RED-S stands for Relative Energy Deficiency in Sport. It was introduced by the International Olympic Committee in 2014, evolving from the earlier concept of the Female Athlete Triad, which focused only on disordered eating, menstrual issues, and bone health.(2) RED-S take things further, recognising that anyone of any gender can be affected, and that low energy availability impacts multiple systems in the body. The 2018 IOC update recognised that RED-S can affect nearly every bodily system - including cardiovascular, gastrointestinal, and psychological health - not just reproductive or skeletal health.(3)

At the heart of RED-S is low energy availability: when the body doesn’t have enough energy (calories) left over after exercise to support everyday functions like hormone production, brain function, immunity, or bone maintenance. And when this goes on for too long, the body starts cutting corners to protect its most vital systems - often at a cost to long-term health.(4)

But.. I’m not an elite athlete?

While elite athletes have carefully tailored nutrition plans, recovery schedules, physiotherapy, and sports science teams, most of us are doing the opposite. We’re squeezing in workouts between lectures or jobs, skipping meals, over-caffeinating, and calling it ‘balance’. You might be running three times a week, going to a spin class, or walking 20,000 steps a day - all while eating light meals, multitasking, and staying up late to finish assignments. It’s easy to fall into low energy availability without noticing. Especially when it’s all praised as discipline, hustle or self-care.(5)

• Constant tiredness, even with enough sleep

• Missed or irregular periods (for females)

• Low libido or hormonal disruptions (in all genders)

• Poor workout recovery, frequent injuries

• Mood changes, anxiety, or difficulty concentrating

• Weakened immunity — getting sick often

• Digestive issues like bloating or constipation

• Plateauing or declining performance

In one study, even mild energy deficits over time led to increased fatigue, lower mood, impaired cognition and disrupted sleep — all of which can make everyday life harder.(4) And these are just the early signs. Over time, RED-S can lead to low bone density, stress fractures, infertility and longer-term metabolic issues.(3,7)

Because it often doesn’t “look” like a problem. Many people with RED-S are in normal weight ranges or even appear fit and healthy. (8) In some sports and fitness circles, the early warning signs - like low appetite, exhaustion, or missing periods, are wrongly brushed off as just ‘part of training’.(9) Plus, RED-S doesn’t always stem from intentional restriction. It might simply be unintentional under-fuelling: skipping meals because you’re busy, eating light to ‘stay healthy,’ or exercising more than you realise without adjusting your intake.(1)

Why does it matter?

You don’t have to be a professional athlete to have high energy needs. In fact, being a student or young adult who trains regularly, and lives a fast-paced lifestyle, can create a perfect storm for RED-S. Ignoring RED-S doesn’t just affect your workouts. It can impact your mental health, immune system, bones, digestion and future fertility. And because it creeps in slowly, it often goes unrecognised until it’s had serious effects.(3,5)

The good news is that RED-S is reversible, especially when caught early. The first step is making sure you’re eating enough to meet your body’s energy demands; this means fuelling regularly throughout the day with balanced meals that include carbohydrates, fats, and protein, and not skipping snacks when you’re active or busy.(11) Rest is just as important; full rest days are essential for recovery and preventing burnout and taking them should never be seen as laziness.(11,3)

It’s also helpful to monitor your body’s signals -  for example, your menstrual cycle can be a key sign of hormonal health, and irregularities like missed periods shouldn’t be ignored.(6) More broadly, it’s important to question the mindset that being busy or ‘always on’ means you don’t need proper fuel. High-achieving, driven people whether students, gym-goers, or casual runners are just as susceptible to RED-S as elite athletes.

Finally, don’t hesitate to seek support. If you’re noticing ongoing fatigue, hormonal changes, or a drop in performance, speak to a GP or registered dietitian with experience in performance nutrition. Early recognition and intervention can make a big difference and may prevent more serious health consequences down the line.(3)