The Hidden Risks of Under-fuelling: Understanding RED-S

If you enjoy staying active, you probably understand the importance of eating well. But did you know that not fuelling your body properly for your activity levels can lead to serious health issues? Relative Energy Deficiency in Sport (REDs) is a condition caused by a chronic mismatch between the energy you take in through food and the energy you use through exercise and daily life.

While RED-S is often associated with competitive athletes, it can affect anyone leading an active lifestyle—whether you’re training for a triathlon, hitting the gym a few times a week, or simply exercising to feel good.

What is REDs?

RED-S occurs when your body doesn’t get enough energy to support both your exercise routine and the essential functions it performs every day. This includes unconscious tasks like maintaining hormone balance, repairing muscles, and strengthening your immune system.

When energy intake is consistently too low, your body is forced to prioritise vital functions, like keeping your heart beating, over things like bone growth and muscle repair. In the short to medium term, this can lead to symptoms like fatigue, recurring illnesses, and slower recovery from injuries. In the longer term, it can lead to serious health complications, affecting nearly every system in your body, including bone, heart, lung, and reproductive health.

Who’s at Risk?

Any active person can develop RED-S, but it often goes unnoticed at first. For people balancing busy lives with regular exercise, it’s easy to underestimate how much energy your body really needs.

RED-S isn’t just about doing too much; it’s also about not eating enough to meet your body’s demands. Sometimes, this happens unintentionally—for example, by skipping meals, dieting, or simply underestimating how much fuel you need.

RED-S isn’t just about over-exercising—it’s also about not fueling your body enough to meet its energy needs. For some, this happens intentionally, like through dieting, skipping meals, or restricting food groups. For others, it’s simply underestimating how much energy your body actually requires.

Could This Be You? 

Spotting the early signs of RED-S is crucial to prevent it from taking a toll on your health and fitness. Common signs to look out for include:

• Persistent tiredness or low energy

• Feeling cold more often than usual

• Changes in mood or difficulty concentrating

• Missing or irregular periods among females

• More frequent colds, injuries, or slow recovery after workouts

If your fitness routine is leaving you feeling drained instead of energised, it might be worth taking a closer look at your nutrition and energy balance.

Why Does It Matter?

The effects of RED-S go beyond feeling tired or unwell. Without enough fuel, your body may lose bone density, increasing the risk of stress fractures or osteoporosis later in life. Hormonal disruptions can also impact fertility and overall health and well-being. 

Even in the short term, under-fuelling can take the joy out of staying active. Constant fatigue, recurring injuries, or a lack of progress can leave you feeling frustrated and unmotivated.

How to Stay Fuelled

The good news is that RED-S is preventable, and even if you notice signs, you can take steps to address it. Here’s how:

• Eat enough to match your energy needs. Remember, your body requires energy for more than just exercise. Everyday activities like walking, thinking, and even sleeping all burn calories.

• Balance your meals. Include carbohydrates for energy, protein to support muscle recovery, and healthy fats for hormone health and sustained energy.

• Refuel after workouts. Aim to eat within 30 minutes of exercising. Options like a smoothie, toast with nut butter, or an energy bar can help kickstart recovery.

• Pay attention to your body. Unusual fatigue, repeated injuries, low moods, menstrual changes, and erectile dysfunction are signs that something might be off. Don’t ignore them.

Take the Long View

Staying active is one of the best things you can do for your health, but only when you give your body the energy it needs to keep up. By prioritising proper nutrition and tuning into your body’s signals, you can avoid the risks of under-fuelling and enjoy a strong, healthy, and active lifestyle for the long haul.

Head to Project RED-S at www.red-s.com for more information and advice.

Words by Pippa Woolven, founder and CEO of Project RED-S.