What is RED-S, and why should I take it seriously?

RED-S stands for Relative Energy Deficiency in Sport.

It is one of those terms that can sound a bit academic, but the concept is actually very practical.

It means the body does not have enough available energy to support both training and normal biological function.

In simple terms:

You are asking a lot from the body, but not giving it enough back.

That mismatch can affect health, performance, recovery, hormones, bone, immunity, mood and injury risk.

And importantly, RED-S is not just a problem for elite athletes.

It can affect runners, cyclists, triathletes, dancers, gym athletes, school athletes, recreational exercisers, endurance athletes, people trying to lose weight, and people who simply train hard while under-fuelling.

The International Olympic Committee defines RED-S as a syndrome of impaired physiological and/or psychological functioning experienced by female and male athletes exposed to low energy availability.

That matters.

Because RED-S is not just about food.
It is not just about periods.
It is not just about being thin.
And it is definitely not just a “female athlete problem”.

It is a whole-system issue.

What is low energy availability?

Energy availability is the energy left over after exercise for the body to run its normal functions.

Training costs energy.
Life costs energy.
Hormones cost energy.
Bone remodelling costs energy.
Immune function costs energy.
Repair costs energy.

If training load is high and intake is too low, the body starts making compromises.

At first, those compromises can be subtle.

You might feel tired.
You might not recover as well.
Your mood may shift.
You may get injured more often.
Performance may plateau.
Sleep may worsen.
You may feel cold.
You may lose your menstrual cycle, or it may become irregular.
You may develop bone stress injuries.

This is the body trying to survive the maths.

Why RED-S matters for bone

This is where RED-S becomes very relevant to Bone Health Studio.

Bone is not just a hard structure sitting there doing nothing. It is living tissue. It remodels. It adapts. It responds to load, hormones, nutrition and recovery.

If an athlete is under-fuelled, the bone may not respond properly to training load.

That is a major issue.

Especially in endurance sport, where athletes often do a lot of repetitive loading but may not do enough resistance training, may not eat enough, and may be operating close to the edge for long periods of time.

RED-S is associated with negative health and performance consequences, and the IOC consensus highlights bone health as one of the key systems affected by low energy availability.

This is why recurrent stress reactions or stress fractures should never be viewed as “just bad luck”.

Sometimes they are the signal.

RED-S can hide behind discipline

This is the tricky part.

In sport, many RED-S behaviours can initially look like commitment.

Training more.
Eating “clean”.
Staying lean.
Pushing through fatigue.
Never missing sessions.
Doing extra cardio.
Ignoring soreness.
Controlling food tightly.

None of these things automatically mean RED-S.

But in the wrong context, they can become part of the problem.

And the athlete may not realise it, because the early rewards can be seductive. They may get lighter. They may get faster for a while. They may feel in control.

Until they do not.

Then comes fatigue, flat performance, injury, hormone disruption, low mood, poor recovery, illness, or bone stress injury.

The problem is not discipline.

The problem is when discipline is pointed in the wrong direction.

RED-S affects males too

This needs to be said clearly.

RED-S affects males.

Historically, this conversation often sat under the “Female Athlete Triad”, which focused on low energy availability, menstrual dysfunction and low bone mineral density. That model was important, but it did not capture the full picture.

RED-S is broader. It recognises that low energy availability can affect multiple body systems and can occur in both females and males.

In male athletes, RED-S may show up as low libido, fatigue, low testosterone, poor recovery, recurrent injury, irritability, low mood, reduced performance or bone stress injury.

So if you are a male endurance athlete with recurring bone stress problems, persistent fatigue, or unexplained performance decline, RED-S should be on the radar.

Why gym work matters

Resistance training does not “fix” RED-S by itself.

Let’s be clear about that.

If the athlete is under-fuelled, the first priority is to correct the energy mismatch. This often requires input from a sports dietitian and, at times, a medical team.

But resistance training can play an important supporting role.

It can help build:

• bone loading capacity

• muscular strength

• tendon capacity

• movement control

• robustness

• confidence

• better tolerance to training load

For endurance athletes, this is huge.

Many runners and cyclists are incredibly fit but not always structurally strong. They may have a big engine, but the chassis is underbuilt.

That is not a criticism.

It is just a training gap.

At Bone Health Studio, our role is to help fill that gap safely and intelligently.

When should you take RED-S seriously?

Take it seriously if you have:

• recurrent stress fractures or stress reactions

• menstrual irregularity or loss of menstrual cycle

• unexplained fatigue

• repeated illness

• declining performance despite training hard

• poor recovery

• low mood or irritability

• low libido

• restrictive eating patterns

• fear around food or weight gain

• persistent soreness

• history of disordered eating

• high training load with low food intake

You do not need every sign.

One or two may be enough to ask better questions.

RED-S is not a character flaw

This is important.

RED-S is not weakness.
It is not laziness.
It is not lack of discipline.

Often, it is the opposite. It appears in highly driven people who are trying very hard to be good at what they do.

But the body does not care about intention.

It cares about physiology.

If the energy is not there, eventually the system will downregulate or break down.

The goal is not to train less forever

Many athletes fear that if RED-S is identified, they will be told to stop training completely.

Sometimes training does need to be reduced, especially if there is significant medical risk or bone stress injury. But the long-term goal is not to make the athlete smaller, softer or less competitive.

The goal is to help them become healthier and more durable.

Fuel better.
Recover better.
Lift better.
Adapt better.
Perform better.

That is the direction.

RED-S should be taken seriously because it is not just about today’s training session.

It is about the athlete’s future body.

And if you want that body to keep giving you performance, freedom and enjoyment, you need to give it enough back.

References

Mountjoy M et al. 2023 International Olympic Committee’s consensus statement on Relative Energy Deficiency in Sport — REDs. British Journal of Sports Medicine, 2023.

Mountjoy M et al. IOC consensus statement on relative energy deficiency in sport — RED-S: 2018 update. British Journal of Sports Medicine, 2018.

International Society of Sports Nutrition. Protein and exercise position stand; relevant to fuelling and muscle adaptation in exercising individuals.