More Than Miles: How to Fuel, Recover and Build Endurance That Lasts
Ultra running demands more than training. Learn how nutrition, recovery and energy availability can help runners avoid REDs and build endurance that lasts.
Ultra running asks a lot from the body. Training matters, but so do nutrition, recovery and the ability to listen to your body.
Ultra runners are usually people who are resilient, curious and willing to explore what the human body can do. The sport asks a lot: long training days, early starts, late finishes, challenging terrain, unpredictable weather, and the willingness to push our limits again and again.
When it comes down to it though, the strongest runners aren’t simply the ones who can do the most. They’re the ones who can adapt the best and who prioritise recovery, nutrition, and consistency.
To build endurance that lasts, we need to think about the balance between training, nutrition, recovery and life. That’s where understanding REDs can make a real difference.
What is REDs?
REDs, short for Relative Energy Deficiency in Sport, is a clinical condition caused by a chronic mismatch between energy intake and expenditure. When the energy demands of training and other life stressors (work, studies, parenting, travel, etcetera) are repeatedly greater than the energy consumed through nutrition, the body starts to struggle with low energy availability.
If maintained over a period of weeks or months, low energy availability can lead to REDs, which adversely impacts almost every aspect of health and performance. This includes hormones, bone health, immunity, cardiovascular health, fertility, recovery, speed and endurance.
At first, the signs can be subtle: feeling a little more fatigued than usual, slower recovery, changes in mood, poor sleep, frequent illness, recurring injury or a general loss of enthusiasm for training. These are things athletes, and ultra endurance athletes in particular, sometimes normalise as part of being “committed”. You might still be training, you might still be racing, you might even be praised for being disciplined or dedicated, but underneath the surface, the body might be struggling to keep up.
Why REDs Matters for Ultra Runners
REDs can affect anyone, regardless of gender, body shape, age, speed or experience level. You don’t need to look a certain way to be affected. Many athletes with REDs look “fine” from the outside, which is one reason it can be missed.
For ultra runners, this matters because training loads can be high, energy demands can be huge, and the culture of endurance sport can sometimes celebrate toughness at the expense of recovery. But the very nature of the sport requires endurance, strength, patience and consistency, all of which rely on adequate energy availability.
Signs your body may need more support
REDs presents differently from one athlete to another, but common signs include:
- Persistent fatigue or feeling unusually flat in training
- Frequent illness or slow recovery from colds and infections
- Recurrent injuries, including bone stress injuries
- Difficulties getting to sleep or waking during the night
- Feeling cold more often than usual
- Loss of motivation, low mood or increased anxiety around training and food
- Digestive issues
- Plateauing or declining performance despite working hard
- Irregular or missing periods
- Reduced frequency of morning erections
- Reduced libido
- Increased preoccupation with food, body composition or feeling the need to“earn” food through training
One missed session is not a crisis and one tired week does not mean you have REDs, but if several of these signs are present, or if something feels off for longer than expected, it’s well worth paying attention.
Practical ways to protect yourself from REDs
The good news is, REDs is entirely avoidable. When it comes to nutrition and recovery there are plenty of things you can do to protect yourself from the likelihood of an energy deficit creeping in. Perfection is not the goal, but consistent habits can make all the difference.
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Eat enough across the whole day
Your body requires regular energy throughout the day, especially when you are training for an event. Long periods of under-fuelling within a day, for example training early, delaying breakfast, skipping lunch or leaving big gaps between meals, may place extra stress on the body, even if total daily intake looks reasonable on paper.
Before training, give your body accessible energy. During longer sessions, practise taking on carbohydrates and fluids. After training, prioritise a proper recovery meal or snack that includes carbohydrate, protein and enough overall energy. A useful rule of thumb is to try to eat something every 2 to 4 hours.
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Carbohydrates are key
Carbohydrates are our bodies main fuel source. Research suggests that low carbohydrate availability may overlap with, contribute to, or in some cases mimic some of the effects of low energy availability, even when total calorie intake isn’t obviously low. This means an athlete may be eating a reasonable amount overall, but still not giving their body enough accessible carbohydrate to support training quality, recovery, hormones, immune function and adaptation.
For ultra runners, the question is not just “Am I eating enough?” but also “Am I giving my body enough carbohydrate at the times it needs it most?”
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Respect rest days
Rest days are not days to let your nutrition slide. Rest is when adaptation happens. Eating well on easier days supports repair, hormones, immune function and readiness for the next session.
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Watch for patterns
Everyone has off days, but repeated illness, injury, mood changes, disrupted sleep or declining performance are useful signals. Keeping a simple note of energy, sleep, menstrual cycle if relevant, mood and injuries can help you spot trends early.
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Be careful with body composition goals
Ultra running already places high demands on the body. Chasing a lower weight or leaner body while training hard can increase REDs risk, especially if done without professional support. Lighter is not always faster. Under-fuelled athletes are often less adaptable, less robust and more vulnerable to injury.
REDs recovery is possible
For athletes who are experiencing REDs, recovery can feel frustrating – especially if it involves reducing training, eating more, resting more or changing long-held beliefs about performance and/or body composition. But this shouldn’t be the end of your athletic identity. In fact, it’s often the beginning of a healthier and more sustainable one.
Many athletes return from REDs stronger, wiser and more connected to their bodies. They learn how to train with themselves rather than against themselves. They discover that health and performance are not enemies. In the long run, they are partners.
If something feels off, don’t wait until performance drops or your body forces you to stop. Speak to someone you trust and seek help from a qualified health professional, sports doctor or sports dietitian.
A better kind of endurance
Ultra running is about more than suffering. It is about exploration, community, courage and pushing limits. To stay in the sport, we need bodies that are supported, not depleted. We need to celebrate athletes who fuel well, rest well and speak honestly when things are not right. We need to move away from the idea that doing less is always failure, and towards the understanding that smart athletes adapt.
A REDs resource for ultra runners
Ultra X has partnered with Project REDs to create a toolkit for ultra runners, coaches and support teams. This resource explains what REDs is, why ultra runners may be at increased risk, the signs to look out for, and how athletes can fuel, recover and seek support earlier.
This resource is educational and is not a substitute for personalised medical advice.