other causes out that could result in your symptoms.

Challenges With Food Journals and Predictive Equations

We all have different resting metabolic rates (RMR), which can change throughout a season and with changing energy availability. RMR is the number of calories required for the body’s basic functions of physiology at rest including but not limited to digestion, brain function, muscle protein synthesis, circulation, and bone remodelling.

Although we can make estimates of RMR, predictive equations are not always accurate which poses one challenge. A few of the equations easily available for you online include; the Harris Benedict, Cunningham and Mifflin St. Joer equations. Multiplying our fat free mass in kg by 30kcal can also give us an estimate of our RMR. By knowing our RMR we can have an idea of our caloric needs for basic functions of daily living. This doesn’t include our caloric needs to replace energy expended through exercise. If you are able to measure changes in RMR over time (and see a decrease), this could be an indicator of the syndrome.

Logging an accurate food journal to measure energy availability can also be challenging. If you’re working with a sports dietitian, exercise physiologist or sports nutritionist you may leave out foods that you are consuming if you fear you will be judged for eating “junk” or the journaling could create a “halo” effect, where you suddenly eat healthier food, since you know someone will review the journal. This makes it difficult to have accurate dietary analysis. If you are journaling for yourself, be honest, don’t skip anything, be as accurate as you can.

Long term food journals (months) would be more revealing of energy intakes, however the downside is accuracy. Timing of nutrition intake should also be taken into consideration when journaling your food. Not everyone is committed to journaling food, or it may not be in your best interest if you’re struggling with an eating disorder or lean towards obsessive behaviours, which poses its own challenges and should be dealt with through the appropriate professional. If you’re an athlete working with a professional, there should be some discussion about whether journaling will be constructive or destructive during the process.

To compound the factors above, if you’re working with a professional and experiencing symptoms of RED-S, then you fill an acute 7-day food journal, the reality is you could be misrepresenting what you’ve have been consuming in the weeks or months before this journal entry. A snapshot is not always reflective of long-term behaviours and transparency is key.

Other compounding factors of RED-s, more specific to the foods themselves, include the quality of the diet, high fiber intake, which may reduce circulating estrogen levels, as well as the timing of nutrient intake within the day and around training[7],[1],[8],[9],[10].

Despite its shortfalls, I believe there is value to food journaling as it can provide an opportunity to learn about the contents of your nutrition and your nutrient timing. Even if lacks accuracy, you can still learn a lot about your energy intake. Many athletes can benefit from a better understanding of the basic foundations of nutrition. Journaling while working with a professional can provide a great learning opportunity.

Challenges of Measuring Energy Expenditure

Measuring energy expenditure also comes with error. The devices used will not be exact. Devices will not incorporate non exercise activity thermogenesis (NEAT); the energy we expend for everything we do that isn’t sleep, exercise or eating; or the thermic effect of food, which simply put is the energy required for digestion and absorption of food. We all know the athlete who finishes the 5-hour ride and then goes for a walk to the market, a short hike and moves all day. In comparison to the athlete who finishes training and literally puts their legs up and rests for the remainder of the day, the discrepancies in NEAT between these athletes can be significant.

Based on the factors noted above, experienced nutrition professionals and/or exercise physiologists will play an important role when assessing energy intake and expenditure in athletes. I recommend contacting one if you have red flags after reading this or other related articles. Alternatively you can learn more by reading from quality resources.

Ultimately the best methods for assessing RED-s will include blood testing of sex hormones thyroid hormones (several times throughout the season), fracture history and possible bone mineral density testing, as well as questionnaires, food journal, lab measures of FFM and energy intake/expenditure.

On top of all the science, if you’re working with a coach, the information that you are willing to share will depend somewhat on the trust and open communication that you’ve built with your coach. Good coach athlete relationships will benefit everyone in the quest to gather the most valuable information. If your coach is informed and concerned, they may be the one to breach this topic with you.

The Role of Sports Organizations

With more awareness about RED-s and eating disorders/disordered eating in sport, it’s encouraging that there are coaches and organizations who are taking athlete health more seriously, engaging in discussions, asking the right questions and creating a safe welcoming culture. Whether or not those discussions will lead to actionable changes will likely be dependent on the support systems put in place to help athletes act on the knowledge with the help of sports dietitians and sports nutrition professionals. It's also the athlete's responsibility to get informed as much as possible about fueling for their sport. Connecting the physiological changes that can result from action to performance outcomes, will be important in motivating athletes to act.

Sporting organizations must prioritize athlete health and realize the ‘winning at all costs’ mentality doesn’t serve the athlete short or long term. Medal counts are great, but not at the expense of athlete physical and mental health. Unhealthy dieting practices and shaming athletes have no place in sport. Coaches and sporting organizations must respect athletes as human beings. If organizations follow a science-based approach to nutrition, they will learn that healthy athletes meeting energy needs are more likely to have career longevity and consistently perform at their best. The sooner coaches and organizations who perpetuate unhealthy cultures learn this, the better.

If you’re the athlete who doesn’t belong to a sporting organization, bringing more awareness to RED-S and the sport science surrounding it will hopefully help you prevent the syndrome altogether or help you recognize red flags that you can address with more knowledge and resources.

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1. Mountjoy M, Sundgot-Borgen JK, Burke LM, et al. IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. Br J Sports Med. 2018;52(11):687-697. doi:10.1136/bjsports-2018-099193

2. Updated A, Review N, Logue DM, et al. Low Energy Availability in Athletes 2020 : on Sports Performance. 2020:1-19.

3. Deutz RC, Benardot D, Martin DE, Cody MM. Relationship between Energy Deficits and Body Composition in Elite Female Gymnasts and Runners. Vol 32.; 2000.

4. Burke LM, Close GL, Lundy B, Mooses M, Morton JP, Tenforde AS. Relative energy deficiency in sport in male athletes: A commentary on its presentation among selected groups of male athletes. Int J Sport Nutr Exerc Metab. 2018;28(4):364-374. doi:10.1123/ijsnem.2018-0182

5. Hackney AC, Lane AR, Register-Mihalik J, O’Leary CB. Endurance Exercise Training and Male Sexual Libido. Med Sci Sports Exerc. 2017;49(7):1383-1388. doi:10.1249/MSS.0000000000001235

6. Sygo J, Coates AM, Sesbreno E, Mountjoy ML, Burr JF. Prevalence of indicators of low energy availability in elite female sprinters. Int J Sport Nutr Exerc Metab. 2018;28(5):490-496. doi:10.1123/ijsnem.2017-0397

7. Barron E, Cano Sokoloff N, Maffazioli GDN, et al. Diets High in Fiber and Vegetable Protein Are Associated with Low Lumbar Bone Mineral Density in Young Athletes with Oligoamenorrhea. J Acad Nutr Diet. 2016;116(3):481-489. doi:10.1016/j.jand.2015.10.022

8. Gaskins AJ, Mumford SL, Zhang C, et al. Effect of daily fiber intake on reproductive function: The BioCycle Study. Am J Clin Nutr. 2009;90(4):1061-1069. doi:10.3945/ajcn.2009.27990

9. Melin A, Tornberg Å, Skouby S, et al. Low-energy density and high fiber intake are dietary concerns in female endurance athletes. Scand J Med Sci Sports. 2016;26(9):1060-1071. doi:10.1111/sms.12516

10. Barr SI. Vegetarianism and menstrual cycle disturbances: Is there an association? Am J Clin Nutr. 1999;70(3 SUPPL.):1-6. doi:10.1093/ajcn/70.3.549s

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