RED-S in teenage girls: the three things every football parent should know

You have read about the signs. You have noticed some of them in your daughter. Now you want to know what the condition is actually called, what it does to her body, and what the medical team will say.

The medical name is Relative Energy Deficiency in Sport, or REDs. It used to be called the Female Athlete Triad. The condition was renamed in 2014 and the medical definition was updated again in 2023, and a further clinical update came in 2025. What it describes is the same thing: a teenage athlete who is burning more fuel than she takes in for long enough that her body starts switching off things it needs (periods, bone building, sleep, immune function) to save energy.

There are three things to understand. First, the condition is not really about food on her plate. Second, some of the damage may not fully recover, and adolescence is the window where that risk is highest. Third, recovery takes many months and the fix is a team of professionals working together, not one GP and not the parent guessing. If your daughter has REDs, this is a months-long conversation with a sports medicine doctor, a dietitian, and sometimes a psychologist. The earlier that team starts, the better.

This article gives you the bones of the condition and the words to use with the medical team. The full sign list is in the signs article. The period logistics are in the period article.

Thing one: it is the gap, not the plate

The first hard idea is that REDs is not about how much your daughter eats. It is about what is left after training has taken its share.

A teenage athlete in heavy training will burn through a lot of energy. If her body uses 30 calories per kilogram of muscle per day or less for everything outside of training, the body starts shutting down "non-essential" systems. The 30-number is the research benchmark used since the early 2000s, though the most recent 2025 clinical guidelines have started moving beyond a single fixed threshold because real bodies vary. The principle is the same: leave enough fuel after training, and the body works. Take too much fuel out, and the body protects the heart and lungs by cutting the periods and the bone building.

This is why a girl can eat what looks like a perfectly normal dinner and still be in deep deficit. Five trainings a week plus a game leaves a much bigger hole than three trainings and a rest day. Two cross-training sessions on top of football leaves a bigger hole again. Most parents look at the plate. The medical team looks at the plate and the training schedule together. So should you.

This means the fix is rarely just "feed her more." It is "feed her more and reduce the training load enough that the new food actually leaves fuel left over." If one happens without the other, the deficit stays.

Thing two: some of the damage may not fully recover

This is the hardest fact about REDs and the most important reason to act early.

Bone density is built in adolescence. More than 90 percent of peak bone mass is laid down by age 18. Once that window closes, what was not built then is not easily built later. So when a teenage girl spends 12 or 24 months in low energy availability with absent or irregular periods, the bone that should have been laid down during those months is missing. A 2008 study in Pediatrics of adolescent athletes with amenorrhoea found significantly lower bone density at the spine and whole body compared to athletes with regular periods, even though the two groups had similar muscle mass and trained at similar levels.

A more recent 2019 study of 390 elite teenage athletes found something even more sobering. Those who lost their periods during their teens carried lower bone density into their twenties, and the effect did not fully resolve when periods later returned. Some of the loss is permanent.

This is the part of REDs that does not respect "she will catch up later." The body has a window for bone building. If energy was not there during the window, the building did not happen, and the building does not get rerun.

This is also why hormone replacement is not a quick fix. A controlled trial that gave HRT to amenorrhoeic athletes for two years showed only a 1.5 percent improvement in spinal bone density. Hormones alone do not rescue the bone if the underlying fuel problem is not solved.

What it means for you as a parent: the months your daughter spends in REDs are months of permanent loss potential. Acting at month two is meaningfully better than acting at month six. Acting at month six is meaningfully better than acting at month twelve.

Thing three: recovery takes months, and the fix is a team

Recovery happens in a specific order, and each step takes its own time.

Energy availability first. Once she increases her intake and reduces her training load, her metabolism starts to climb back to normal in weeks. This is the fastest piece.

Periods second. Once energy is restored, the menstrual cycle can take anywhere from a few weeks to nine months to come back, depending on how long she was amenorrhoeic. A short period (a few months) of amenorrhoea can resolve in a few weeks of treatment. Two years of amenorrhoea can take nine months or more. The wider research range is well documented in intervention studies.

Bone density last. This is the slow one. The REFUEL randomised controlled trial in 2022 tracked exercising women with menstrual disturbance over 12 months of increased energy intake. Bone density improvements were measurable but modest. A case study of a former amenorrhoeic runner showed that lumbar spine bone density took six years to return to a normal range, even with focused treatment. Bone moves on its own clock.

The team that runs all of this is not one GP. The current Endocrine Society Clinical Practice Guideline on Functional Hypothalamic Amenorrhoea (the formal medical name for athletic amenorrhoea) explicitly calls for a multidisciplinary team: a sports medicine physician to coordinate, an Accredited Practising Dietitian with experience in adolescent athletes to set the food plan, and a mental health professional when there is disordered eating, anxiety, body image concerns, or any kind of restriction pattern. In Australia, the Australian Institute of Sport and the National Eating Disorders Collaboration published a joint position statement in 2020 setting out essentially the same team structure for high-performance and developing athletes.

So when your daughter is told she has REDs, the question is not how to fix this. The question is who is on her team, and how they coordinate. If the GP is treating only the period issue in isolation, or only the stress fracture in isolation, that is not a complete response. The condition is one thing affecting multiple systems, and it needs treatment that matches.

Some athletes also need a temporary reduction in training, not just an adjustment. The 2014 Female Athlete Triad Coalition Treatment guidelines and the 2023 IOC consensus both use a Red Light, Yellow Light, Green Light clinical assessment tool. Red means stop training and treat. Yellow means modify training while treating. Green means continue with monitoring. A sports doctor may use this exact framework to make the call.

What you say to the doctor: the language

These are the words the medical team will use, so you can follow along. You do not need to use them yourself.

REDs, or Relative Energy Deficiency in Sport. The current name. Replaced the older "Female Athlete Triad" model in 2014 and expanded in 2023.

LEA, or low energy availability. The underlying problem. Energy intake minus training expenditure, per kilogram of muscle.

FHA, or functional hypothalamic amenorrhoea. The medical name for the missing periods caused by low energy availability. The hypothalamus (a part of the brain) shuts down the hormones that drive ovulation.

Bone mineral density, often shortened to BMD. Measured by a DXA scan (dual-energy X-ray absorptiometry). The team may order one for your daughter to set a baseline. The Endocrine Society guideline recommends repeating the scan every 6 to 12 months while she is in treatment.

Z-score. The way bone density is reported for younger people. Z-score of zero is average for her age. Negative numbers mean less bone than average. The team will care about how the number moves over time more than the absolute value.

IOC REDs CAT2, or Red / Yellow / Green Light. The clinical assessment tool the sports doctor may use to decide whether your daughter trains, modifies training, or stops training during treatment.

If the doctor uses any of these terms and you do not follow, ask them to put it in plain English. A good doctor will be glad to.

What to do this week

Write down what your daughter has had: any period changes, any injuries, any sleep or mood changes, and what her training and game schedule actually looks like across an average week. Take that list to a GP and ask for the two referrals: a Sports and Exercise Medicine physician and an Accredited Practising Dietitian experienced with adolescent athletes. If the GP suggests treating the period or the injury alone, mention the words "REDs" or "low energy availability" and ask whether the bigger condition should be assessed.

This is a long road. Periods may come back in months. Bone may take a year or more. The right team running it from the start is the difference between a teenager who recovers fully and an adult who carries the deficit forward.

USI helps you spot the pattern. Your daughter's medical team makes the call.