STRATARED-S and low energy availability: what coaches and Athletic Trainers need to see
One of the most serious health problems in sport does not announce itself. It is quiet. It is easy to praise by mistake: the athlete who trains hard, eats too little, and slowly runs out of fuel for their own body. It has a name: RED-S.
Think of it as an energy budget. An athlete takes in a certain amount of fuel each day, and training spends a big share of it. Whatever is left has to run everything else: building bone, balancing hormones, fighting off illness, focusing in class, and, in a teenager, simply growing. When training keeps taking and the plate does not keep up, the body starts making cuts. That shortfall has a name, low energy availability, and when it drags on it becomes RED-S.
What RED-S actually is
RED-S stands for Relative Energy Deficiency in Sport, a term from the International Olympic Committee. It describes what happens when energy availability stays too low for too long. The body cannot afford to run every system at once, so it quietly powers down the ones it can do without for now.
This idea grew out of the older female athlete triad, which linked low energy availability, menstrual changes, and weakened bone in women. Research since then made two things clear. The same shortfall harms male athletes too, and the damage reaches well beyond bone and periods. RED-S is the fuller picture, and it reaches athletes of every gender and every sport.
One point matters more than the rest, and it is the one people miss: this is not about weight, and it is not about looking a certain way. It is about the gap between fuel taken in and energy demanded by training and growth. Sometimes that gap opens on purpose, through restrictive eating. Just as often it opens by accident, when appetite does not keep pace with a heavy training block, a packed schedule, or a growth spurt.
Why it hides in athletes who look fit
Underfueling does not have a look. An athlete can be lean, strong, setting personal bests, and running a deficit the entire time. Early on, the body guards performance and trims the quieter systems first. So the warning signs turn up in bones, hormones, and lab work long before they turn up in the box score. By the time results clearly slide, the shortfall has usually been building for a while.
The athletes most at risk are often the ones we admire most. Think high training loads, a culture that whispers "lighter is faster," and the kind of discipline that makes skipping meals feel like commitment. Looking fit and working hard is exactly why RED-S gets missed. It is exactly why we have to look past the surface.
The warning signs
No single item below proves anything on its own. What should get your attention is the pattern over weeks: several of these showing up together.
- Chronic fatigue and slow recovery that a normal rest day does not fix.
- Getting sick often, or one nagging injury after another that will not fully heal.
- Stress fractures or other bone injuries, sometimes repeated.
- In female athletes, periods that become irregular, lighter, or stop altogether. This is a signal to take seriously, never something to wave off as "normal for athletes."
- Performance that has plateaued or is sliding despite hard, consistent training.
- Restrictive eating, cutting out whole food groups, anxiety around meals, or extra exercise piled on top of practice to "earn" food.
- Mood changes: irritability, low mood, trouble concentrating, or the loss of an athlete's usual spark.
Why it is a health issue, not just a performance one
RED-S deserves real care for one reason: a long energy deficit quietly damages the systems that keep an athlete healthy for life, not just for a season.
- Bone. Low energy and the hormonal changes that come with it weaken bone, raising the risk of stress fractures now and lower bone density that can follow an athlete for decades.
- Hormones. The body dials down reproductive and other hormones to save energy. In females this shows up as menstrual changes; in males it can mean lower testosterone. In teenagers it can interfere with normal growth and development.
- Immune system. More frequent illness, slower healing, and more time lost to being run down.
- Heart and metabolism. Prolonged low energy availability can affect cardiovascular and metabolic health.
- Mental health. RED-S is tangled up with mood, anxiety, and disordered eating, and it can coexist with an eating disorder that needs its own specialized care.
That is why RED-S is a clinical diagnosis, worked up and managed by medical professionals. It is not a training tweak. And it is not something you fix by telling an athlete to "eat more."
How to respond
If you see the pattern, the next few minutes matter more than you would think. Handle it with care, and an athlete opens up and gets help. Handle it clumsily, and they go quiet and hide it. Lead with health and care. Never with weight, never with performance.
- Keep it privateOne quiet, caring conversation. Never in front of teammates, never a public weigh-in, never a callout at practice.
- Lead with the person, not the plate"I want to make sure you are taking care of yourself" lands better than any comment about food or the scale. You are opening a door, not delivering a verdict.
- Loop in your Athletic TrainerThey can screen, watch it over time, coordinate care, and keep the information appropriately private.
- Refer outA physician for the medical evaluation, and a Registered Sports Dietitian (RD/CSSD) for fueling. If disordered eating is in the picture, that gets specialized care too.
Screen gently, monitor over time. Simple, respectful check-ins tell you far more than any one-time survey: ask about energy, recovery, injury history, and, for female athletes, menstrual history. The goal is to catch trends early and open a caring conversation, not to interrogate anyone or hang a label on them.
You cannot diagnose RED-S from the sideline. It takes a medical evaluation to rule out other causes and build a coordinated plan. Your job, whether you coach or work as an Athletic Trainer, is simpler: recognize the pattern and refer, early and without shame, to a physician and a Registered Sports Dietitian (RD/CSSD). This article is education, not medical advice.
Catch underfueling before it becomes a diagnosis
Strata watches the quiet signals: fuel, sleep, recovery, training load, and, where the athlete opts in, menstrual history. Anything of concern routes to the Athletic Trainer and no one else. Never a shame screen, never the sport coaches. It is built to open a caring conversation early, not to police anyone.
See it with your school's branding →Frequently asked
Is RED-S only a problem for female athletes?
No. The concept grew out of the female athlete triad, which focused on women. But the research is clear that low energy availability harms male athletes too, affecting hormones, bone, and performance. RED-S reaches across every sport and every gender.
Does an athlete have to look underweight to have RED-S?
No. It comes down to the gap between fuel taken in and the energy demanded by training and growth, not body size. An athlete at any weight can be underfueled, including one who looks fit and is performing well.
What is the difference between RED-S and an eating disorder?
They are related, but they are not the same thing. RED-S is the health fallout of low energy availability, and it can happen entirely by accident. An eating disorder is a mental health condition. The two often overlap, and both need professional care, so refer either concern out rather than trying to sort it yourself.
Sources & further reading
- IOC Consensus Statement on Relative Energy Deficiency in Sport (REDs).
- Female and Male Athlete Triad Coalition, clinical resources on low energy availability.
- Refer suspected cases to a physician and a Registered Sports Dietitian (RD/CSSD).