Movement & Fitness
·
4 min
Dr Thiviya Sivakanthan
MBBS
Training harder than ever but feeling exhausted, struggling with recovery, or watching your performance decline? Discover how Relative Energy Deficiency in Sport (RED-S) affects everyone from elite athletes to dedicated gym-goers, and learn why fuelling your body properly is just as important as your training itself.
Introduction
You don’t have to be an Olympian to fall into the trap of doing too much and eating too little. We live in a culture that glorifies discipline, calorie tracking, and “no days off.” But when your training load climbs and your energy intake doesn’t keep up, your body quietly starts to rebel.
That’s the world of Relative Energy Deficiency in Sport (RED-S), a condition where your body simply doesn’t have enough fuel to perform and stay healthy.
Originally thought to affect only female athletes (the so-called 'Female Athlete Triad' of menstrual issues, low bone density, and disordered eating), RED-S is now known to affect men and women alike, in every type of sport — from elite runners to your friend who hits F45 five days a week and wonders why they’re always exhausted.
What 'Energy Availability' Really Means
Think of your body like a smartphone. You’ve got limited battery power. You spend some on training, some on work, some on basic functions like digestion, hormones, and repair. If you’re constantly burning through energy in the gym or on the track but only charging your phone halfway (i.e. not eating enough), eventually, the “non-essential” apps shut down. These are things like your menstrual cycle, libido, mood, or even bone formation.
That’s low energy availability.
It’s not about willpower or being “clean” with your diet. It’s about not fuelling your body to do the job you’re asking of it.
How RED-S Happens (and Who’s at Risk)
Sometimes, it’s unintentional: you start training more, walking extra steps, skipping breakfast, or underestimating what your workouts burn.
Other times, it’s deliberate: cutting calories for a race weight, chasing abs, or fearing that more food means more fat.
It’s especially common in:
Runners who “eat clean” but under fuel overall
Lifters trying to stay lean year-round
Dancers, cyclists, or gym enthusiasts who train daily but rarely rest
Anyone who equates discipline with deprivation
But RED-S doesn’t care how “fit” you look, it shows up when your energy input doesn’t match your output, no matter how strong or athletic you are.
How Common Is RED-S?
Pinning down exact numbers is tricky because RED-S often flies under the radar. Many athletes don’t realise their symptoms are linked to underfueling. That said, research gives us a good estimate of how widespread it is:
Up to 60% of female athletes in endurance or aesthetic sports show signs of low energy availability.
Around 30–50% of male athletes in similar sports (like cycling, running, or rowing) are also affected, though they’re less likely to be diagnosed.
Even among recreational athletes and gym-goers, studies suggest 15–25% have symptoms consistent with RED-S often without realising it.
In short: it’s common. Much more common than people think.
Is RED-S a Controversial Diagnosis?
When the International Olympic Committee (IOC) first introduced the concept of Relative Energy Deficiency in Sport (RED-S) in 2014, it represented an expansion of the older Female Athlete Triad — which focused only on menstrual dysfunction, low bone density, and disordered eating in women. RED-S broadened the picture, recognising that low energy availability can affect every body system and occurs in both men and women.
At first, some clinicians questioned whether RED-S was too broad or hard to diagnose because its symptoms span everything from metabolism and mood to bone and hormonal health. But since then, growing research and consensus statements — including the IOC’s 2018 update — have reinforced RED-S as a valid and clinically useful framework.
Today, RED-S is widely accepted in sports and exercise medicine as a comprehensive model that better captures the whole-body consequences of under-fuelling, rather than focusing on one triad of symptoms or one gender.
What RED-S Does to Your Body
Your body is smart: it’ll always prioritise survival over performance. So when it doesn’t get enough fuel, it starts dimming the lights on different systems to save energy.
Metabolism
Your resting metabolic rate slows down, so you feel cold all the time, tired, and sluggish. Weight loss plateaus even though you’re eating less.
Hormones
For women: your periods become irregular or disappear. For men: testosterone drops, libido tanks, and recovery stalls. Cortisol (your stress hormone) climbs, leaving you wired but tired.
Bones
Your bones weaken because your body can’t spare the energy to keep them strong. Stress fractures start creeping in, even if your form is perfect.
Mind & Mood
You feel irritable, anxious, foggy, or detached from your training. Food becomes a constant thought: when to eat, what to eat, what not to eat.
Performance
You’re training harder than ever, but your results are slipping. You’re slower, weaker, and constantly sore. Your motivation is gone.
Sound familiar? That’s RED-S whispering through your system.
The Everyday Version
You don’t have to be a pro triathlete to have RED-S.
It can look like:
Skipping dinner after evening training because you’re “not hungry”
Always feeling cold, bloated, or moody
Working out six days a week but never feeling rested
Thinking your period disappearing is a sign of being “fit”
Relying on caffeine to get through workouts
Frustration that your progress has stalled despite “doing everything right”
If you’ve ever wondered, “Why am I so tired all the time even though I’m fit?” … this could be why.
How It’s Diagnosed
There’s no single blood test or scan that screams “RED-S!”. It’s a clinical diagnosis; a combination of symptoms, history, and sometimes lab results.
Doctors and sports dietitians look for:
Changes in menstrual cycle (for women)
Drop in libido or morning erections (for men)
Fatigue, low mood, frequent injuries, or illness
Slowed recovery and unexpected performance decline
Blood tests might show low sex hormones, low thyroid (T3), high cortisol, or nutrient deficiencies like iron and vitamin D. A bone scan (DEXA) can check for early bone loss.
Recovering from RED-S
The goal isn’t just to “eat more.” It is to give your body the consistent fuel it needs so it feels safe to function and perform at its best again.
Nutrition
Add consistent meals and snacks especially pre- and post-workout fuel.
Don’t fear carbs or fats; they’re your hormones’ best friends.
Make sure you’re eating enough even on rest days (recovery takes energy too!).
Training
Scale back intensity or frequency for a while. Remember recovery is also training.
Prioritise sleep and active recovery over another HIIT class.
Support
Work with a sports dietitian, doctor, or psychologist if needed.
Address the mindset around food, weight, and performance. This is often the hardest part.
Prevention: Fuel Like You Train
The easiest way to prevent RED-S is to respect your energy balance.
Eat regularly.
Rest deliberately.
Don’t glorify exhaustion or restriction.
Remember that eating enough isn’t indulgent, it’s essential.
Your body performs best when it feels safe, nourished, and supported and not when it’s running on fumes.
Key Takeaways
RED-S = not enough energy to support both training and life.
It can affect anyone.
Symptoms include fatigue, menstrual issues, low libido, poor recovery, mood changes, and stress fractures.
You can’t out-discipline biology.
The fix is fuel, rest, and self-compassion, not more training.
Final Thoughts
The best athletes and healthiest gym-goers aren’t the ones who grind the hardest. They’re the ones who listen to their bodies. If your training, diet, or mindset leaves you constantly tired, anxious, or flat, it’s not a sign to push harder. It’s a sign to refuel.
Your body wants to perform for you, it just needs enough energy to do it.
References
1. Mountjoy M, et al. (2018). The IOC Consensus Statement on RED-S: 2018 Update. Br J Sports Med.
2. Loucks AB, et al. (2011). Low Energy Availability in the Marathon Runner: Physiology and Consequences. Med Sci Sports Exerc.
3. De Souza MJ, et al. (2014). Female Athlete Triad Coalition Consensus Statement on Treatment and Return to Play. Curr Sports Med Rep.
4. Logue D. et al., Int J Sport Nutr Exerc Metab (2020) — prevalence of low energy availability in athletes.
5. Koehler K. et al., Front Nutr (2021) — RED-S and energy deficiency in male athletes.
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