Relative Energy Deficiency in Sport (RED-S): The Most Dangerous Dietary Trap for Endurance Athletes

Introduction

Relative Energy Deficiency in Sport (RED-S) is a syndrome formally named by the International Olympic Committee (IOC) in 2014, replacing the former term “Female Athlete Triad,” as research found that male athletes are equally affected. The core definition of RED-S is: energy intake insufficient to support training demands, resulting in chronically low Energy Availability (EA). The consequences extend beyond performance decline to systemic physiological damage, some of which (such as reduced bone density and hormonal disruption) may persist for years even after cessation of exercise.

Calculating Energy Availability (EA)

EA = (Dietary Energy Intake − Exercise Energy Expenditure) ÷ Fat-Free Mass (FFM, kg)

Example calculation: A female runner weighing 55 kg with 20% body fat (FFM = 44 kg), consuming 1,600 kcal daily, expending 700 kcal in training:
EA = (1,600 − 700) ÷ 44 = 20.5 kcal/kg FFM (severely deficient)

Body Systems Affected by RED-S

High-Risk Groups in Taiwan’s Endurance Sports Community

• Female runners: The combination of weight-loss goals and high training volume is most dangerous
• Lightweight cyclists: The cult of power-to-weight ratio (W/kg) drives improper dieting
• Swimmers (adolescents): Appetite is suppressed in water, leading to chronic underestimation of needs
• Triathletes: Training volume across three disciplines is extremely high; without a corresponding increase in dietary intake, RED-S is inevitable

Warning Signs of RED-S

Early stage (often overlooked):

• Training performance plateaus or declines without obvious cause
• Recurrent minor injuries, strong fatigue
• Poor sleep quality, elevated morning heart rate
• Menstrual cycle lengthens or disappears (female)
• Excessive guilt or obsessive thoughts about food

Middle-to-late stage (seek immediate medical attention):

• Stress fractures (especially in high-risk sites: tibia, fibula, metatarsals)
• Amenorrhea lasting more than 3 months
• DXA bone density T-score < −1.0
• Blood tests: low T3, low IGF-1, low hormones

Recovery Strategies

The primary intervention for RED-S is increasing energy intake, not reducing training volume (although training volume should also be adjusted under medical supervision):

1. Target EA ≥45 kcal/kg FFM: Gradually increase daily caloric intake; no need for rapid large increases (which may cause digestive discomfort)
2. Increase carbohydrate intake: Carbohydrates are the most important macronutrient for restoring hormonal function
3. Seek professional help: Sports nutritionist + sports medicine physician + (if necessary) psychological counseling
4. Bone density monitoring: DXA scan every 12–18 months

Practical Recommendations

• Calculate your own EA; if it falls below 45 kcal/kg FFM, proactively increase dietary intake.
• Menstrual irregularities are not a “badge of training intensity”—they are your body crying for help.
• When choosing a coach, be wary of coaching styles that emphasize “lighter and faster” without equally emphasizing “eat enough to be strong.”
• 7-Eleven food is not “unhealthy”—athletes in race preparation periods sometimes need energy-dense foods; there is no need to obsess over “clean eating.”

Conclusion

RED-S is the most underestimated injury in endurance sports because it causes no immediate acute pain, yet silently erodes health and performance. Understanding it and staying vigilant against it will protect your long-term athletic career more than any training method.

Related Reading

• RED-S Relative Energy Deficiency: Energy Supply Warning Signs for Female Athletes
• Relative Energy Deficiency in Sport (RED-S): Causes, Warning Signs, Effects on Bone and Endocrine Health, and How to Seek Help
• RED-S Relative Energy Deficiency: The Most Overlooked Health Breakdown in Endurance Athletes
• Energy Deficiency in Female Runners (RED-S): Identifying the Risks and Prevention