What Is Relative Energy Deficiency in Sport (REDs)?

What Does REDs Mean?

Relative energy deficiency in sport is impaired physical or psychological functioning linked to problematic low energy availability. In everyday language, the athlete is not taking in enough usable energy to cover exercise and the body’s normal work, including brain function, circulation, immunity, digestion, temperature control, hormone production, tissue repair, and bone remodeling.

Low Energy Availability Is the Engine Behind REDs

Energy availability describes the dietary energy remaining for normal physiological functions after exercise energy expenditure is considered. When too little remains, the body starts making trade-offs. It may slow reproductive hormone activity, reduce bone-building processes, alter metabolism, and compromise recovery.

A brief mismatch does not automatically mean REDs. The concern is low energy availability that is severe, prolonged, frequent, or poorly matched to the athlete’s needs.

REDs Is Broader Than the Female Athlete Triad

The female athlete triad centers on low energy availability, menstrual dysfunction, and impaired bone health. REDs includes those concerns but covers more body systems, all genders, and psychological and performance effects. Menstrual changes are important, but their absence does not rule out REDs. Male athletes may notice low libido, reduced morning erections, fatigue, or impaired recovery.

What Causes Relative Energy Deficiency in Sport?

REDs can develop through intentional restriction, accidental under-fueling, or both. An eating disorder may be involved, but many affected athletes do not have one. Sometimes the problem is simple arithmetic: more training, fewer eating opportunities, and no extra hours in the day.

Common Pathways to Under-Fueling

• Training volume increases: Mileage, practices, competitions, or strength sessions rise without a matching increase in food.
• Sport culture rewards leanness: Athletes may believe a smaller body always performs better, even when strength, concentration, and recovery decline.
• Weight-class or aesthetic pressures: Wrestling, rowing, combat sports, gymnastics, diving, figure skating, dance, and endurance sports may create extra pressure around body composition.
• Busy schedules: School, work, travel, and back-to-back practices can turn meals into whatever survives at the bottom of a backpack.
• Dietary rules: Cutting carbohydrates, fats, animal products, or entire food groups without careful replacement can reduce total energy intake.
• Reduced appetite: Intense exercise sometimes suppresses hunger, particularly immediately after training.
• Food insecurity or limited access: Athletes may not consistently have enough food, cooking facilities, money, or time.
• Injury-related confusion: An injured athlete may sharply restrict intake because training has decreased, even though healing still requires energy and nutrients.

REDs is not a character flaw. It often reflects an interaction among physiology, beliefs, coaching messages, finances, mental health, and sport culture.

Signs and Symptoms of REDs

REDs can be difficult to spot because its early symptoms resemble ordinary training fatigue. The difference is that normal fatigue generally improves with reasonable recovery. REDs-related problems tend to persist, cluster together, or worsen as the athlete pushes harder.

Physical and Hormonal Warning Signs

• Ongoing fatigue or unusually slow recovery
• Repeated bone stress injuries or stress fractures
• Frequent colds, infections, or lingering illness
• Feeling cold when others are comfortable
• Sleep disruption
• Gastrointestinal problems such as bloating, constipation, or abdominal discomfort
• Hair loss or changes in skin and nails
• Rapid or unintended weight loss, although weight may remain stable
• Irregular, infrequent, or absent menstrual periods
• Low libido or signs of reduced sex-hormone function

Psychological and Performance Clues

• Irritability, anxiety, low mood, or emotional volatility
• Difficulty concentrating or making decisions
• Increasing preoccupation with food, weight, or “earning” meals
• Reduced endurance, strength, speed, coordination, or training response
• More injuries despite careful technique
• Plateauing or declining performance while training load increases
• Loss of enjoyment and a sense that every session feels harder than it should

No single symptom proves REDs. Fatigue, menstrual changes, low testosterone, gastrointestinal symptoms, and poor performance can have many causes. The pattern matters, which is why self-diagnosis based on one social-media checklist is not enough.

How REDs Affects the Body

When energy is repeatedly scarce, the body prioritizes immediate survival. Bone formation, reproductive function, training adaptation, and tissue repair may be downregulated.

Bone Health and Injury Risk

Low energy availability can disrupt hormones and bone remodeling, increasing the risk of low bone mineral density and bone stress injury. This is especially concerning during adolescence and early adulthood, when peak bone mass is still developing.

Hormones and Reproductive Function

The brain may reduce reproductive hormone signaling when energy is scarce. Athletes who menstruate may develop irregular cycles or amenorrhea; male athletes may experience lower libido and impaired recovery. Fertility may also be affected.

Immunity, Metabolism, and Cardiovascular Function

REDs may contribute to recurrent illness, altered metabolism, abnormal blood markers, and cardiovascular changes. A low resting heart rate can reflect fitness, under-fueling, or both, so clinicians must interpret it in context.

Mental Health

Low energy availability and mental health can reinforce each other. Under-fueling may worsen irritability, anxiety, depression, rigid thinking, and food preoccupation, while perfectionism, body dissatisfaction, or an eating disorder can drive restriction. Treatment may therefore require psychological supportnot just a larger plate of pasta and a motivational quote.

Who Is Most at Risk?

Any active person can develop REDs, but risk rises when performance is closely associated with leanness, appearance, endurance, or making weight. Adolescents are particularly vulnerable because they must fuel growth, school, daily life, and training at the same time.

Risk may also rise during sudden training increases, altitude camps, tournament travel, injury rehabilitation, dietary transitions, or periods of emotional stress. Para athletes may face additional energy-estimation challenges, accessibility barriers, gastrointestinal issues, or body-composition changes requiring specialized assessment.

Body size is a poor screening shortcut. An athlete can have REDs at a low, average, or high body mass index. Weight can remain stable because metabolic adaptations or changes in fluid and body composition hide the deficit. Looking “healthy” is not a laboratory test.

How Is REDs Diagnosed?

There is no single blood test, scan, questionnaire, or calorie formula that independently diagnoses REDs. Evaluation generally combines medical history, symptoms, training patterns, eating behaviors, injury history, menstrual or hormonal function, physical examination, and targeted testing.

What a Clinical Evaluation May Include

• A detailed discussion of training load, recovery, sleep, stress, and recent performance
• A nutrition history examining meal timing, food variety, dietary restrictions, and access to food
• Screening for disordered eating, eating disorders, anxiety, or depression
• A review of menstrual function or signs of hormonal suppression
• Blood tests selected to investigate anemia, iron status, thyroid concerns, vitamin deficiencies, hormone function, or other conditions
• Bone imaging or bone-density testing when clinically appropriate
• An assessment of whether continued sport participation is currently safe

The International Olympic Committee’s REDs Clinical Assessment Tool, known as IOC REDs CAT2, helps qualified clinicians organize screening, risk assessment, diagnosis, and participation decisions. It is not designed as a do-it-yourself scorecard. REDs can overlap with thyroid disease, anemia, gastrointestinal disorders, infection, overtraining, sleep problems, and other medical conditions, so ruling out alternatives is essential.

How Is REDs Treated?

Treatment aims to restore sufficient energy availability while addressing medical, nutritional, psychological, and training-related contributors. That may mean eating more, temporarily reducing exercise, improving meal timing, or all three.

Build a Multidisciplinary Team

Care may involve a sports-medicine clinician, sports dietitian, mental-health professional, and athletic trainer. Suspected eating disorders require appropriately trained professionals. Coaches and families can support recovery, but they should not become amateur nutrition police.

Increase Fuel and Improve Timing

A sports dietitian can help establish regular meals and snacks, restore unnecessarily restricted carbohydrates and fats, and improve fueling before, during, and after training. Plans should consider growth, injury healing, travel, culture, budget, and gastrointestinal tolerance. There is no universal REDs meal plan; progress is judged by health, recovery, and performance, not by chasing an impressive calorie number.

Modify Training When Necessary

Some athletes can continue modified training. Others need a temporary reduction or pause, particularly with high-risk bone injuries, medical instability, severe psychological symptoms, or an active eating disorder. Return-to-sport decisions should be individualized and reassessed.

Track Recovery Beyond the Scale

Recovery markers may include better energy and sleep, restored hormonal function, fewer illnesses, healing injuries, improved mood, normalized tests, and a stronger training response. Weight may change, but it should not be the only measure.

Can REDs Be Prevented?

Prevention works best when the sports environment supports fueling instead of treating food as a reward for suffering. Nutrition is part of training, alongside technique, sleep, and strength work.

Practical Prevention Strategies

• Increase food intake when training volume or intensity rises.
• Schedule meals and portable snacks around practices, school, work, and travel.
• Avoid routine weigh-ins or body-composition testing unless there is a valid purpose, informed consent, privacy, and qualified oversight.
• Investigate missed periods, recurrent stress injuries, persistent fatigue, and unexplained performance decline.
• Use neutral language about bodies and avoid praising weight loss as automatic evidence of dedication.
• Teach coaches and parents that male athletes and athletes in larger bodies can also develop REDs.
• Provide confidential access to medical, nutrition, and mental-health professionals.

A healthy performance culture asks, “What helps this athlete adapt?” rather than, “How little can this athlete eat and still finish practice?” The first question builds careers.

When to Seek Medical Help

An athlete should speak with a qualified healthcare professional when fatigue persists, periods become irregular or stop, libido changes, performance declines without explanation, injuries recur, eating becomes rigid or frightening, or food restriction feels difficult to control.

Prompt evaluation is especially important for fainting, chest pain, severe weakness, rapid weight loss, repeated stress fractures, signs of dehydration, a very low heart rate with symptoms, or suspected eating-disorder complications. Immediate help is warranted for thoughts of self-harm or other mental-health emergencies.

A Composite Athlete Experience: From Running on Empty to Rebuilding Trust

The following story is a fictional composite based on commonly reported REDs experiences. It does not describe one identifiable athlete.

“Maya” was a college distance runner who believed she was doing everything right. She added easy miles after practice, replaced full breakfasts with coffee and fruit, and saved most of her eating for dinner. Her weight barely changed, so neither she nor her teammates thought under-fueling was possible. Besides, she was still completing workouts. In athlete logic, completing a workout can sometimes become proof that absolutely nothing is wrongeven when the workout feels like it was performed while towing a refrigerator.

The first signs were easy to explain away. Maya felt cold in class, struggled to concentrate, and became unusually irritable. Her normal pace required more effort, but she assumed she needed additional training. Then her menstrual cycles became irregular. She told herself that was common among runners and therefore harmless. A few months later, pain in her shin became a bone stress injury.

Her sports-medicine evaluation changed the conversation. The clinician did not diagnose REDs from appearance or weight. Instead, the care team reviewed her training, meal timing, menstrual history, sleep, stress, injury pattern, and laboratory results. A sports dietitian showed Maya that the biggest gap was not one “bad” food choice. It was the long stretches of the day when she expected her body to train, study, recover, and repair bone with almost no incoming energy.

Recovery was emotionally harder than she expected. Eating more sounded simple on paper, yet it challenged beliefs she had absorbed about discipline, body size, and deserving rest. Temporarily reducing training felt like losing her identity. A therapist helped her separate athletic commitment from compulsive rules. Her coach stopped commenting on athletes’ bodies and began scheduling protected snack breaks during travel.

Progress arrived in small, unglamorous pieces. Maya ate breakfast before class, carried two snacks, fueled immediately after workouts, and included carbohydrates at every main meal. Her training was gradually adjusted around bone healing. At first, she worried that more food and less mileage would erase her fitness. Instead, her sleep improved, her mood steadied, and easy runs started feeling easy again.

Several months later, her menstrual cycle became more regular, and she returned to structured training under medical guidance. Her first races back were not personal records, but they were consistent. More importantly, she no longer treated hunger as an opponent or fatigue as a personality test. She learned that recovery was not a detour from performance; it was part of performance.

Maya’s experience also changed the people around her. Teammates began discussing fueling without turning meals into moral report cards. The coaching staff used performance trends, health history, and athlete feedback instead of assuming that lighter always meant faster. One athlete’s injury had revealed a system problem, and the system improved.

The lesson is not that every tired athlete has REDs or that every training slump can be solved with a snack. It is that persistent fatigue, hormonal changes, recurring injuries, and declining performance deserve curiosity rather than blame. Athletes often pride themselves on tolerating discomfort. REDs recovery asks for a different kind of toughness: reporting symptoms, accepting help, changing routines, and trusting that a well-fueled body is not less disciplinedit is better equipped to do the work.

Conclusion

Relative energy deficiency in sport is a serious but treatable syndrome linked to prolonged or severe low energy availability. It can affect athletes of any gender, body size, age, or ability level, and its effects may reach far beyond performance. Bone health, hormones, immunity, cardiovascular function, digestion, mood, concentration, and recovery can all be involved.

The most important message is simple: training creates the demand, but fuel and recovery create the adaptation. When effort rises while energy availability falls, working harder may drive an athlete farther from the result they want. Early recognition and individualized care can help restore health, reduce injury risk, and rebuild sustainable performance.