Relative Energy Deficiency in Sport Explained

Relative Energy Deficiency in Sport, or REDs, is a syndrome of impaired health and performance associated with problematic low energy availability. Energy availability is the dietary energy left for normal physiology after accounting for exercise. When that remainder is too low for an athlete's needs, several body systems may adapt or become impaired.

REDs can affect women, men, and gender-diverse athletes across sports and performance levels. A lean appearance, a particular body mass index, or high achievement neither proves nor excludes it.

Key points#

• Low energy availability can be intentional or unintentional and may occur with or without an eating disorder.
• Menstrual change is an important sign for many athletes, but REDs is broader than menstruation and affects athletes of any sex.
• Bone stress injury, impaired recovery, recurrent illness, endocrine change, mood symptoms, and declining performance can form a pattern.
• No single questionnaire, hormone, or energy calculation establishes the diagnosis.
• Assessment and return-to-sport decisions should be individualized by a qualified multidisciplinary team.

Energy availability is not simply calorie balance#

Energy availability is often described conceptually as:

energy intake minus exercise energy expenditure, relative to fat-free mass

It is not the same thing as whether your body weight changes. The body can conserve energy by altering reproductive, metabolic, and other processes while the number on the scale stays put. Short periods of reduced availability may be part of ordinary training, while prolonged, severe, or poorly timed deficits are more concerning.

Direct calculation is difficult outside research. Food records underestimate or alter intake, exercise-energy estimates are imprecise, and fat-free-mass measurements vary by method. A numerical threshold should not be treated as a universal diagnostic cutoff. Low availability can follow deliberate restriction, disordered eating, an eating disorder, appetite suppression during heavy training, limited food access, dietary exclusions, travel, financial constraints, injury, or simply underestimating increased needs. Which pathway you are on matters, because treatment and support differ.

REDs extends the earlier triad framework#

The Female Athlete Triad linked low energy availability, menstrual dysfunction, and low bone mineral density. That framework remains clinically useful and its risk-stratification work informs care.

The REDs model broadened the concept. The 2023 IOC consensus describes potential effects across reproductive, skeletal, and metabolic domains. The list continues with hematologic, immune, and cardiovascular domains. It ends with gastrointestinal, growth and development, and psychological domains. It also includes performance consequences such as reduced training response, impaired recovery, lower power or endurance, and increased injury risk.

Broad models can increase recognition but also create a specificity problem. Fatigue, low mood, gastrointestinal symptoms, recurrent infections, and poor performance have many causes. REDs should not become a label applied whenever an athlete struggles. The diagnosis requires a coherent history, examination, appropriate testing, and exclusion of alternatives.

Signs differ among athletes#

Potential clues include:

• menstrual cycles becoming less frequent or stopping;
• low libido or other reproductive-hormone changes;
• recurrent bone stress injuries or delayed bone healing;
• persistent fatigue and impaired recovery;
• recurrent illness;
• iron deficiency or other nutritional deficits;
• gastrointestinal disturbance;
• mood change, anxiety around food, or rigid training behavior;
• declining or inconsistent performance;
• growth concerns in younger athletes.

Menstrual dysfunction should not be normalized as a sign of fitness. Hormonal contraception can mask spontaneous cycle patterns, so your medication history matters. In male athletes, reproductive effects may be less visible and testosterone is influenced by timing, illness, sleep, and training.

Bone stress injuries are not all equivalent. Site, recurrence, and imaging grade influence risk. So do bone density, menstrual or hormonal history, nutrition, and biomechanics. Injuries at higher-risk skeletal sites may require more restrictive activity decisions. Psychological symptoms can precede low energy availability, result from it, or both. Care should avoid blame and account for the social environment. That includes coaching, weight-class rules, and judging. It includes body-composition practices and team culture.

Limits of screening and the IOC CAT2#

The IOC REDs Clinical Assessment Tool version 2 uses a three-part process. First is screening for possible risk. Second is assessment of indicators and severity. Third is physician-led diagnosis and risk stratification to guide participation.

The tool uses primary indicators and secondary indicators rather than one defining test. Serious medical indicators can require immediate attention. Risk is then stratified with clinical judgment, recognizing that the evidence supporting individual indicators varies.

Screening questionnaires can identify athletes who need further evaluation, but false positives and false negatives occur. An athlete may underreport because of stigma or fear of losing participation. A questionnaire designed in one population may not perform equally in another language, sport, age, or sex. The CAT2 authors explicitly position it for use by trained clinical professionals. It is not a point score that coaches, teams, or athletes should use alone to clear participation.

Assessment is a differential diagnosis#

A careful history includes training load, recent changes, and food access and pattern. It includes dietary restriction, injuries, and sleep. It includes menstrual or reproductive health, gastrointestinal symptoms, and medications. It includes supplements, mental health, and social context. The tone should support disclosure and autonomy.

Examination and testing are guided by findings. Possible evaluations include vital signs, growth trajectory, and blood count. They include iron studies, electrolytes, and thyroid tests. They include vitamin status, reproductive hormones, and electrocardiography. They include pregnancy testing when relevant or bone-density assessment. None is a universal REDs panel.

Alternative or coexisting causes include anemia, thyroid disease, and celiac disease. They include inflammatory illness, infection, and depression. They include overtraining, sleep disorder, and medication effects. They include pregnancy and primary endocrine disorders. Low energy availability can coexist with these rather than replacing them. Resting metabolic rate, bone turnover markers, and hormonal tests may add context in specialist care or research, but reference ranges and day-to-day variation limit stand-alone interpretation.

Bone health keeps a long memory#

Peak bone mass develops through adolescence and early adulthood. Prolonged low energy availability during these years can affect a window you cannot easily recreate later, and menstrual or reproductive suppression and inadequate calcium or vitamin D may add risk, while impact loading can support bone only when recovery and nutrition are adequate.

Dual-energy X-ray absorptiometry measures areal bone mineral density. Athletes in weight-bearing sports may be expected to have higher bone density than nonathletes, so a technically “normal” result may still be unexpectedly low for the context. Z-scores, site, and age matter. So do sex, sport, fracture history, and scan comparability. Improved energy availability can support recovery, but bone density and reproductive function may recover on different timelines, so feeling better does not automatically mean your skeletal risk has normalized.

Treatment addresses cause and consequence#

The central aim is to restore adequate and appropriately timed energy availability while treating medical and psychological consequences; this may involve increased intake, changed nutrient timing, reduced training load, or a combination.

A sports dietitian can turn an energy requirement into meals and snacks you will actually eat, while a physician assesses medical stability, differential diagnoses, bone and endocrine concerns, and participation risk. Mental-health support is important when an eating disorder, anxiety, depression, compulsive exercise, or body-image distress is present. Coaches and family may need a role with the athlete's consent and appropriate privacy.

Weight alone is a poor recovery target. Useful outcomes can include vital-sign stability, symptom improvement, and restored reproductive function where applicable. They can include injury healing, laboratory recovery, and normalized eating behavior. They can include psychological safety and sustainable training.

Return to sport is a risk decision, not a reward. Some athletes can continue with monitoring and modification. Others need temporary restriction because immediate medical or bone risk outweighs participation. The plan should define reassessment and avoid punitive language.

Prevention belongs to the sport system#

Education should reach athletes, families, and coaches. It should reach clinicians, dietitians, and administrators. Practical prevention includes access to adequate food, protected meal time, and safe body-composition policies. It includes confidential medical care, realistic training progression, and routes to report harmful pressure.

Frequent weighing and public body-composition targets can increase risk and should have a clear health purpose, validated method, qualified oversight, confidentiality, and an action plan; a culture that praises under-fueling as discipline can undermine even good individual counseling.

Research still has gaps. Many studies are cross-sectional, definitions vary, and evidence is stronger in some athlete groups than others. The 2023 IOC methodology review calls for more consistent measures. Consensus models should guide careful assessment while remaining open to revision as validation improves.