RED-S occurs when the body doesn’t get enough energy over a long period — meaning it doesn’t take in enough calories from food to cover both training demands and basic daily functions.
When the body lacks energy, it starts saving where it “can” — for example, healing slows down, hormonal balance is disrupted, immunity weakens, sleep quality drops, mental well-being suffers, and sports performance declines.
How does RED-S develop?
RED-S usually occurs for two main reasons:
- Not enough food (low energy intake) – for example due to dieting, skipping meals, eating disorders, or simply not knowing what and how much to eat.
- Too much training without proper recovery – intense training phases, new training plans, or increased volume without adjusting nutrition.
Sometimes RED-S starts unintentionally – for instance, when an athlete changes their training plan or has a busy schedule and doesn’t manage to eat regularly. Problems arise when the energy deficit is long-term, which can lead to serious health and performance issues.
Who does RED-S affect?
RED-S can affect both women and men. While research initially focused on women (especially problems such as missed periods or low bone density), we now know it also affects men – for example through low testosterone or decreased bone density.
Teen athletes are the most at risk because they have high energy needs due to growth, but often lack proper nutrition knowledge. Social pressures about body image or weight can make this worse.
Which sports are higher-risk?
Certain sports have a higher risk for RED-S, especially those emphasizing weight, appearance, or high training volume:
- Endurance sports (long-distance running, triathlon, swimming, cycling)
- Aesthetic sports (gymnastics, figure skating, synchronized swimming)
- Jumping or gravity sports (climbing, ski jumping, freestyle skiing)
- Weight-class sports (wrestling, boxing, rowing, horse racing, weightlifting)
- Athletes in intense training without sufficient food or recovery
- Athletes with eating disorders or severe food restrictions
What are the symptoms of RED-S?
RED-S happens when an athlete doesn’t take in enough food to meet their body’s and training’s demands. Common symptoms include:
- Fatigue
- Rapid weight loss
- Missed periods or delayed development in girls
- Low libido (in boys/men)
- Frequent illness (colds, weakened immunity)
- Hair loss
- Trouble focusing or maintaining attention
- Feeling cold or chilled
- Irritability, anxiety, or depressive mood
How does RED-S affect sports performance?
In the beginning, the body may temporarily compensate and still perform well, but this doesn’t last. Performance eventually declines. Athletes may push themselves even harder, which only worsens the energy deficit.
RED-S can lead to:
- Decreased strength and endurance
- Higher risk of injuries
- Slower recovery after training
- Impaired coordination, decision-making, and concentration
How is RED-S diagnosed?
RED-S often goes unnoticed because it doesn’t show up as a single symptom. Proper diagnosis includes:
- A medical interview about overall health, performance, training load, menstrual cycle (for girls), eating habits, and relationship with food
- Physical examination, including blood pressure, heart rate, weight, and possibly blood tests
The doctor may then determine risk levels:
- High risk – extreme weight loss, eating disorders, serious health issues
- Moderate risk – weight loss of 5–10% in the past month, irregular menstruation, stress fractures
- Low risk – good overall health, balanced diet, no extreme training or eating patterns
How is RED-S treated?
The goal of treatment is to allow the athlete to continue sports safely, while restoring energy reserves and health. Treatment depends on severity.
A care team may include:
- Doctor – monitors health and provides medical care
- Nutritionist – helps adjust diet and explains how food fuels performance
- Psychologist/therapist – supports mental health, especially if there are eating disorders or body image issues
Sometimes it’s necessary to reduce training, adjust eating habits, or even take a break from sports to let the body recover.
Can RED-S be prevented?
Yes, RED-S is preventable, but it requires a shift in sports culture. Key steps include:
- Education for athletes, parents, coaches, and doctors about proper energy intake
- Safe, healthy monitoring of weight and performance, without pressure or extreme diets
- Creating a supportive environment where athletes don’t feel ashamed of their body or weight
RED-S is real and serious, and it doesn’t just affect elite athletes. Recreational athletes can also suffer from low energy if they eat poorly or overtrain. The key is balance — training, rest, and proper nutrition.
If you suspect RED-S in yourself or someone you know, consult a sports doctor or nutrition specialist.