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Are you under-fuelling?: How RED-S is affecting your performance

Updated: Jun 26

As an athlete, you're no stranger to pushing your body to its limits in pursuit of peak performance. This is often celebrated as physical and mental resilience. I mean, how else are you going to get stronger, faster, and better without pushing harder? While dedication and hard work are essential for success, taking it too far can actually have far more negative long-term consequences.

When athletes are under-fuelling, they can develop a condition known as Relative Energy Deficiency in Sport (RED-S). This condition is particularly concerning as it affects not just performance but overall health.

What is RED-S?

RED-S is a clinically diagnosed condition characterized by insufficient energy intake to meet the body's demands during exercise and essential daily functions like growth, breathing, and digestion. Originally known as the Female Athlete Triad, which focused on disordered eating, menstrual dysfunction, and osteoporosis in women, RED-S has been expanded to encompass a broader range of physical and psychological effects that affect both male and female athletes.

When we underestimate the energy demands of exercise or restrict how much we consume, our bodies enter a state of ‘low energy availability’. Similar to your phone getting a low battery, it will go into 'power saver mode' and switch off important but non-essential functions. It will begin to prioritize vital processes, often at the expense of other systems.

Who’s at Risk?

RED-S can occur in both active females and males across many sports regardless of age, participation level, ability, and body shape/size. Some athletes are more at risk due to the nature of their sport and/or individual characteristics.

Athletes who participate in endurance sports like running, cycling, and swimming demand high energy expenditure, making it challenging to match energy intake with output. Athletes in sports where body appearance is emphasized, such as gymnastics, dance, figure skating, and bodybuilding, are also more susceptible due to the pressure to maintain a certain physique.

One common misconception is that athletes may think they are not ‘thin enough’ to have this problem. Everyone responds to low energy availability differently, and since our bodies are genetically programmed to protect themselves from starvation, they will counteract weight loss by decreasing metabolism and increasing the stress response (e.g., slow digestion). So, even in the face of severe low energy availability, weight loss may not occur, and it is possible (and common) to experience RED-S while remaining within or even above a ‘healthy’ BMI.

Warning Signs

Recognizing the warning signs of RED-S is crucial for early intervention. Every case of RED-S is unique, but there are common signs and symptoms.

Among female athletes, one of the hallmark signs is the loss of periods, known as amenorrhea. While it may seem inconsequential or even a sign of peak fitness, the reality is quite the opposite. There are many reasons why women don't share that they've lost their period. For example, they don’t see it as a problem, thinking it’s a sign of fitness, being told “it’s part of the game,” ignorance of its long-term consequences, and other reasons.

While regular periods are an indicator of good health, they can be inconvenient (or worse) for many female athletes. The issue is that when periods stop, despite being unhealthy, it is often seen as a relief from monthly cramps, headaches, and mood swings, all of which can negatively affect training and competition.

I want to be very clear, not having periods or experiencing irregular periods is not normal or healthy for any female, including competitive athletes

Other signs and symptoms include a combination of the following for both male and female athletes: 

  • Persistent fatigue 

  • Declines in strength, endurance, speed and agility 

  • Low sex drive and decline in morning erectile function in males

  • Lack of expected growth and development in adolescent athletes

  • Frequent injuries and/or illness 

  • Gastrointestinal issues, such as constipation or bloating

  • Iron deficiency 

  • Appetite changes 

  • Restrictive eating patterns, such as cutting out certain food groups

  • Avoiding food-related social activities

  • Being secretive about food 

  • Anxiety around food 

  • Preoccupation with food, calories, body shape, and weight

  • Unwillingness to take rest days (including continuing to train when in pain or fatigued)

  • Feeling cold a lot of the time

  • Difficulty concentrating 

  • Body image dissatisfaction 

  • Mood disturbances 

Impact on Health 

The primary health impacts of RED-S were initially centered on amenorrhea and bone health. Amenorrhea leads to low estrogen levels and, when combined with inadequate calorie intake, results in poor bone health. Similarly, in male athletes, inadequate calorie intake results in decreased testosterone production, which negatively affects bone health. Young athletes are typically not concerned about these altered levels of sex hormones, but this increases the risk of bone stress injuries (aka stress fractures) during training and competition. In later years, it can increase the risk of osteoporosis as peak bone mass is developed during adolescence until the late 20s.

But the repercussions of RED-S extend beyond missed periods and stress fractures. The condition can cause a cascade of physiological disruptions that significantly impact both female and male athlete's health:

  • Metabolic function: Metabolism decreases. This explains why an athlete with RED-S can have a stable body weight despite being in a calorie deficit, as the amount the body needs has decreased.

  • Heart health: While physical activity is generally seen to be beneficial to heart health, prolonged energy deficiency can negatively impact heart function and increase the risk of cardiovascular disease. 

  • Digestion: A decreased metabolism means your body will slow down processes like digestion. This slowed movement of food through the GI tract along with the types of foods that the athlete is choosing results in bloating, discomfort, constipation and/or diarrhea. This can be problematic for athletes as it may cause them to believe they are lactose or gluten intolerant and restrict foods further. 

  • Mental health: Irritability, depression, and anxiety can arise from hormonal imbalances and the psychological stress of dealing with chronic fatigue and underperformance. 

  • Immune function: A low intake can lead to a compromised immune function, leading to more frequent infections and colds. 

Impact on Performance 

From a performance perspective, RED-S has detrimental effects that can hinder an athlete's career progress and goals: 

  • Slower recovery times: Recovery becomes prolonged due to the insufficient nutrients needed to replenish glycogen stores (AKA your fuel tank) and repair muscles. This continuous reduction in glycogen stores over time results in an athlete's decreased tolerance to training and competition demands.

  • Decreased physical capabilities: Decreased strength, endurance, power, speed, agility, and overall physical fitness can occur as the body lacks the necessary fuel to perform at peak levels. With a lower metabolism, even minimal physical activity feels exhausting. 

  • Decreased participation: Getting sick often leads to more lost or modified training and competition days 

  • Slower reaction time: Cognitive function can be impaired, leading to decreased concentration, poor decision-making, and reduced strategic thinking during competitions. 

  • Lower motivation: The combination of physical fatigue and mental stress from underperformance can sap an athlete’s motivation and enthusiasm for their sport.

Treatment & Recovery

The danger of RED-S lies not just in its symptoms but in our failure to recognize them as symptoms. Many doctors have little knowledge of the condition, which further delays diagnosis. Unfortunately, the initial short-term "pros" of the condition, such as achieving a faster time with a lower body weight, are often applauded by coaches for the same reasons as the athletes themselves, thus masking the syndrome.

If RED-S is due to unintentional low energy availability, nutrition education and counseling from a registered dietitian may suffice. However, if an athlete is struggling with disordered eating or a clinical eating disorder, ongoing support will be required from a physician, a registered dietitian, and a therapist. 

Coaches and trainers should work together with the athlete and the treatment team to adjust the training load as needed. In some cases, this may mean to temporarily discontinue training, depending on the athlete's clinical presentation.

There is no fast lane to recovering from RED-S. Recovery is a gradual and highly individualized process. My advice is to seek support as soon as possible, stay patient, and trust the process. The sooner you can make choices that prioritize your recovery, the sooner you’ll get there. Your coach(es), teammates, family, friends, and health team are with you all the way.


2023 International Olympic Committee’s (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs) 

Absence of menstruation in female athletes: why they do not seek help: 

Project RED-S

Relative Energy Deficiency in Sport: What Coaches Need to Know 


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