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Relative Energy Deficiency In Sport (RED-S): A Guide For Runners
Feeling tired after a demanding run is normal. Feeling persistently drained, getting injured repeatedly or watching your performance decline despite consistent training deserves a closer look. Sometimes the issue is that the body is not getting enough energy to support both running and normal health.
Relative energy deficiency in sport, usually shortened to RED-S, describes a pattern of health and performance problems associated with problematic low energy availability. It can affect recreational runners as well as competitive athletes, and it can happen without deliberate dieting. Understanding the warning signs can help you seek support before the problem gets worse.
What Is Relative Energy Deficiency In Sport?
Energy availability is the energy left for your body to function after accounting for the energy used in exercise. Your body needs that energy to maintain bones and other tissues, regulate hormones, support your immune system and handle everyday life. If food intake is too low for your training demands, the energy available for those functions can fall short.
Low energy availability and RED-S are related, but they are not interchangeable. A brief mismatch between eating and training does not mean you have developed the syndrome, and feeling hungry after a run is not a diagnosis. A clinician looks for a broader pattern of health and performance effects rather than relying on one symptom or a calorie calculation.
How Can Runners Develop RED-S?
Sometimes training increases while eating habits stay the same. You might add a run, extend your weekend mileage or begin training for a marathon without making room for more food. An early session followed by a missed breakfast, a busy day with little lunch or a poor appetite after a hard workout can make it difficult to catch up.
Low energy availability can also be linked to attempts to lose weight, strict food rules or an eating disorder. Not everyone affected has an eating disorder, and lack of time, money or access to suitable food can also play a part. The cause matters because support needs to address the runner’s circumstances as well as their food intake.
What Are The Warning Signs For Runners?
There is no single symptom that proves a runner has RED-S. Possible clues include persistent tiredness, performance that declines despite training, repeated illness, frequent injuries, changes in mood and a struggle to recover between sessions. Bone stress injuries deserve particular attention because problems with bone health can become serious if you continue to run through pain.
For people who menstruate, periods becoming irregular or stopping can be another warning sign. RED-S can also affect male runners, whose warning signs may include persistent fatigue, declining performance and repeated injuries. Weight loss may occur, but appearance and weight alone cannot tell you whether your body has enough energy for its needs.
These signs can have many other causes, including illness, iron deficiency or training that has increased too quickly. Their value is in prompting a proper assessment, especially when several appear together or do not improve. Do not assume every disappointing run is a nutrition problem, but do not dismiss a persistent pattern as something all runners have to endure.
Why Does RED-S Matter Beyond Running Performance?
A runner might first notice that familiar paces feel harder or that recovery is taking longer. The potential effects reach beyond race times: problematic low energy availability can affect hormonal function, bone health, immune function and mental wellbeing. The pattern and severity vary between individuals, so two runners may not experience the same symptoms.
Trying to train harder through the problem can make it more difficult to recover. If you have pain in one specific spot that may be coming from a bone, especially if it worsens with running or begins to affect walking, stop running and arrange a medical assessment. Getting help early gives you a better chance of addressing the underlying issue and protecting your health.
How Is RED-S Diagnosed?
A clinician considers the whole picture: symptoms, medical history, training, eating patterns and possible alternative explanations. Depending on the situation, assessment may include questions about menstrual or hormonal health, examination for injuries and relevant tests. There is no home test, single blood result or number on the scales that can confirm or rule out RED-S.
The International Olympic Committee has developed a clinical assessment tool to help qualified professionals evaluate risk and guide decisions about training and competition. Assessment is best led by a clinician familiar with sports medicine, with support from a registered sports dietitian where possible. The aim is to identify the problem accurately and make a plan suited to the person, rather than attach a label based on an online checklist.
What Does Recovery Involve?
Addressing insufficient energy intake is central to care. A sports dietitian can help a runner eat enough across the day and around training, while a clinician may recommend reducing or pausing exercise for a period depending on the symptoms and risk. Treatment may also need to address a bone injury, hormonal changes, an eating disorder or other health concerns.
Recovery does not follow a single timetable, and adding a snack is not a substitute for assessment if symptoms are significant. Follow the plan agreed with your healthcare team and let them advise when to increase running again. If restrictive eating or anxiety about food is involved, psychological support may be an important part of that plan.
How Can You Reduce The Risk?
As your running grows, check whether your meals and snacks have grown with it. Regular food across the day, something practical after a run and a plan for long training days can help you avoid repeatedly missing opportunities to eat. Fuel during longer runs has a role, but gels alone cannot make up for too little food in the rest of your routine.
Take changes in health seriously instead of treating them as proof that you need more discipline. A missed period, recurring bone pain or weeks of unusual fatigue are reasons to seek advice, not badges of hard training.
When Should You Ask For Help?
Speak to a healthcare professional if several warning signs persist, or if you have concerns about restrictive eating. Arrange an assessment promptly if you suspect a bone stress injury. Tell the clinician about your training and food routine so they can consider RED-S alongside other possible causes.
RED-S can affect runners at different levels and of any sex. You do not need to wait until your weight changes or your running stops completely before asking for help. The goal is to support both your health and the running you want to keep enjoying.
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