Recognising Under-Eating: How to Fuel for Peak Performance
Are You Fuelling Your Body Enough?
Under-eating is more common than most female endurance athletes realise. It sneaks up in different ways—whether you’re trying to lose fat, struggling with appetite after long sessions, or simply not eating enough to match your energy output.
As women training for running, triathlon, or endurance goals, we often focus on hitting the sessions, ticking off the miles, and progressing in the gym. But what happens when you’re not fuelling enough to support your performance? Fatigue creeps in. Your recovery slows down. Performance plateaus or drops. And worst of all, your health can take a hit.
This guide will help you recognise the warning signs of under-eating, understand its impact on performance and health, and take actionable steps to fix it.
The Signs You’re Under-Eating
If you’re training regularly for running, triathlon, or endurance sports, but feeling sluggish, sore, or just ‘off’, under-fuelling might be the cause. Here are the key signs to look out for:
1. Reduced Performance & Training Plateaus
Your paces feel harder than they should.
You’re not progressing in strength sessions.
Your endurance feels like it’s declining instead of improving.
Increased perception of effort – what used to feel manageable now feels exhausting.
2. Persistent Fatigue & Low Energy
Constant lethargy, even after rest days.
Struggling to get through daily life, let alone training.
Waking up already feeling exhausted.
Afternoon crashes despite eating regularly.
3. Frequent Illness & Injury
Regular colds, flu, or infections – your immune system is struggling.
Increased injury risk, stress fractures, or niggling pains that don’t go away.
Slow recovery from workouts – soreness lasts longer than normal.
4. Mood Swings, Irritability & Anxiety
Feeling snappy, emotional, or anxious without a clear reason.
Losing motivation to train – the sport you love feels like a chore.
Increased stress or brain fog – struggling to focus on work or life.
5. Menstrual Irregularities & Hormonal Imbalances
Missed or irregular periods (a huge red flag!).
Symptoms of low oestrogen, such as brittle nails, dry skin, or hair thinning.
Low libido, disrupted sleep, or digestive issues – signs your body is under stress.
RED-S: When Under-Eating Becomes More Serious
Under-eating can escalate into Relative Energy Deficiency in Sport (RED-S), a condition where low energy availability impacts not just performance, but long-term health.
How RED-S Affects Athletes
Decreased endurance – struggling to complete sessions.
Muscle loss & weakness – feeling ‘flat’ or losing power.
Poor bone health – increased risk of stress fractures.
Low iron levels – leading to fatigue and anaemia.
Your body sees training as a ‘luxury’ – and if it doesn’t have enough fuel, it will start shutting down non-essential functions (like your menstrual cycle) to conserve energy.
Ignoring the signs won’t make you stronger – it will make you burn out.
How to Tell If You’re Under-Fuelling
If any of the above signs feel familiar, it’s time to take a closer look at your nutrition. Here’s how:
1. Track Your Intake & Training Load
Keep a food diary for a few days to assess what you’re eating vs. what you’re burning.
Are you skipping meals, under-eating carbs, or cutting portions?
2. Monitor Energy Levels & Recovery
Are you constantly fatigued, sore, or not recovering well from training?
Do you feel hungry all the time but ignore it?
3. Use a Menstrual Health Check
If you miss two periods in a row, it’s time to take action.
4. Work with a Nutrition Coach or Dietitian
If you’re unsure how much to eat for your sport, get professional guidance to avoid RED-S and optimise performance.
How to Fix Under-Fuelling & Recover Stronger
The fix isn’t just ‘eat more’ – it’s about fuelling smarter to train, perform, and recover.
1. Prioritise Carbohydrates
Carbs are your body’s preferred energy source for endurance training.
Eat carbs before & after training – don’t train fasted.
Include wholegrains, fruits, starchy veg, and easy-to-digest carbs (rice, oats, sourdough).
2. Increase Protein for Recovery
Aim for 1.6-2.2g of protein per kg of body weight to support muscle repair.
Add lean proteins, fish, dairy, tofu, beans, or protein shakes.
Spread protein evenly across the day – not just one big serving at dinner.
3. Stop Skipping Fats
Fats are essential for hormone balance & recovery.
Eat avocados, nuts, seeds, olive oil, and oily fish for healthy fats.
Avoid excessive restriction – your body needs at least 20-30% of total intake from fats.
4. Eat Regularly & Listen to Hunger Cues
Have 3 main meals & 2-3 snacks to keep energy levels stable.
If you’re always hungry, you need more food – don’t ignore it.
5. Recover Properly Post-Training
Within 30-60 minutes post-workout, refuel with:
Carbs (oats, rice, banana, toast, cereal).
Protein (eggs, yogurt, protein shake).
Electrolytes & hydration – don’t just drink water, replenish sodium too.
6. Reduce Stress & Improve Sleep
Chronic stress and poor sleep increase cortisol, which worsens recovery and increases cravings.
Sleep 7-9 hours per night.
Reduce caffeine, wind down properly, and eat enough before bed.
Final Thoughts: Fuel to Perform, Not Just to Train
If you’re struggling with low energy, performance dips, or irregular periods, under-eating might be the root cause. The solution isn’t just “eat more” – it’s learning how to fuel smarter so you can train, recover, and feel strong in your sport.
✔ Listen to your body – low energy is NOT normal.
✔ Prioritise carbs, protein & healthy fats.
✔ Track your intake & work with a coach if needed.
✔ If your period is missing – take action.
Your performance, health, and longevity as an athlete depend on it.
Ready to take control of your fuelling?
At Pretty Strong Coaching, we help busy women like you train smarter, fuel better, and achieve your running and triathlon goals - without burnout or overwhelm. If you're ready for personalised coaching that fits into your life, let's chat!
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