What is the underlying cause of RED-S?

December 11, 2025 •

3 min read

According to the International Olympic Committee, the underlying cause of RED-S is low energy availability, which occurs when an athlete's energy intake from food is insufficient to support the energy they expend during exercise and daily life. This energy mismatch forces the body to conserve fuel, leading to a cascade of negative health and performance consequences.

Quick Summary

The root cause of RED-S is insufficient energy intake relative to energy expenditure, known as low energy availability (LEA). This triggers a body-wide energy conservation response that impairs multiple physiological functions and significantly reduces athletic performance.

Key Points

Core Cause: The main cause of RED-S is Low Energy Availability (LEA), an imbalance where energy consumed is less than energy expended during exercise and daily life.
Systemic Impact: LEA forces the body to shut down 'non-essential' physiological functions to conserve energy, affecting multiple body systems, not just reproduction and bone health.
Diverse Triggers: Factors leading to LEA include intentional or unintentional under-fueling, high training loads, psychological pressure, and a toxic sports culture.
Broadened Understanding: RED-S is a broader concept that replaced the 'Female Athlete Triad' to include males and acknowledge the syndrome's systemic effects.
Multidisciplinary Treatment: Effective recovery involves a team of healthcare professionals to address both the nutritional deficit and underlying psychological factors.
Focus on Prevention: Prevention relies on promoting adequate fueling, nutritional education, and fostering a healthy, supportive sports environment.

The Central Role of Low Energy Availability (LEA)

Low Energy Availability (LEA) is the core physiological cause of Relative Energy Deficiency in Sport (RED-S). It is not an eating disorder, though it can be intentionally or unintentionally caused by poor eating patterns or high training loads. When an athlete consistently consumes too few calories relative to their exercise demands, the body enters a state of energy deficit. The body's biological response is to shut down or reduce 'non-essential' functions to save energy for vital organs. This energy conservation effort disrupts almost every bodily system, explaining the widespread and serious symptoms of RED-S.

How Does LEA Impact the Body?

When energy is consistently restricted, the brain, specifically the hypothalamus, interprets this as a threat to survival. This triggers a reduction in key hormones that regulate various bodily functions. This can have systemic effects including endocrine disruption impacting reproductive hormones, a metabolic slowdown to conserve energy, compromised bone health increasing fracture risk, impaired immunity making athletes prone to illness, cardiovascular strain, and gastrointestinal issues.

Triggers of Low Energy Availability

LEA is not a single-factor issue; it arises from a complex interplay of physical, psychological, and environmental factors. For some, under-fueling is unintentional due to a lack of nutritional knowledge, while for others, it is a deliberate action influenced by body image pressure. Common triggers include intentional undereating, often driven by a desire for weight loss in sports emphasizing a lean physique, and unintentional undereating due to underestimating energy needs or lack of nutrition education. Intense training loads can also create an energy gap if not matched by increased caloric intake. Psychological pressures, such as the drive for perfection and competitive stress, along with societal and sports culture that promote thinness, can significantly contribute to LEA.

Comparing the RED-S and Female Athlete Triad Concepts

The understanding of energy deficiency in athletes has evolved. The concept of the Female Athlete Triad was a precursor to RED-S but was limited in its scope.


Feature	Female Athlete Triad	Relative Energy Deficiency in Sport (RED-S)
Focus	Historically focused only on female athletes.	Inclusive of both male and female athletes.
Scope of Impairment	Limited to three interrelated conditions: disordered eating, amenorrhea (missed periods), and osteoporosis (bone loss).	Expands to include a wide array of physiological and psychological impairments.
Causation	Defined by the triad of symptoms, primarily focusing on disordered eating.	Explicitly identifies the root cause as Low Energy Availability (LEA).
Affected Systems	Primarily reproductive and musculoskeletal systems.	Includes endocrine, metabolic, cardiovascular, gastrointestinal, immunological, and psychological systems.
Performance Impact	Often implies a reduction in performance as a consequence of the triad.	Integrates the impact on performance directly into the syndrome's definition.

Conclusion

The underlying cause of Relative Energy Deficiency in Sport (RED-S) is a state of Low Energy Availability (LEA), which is a critical energy mismatch between an athlete's intake and expenditure. This deficit triggers a systemic energy-conservation response that affects multiple bodily functions beyond just reproductive and bone health. Recognizing the diverse triggers, from intentional under-fueling to psychological pressures, is crucial for both prevention and treatment. Addressing the core issue of LEA is the foundation of recovery, requiring a multidisciplinary approach that may involve medical professionals, dietitians, mental health counselors, and coaches. Early intervention is key to reversing the health and performance impacts of this serious syndrome. For more comprehensive insights, the International Olympic Committee's 2014 consensus statement provides an authoritative overview.

Prevention Strategies for LEA

Prevention of LEA in athletes involves several key strategies. Ensuring adequate caloric intake, particularly carbohydrates, to match training demands is fundamental. Coaches and medical staff play a vital role in recognizing early signs like fatigue and mood changes. Regular monitoring of athletes' energy balance and health markers can aid early detection. Promoting a healthy, positive body image and providing nutritional education are crucial to combat pressures and prevent unintentional under-fueling. A multidisciplinary support system involving healthcare professionals is essential for both prevention and treatment. Ultimately, prioritizing long-term health over short-term performance goals is key to fostering sustainable and healthy athletic careers.

Frequently Asked Questions

RED-S stands for Relative Energy Deficiency in Sport. It is a syndrome caused by a mismatch between an athlete's energy intake and energy expenditure.

No, RED-S is not the same as an eating disorder, though disordered eating can be a contributing factor. An athlete can develop RED-S unintentionally due to a lack of nutritional knowledge or an unexpectedly high training volume.

Any athlete, regardless of gender, sport, or skill level, is at risk of developing RED-S. Athletes in sports that emphasize a lean body type, or those with heavy training schedules, may be at a higher risk.

Common symptoms include persistent fatigue, recurring injuries like stress fractures, frequent illness, mood changes, decreased performance, and irregular or absent menstrual cycles in female athletes.

The Female Athlete Triad was an older, more limited concept that focused on female athletes and three symptoms (disordered eating, amenorrhea, bone loss). RED-S is a more comprehensive and inclusive term that applies to all athletes and recognizes the broader systemic health consequences of low energy availability.

Yes, most of the health consequences of RED-S can be reversed with early detection and proper treatment. Treatment involves increasing energy intake, potentially reducing training load, and addressing any underlying psychological factors.

The key to prevention is ensuring adequate energy intake relative to energy expenditure. This includes consistent fueling, nutritional education, and fostering a healthy, supportive sports environment.