Understanding Low Energy Availability and REDs in Athletes

November 19, 2025 •

3 min read

Recent research indicates that up to 66% of female athletes are at risk of low energy availability and its related health syndrome, REDs. This serious condition affects individuals across all sports and competitive levels, impacting both their physical health and athletic performance.

Quick Summary

Low energy availability is a state where energy intake is insufficient for exercise and physiological functions. This deficit leads to Relative Energy Deficiency in Sport (REDs), a multisystemic syndrome with severe health and performance consequences for athletes of all genders.

Key Points

Low Energy Availability (LEA): An energy deficit caused by consuming fewer calories than the body needs to support both daily activity and exercise.
Relative Energy Deficiency in Sport (RED-S): A broader syndrome resulting from prolonged LEA that impairs multiple body systems, affecting both male and female athletes.
Multi-Systemic Effects: LEA can harm metabolic rate, reproductive function, bone health, immune response, and psychological well-being.
Performance Decline: Despite possible short-term weight loss, chronic LEA leads to decreased strength, endurance, and coordination over time.
Risk Factors: High-risk sports include endurance, aesthetic, and weight-class disciplines, but any athlete, including recreational, can be affected.
Treatment Requires Teamwork: Recovery is managed by a multidisciplinary team (physician, dietitian, psychologist) who focus on restoring energy balance and addressing root causes.

The Foundation: What is Low Energy Availability (LEA)?

Low energy availability (LEA) occurs when an individual doesn't consume enough calories to support both their exercise demands and essential bodily functions. This energy deficit causes the body to conserve energy by suppressing non-essential systems.

LEA can happen unintentionally, often due to a lack of nutritional knowledge when training intensity increases, or intentionally, as a result of deliberate calorie restriction sometimes linked to disordered eating. Other contributing factors can include poor meal planning and dietary trends.

Energy availability (EA) is defined as dietary energy intake minus exercise energy expenditure, per kilogram of fat-free mass (FFM) per day. Research suggests that in females, an EA below 30 kcal/kg FFM/day can lead to health problems.

Beyond the Triad: Unpacking Relative Energy Deficiency in Sport (RED-S)

Relative Energy Deficiency in Sport (RED-S) is the clinical syndrome caused by sustained LEA. Introduced by the International Olympic Committee in 2014, RED-S replaced the term "Female Athlete Triad" to reflect that LEA's impact is broader than just disordered eating, menstrual issues, and bone loss, and affects male athletes as well.

RED-S impairs multiple body systems due to the body's adaptive response to conserve energy during an energy deficit.

Multi-systemic Health Consequences

RED-S can lead to various health problems across different body systems:

Metabolic: Slowed resting metabolic rate and fatigue.
Reproductive: Menstrual dysfunction in women and low testosterone in men.
Bone Health: Increased risk of stress fractures and potential osteoporosis due to impaired bone formation.
Immune System: Higher susceptibility to illness.
Cardiovascular: Low heart rate and blood pressure.
Gastrointestinal: Issues like bloating and constipation.
Psychological: Mood changes, irritability, and difficulty concentrating.

Comparison Table: Signs and Effects of RED-S


Aspect	Healthy State (Adequate Energy)	RED-S (Low Energy Availability)
Energy Levels	Consistent, high energy	Chronic fatigue, lethargy
Recovery	Quick healing from training and illness	Slow recovery, increased injury/illness
Hormonal Function	Balanced sex hormones (estrogen, testosterone)	Disrupted reproductive hormones, low libido, menstrual issues
Bone Health	Strong bone density	Decreased bone density, higher risk of stress fractures
Mental State	Positive mood, high concentration	Increased irritability, anxiety, depression, poor focus
Performance	Peak performance, strong training response	Plateaued or decreased performance, reduced endurance and strength
Training Enjoyment	High motivation and enjoyment	Loss of interest, feeling obligated to train

Who is at Risk for Low Energy Availability and RED-S?

RED-S is not limited to elite athletes; recreational exercisers and young athletes can also be at risk due to a consistent energy deficit.

However, certain sports have a higher prevalence:

Endurance Sports: High energy expenditure can make it hard to match intake.
Aesthetic Sports: Emphasis on lean physique can lead to under-fueling.
Weight-Class Sports: Requirements to make weight can encourage restrictive dieting.

Diagnosis and Treatment: A Multidisciplinary Approach

Diagnosing RED-S can be difficult as athletes may not report symptoms. Diagnosis typically involves a medical history, physical exam, and potentially blood tests or a bone density scan.

Treatment requires a team approach, including a sports physician, registered sports dietitian, and a psychologist or therapist, to restore energy balance and address underlying issues. Restoring energy balance by increasing intake or decreasing exercise is key. For severe cases, reduced training may be necessary.

Conclusion: Prioritizing Health for Sustainable Performance

Low energy availability and RED-S pose significant health risks to athletes across all levels. While short-term undereating might seem beneficial for performance, it ultimately leads to decline, injury, and potential long-term health problems. Sustainable high performance relies on proper fueling, rest, and a healthy relationship with food. Coaches and athletes must prioritize health and recognize the risks of RED-S. For more information on RED-S, a resource from the IOC can be a valuable guide.

Frequently Asked Questions

No, RED-S can affect athletes of any gender and ability level, including recreational and collegiate athletes. Research shows that recreational athletes can have a higher prevalence of LEA than their elite counterparts, potentially due to less access to nutritional support and education.

Low Energy Availability (LEA) is the physiological cause, defined as the state where energy intake is insufficient for exercise energy expenditure and vital body functions. Relative Energy Deficiency in Sport (RED-S) is the broad syndrome of negative health and performance consequences that result from prolonged LEA.

A diagnosis is typically made by a sports medicine physician who will conduct a thorough medical history review, including questions about training load, eating habits, and mood. Physical exams and lab tests to check hormone levels or bone density may also be used. Screening tools like the RED-S Clinical Assessment Tool (RED-S CAT) help evaluate risk.

A sports dietitian is crucial for creating an individualized nutrition plan to increase energy intake safely. They help correct fueling gaps, provide meal and snack strategies, and ensure adequate intake of carbohydrates and other key nutrients to support recovery and performance.

Yes, RED-S affects both male and female athletes. While female reproductive issues like amenorrhea are a more obvious symptom, male athletes can experience decreased libido, low testosterone levels, mood changes, and compromised bone density due to LEA.

Many of the health consequences of REDs are reversible, especially with early detection and intervention. Restoring energy balance is the primary treatment, which can lead to improvements in hormonal function, bone density, and overall health over time.

Early signs can be subtle and include constant fatigue, difficulty recovering from workouts, recurring injuries (like stress fractures), frequent illness, irritability, and a plateau or decline in athletic performance.