Background
I am a big fan of Lionel Sanders! If you haven’t heard of him, he is a Canadian professional triathlete currently living in Tucson, AZ. He has been a pro in the sport for a while now, since 2013. He also has many, many accolades to his name, including the placing 1st at the 2017 ITU Long-Distance Triathlon World Championships, 2nd at the Ironman World Championships twice (2017 and 2021), and is the winningest Ironman professional in history, with over 30 professional wins at Ironman-branded half and full-distance races.
Lionel Sanders was an up and coming pro when I first got into triathlon myself back in 2014. He was the OG when it came to professional triathletes having a social media presence, particularly on YouTube. He was known for being super raw, unfiltered, and somewhat insane. He usually posted uncut videos of himself training for long hours on his bike trainer and treadmill in a dimly lit room in his home, then in Windsor Canada, whilst mostly staring at a blank wall. Many, many people soon came to follow Lionel Sanders when he hired a videographer in 2017, a breakout year for him, and started producing higher quality and more frequent videos. Today, he has one of the biggest, if not the biggest, individual pro triathlete YouTube following, with over 200,000 subscribers.
Lionel was an inspiration to me. He was gritty, very raw, and wasn’t afraid to be brutally honest in his videos. He has put, for the most part starting in 2017, his entire professional triathlon career on YouTube. All of the highs, all of the lows, and everything else in between. It’s all on his channel. As of the time I’m writing this, June 20th, 2025, his latest YouTube video was one in which he discussed an extremely important, but very often overlooked and misunderstood topic among male endurance athletes: Relative Energy Deficiency in Sport, or RED-S, as it is most commonly known. Take a break from the article here to watch the video:
Over the course of his career, Lionel has endured many disappointments, including injury, illness, bouts of overtraining, and more. However, this was a new topic being explored in Lionel’s professional journey that he displays so publicly. I found this video fascinating as he is very, very honest about how he concluded that he is suffering from RED-S. Lionel even admits in the video that he had heard of the term, but largely ignored thinking about it and how it could relate to him as a male athlete given it is so commonly associated with eating disorders (something he was not currently struggling with) and female athletes. However, RED-S is something that can fly under male endurance athletes’ radars far too often given the misconceptions that surround it and with how it can present in men. So, I want to take this opportunity to focus on discussing RED-S in more detail, particularly how it can present in men, what factors can make men at risk of experiencing it, and how it can negatively impact performance and health.
What is Relative Energy Deficiency in Sport (RED-S)?
Relative Energy Deficiency in Sport, referred to as RED-S moving forward, has its historical roots in the Female Athlete Triad (3). The Female Athlete Triad is a condition affecting female athletes and is characterized by low energy availability, menstrual dysfunction, and low bone mineral density. This disorder was often associated with female athletes that engaged in disordered eating practices. While the Female Athlete Triad can manifest in female athletes not engaging in disordered eating, the misconception that it was only associated with female athletes engaging in disordered eating grew over time.
In 2014, the International Olympic Committee (IOC) established RED-S as a new condition that referred to a broader set of physiological and psychological impairments that occur in both males and females due to a relative energy deficiency whilst engaging in sport (3). This was an important milestone as it formed a diagnosis applicable to both male and female athletes. It also established a condition with a much broader set of signs and symptoms not limited to just sexual function and bone health. The most current RED-S models demonstrate that this condition can impact many systems, including the immune system, reproductive/sexual function, bone health, endocrine function, metabolic health, cardiovascular function, gastrointestinal function, psychological health, growth and development, and sport performance (4).
RED-S is currently defined as a “syndrome of impaired physiological and/or psychological functioning experienced by female and male athletes that is caused by exposure to problematic (prolonged and/or severe) low energy availability” (4). Energy availability (EA) is defined as the amount of energy remaining to support an athlete’s bodily functions after exercise energy expenditure (EEE) is subtracted from dietary energy intake (EI). It is typically calculated as follows (1):
EI comprises the total amount of energy consumed from food in the form of calories (kcal). EEE refers to the total amount of energy expended through exercise or physical activity, also in the form of kcal. EEE is subtracted from EI to leave us with the energy leftover that is available to support daily bodily functions. The energy required to support daily bodily functions required for sustaining life is often referred to as one’s basal metabolic rate (BMR). BMR is important as this captures the energy required for things such as proper immune function, bone growth and remodeling, healthy functioning of the brain and nervous system, healthy cardiovascular functioning, healthy skin, and much more. BMR covers a lot of the basic things that we often don’t think about as they occur in the background of daily life, but that are essential to us feeling healthy, happy, and functioning at our best.
Low energy availability (LEA) is a state in which energy intake is too low to meet the body’s energy needs to support BMR (4). There is currently a lack of literature to establish a clear cutoff that defines LEA; however, it is currently thought that an EA of >45 kcal/kgFFM/day is optimal for support of performance gains and healthy physiological functions, 30-45 kcal/kgFFM/day is suboptimal and increases the risk of impaired physiological function, and <30 kcal/kgFFM/day is considered LEA and places an athlete at serious risk for developing RED-S long-term (1). Some research literature argues that the cutoff for LEA is slightly lower than <30kcal/kgFFM/day; however, this is currently accepted as a cutoff by many researchers in this area. LEA can be achieved by any of the following:
Increasing exercise energy expenditure
Purposefully decreasing energy intake
Unknowingly consuming insufficient energy to meet EA needs
Let’s take a look at a hypothetical male athlete to put these numbers and scenarios into context.
Todd is a 30-year-old male distance runner that weighs 155 lbs (~70.5 kg) and has a body fat of 14% (FFM = ~60.6 kg). Todd trains for ~2 hours daily on 6 days each week. The remaining day of the week, Todd exercises ~1 hour. Todd’s daily EI averages ~3500 kcal/day, his daily EEE is ~1500 kcal/day. Therefore, Todd’s EA can be calculated as follows:
Todd’s EA equates to 33 kcal/kg/FFF/day. This would place Todd in the “suboptimal” category of EA using the guidelines described above. In order to achieve an “optimal” EA while exercising at his current levels, Todd would need to increase his daily EI to ~4250 kcal/day or more. If Todd decreased his daily EI to just ~3300 kcal/day or less, he would then be at serious risk of developing RED-S long-term.
Keep in mind, this area of research, particularly in male athletes, is very new and much more research needs to be done to establish better criteria around EA levels and what is considered optimal. Furthermore, a lot of numbers used in the calculation of EA are error-prone, subject to bias, and difficult to measure accurately without expensive research-grade laboratory equipment. For example, measuring FFM accurately is very expensive, and many of the current tools that athletes may have access to for calculating this value can be unreliable and inaccurate (e.g., electronic scales and handheld body fat measurement devices). Furthermore, EI is typically calculated using dietary recall, which is prone to athletes under-reporting the serving sizes of foods consumed and, therefore, the number of calories consumed on a daily basis. EEE is also very difficult to measure precisely. Many athletes rely on smartwatches to collect training and lifestyle data for the measurement of energy expenditure from exercise and other physical activities. These devices can be both unreliable and inaccurate, and the reliability and accuracy can vary wildly depending on the device, manufacturer, and equations used in the calculation of EEE. All of this is to say that the EA numbers calculated, especially if you are doing this for yourself or athletes you coach, without highly specialized and calibrated laboratory equipment, should be used within the context of other factors. More specifically, use EA numbers as another data point when assessing the risk that an athlete may be at for RED-S.
Other factors to consider include the signs and symptoms of RED-S, which can be captured through regular interaction and discussion with athletes or regular check-ins with yourself if you are self-coached. There are many signs and symptoms of RED-S in men, including (4):
Impaired reproductive function/sexual health
e.g., reduced testosterone levels, erectile dysfunction and decreased libido, lack of regular “morning erections”
Impaired bone health
e.g., low bone mineral density scores as measured by dual energy x-ray absorptiometry (DXA), bone stress injuries
Impaired gastrointestinal (GI) function
e.g., abdominal pain, cramps, bloating, and changes in bowel movements
Impaired energy metabolism
e.g., reduced resting metabolic rate or BMR, increased cortisol levels, weight loss (but sometimes no weight loss if already very lean)
Impaired glucose and lipid metabolism
e.g., elevated total cholesterol and LDL cholesterol, reduced fasting glucose and insulin levels
Mental health issues
e.g., depression, exercise dependence, other mood disorders
Impaired cognitive function
e.g., reduced memory, impaired decision-making, reduced spatial awareness, reduced executive function
Sleep disturbances
e.g., difficulties with falling asleep, staying asleep, or waking frequently throughout the night
Reduced skeletal muscle function
e.g., loss of muscle mass and strength
Impaired growth and development
e.g., particularly in younger athletes, a deviation from expected growth curve for age
Reduced immunity
e.g., increased rate of infections and illness, lower immune cell counts in CBC lab tests
Impaired cardiovascular function
e.g., ECG abnormalities, low blood pressure, dizziness from sitting/lying to standing, very low resting heart rate (<40 bpm)
Reduced overall performance
e.g., underperforming in training sessions and races, inability to exercise at high intensities, decreased endurance, reduced strength and power, longer recovery times after typical training sessions, etc.
Some symptoms carry with them a more severe risk as it relates to RED-S compared to others, particularly bone stress injuries in certain areas, low testosterone levels, and the presence of disordered eating. The presence of these symptoms are typically some of the most common and reliable indicators of RED-S when compared to others (4). Still, the presence of one of these symptoms in isolation does not guarantee that RED-S is the cause as these symptoms can be related to other conditions or situations.
It is, for example, entirely possible for a male athlete to have a bone stress injury and not be in a state of RED-S. An athlete could also have low testosterone levels and not have RED-S. The signs and symptoms of RED-S usually occur in multiples or clusters and usually include some of the more severe signs and symptoms (i.e., bone stress injury, low testosterone) and some of the other less severe signs and symptoms (i.e., depression, fatigue, sleep disturbances, etc.). For example, if you watched Lionel Sanders’ YouTube video I mentioned initially, he discussed a group of symptoms that, when he looks back now, fit into the diagnosis of RED-S (i.e., repeated bone stress injuries, low testosterone levels, frequent infections/illness, erectile dysfunction and reduced frequency of morning erections). Then, once he took a deeper look at the number of calories he was consuming on a daily basis versus what he should (approximately) be consuming to have adequate EA for EEE and BMR, he was falling well short of this rough calorie goal. Altogether, Lionel Sanders seemed to fit into the diagnostic criteria for RED-S.
How Do You Avoid RED-S?
Put very simply, to avoid RED-S, consume enough energy to support your exercise levels and your BMR. It sounds simple, but as I mentioned previously, it is difficult to calculate precise energy needs, i.e., calorie needs, for things such as exercise energy expenditure and BMR. If you are an athlete that likes to have specific data points to aim for, there are many online calculators that can estimate your BMR, daily exercise energy expenditure, and then total calorie needs to maintain your weight. Additionally, many smartwatches nowadays can estimate some of these numbers as well, particularly exercise energy expenditures. Some smartwatches will use individual data points, such as age, height, weight, gender, and more to estimate your resting metabolic rate as well (slightly different than BMR and considers BMR plus the small caloric needs to support very light daily activities while awake). Using whatever is available to you to get an estimate, and I will emphasize here these numbers are a very rough estimate, can help provide some sort of reference point when determining a daily calorie goal to support health and performance.
Additionally, and perhaps more importantly, it is important to monitor overall health and performance on a regular basis to keep an eye out for any of the signs and symptoms mentioned previously. Regular health monitoring can be done through blood work to look for abnormalities in blood counts, hormone levels, vitamin and mineral levels, and more. Seeing a primary care provider on a regular basis, particularly one that is familiar with the needs of athletes, can be a useful way of checking overall health and body system functioning as well as providing a space for dialogue about your health to see if there are any signs of concern. Monitoring your training and performance can be done in many ways. If you are coached, this is something your coach should be doing for you to some degree in collaboration with yourself. If you are self-coached, using online training platforms (e.g., TrainingPeaks, etc.) can be incredibly valuable as you can access a plethora of data points on daily, weekly, monthly, and annual basis. When monitoring performance, keep an eye out for periods of consistent underperformance, poor recovery, inconsistent training due to excessive fatigue, patterns of mismatches in mood and perceived exertion for the demands of training sessions (e.g., low mood and high perceived exertion on easy sessions), and periods of low motivation to train.
The difficulty with RED-S identification is that there is not a single tell-tale sign or symptom indicative of the condition. RED-S is often identified in athletes after they have suffered multiple signs and symptoms for a long period of time and as other possible causes or diagnoses have been ruled out. However, being aware of RED-S, understanding the cause of it, and knowing the signs and symptoms can help both athletes and coaches catch it early on, before it starts to have serious impacts on one’s health and performance or possibly before any signs and symptoms develop in the first place. Remember, RED-S is simply putting oneself in a significant energy deficit, or state of low energy availability, for prolonged periods of time. Checking in regularly with daily EI and comparing this to what daily EI needs are can be valuable in catching periods of time where an adjustment to either EI or EEE is needed to avoid a prolonged period of LEA.
For many athletes, counting calories and focusing on food consumption can be a sensitive topic, particularly in those with histories of disordered eating or eating disorders. For athletes that are not sensitive to calculating daily EI and monitoring weight, checking in with these metrics on a somewhat regular basis can provide good data points to monitor over time. For example, once a week, you could get your morning body weight and keep track of this on your online training platform or on an excel spreadsheet. Once a month, you could check-in with your daily EI by keeping a 3-day food diary and using calorie counting programs or apps to calculate an estimate of daily EI. These two data points alone can be valuable for monitoring EI versus energy needs over time.
Monitoring EI doesn’t necessarily need to be done by counting calories and tracking body weight. A coach might have you keep a daily food intake diary for a few days and then calculate your daily EI for you so that you don’t have to be involved in the calorie counting process. Your coach can then do these check-ins related to EI on a somewhat regular basis and have a data point related to an estimate of EI that they can monitor for signs of concern.
If you don’t have access to a coach that can assist you with this and you are particularly sensitive to keeping food diaries, calculating daily EI, and monitoring body weight, you can simply create regular check-in points for yourself to reflect on overall health and performance. Use the signs and symptoms of RED-S to form a checklist in which you can identify the presence of any signs and symptoms of RED-S. If you start to notice that, over time, more and more signs and symptoms related to RED-S are present, then this could be an indicator to meet with your primary healthcare provider to discuss these concerns in more detail. Finally, simply being aware that RED-S is related to prolonged and severe LEA while simultaneously making a point to fueling well for health and performance can go a long way in avoiding LEA. You don’t necessarily need to count calories to do this. Fueling well for health and performance can look like the following:
eating regular meals throughout the day (breakfast, lunch, dinner) consuming protein, carbohydrates, and healthy fats with each of those meals
fueling before, during (especially on sessions lasting >1 hour), and after training to support performance and recovery
before: mostly carbohydrates with some protein and fat if desired
during: primarily carbohydrates
after: protein and carbohydrates with small amounts of fat if desired
Taking a simple approach to fueling like this does not require counting calories, calculating macronutrient intake, etc. There is simply a focus on fueling regularly with the goal of supporting overall health and performance. Taking this simple approach can go a long way in supporting healthy daily EI levels and avoiding prolonged and/or severe bouts of LEA.
What If I am Concerned That I Have Signs and Symptoms of RED-S?
If you have some signs and symptoms related to RED-S, and you are concerned about it, set up an appointment with your primary healthcare provider. Your healthcare provider will be able to discuss these concerns with you, recommend testing if necessary, and refer you to receiving more specialized testing and/or care if needed. I am aware that a discussion of diet and some of the symptoms of RED-S, namely weight and sexual health, can be uncomfortable and emotionally triggering for some men. However, if there is any concern at all, it is far safer to get an appointment with a healthcare provider and discuss the concerns as opposed to waiting and these symptoms getting worse.
RED-S is not something that you would want to try and self-diagnose and self-treat by any means. This sort of situation is one that is best monitored and managed by a healthcare team. Primary care physicians, dieticians, and more specialized physicians specializing in sports medicine or men’s health may all be a part of a team that helps monitor and address RED-S in a male athlete. Typically, treatment of RED-S, once diagnosed, includes treating the symptoms that an athlete is experiencing while simultaneously restoring a sufficient EA to support health and performance (4). Improving EA may be accomplished by either increasing EI, reducing EEE, or both depending on the severity of the condition (4). RED-S is something that can range in severity from very mild with minimal symptoms to quite severe and dangerous to one’s health at worst and if left untreated for too long. Therefore, as a male athlete, it is wise to err on the side of caution with this and see a healthcare provider if there is any concern that you may be dealing with RED-S.
Conclusions
RED-S is a challenging condition for many reasons. It is often shrouded in misconceptions and can be difficult to identify and diagnose when present. However, it is a condition that is rightfully receiving more attention as more athletes speak out about their experience with it. Creating safe places for these conversations to happen can make other athletes more open to discussing their experience with it, can help to reduce the stigma associated with it, and can help increase overall awareness of RED-S. Cultivating greater awareness of RED-S may help many male athletes in avoiding it altogether or in seeking help if they identify with some of the key symptoms associated with the condition. Hopefully with more awareness of RED-S and the dangers of chronic LEA, fueling for both performance and health becomes an integral part of every athlete’s training plan.
References:
1. Cupka, M., & Sedliak, M. (2023). Hungry runners–low energy availability in male endurance athletes and its impact on performance and testosterone: mini-review. European Journal of Translational Myology, 33(2), 11104.
2. Lee, B. L. (2024). Low Energy Availability (LEA) in Male Athletes: A Review of the Literature. Sport Journal.
3. 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 medicine, 48(7), 491-497.
4. Mountjoy, M., Ackerman, K. E., Bailey, D. M., Burke, L. M., Constantini, N., Hackney, A. C., ... & Erdener, U. (2023). 2023 International Olympic Committee’s (IOC) consensus statement on relative energy deficiency in sport (REDs). British journal of sports medicine, 57(17), 1073-1098.
Happy training and racing!
-Ryan Eckert, MS, CSCS
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