I have had RED-S twice. The first time at fifteen, the second at twenty-eight. The second time, I was a practising sports physiotherapist. I had studied it, I had assessed patients for it, and I still didn’t recognise it happening in my own body until I had a stress fracture in my foot.
That’s the thing about relative energy deficiency in sport. It isn’t obscure or rare. The warning signs are genuinely easy to miss because there’s almost always a more comfortable explanation sitting right next to the real one.
This article covers what RED-S is, what it does to your body, the symptoms most athletes overlook, and the practical steps that actually help. I’m also sharing my own story in detail, because I think the clinical description only tells part of it.
What Is RED-S?
RED-S stands for relative energy deficiency in sport. It occurs when an athlete’s energy intake, from food, consistently falls short of what the body needs to cover both the demands of training and normal daily function. That daily function includes hormone production, immune activity, bone maintenance, cardiovascular regulation, and basic organ operation.
The word “relative” is important. RED-S isn’t only about eating too little in absolute terms. It’s about the gap between energy in and energy out, and that gap doesn’t need to be large or deliberate to cause damage. Sustained over weeks or months, even a modest deficit pushes the body into a kind of power-save mode. Non-essential systems get dialled down to protect the critical ones. The result is a cascade of health effects and a gradual but measurable drop in performance.
RED-S vs the Female Athlete Triad
If you’ve come across the term “female athlete triad,” the two concepts are closely connected. The triad, a term established in clinical use through the 1990s, describes three specific conditions in female athletes: disordered eating, loss of menstrual function, and low bone density.
RED-S is the updated model. It includes male athletes, and it recognises a much broader range of health consequences beyond those three, covering metabolic function, gastrointestinal health, cardiovascular changes, mood and cognition, and more.
Both terms are still in use. Many athletes and coaches still search for “female athlete triad” and a lot of the current clinical guidance sits under the RED-S umbrella. If you’ve arrived here from a search on the triad, most of what follows applies directly.
RED-S Symptoms: The Warning Signs Athletes Ignore
The difficulty with RED-S is that its early signals are almost designed to look like something else.
The subtle signs
The first symptoms I noticed in myself were a lower resting heart rate than usual, broken sleep on nights after I’d trained, and a heaviness in my legs that lingered two or three days after sessions that shouldn’t have been hard. None of those things, on their own, ring alarm bells. Taken together with a stressful period in my life, they made complete sense as stress symptoms rather than RED-S symptoms. That was the wrong interpretation, but it was a convincing one.
Other early warning signs include:
- Delayed recovery after training that isn’t explained by your training load
- Persistent fatigue even on rest days
- Getting sick more often, or colds that take twice as long to clear
- Digestive discomfort that doesn’t have an obvious cause
- Low iron levels on blood work, particularly in female athletes
Symptoms across the body
As RED-S progresses, the effects reach more systems:
- Hormonal and reproductive: In female athletes, irregular or absent periods are one of the most identifiable signs. These are not a normal side effect of heavy training. They indicate that the body has deprioritised reproductive function due to insufficient energy. Female athletes on the oral contraceptive pill lose this signal entirely because the medication regulates the cycle artificially. That’s exactly what happened to me the second time.
In male athletes, RED-S shows up through testosterone changes: reduced morning erections, changes in libido, and slower beard growth. These signals are less well known and rarely discussed in male athletic settings, which means they get missed far more often.
- Bone health: Stress fractures, recurring soft tissue injuries, and an injury pattern that doesn’t respond predictably to treatment.
- Performance and function: Reduced strength, power and endurance despite a consistent training schedule. Poor concentration. Reduced coordination. Mood swings and irritability that feel disproportionate to what’s happening. A preoccupation with food, weight, or body composition that becomes harder to turn off.
Why Athletes Miss RED-S, Even When They Know Better
My first episode started when I was fifteen. I was competitive in running and doing essentially every other sport available to me. Looking back, missing periods for months at a stretch was the clearest sign. At the time, nobody flagged it, including me. I ate a lot and didn’t restrict deliberately. The mismatch was accidental, the result of high training volume outpacing what I was taking in. The first consequence was shin splints. The second was a lower limb stress fracture that kept me out of sport for months.
The second episode came at twenty-eight, and it was more complicated.
I competed in a triathlon with a river swim and picked up a blood infection in the days afterwards. The illness killed my appetite. Just thinking about food made me feel nauseous. I was weak, I knew I was under-fuelled, and I kept training anyway because I had a 10km target race on the calendar and I didn’t want to give it up. I was also going through a relationship breakdown at the same time. Training was the thing helping me cope. I couldn’t see, or maybe I didn’t want to see, how those two things were reinforcing each other.
I ran the race. A few days later, a deep, sharp pain developed in my foot. A scan confirmed a stress fracture.
The honest reflection on that second episode is that I had all the clinical knowledge and none of the objectivity. Grief and illness gave me permission to keep dismissing the signals. The lesson I took from it wasn’t that RED-S is easy to catch with the right information. It’s that the psychological context around training can make it very hard to hear what your body is actually saying.
RED-S and Stress Fractures: Why Your Bones Pay the Price
Bone is living tissue. It responds to load by remodelling, breaking down slightly and rebuilding stronger. That process depends on adequate energy, calcium, and hormonal function, particularly oestrogen in female athletes and testosterone in males. When energy availability is chronically low, the body deprioritises bone remodelling. Density drops, and bones become less able to absorb repetitive training load.
A stress fracture that appears without a clear spike in training volume, or one that recurs after a normal return-to-sport timeline, should prompt a thorough RED-S assessment. Simply offloading the bone and resting won’t address the underlying cause if the energy deficit is still present. The fracture will heal, but the bone density won’t rebuild, and the next training block carries the same risk.
The connection between RED-S and stress fractures in runners is well established. “Bone fatigue” in an otherwise healthy, trained athlete is rarely just bad luck.
How to Reduce Your Risk of RED-S
1. Fuel for what you’re actually doing
Your body uses energy to keep you alive at rest. Training adds substantially to that demand, and endurance athletes in particular tend to underestimate the gap. Post-exercise appetite suppression is a real physiological effect. You finish a two-hour ride not feeling hungry, eat a normal meal, and think you’ve covered it. You probably haven’t.
For sessions over an hour, take on carbohydrates during the session, not just before or after. Have protein and carbohydrate available immediately after training. If tracking feels useful rather than obsessive, apps like MyFitnessPal or Fuelin can help you see where the gaps are. The goal is a rough picture, not a perfect accounting of every gram.
What I do now that I didn’t do before: I eat on long rides and runs. I have a protein and fruit smoothie after training because I can drink it even when I don’t feel like eating. I use periodised fuelling so that my heavier training days have correspondingly higher intake, not the same flat baseline I used to default to.
2. Stop sorting food into categories
Labelling certain foods as “bad” creates restriction patterns that make under-fuelling far more likely. For an athlete, caloric adequacy matters more than food purity. A burger contains protein, carbohydrates, dairy, and often vegetables. It is not the enemy of athletic performance. The athlete who avoids it because it feels “bad” and finishes the week under-fuelled is at much greater risk than the one who ate the burger and met their energy needs.
There are genuinely better and worse nutritional choices for performance. But fixating on that hierarchy to the point of restriction does more harm than the occasional so-called bad meal ever could.
3. Pay attention to your mindset
The psychological dimension of RED-S is real and often goes unaddressed. As a teenage athlete, I stood on start lines comparing my body to the elite women around me. I weighed myself against peers. I didn’t restrict deliberately, but the habit of comparison was there, and it was doing something.
Even now in my late twenties, I notice the push and pull between knowing I perform better at a certain fuelling level and feeling better aesthetically at a different one. Those two things don’t often align, and I’ve had to learn, slowly, to treat the performance metric as the more reliable one. The thoughts still come. Having the language to name them makes them easier to work with.
If these patterns are persistent or escalating, a psychologist with experience in athlete health is worth seeing. Not as a dramatic intervention, but as a practical tool.
4. Reframe the goal
Performance is a more useful north star than appearance for an athlete. I run faster and further now than I ever have, and it correlates directly with eating more, not less. My stomach doesn’t look the way it did when I was under-fuelled and I don’t care, because the comparison has become too clearly skewed in one direction.
That shift in focus doesn’t happen overnight and it isn’t always comfortable. It is, though, a more accurate picture of what a fuelled athlete body is actually capable of.
5. Modify training during recovery, don’t just stop
Complete rest is sometimes medically necessary with RED-S. It’s also, for many athletes, psychologically damaging in its own right. Training is often tied to social connection, mental health, identity, and routine. Removing it entirely can create a spiral that makes recovery harder.
When I was managing my foot stress fracture, I changed swimming lanes and forced myself to go slowly. I swapped running for Pilates, which kept my mind engaged without bone load. I went to run club on a bike. These weren’t perfect substitutes, but they kept me stable and let the bone heal.
What’s appropriate depends on the severity of the RED-S and the nature of any associated injury. A sports physiotherapist can help you find the boundary between activity that supports recovery and activity that hinders it.
Can Men Get RED-S?
Yes. The condition is not specific to female athletes, and the clinical focus on women has created a misleading impression that it is.
Male athletes in weight-sensitive sports, including cyclists, rowers, wrestlers, and distance runners, carry significant risk. The symptoms present differently: rather than menstrual disruption, males may notice changes in testosterone levels, including reduced morning erections, lower libido, and a slower beard growth rate. Fatigue, recurring injuries, and declining performance are shared across both sexes.
Male athletes rarely discuss these signals, partly because RED-S isn’t framed as a male issue in most athletic communities. If you’re a male athlete with a pattern of bone stress injury, unexplained fatigue, or performance decline that doesn’t respond to normal training adjustments, it’s worth considering.
When to See a Sports Physiotherapist for RED-S
A sports physiotherapist is often the right first contact, particularly if RED-S has led to injury or if you want support staying active through recovery.
At Alpha Sports Medicine, across our Newport, Ascot Vale, and Bacchus Marsh clinics, we work with athletes to assess RED-S presentations, manage bone stress injuries, and build modified training plans that allow recovery without full withdrawal from sport. We also coordinate with other clinicians because RED-S rarely resolves with a single-discipline approach.
Other team members who play a role:
- GP: Blood testing for hormonal health, iron levels, bone density markers, and general health status. This is usually where investigation starts.
- Sports dietitian: A fuelling plan built around your actual training demands, not generic calorie targets. This is where the energy mismatch gets addressed practically.
- Psychologist or mental health professional: Especially relevant where body image concerns, disordered eating patterns, or exercise dependence are part of the picture. These factors increase RED-S risk and don’t resolve without direct attention.
If you’re recognising symptoms in yourself, or in someone you train alongside, getting an assessment is a reasonable and proportionate response.
Frequently Asked Questions About RED-S
| What is RED-S in sport? | RED-S (relative energy deficiency in sport) occurs when an athlete consistently takes in less energy than their body needs to support both training demands and basic daily functions including hormones, immunity, and bone health. The condition affects athletes of all genders and can develop accidentally or as a result of deliberate restriction. |
| What are the most common RED-S symptoms? | Common symptoms include disrupted sleep, slow recovery between training sessions, frequent illness, hormonal changes (irregular or absent periods in females; testosterone changes in males), stress fractures, mood instability, low iron, and declining performance. Symptoms are often subtle and attributed to unrelated causes such as life stress or a hard training block. |
| How long does RED-S recovery take? | It depends on how long the energy deficit has been present and whether bone injury has occurred. Mild cases may stabilise within weeks of addressing energy intake. Stress fractures add 6 to 12 weeks of bone healing time, with a graduated return to full training load after that. A sports physiotherapist can guide the return-to-sport timeline specific to your situation. |
| Can you exercise with RED-S? | Often, yes, with appropriate modification. Reducing intensity, switching to lower-impact activity, and shortening session duration can allow continued movement while the body recovers. Full rest is sometimes necessary but can be counterproductive for mental health and long-term adherence to recovery. What’s appropriate depends on the severity of the condition and whether bone injury is present. |
| How is RED-S different from the female athlete triad? | The female athlete triad is an older clinical model describing disordered eating, loss of menstrual function, and low bone density in female athletes. RED-S is the updated, broader model. It includes male athletes and covers a wider range of health effects beyond the original three. The two terms are sometimes used interchangeably, and the conditions overlap significantly. |
Final Thoughts
RED-S is under-recognised partly because the warning signs are easy to rationalise. Missing periods are “just part of training.” Fatigue is “just life.” A stress fracture is “just bad luck.” The accumulation of these explanations is how athletes spend months in a deficit that compounds the longer it continues.
You don’t need to be restricting deliberately, or training at elite volume, or obviously struggling with food. I was none of those things the first time it happened to me.
If something feels consistently off, your recovery isn’t tracking, or your body is giving you signals you keep explaining away, it’s worth taking seriously. The team at Alpha Sports Medicine in Newport, Ascot Vale and Bacchus Marsh work with athletes at every level and offer both in-clinic and online appointments.
Anna Lawther is a Sports Physiotherapist at Alpha Sports Medicine, Newport. She has a special clinical interest in RED-S, endurance sport injury, and return-to-sport rehabilitation.
