27 Facts You Need to Know about REDs (Relative Energy Deficiency in Sport)
From a Board Certified, REDs-informed Sports Dietitian.
If you know me IRL you know I’m a huge fan of trivia and fun facts. While REDs isn’t fun, there are a lot of interesting (and often surprising) things you need to know about low energy availability and symptoms of REDs.
Rather than give you another summary you could easily Google, I figured I’d share some facts that might change how you think about energy availability, REDs, and bone health. Don’t worry, you’ll also learn what it is along the way (if you don’t already)!
REDs in 27 Facts:
REDs stands for Relative Energy Deficiency in Sport. It used to be called RED-S and some of the researchers wanted people to pronounce it as “reds” instead of “red S” so they changed it. The change was also for social media sharing because RED-S was harder to hashtag!
REDs itself is still hotly debated. In 2024, researchers published a paper, provocatively titled “Does Relative Energy Deficiency in Sport Syndrome Exist?” The authors questioned whether REDs, as currently defined and diagnosed, is an adequately supported clinical syndrome[1].
REDs results from persistent, problematic low energy availability. The underlying issue is that body tissues don’t have enough energy available to support the body’s function relative to demands being placed on it. (More about Low Energy Availability)
REDs can be challenging to diagnose because there isn’t a single test that can definitively diagnose it. The IOC’s clinical approach considers symptoms, risk factors, and other potential explanations[2]. This is part of why a REDs diagnosis can be controversial.
REDs can coexist with other conditions. While diagnosis may require other things to be addressed or ruled out, an athlete can absolutely have PCOS, a GI condition, or a mental health concern and have REDs. Finding another concern doesn’t mean that energy mismatch isn’t also a potential problem!
REDs is described as a syndrome rather than a single disease with one identifiable cause. It should be diagnosed by a physician with expertise in REDs.
There isn’t a magic calorie number or timeline for developing REDs. It can vary by severity, length of time, and the individual athlete.
While REDs is often seen as a health issue, it absolutely is a performance issue as well. Athletes with low energy availability are more likely to have a poor training response and lose training time to illness[3]
The energy mismatch can be due to low intake, high outputs due to training loads, or a combination of both. Recovery from REDs can mean decreasing training loads, but it doesn’t necessarily mean stopping. In many cases, athletes are able to continue to train (with adjustments) as long as it’s safe to do so.
Athletes at any level of competitiveness can experience REDs, even recreational athletes. Recreational and adult athletes can find themselves under-fueled because they may not realize how much energy their activity actually requires!
One key aspect of REDs treatment is addressing the underlying low energy availability. As a sports dietitian, this is where a lot of my focus is- finding the “root cause” of the low energy availability and helping individuals figure out how to logistically meet their energy needs!
Many folks with REDs will benefit from mental health support- navigating body changes, mood changes, and tolerance to decreased exercise or rest.
Sometimes REDs can be confused for Over-Training Syndrome. In reality, they can exist independently or overlap. They can also have very similar presentations.
REDs assessment and treatment is ideally multidisciplinary. Physicians, dietitians, therapists, athletic trainers, physical therapists, coaches, and other members of an athlete’s team can play a role in identifying, assessing, and treating REDs.
The literature has a pretty long list of physical symptoms of REDs. You don’t have to have every single symptom to have problematic low energy availability.
Urinary incontinence is an emerging area of REDs research. UI is a surprisingly common symptom with estimates ranging from 20-50% of female athletes[4]. Low energy availability has been proposed as one potential contributing factor due to decreased pelvic muscle tone and hormonal shifts.
REDs can happen in the context of a restrictive eating disorder, but there are also mental and cognitive effects of undernutrition that parallel or even trigger cognitions we would identify as disordered.
REDs grew out of research on the Female Athlete Triad. The Triad specifically focuses on menstrual dysfunction, low energy availability, and bone health. REDs expanded this concept to include energy availability on a continuum and to include athletes of all sexes. The Triad and REDs overlap, but the terms are not interchangeable.
Weight loss can be a symptom of REDs, but problematic low energy availability can occur in the absence of weight loss.
Changes in body composition or weight don’t tell the whole story. In practice, I also see athletes whose body composition changes in ways that don’t match their assumptions about how they are fueling.
A strong drive for thinness has been associated with lower energy availability in athlete populations. Body image and pursuit of a leaner physique are important pieces of the REDs/LEA conversation.
REDs and low energy availability can happen without intentional restriction or dieting: sometimes high training loads and busy schedules just make it hard to fuel!
Low carbohydrate availability is now part of the conversation- low carbohydrate intake appears to have an independent and potentially additive effect to low energy availability.
While it can be common for athletes to lose their menstrual cycle during heavy training periods, losing your period shouldn’t be normalized! Cycles longer than 35 days, infrequent, or absent periods all require investigation.
REDs isn’t just a women’s health issue:the REDs framework also considers men. Male reproductive function, metabolic health, and performance are also negatively affected by REDs. Researchers are still working to understand the unique presentation and thresholds in male athletes.
One of the most concerning potential consequences of low energy availability is its impact on bone health. REDs has been associated with reduced bone mineral density and increased risk of bone stress injuries, among other musculoskeletal concerns.
Bone health isn’t necessarily a lost cause. Recovery from low energy availability can improve many physiological consequences of REDs, although the extent and timeline can vary. I’ve personally seen athletes make meaningful improvements in bone health after increasing energy availability and addressing their training. I think it’s pretty darn cool how adaptable bodies are!
The Takeaways
REDs is far from simple or cut and dry.
Fueling and smart training loads absolutely matters for all athletes.
The research on REDs is evolving and there’s plenty we don’t know yet. Not every symptom means REDs. It can be challenging to connect the dots to low energy availability, even for experienced athletes and clinicians.
Poor recovery, injury, and inconsistent cycles absolutely can be reasons to take a closer look at how an athlete is fueling.
If you’re someone who supports athletes, keep in mind that an athlete who is under-fueling doesn’t have a required look, gender, or level of competition. For specific concerns, working with a sports dietitian can help! For providers, here are some tips for referring to a nutrition professional.
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[1] Jeukendrup AE, Areta JL, Van Genechten L, et al. Does Relative Energy Deficiency in Sport (REDs) Syndrome Exist?. Sports Med. 2024;54(11):2793-2816. doi:10.1007/s40279-024-02108-y
[2] Mountjoy M, Ackerman KE, Bailey DM, et al
2023 International Olympic Committee’s (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine 2023;57:1073-1098.
[3] Gallant TL, Ong LF, Wong L, et al. Low Energy Availability and Relative Energy Deficiency in Sport: A Systematic Review and Meta-analysis. Sports Med. 2025;55(2):325-339. doi:10.1007/s40279-024-02130-0
[4] Gan, Zoe S, and Ariana L Smith. “Urinary Incontinence in Elite Female Athletes.” Current urology reports vol. 24,2 (2023): 51-58. doi:10.1007/s11934-022-01133-6
