Relative Energy Deficiency in Sport (REDs) is a multisystem syndrome caused by chronic low energy availability (LEA) where an athlete’s dietary intake fails to meet the combined demands of exercise and essential physiological function. According to the International Olympic Committee (IOC) consensus statements, this condition impacts endocrine, reproductive, skeletal, and metabolic health, posing significant risks to both long-term wellness and athletic performance in endurance disciplines like ultra-trail running.
Why are ultra-trail runners uniquely vulnerable to REDs?
Ultra-trail runners face a perfect storm of physiological and cultural stressors that elevate their risk of chronic energy deficiency. Unlike traditional road marathoners, these athletes often spend 10 to 20 hours per week training on technical, mountainous terrain, according to data cited in recent sports medicine reviews. The sheer volume of work creates daily energy expenditures that can exceed 5,000 kcal, making it difficult for runners to replace lost calories during or after exercise.
Logistical barriers—such as remote course locations and the high prevalence of exercise-induced gastrointestinal distress—further complicate fueling. Nausea, bloating, and appetite suppression are common, often leading athletes to consume far less than their body requires. When this happens over months or years, it creates a cumulative energy deficit that the body attempts to manage by downregulating non-essential systems, such as reproductive and bone-remodeling processes.
Research indicates that endurance athletes often normalize symptoms like chronic fatigue, loss of menstrual function, and recurrent injuries. This “culture of endurance” can delay professional diagnosis, as athletes often mistake these red flags for the expected costs of high-level training.
What are the primary health consequences of REDs?
The transition from the “Female Athlete Triad”—which focused specifically on menstrual dysfunction, bone health, and energy availability—to the broader REDs framework recognizes that the syndrome affects all genders. According to the IOC, consequences include:
- Endocrine Disruption: Reduced testosterone in men and menstrual cycle irregularities (such as amenorrhea) in women.
- Skeletal Fragility: Impaired bone mineral density, significantly increasing the risk of stress fractures in the tibia, pelvis, and metatarsals.
- Immune Suppression: A higher frequency of upper respiratory tract infections due to the body’s inability to maintain recovery systems.
- Metabolic Shifts: Hormonal changes, such as reduced T3 thyroid hormone concentrations, which serve as a physiological marker for chronic under-fueling.
How can athletes and coaches screen for REDs?
Diagnosis remains difficult because there is no single “gold standard” test for REDs. According to the IOC’s Clinical Assessment Tool (CAT2), clinicians should look for a combination of clinical history and laboratory markers. While a DEXA scan remains the preferred method for measuring bone mineral density and body composition, it is not a standalone diagnostic tool.
Pro Tip: If you are an athlete, track “non-performance” markers. If your recovery time is increasing, your mood is consistently low, or your libido has dropped while your training load remains high, consult a sports dietitian or physician. Do not wait for a stress fracture to occur before investigating your energy availability.
What is the future of REDs management in trail running?
The sports medicine community is moving toward a “fuel for the work required” model. Instead of maintaining a static caloric intake, experts suggest that athletes dynamically adjust their nutrition to match the intensity and volume of specific training blocks. Future research is now focused on creating sport-specific screening tools for ultra-trail runners, as current surveys like the LEAF-Q were designed for different athletic populations.
There is also a growing call for longitudinal studies to understand the long-term impact of ultra-distance racing on the hypothalamic-pituitary-gonadal axis. As the sport continues to see a rise in participation among both men and women, the focus is shifting from simply “finishing the race” to ensuring athletes can remain healthy and active well into their middle and later years.
Frequently Asked Questions
- Is weight loss in ultra-trail running always a sign of REDs?
- Not necessarily, but rapid or unexplained weight loss is a red flag. If weight loss occurs alongside declining performance or menstrual/hormonal changes, it likely indicates a state of low energy availability.
- Can male athletes suffer from REDs?
- Yes. Research confirms that male endurance athletes are vulnerable to chronic LEA, which often manifests as reduced testosterone, impaired recovery, and bone stress injuries.
- What is the first step if I suspect I have REDs?
- Prioritize a visit to a sports physician or a registered dietitian who specializes in sports nutrition. They can help you assess your energy intake and determine if your training load needs temporary modification.
Have you or a training partner navigated the challenges of fueling for ultra-endurance events? Share your experiences in the comments below, or subscribe to our newsletter for the latest updates on sports science and injury prevention.
