Energy Availability and RED-S

Why eating enough is the foundation of health and performance

Training hard only works if you fuel enough to support it. When you consistently take in less energy than your body needs for exercise plus everyday functions, both health and performance suffer. This is called low energy availability, and it is more common than most people realise, particularly in active women. This guide is for awareness, not diagnosis.

What is energy availability?

Energy availability is the energy left for your body’s basic functions after training. If you burn 1000 kcal in sport and eat 2500 kcal, only 1500 kcal is left for "living". It is measured per kilogram of fat-free (lean) mass.

It is not the same as low intake, or weight loss

You can eat a lot and still be low, if you train a lot.
Common causes: raising training without raising food, no time to plan meals, or cutting out food groups.
Weight can stay stable. The body conserves energy by shutting down non-vital systems, such as the menstrual cycle, so the scales can hide the problem.

Why it matters

Sustained low energy availability is the main driver of Relative Energy Deficiency in Sport (RED-S). It can affect nearly every system in the body, sometimes seriously, and even short periods can cause disruption. Effects include:

Health

Missed or irregular periods (in women)
Weaker bones, higher stress-fracture risk
Hormonal disruption and lower metabolic rate
Reduced immunity

Performance

Poor recovery and more injuries
Reduced muscle protein synthesis
Low mood and concentration
Stalled or declining performance

The foundation

Fuel to match your training, not just your appetite.
Eat regularly and plan food around your sessions.
Do not cut whole food groups without a good reason.
If in doubt, seek qualified help early rather than pushing through.

Where to learn more: the NHS, the British Dietetic Association (BDA) and Sport and Exercise Nutrition register (SENr), the British Association of Sport and Exercise Medicine (BASEM), and the IOC RED-S guidance. If any of this resonates, please speak to your GP or a sports dietitian.

This leaflet is general nutritional guidance and awareness for education only. It is not medical advice, diagnosis or treatment. RED-S is a medical condition that needs assessment by a qualified professional. Always speak to your GP or a registered dietitian, particularly if you have missed periods, recurring injuries, or a health condition.