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What is RED-S and Why Should You Care About It?

Young athletes growing into their sport are conditioned to think that being constantly sore or exhausted is normal, and that feeling worn out just means they're doing something right with their training. The feeling of always running on empty is romanticized, and side effects of RED-S are seen as normal or just part of being an athlete. Because of this, far too few people are aware of its existence and of the long term impact it can have on an athlete's health and well-being, and it is often not addressed until it has become a serious problem. Read on to learn more about RED-S and the impact is has on an athlete's health and performance!

Relative Energy Deficiency in Sport, or RED-S, is a state of low energy availability caused by a mismatch in the amount of energy an athlete needs and the amount of energy they’re actually taking in. This discrepancy can happen intentionally through eating disorders or disordered eating behavior, but often occurs unintentionally when an athlete doesn't realize or struggles to meet their energy needs. Previously referred to as the Female Athlete Triad due to its high prevalence in females and often the loss of their menstrual cycle known as amenorrhea, we now know that RED-S can happen to anyone in any sport at any level if the athlete’s nutrition is not sufficient to support their training, with or without amenorrhea.

What may begin as the feeling of low perceived energy or chronic soreness can quickly escalate to more serious symptoms that can negatively impact an athlete’s performance and, most importantly, their long term health.

Does this sound like something you or an athlete you coach is experiencing? If so, read on to learn more about the consequences of RED-S.

While every athlete with RED-S will experience it differently, here are some of the health consequences of low energy availability:

This figure from the IOC Consensus Statement on RED-S shows how Relative Energy Deficiency in Sport has an impact on a number of systems in the body and therefore, on many areas of performance. 2018. Mountjoy et al.

Metabolic damage. A large portion of athletes who find themselves with the sort of low energy availability that leads to RED-S do so on purpose with the goal of losing weight. What they don't realize is they are actually making it harder on themselves to see body composition changes, and are more likely to see an increase in fat mass and sometimes even in weight due to under fueling. Prolonged low energy availability is associated with a decrease in resting metabolic rate and slowed weight loss in both sexes, and this restriction is just driving the body to store more energy in order to prevent starvation. This impacts an athlete's ability to build lean mass and use dietary energy to perform at their highest potential, and the athlete often feels frustrated that they aren't seeing the results of their training.

Gastrointestinal dysfunction. Low energy availability increases an athlete's chances of experiencing stomach issues, both during and around training. It can take longer for food to move through the GI tract, and it is often digested less efficiently. This can create an unhealthy balance of good and bad bacteria in the gut, creating a poor environment for digesting and absorbing nutrients needed to support health and performance. Athletes with low energy availability are also more likely to experience constipation, as well as needing to take frequent bathroom stops during training. I often see athletes who struggle with stomach issues around exercise eat less to try to prevent this from happening, not realizing that they may actually be making the problem worse.

Amenorrhea. In biological females, a scarcity of energy, especially energy from carbs and healthy fats, negatively effects the regulation of hormones by the hypothalamus. If this continues for an extended period of time, the menstrual cycle will become irregular or stop altogether. Unfortunately some coaches and doctors tell their female athletes that losing their period is normal when training hard, but a regular menstrual cycle is a major marker of health and actually affords some performance advantages to biologically female athletes. Losing your period is a major red flag that something is wrong, and should not be brushed off or taken lightly. This state of low energy availability will also impact fertility, and can make it harder for an athlete to conceive now or in the future. Taking birth control to "jumpstart" an athlete's period also does not fix the underlying issues that caused them to lose it in the first place.

Poor bone health. Contrary to what most people think, the most important factor for strong, healthy bones is actually getting enough calories. In athletes with low energy availability, low calorie intake, most commonly combined with low calcium intake and poor vitamin D status, can lead to a decrease in bone density and an increased risk for bone related injuries such as stress fractures. In the case of younger athletes, low energy availability can also halt the release of hormones important in directing the normal, timely growth of the skeleton. Peak bone density is typically achieved in the early to mid 20's, which also coincides with most athlete's career peak, so under fueling during this time can lead to osteoporosis or other lifelong issues related to poor bone health.

Impaired immunity. Each time an athlete trains or competes, the immune system is temporarily suppressed. This immunosuppression is worsened by inadequate energy intake because many nutrients, especially protein, play a role in our body's ability to fight off diseases. Not only is chronically obtaining insufficient calories to meet the demands of life and sport a form of stress that can lure the body into a diseased state, but it also affords less energy to the immune system when it needs to fight diseases from outside the body. Frequent or lingering illnesses, especially upper respiratory infections, are typically a sign that an athlete is in a state of low energy availability.

Lagging protein synthesis. Much like iron and calcium, adequate protein intake is almost impossible to achieve through a diet that does not meet an individual’s overall calorie needs. When at a loss for adequate protein, the body will struggle to repair and rebuild damaged muscles, making it much harder to see the benefits of training. Additionally, any protein successfully used to build muscle will likely be squandered, as a body that is chronically under-fueled will begin to breakdown muscle tissue for fuel. This negatively impacts performance, and makes it much more difficult for an athlete to build and maintain lean muscle mass. The amino acids that are the building blocks of protein are also the building blocks for many other components of the body, including immune cells, hair, skin, and nails. A protein deficiency not only impacts muscle mass, but also immune health and can cause brittle nails, hair loss, and poor skin quality.

Decreased cardiovascular health. In the most severe cases of low energy availability, often those stemming from a restrictive eating disorder such as anorexia nervosa, the body will slow down cardiovascular endothelial function (and therefore heart rate) as one method of conserving energy in the energy-scarce state. Many athletes brag about their low resting heart rate, but one that is too low (usually under 40 beats per minute) can indicate a bigger problem. Declining cardiovascular health is detrimental to sport, as it impacts blood flow to the muscles and reduces cardiovascular fitness and endurance capacity. An additional effect in under-fueled individuals is dyslipidemia, elevated lipids in the blood, which can increase risk for heart disease.

Micronutrient deficiencies. Like so many other micronutrients, iron (especially in female athletes) is typically low in any athlete who is not consuming adequate calories to support their training. Being low in iron, along with other key blood components, decreases the quality and efficiency of the blood being pumped through an athlete’s body due to decreased oxygen and nutrient-carrying abilities. Iron deficiency at any stage can negatively impact performance, and can make even the easiest of efforts feel challenging. Other micronutrients that often decrease with low energy availability include, but are not limited to, vitamin D, vitamin B12, and folate.

Declining mental health. While poor mental health can be a cause of the behaviors that lead to low energy availability, poor mental health can also be a consequence of low energy availability. For many athletes, inconsistent and insufficient fuel can result in an increase in irritability and/or mood swings. With low energy availability comes a decrease in hormone production, a suppression of testosterone, and an increase in cortisol that impacts the production of serotonin and other neurotransmitters responsible for feelings of happiness and reward. In addition to these hormone imbalances, the lethargy associated with low energy availability and the negative impacts on physical performance can also lead to symptoms of depression or anxiety for many athletes. This is a dangerous side effect of RED-S, as poor mental health and behaviors causing low energy availability often evolve into a worsening cycle that becomes harder to undo as it intensifies.

Now that you know a bit more about RED-S and why it is so important, how do you know if you or an athlete you work with may be suffering from RED-S?

How to Identify RED-S

Many cases of RED-S go unidentified because awareness of it is incredibly low, and individuals who purposefully restrict their energy intake are often very good at hiding their behaviors.

As a parent or coach, it may be helpful to monitor athletes for these things:

  • Uncharacteristic mood swings, depression, or anxiety

  • New or worsening fatigue or a decline in performance

  • Missed periods in biological females

  • Frequent or recurring injuries or illnesses

  • Disordered eating behaviors, such as suddenly cutting out major food groups or claiming new food allergies that haven't been diagnosed

  • Exercise addiction, such as refusing to take off days or if injured, cross training for hours on end multiple times a day

As an athlete, in addition to what is mentioned above, it may be helpful to monitor oneself for these signs of low energy availability:

  • Constantly feeling sore or struggling to recover from hard sessions

  • New or worsening difficulties falling asleep or staying asleep

  • Difficulty staying awake throughout the day, or struggling to do anything but lay on the couch after a hard workout

  • Inability to build muscle mass or see training adaptations despite a high training load

  • A change in appetite. Some athletes feel hungry all the time, whereas some see a decrease in their appetite.

Biological female athletes not utilizing birth control should consider tracking their menstrual cycle in order to better monitor irregular patterns in their cycle. Additionally, all athletes can benefit from getting pre-season blood work, having an annual physical with physician, and even meeting with a dietitian to ensure your fueling supports your training needs, as these steps can help preemptively identify many of the risk factors for RED-S.

Getting Treatment for RED-S

While wanting to self-treat or peer-treat RED-S may be well-intentioned, it is safest and most effective for athletes to be treated by professionals. Seeing that RED-S stems from low energy availability, most athletes showing symptoms of RED-S can benefit from working with a Registered Dietitian, especially one specializing in sports nutrition. Sports medicine physicians can also help monitor blood work, hormone levels, bone density and ensure there is no medical problem contributing to symptoms. Athletes suffering from low energy availability due to disordered eating/exercising behaviors or other mental illness should also work with a psychologist or psychiatrist in order to address these thought patterns and behaviors.

You only get one body, both for your time as an athlete and beyond.

It's important to remember that you only get one body, both for your time as an athlete and beyond. Under fueling in order to shave a few seconds off of your PR or look a certain way in your uniform is not worth the short and long term consequences you will endure down the road. Unfortunately, many athletes buy into the myth that if you are lighter you will be faster. The hardest part about this is that yes, initially an athlete who loses weight might see a temporary improvement in performance. But, this improvement is not permanent and will almost certainly lead to detrimental physical and mental health consequences down the road. I can tell you without a doubt that being well fueled and weighing more will allow you to perform better than weighing a few pounds less, but being under fueled. Not only that, but fueling properly will also allow you to have a long and healthy career in the sport you love.

Interested in working together to help you manage or prevent RED-S? Visit my Make an Appointment page to see if we would be a good fit!

Maddie Alm MS, RD

Amelia Valdez


Mountjoy, M., Sundgot-Borgen, J. K., Burke, L. M., Ackerman, K. E., Blauwet, C., Constantini, N., ... & Budgett, R. (2018). IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. British journal of sports medicine.

Torstveit MK, Fahrenholtz IL, Lichtenstein MB, et alExercise dependence, eating disorder symptoms and biomarkers of Relative Energy Deficiency in Sports (RED-S) among male endurance athletes. BMJ Open Sport & Exercise Medicine 2019;5:e000439. doi: 10.1136/bmjsem-2018-000439

Kuikman, MA., Stellingwerff, T., Mountjoy, M., Burr, JF. A Review of Nonpharmacological Strategies in the Treatment of Relative Energy Deficiency in Sport. 2021. Human Kinetics.

Rogers, MA., Newcomer Appaneal, R., Hughes, D., Vlahovich, N., Waddington, G., Burke, LM., Drew, M. Prevalence of impaired physiological function consistent with Relative Energy Deficiency in Sport (RED-S): an Australian elite and pre-elite cohort. 2020. Br J Sports Med.

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