Understanding Relative Energy Deficiency in Sport (RED-S): Causes and Care
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Relative Energy Deficiency in Sport (RED-S) is a health condition that occurs when an individual consistently burns more calories through exercise than they consume. [1] This energy mismatch prevents the body from performing essential functions, leading to fatigue, bone density loss, and decreased athletic performance. [1] Formerly known as the female athlete triad, RED-S is now recognized as affecting all genders and ages. [1] Management involves balancing caloric intake with activity levels, often requiring the guidance of a dietitian and, in some cases, a temporary break from training. [1]
Quick Answer
Relative energy deficiency in sport (RED-S) is a condition caused by a sustained calorie deficit in which energy spent exceeds energy taken in. [1] [2] It affects nearly every body system, from heart function to bone health. Common signs include recurring stress fractures, chronic fatigue and reduced stamina. [1] Treatment focuses on nutritional rehabilitation and rest so the body can recover. [1]
What the research says
Low energy availability is common in athletes and is linked to poorer bone health. A systematic review and meta-analysis of 59 studies found low energy availability in 2,737 of 6,118 athletes (44.7%) across 46 studies, including 44.2% of female and 49.4% of male athletes, and 63.0% (460 of 730) of athletes in eight studies were at risk of RED-S; most studies concluded that athletes with low energy availability have impaired bone health and a higher risk of bone stress injuries (Gallant et al., Sports Medicine, 2025 [2]).
Higher triad-related risk scores predict later bone stress injuries. In a cohort of 239 collegiate female athletes across 16 sports, 29% were classified as moderate or high risk on the Female Athlete Triad Cumulative Risk Assessment; moderate-risk athletes were 2.6 times (95% CI 1.3 to 5.5) and high-risk athletes 3.8 times (95% CI 1.8 to 8.0) as likely as low-risk athletes to sustain a bone stress injury (adjusted for age and cross-country participation) (Tenforde et al., The American Journal of Sports Medicine, 2017 [3]).
What is relative energy deficiency in sport (RED-S)?
Relative Energy Deficiency in Sport (RED-S) is a serious health condition that arises when an athlete's caloric intake is insufficient to support both their training demands and basic physiological functions. [1] Calories are not merely fuel for workouts; they are the energy the body requires to keep organs working properly and maintain life. [1] When a deficit becomes chronic, the body begins to prioritize immediate movement over long-term health, leading to systemic deterioration.
Historically, this condition was referred to as the "female athlete triad." However, medical professionals have updated the terminology to RED-S to reflect that this energy deficiency can affect anyone, regardless of gender or age. [1] While it remains more common in female athletes, male athletes and highly active individuals are also at significant risk. [1] The "relative" nature of the condition means that energy needs vary significantly based on an individual's age, body size, metabolism, and activity level. [1]
Aspect | Description |
Core Issue | Sustained calorie deficit (expenditure > intake) |
Target Group | Athletes and highly active individuals of all genders |
Former Name | Female Athlete Triad |
Primary Risk | Systemic organ dysfunction and bone health decline |
What are the symptoms and physical effects of RED-S?
The symptoms of RED-S are often diverse and may not initially seem related to one another. Athletes frequently notice a significant drop in their stamina and performance, accompanied by persistent fatigue and longer recovery times between sessions. [1] Because the body lacks the energy to repair itself, injuries become more frequent, and healing takes much longer than expected. [1]
Beyond performance, RED-S impacts biological systems. Females may experience irregular or missing periods, while individuals of all genders may face digestive issues like bloating or constipation, hair loss, and trouble sleeping. [1] One of the most critical indicators is the occurrence of recurring stress fractures, often in the same bone, which points to underlying bone density loss. In younger athletes, the condition can lead to stunted growth or delayed puberty. [1]
What causes relative energy deficiency in sport?
The primary cause of RED-S is a consistent mismatch between energy intake and energy expenditure. [1] This can happen unintentionally when an athlete is unaware of the high caloric demands of their training regimen. [1] In other cases, individuals may intentionally restrict their diet to meet weight goals or improve performance, not realizing that even a planned deficit must still provide enough energy for the body to function.
Contributing factors include:
Natural Metabolism: Differences in how individuals process energy. [1]
Intense Training: High-frequency workouts that burn calories faster than they are replaced. [1]
Eating Disorders: Complex mental health conditions that lead to severe caloric restriction. [1]
Nutritional Misconceptions: The belief that "less is more" in terms of nutrition for competitive athletes.
How is RED-S diagnosed and treated?
Diagnosing RED-S requires a comprehensive evaluation by a healthcare provider. The process typically includes a physical exam and a detailed discussion about the athlete's training patterns, nutrition, and any negative thoughts regarding food or body image. [1] Providers may order X-rays to check for stress fractures, blood tests to identify deficiencies, and bone density tests (DEXA scans) to evaluate the long-term impact on the skeletal system. [1]
The most critical component of treatment is restoring the balance between calories consumed and calories burned. [1] This often involves working with a registered dietitian to create a personalized eating plan that supports both performance and health. [1] Athletes may need to take a temporary break from their sport to allow their body to exit the unsafe calorie deficit. [1] Mental health specialists can also be a vital part of the care team if the athlete finds it difficult to adjust their exercise habits or manage their relationship with food. [1]
Conclusion
RED-S is a manageable condition, but it requires athletes to shift their perspective on nutrition. Pushing limits is a part of sports, but neglecting the body's basic energy needs can lead to serious, long-term health consequences. By recognizing the early signs of energy deficiency and seeking help from medical and nutritional professionals, athletes can protect their health and ensure they perform at their best for years to come.
Frequently Asked Questions
What is the difference between the female athlete triad and RED-S?
RED-S is a broader term that includes the female athlete triad but acknowledges that energy deficiency affects athletes of all genders and ages. It also covers a wider range of physiological systems beyond just bone health and reproductive function. [1]
Can you have RED-S without an eating disorder?
Yes. While eating disorders can lead to RED-S, many athletes develop the condition unintentionally by simply not eating enough to keep up with the high energy demands of their training and daily life.
Why does RED-S cause stress fractures?
When the body is in a chronic energy deficit, it lacks the nutrients and energy needed to maintain bone density. This makes the bones weaker and more susceptible to fractures during normal athletic activity.
How long does it take to recover from RED-S?
Recovery time varies depending on the severity of the deficiency. Athletes can typically resume training once they have established a safe caloric intake and their performance and stamina begin to recover.
What are the mental health effects of RED-S?
A sustained energy deficit can lead to increased feelings of anxiety and depression. [1] Additionally, the pressure to perform or maintain a certain body weight can contribute to significant mental stress.
Is weight loss always a sign of RED-S?
Unintended weight loss is a common symptom, but RED-S can occur even if an athlete's weight remains stable if their body is still not getting enough energy to function properly.
What should I do if I think I have RED-S?
The first step is to see a healthcare provider for a physical exam. They may refer you to a registered dietitian or a mental health specialist to help create a recovery plan. [1]
Can RED-S affect growth in teenagers?
Yes. In children and teens, a chronic lack of energy can lead to stunted growth and delayed puberty, as the body does not have enough energy to support normal development. [1]
Do I have to stop exercising if I have RED-S?
In many cases, a temporary break or reduction in training is necessary to help the body leave the unsafe calorie deficit and begin the healing process. [1]
References
Cleveland Clinic. Relative Energy Deficiency in Sport (RED-S). Cleveland Clinic. June 9, 2026. https://my.clevelandclinic.org/health/diseases/relative-energy-deficiency-in-sport-red-s
Gallant TL, Ong LF, Wong L, et al. Low energy availability and relative energy deficiency in sport: a systematic review and meta-analysis. Sports Medicine. 2025;55(2):325-339. PMID 39485653. https://doi.org/10.1007/s40279-024-02130-0
Tenforde AS, Carlson JL, Chang A, et al. Association of the female athlete triad risk assessment stratification to the development of bone stress injuries in collegiate athletes. The American Journal of Sports Medicine. 2017;45(2):302-310. PMID 28038316. https://doi.org/10.1177/0363546516676262
Medical disclaimer
The information provided in this article is for educational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
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