In endurance sport, discipline is often mistaken for deprivation. Many athletes normalize constant fatigue, stalled performance, frequent injuries, and hormonal disruption as the “price of commitment.” In reality, these are often signs of chronic energy deficit—a condition now formally recognized as Relative Energy Deficiency in Sport (RED-S).
RED-S is not about body fat or body weight. It is about energy availability: the amount of dietary energy left to support normal physiological function after the cost of training is subtracted. When that balance stays negative for too long, performance suffers—and so does long-term health.
What Is Chronic Energy Deficit?
Chronic energy deficit occurs when athletes consistently fail to consume enough calories to support both training demands and essential physiological processes. This leads to low energy availability (LEA), the underlying driver of RED-S.
The International Olympic Committee defines RED-S as a syndrome of impaired physiological function affecting metabolic rate, menstrual function, bone health, immunity, protein synthesis, and cardiovascular health.
Unlike short-term dieting, chronic energy deficit develops subtly—often reinforced by performance culture, aesthetic pressures, or misguided nutrition advice.
Why Endurance Athletes Are Especially Vulnerable
Endurance athletes face a perfect storm for RED-S:
- High training volumes with large caloric expenditures
- Appetite suppression after intense exercise
- Emphasis on leanness or “race weight”
- Normalization of fatigue and hunger
- Poor recovery between sessions
Research shows endurance athletes—particularly runners, cyclists, and triathletes—exhibit some of the highest rates of low energy availability across all sports.
The Physiological Cost of RED-S
1. Hormonal Suppression
Low energy availability downregulates reproductive and thyroid hormones, even in male athletes. Reduced estrogen or testosterone impairs recovery, bone turnover, and metabolic efficiency.
2. Bone Stress and Injury Risk
RED-S is strongly associated with decreased bone mineral density and increased stress fracture risk—often before changes appear on scans.
3. Metabolic Adaptation
Chronic underfueling reduces resting metabolic rate and exercise economy, undermining the very performance athletes are trying to enhance.
4. Performance Decline
Despite high training loads, athletes in energy deficit often experience stagnant or declining VO₂max, reduced power output, and poor race execution.
Psychological and Behavioral Consequences
RED-S is not purely physiological. Chronic energy deficit is associated with:
- Increased anxiety around food
- Rigid eating behaviors
- Reduced motivation
- Burnout and loss of enjoyment
These patterns can persist even after performance declines, reinforcing a destructive cycle.
RED-S Is Not Just the Female Athlete Triad
While the Female Athlete Triad laid early groundwork, RED-S expands the model to include male athletes and multiple physiological systems. Men experience suppressed testosterone, impaired immunity, and increased injury risk under chronic energy deficit.
Reversing Chronic Energy Deficit: What Actually Works
Recovery from RED-S requires strategic fueling, not simply “eating more.”
Key principles include:
- Establishing adequate daily energy availability
- Fueling before, during, and after training
- Periodizing nutrition alongside training load
- Normalizing maintenance phases
- Monitoring performance, mood, and recovery—not just weight
➡️ Maintenance Calories and Metabolic Health
Performance and Longevity Are Not Opposites
Endurance performance does not improve through deprivation. It improves through adaptation, and adaptation requires energy.
Athletes who fuel adequately train harder, recover faster, maintain hormonal health, and sustain performance over longer careers.
➡️ Fiber Performance Enhancer: The Most Underrated Edge
Final Takeaway
Chronic energy deficit is one of the most underrecognized performance limiters in endurance sport. RED-S is not a failure of discipline—it is often the result of following advice that prioritizes leanness over physiology.
Fueling is not a weakness.
It is a performance skill.
References
Heikura, I. A., Uusitalo, A. L. T., Stellingwerff, T., Bergland, D., Mero, A. A., & Burke, L. M. (2017). Low energy availability is difficult to assess but outcomes have large impact on bone injury rates in elite distance athletes. International Journal of Sport Nutrition and Exercise Metabolism, 27(4), 330–338.
Loucks, A. B., Kiens, B., & Wright, H. H. (2011). Energy availability in athletes. Journal of Sports Sciences, 29(S1), S7–S15.
Melin, A., Tornberg, Å. B., Skouby, S., Møller, S. S., Sundgot-Borgen, J., Faber, J., & Sjödin, A. (2015). Energy availability and the female athlete triad in elite endurance athletes. Scandinavian Journal of Medicine & Science in Sports, 25(5), 610–622.
Mountjoy, M., Sundgot-Borgen, J., Burke, L., Ackerman, K. E., Blauwet, C., Constantini, N., … Budgett, R. (2018). IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. British Journal of Sports Medicine, 52(11), 687–697.
Nattiv, A., Loucks, A. B., Manore, M. M., Sanborn, C. F., Sundgot-Borgen, J., & Warren, M. P. (2007). American College of Sports Medicine position stand: The female athlete triad. Medicine & Science in Sports & Exercise, 39(10), 1867–1882.
Tenforde, A. S., Barrack, M. T., Nattiv, A., & Fredericson, M. (2016). Parallels with the female athlete triad in male athletes. Sports Medicine, 46(2), 171–182.