RED-S: when training more does harm (and how to catch it early)

RED-S is what happens when the energy an athlete takes in isn't enough to cover training and growth: the body shuts down essential functions — periods, bones, recovery, mood. What the 2023 IOC consensus says, the signs to know, why 44% of adolescent athletes wrongly believe losing their period is normal — and why this is monitored, not diagnosed.

There's a dangerous idea in youth women's sport: that training harder is always better. But an adolescent athlete's body is not an engine you can push forever. When the energy coming in isn't enough to cover what goes out — across training, school and growth itself — the body starts to cut the functions it deems least urgent. That is the heart of a condition science calls RED-S.

In short

  • RED-S (Relative Energy Deficiency in Sport) stems from low energy availability: eating less than what training and growth require.
  • It isn't only about eating disorders: it can happen unintentionally, simply by not refuelling enough.
  • Adolescents are more exposed, because growth adds an energy cost that is often ignored.
  • A vanishing period, chronic fatigue and recurring injuries are signals to listen to, not to hide.
  • You monitor and bring it to a professional: you don't self-diagnose.

What is the difference between the Female Athlete Triad and RED-S?

The Triad described three problems — energy, periods, bones — while RED-S describes a syndrome affecting the whole body. Same starting phenomenon, read more broadly.

For years the focus was the Female Athlete Triad: the combination of low energy availability, menstrual dysfunction and reduced bone health (De Souza et al., Female Athlete Triad Coalition, 2014).

In 2014 the International Olympic Committee broadened the picture with RED-S, recognising that energy shortfall affects not only bones and the cycle but also the immune system, metabolism, mood, cardiovascular health and — yes — performance (Mountjoy et al., 2014). In 2023 the consensus was updated with new risk-assessment tools (Mountjoy et al., 2023).

The underlying message is counter-intuitive but crucial: energy shortfall can reduce performance, not raise it. The idea "eat less, weigh less, go faster" is, in the long run, a dead end.

What does "low energy availability" mean?

It means that, after covering the cost of training, the body doesn't have enough energy left to run everything else — periods, bones, immune system, recovery. It is not a judgement about food, nor a diagnosis of an eating disorder: it's a balance that doesn't add up, and it can happen without anyone noticing.

Energy availability is, put simply, the energy left for the body to function after subtracting what's spent in exercise. When this margin is too low — from too little food, too much training, or both — the body enters "saving mode".

An important, often misunderstood point: an eating disorder is not required for it to happen. Many athletes reach low energy availability without realising it, simply because no one explained how much growth and training increase their needs.

Why are teenage female athletes more exposed to RED-S?

A 13-14-year-old body is still growing: building bone, tissue, mass. Growth is itself energetic work. Add several training sessions a week and the margin thins fast.

Yet research struggles to keep up: only 6% of sport-science studies are conducted exclusively on women (Cowley et al., 2021, Invisible Sportswomen). Much of what we know is inferred from adult athletes, and transferability to younger ones is limited. All the more reason to observe the individual athlete rather than apply population averages.

What are the signs of RED-S to know?

None of these signs, alone, "makes a diagnosis". But together they deserve attention and, if they persist, a professional's opinion:

Here lies a cultural problem. In a study of 90 adolescent athletes, 44% believed losing the period was a normal response to high load (Armento et al., 2021). Misinformation starts early: normalising a warning sign is exactly what delays action.

How is RED-S risk assessed, and by whom?

There are tools designed to flag who needs a closer look, not to label. The best known:

One principle guides them all: they are filters, not verdicts. Clinical assessment belongs to doctors, dietitians and specialists — never to an app or a coach.

What can the people around the athlete actually do?

Four things, split by role — and none of them requires making a diagnosis. The common thread is taking away the burden of the athlete having to explain herself alone.

BAB's role

BAB does not diagnose and does not replace a doctor. It helps the athlete recognise her own signals in private — energy, mood, recovery, sleep — over time, and reflects them back as a personal mirror. To clubs it offers only aggregated, anonymous signals: never an individual's health data. Because understanding your own body should never cost you your privacy — and because a signal heard in time is worth more than a thousand measurements collected too late.

Sources

This article is for informational purposes and does not constitute medical advice. If signals persist, consult a healthcare professional.

What is RED-S?

RED-S (Relative Energy Deficiency in Sport) is a syndrome caused by low energy availability: when the energy taken in through food isn't enough to cover what's spent in training and growth, the body reduces functions such as the menstrual cycle, bone health and recovery. It is described in the International Olympic Committee (IOC) consensus statement (2014, updated in 2023).

Is losing your period because you train hard normal?

No. A missing or irregular period is not a sign of good training but a possible signal of low energy availability that deserves attention. In a study of 90 adolescent athletes, 44% mistakenly believed that losing the period was a normal response to high training loads (Armento et al., 2021).

Can an app diagnose RED-S?

No, and no one should try to via an app. RED-S is assessed by healthcare professionals. Tools like BAB help an athlete observe her own signals day by day and, if she wishes, bring them to a trusted adult or doctor: monitoring is not diagnosing.

What are the early signs of RED-S in a teenage athlete?

No single sign is diagnostic, but these deserve attention if they persist: an absent or irregular period after menarche with no other explanation; fatigue that doesn't lift with normal recovery; recurrent overuse injuries, including stress fractures; performance dropping despite increased effort; disturbed sleep, low mood and frequent illness. These are the domains described in the IOC consensus (Mountjoy et al., 2023). If they persist, the next step is a healthcare professional, not self-diagnosis.

What's the difference between the Female Athlete Triad and RED-S?

The Triad describes three linked elements: low energy availability, menstrual dysfunction and impaired bone health (De Souza et al., 2014). In 2014 the International Olympic Committee widened the frame with RED-S, recognising that energy deficiency also affects the immune system, metabolism, mood, the cardiovascular system and performance itself (Mountjoy et al., 2014), updating it in 2023 with new risk-assessment tools. RED-S doesn't replace the Triad: it contains and extends it, and applies across sexes.

How is RED-S risk assessed?

With screening tools, designed to flag who merits further assessment rather than to label anyone: the LEAF-Q questionnaire, validated across gastrointestinal symptoms, menstrual function and injuries (Melin et al., 2014); the Female Athlete Triad Cumulative Risk Assessment, a points-based score; and REDs CAT2, the traffic-light tool from the 2023 IOC consensus. They are filters, not verdicts: clinical assessment belongs to doctors, dietitians and specialists — never to an app or a coach.