Recognising Under-Eating: How to Fuel for Peak Performance
Under-eating is the single most common thing I see in female athletes. And almost nobody who's doing it knows they're doing it.
It sneaks up. You're training more. You're focused on hitting the sessions. You're maybe trying to "stay lean". You skip a snack. You under-fuel a long ride. You think the constant tiredness is normal because you train so much.
It isn't. It's a fuelling gap. And left long enough it tips into RED-S, missing periods, stress fractures, and a body that stops trusting you.
This is the post I wish every female endurance athlete read before they came to me with three missing cycles and a stress fracture.
The Five Signs You're Under-Eating
If you train regularly for running, triathlon, or any endurance sport but feel sluggish, sore, or generally off, work through these.
1. Constant fatigue and slow recovery
Waking up tired even after a full night's sleep
Soreness that hangs around longer than it used to
Afternoon energy crashes despite eating regularly
2. Underperforming in training
Workouts feel harder than they should
Hitting the same paces feels like a fight
Power, pace, or strength has plateaued or dropped
3. Frequent illness and injury
Catching every cold going round
Niggles that won't go away. Stress fractures. Tendon flare-ups
Recovery from sessions taking days, not hours
4. Mood swings, irritability, anxiety
Snapping at the people you love
The sport you love starts feeling like a chore
Brain fog. Trouble focusing at work or at home
5. Cycle changes and hormonal red flags
Missed or irregular periods (the biggest red flag of all)
Brittle nails, dry skin, hair thinning
Low libido, disrupted sleep, digestive issues
When Under-Eating Becomes RED-S
Relative Energy Deficiency in Sport (RED-S)
When low energy availability has been going on long enough, your body stops just adapting and starts shutting down. This is RED-S.
What it looks like in female athletes:
Decreased endurance. Sessions that used to feel easy feel impossible
Muscle loss. Strength dropping despite training
Poor bone health and increased stress fracture risk
Low iron, persistent fatigue, anaemia
Menstrual cycle stopping entirely
Your body sees training as a luxury. If it doesn't have enough fuel, it starts cutting non-essential functions to conserve energy. Your cycle is the first thing to go.
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 signs above feel familiar, work through this. Honestly.
Track your intake and training for 5-7 days. Not forever. Just enough to see if there's a gap between what you're putting in and what you're putting out.
Audit your energy and recovery. Are you constantly fatigued? Always sore? Snacking out of nowhere at 4pm? Hungry all the time but ignoring it?
Watch your cycle. If you miss two periods in a row, that's the moment to act. Not in three months.
Get professional input. A qualified Nutritionist who actually understands female endurance physiology will spot what you can't.
The 75/15/10 Rule guidebook
The simplest fuelling framework I give my clients. No tracking. No counting. Just the food categories that move the needle for female endurance athletes. Eat More, Eat Some, Eat Less. PDF, straight to your inbox.
How to Fix Under-Fuelling and Recover Stronger
The fix isn't just "eat more". It's eating smarter so you can train, perform, and recover properly.
1. Prioritise carbohydrates
Carbs are your body's preferred fuel for endurance. Stop fearing them.
Eat carbs before and after training. Don't train fasted as a habit.
Include wholegrains, fruit, starchy veg, easy-to-digest carbs (rice, oats, sourdough).
2. Increase protein for recovery
Aim for 1.6 to 2.2g per kg of bodyweight to support muscle repair and lean mass.
Lean meats, fish, dairy, eggs, tofu, beans, protein shakes
Spread it across the day, not just one big serving at dinner
20-30g per meal is the target
3. Stop skipping fats
Fats are essential for your hormones and your recovery. Cutting them too low is one of the fastest ways to lose your cycle.
Avocados, nuts, seeds, olive oil, oily fish
At least 20-30% of total daily intake should come from fats
4. Eat regularly. Listen to hunger
Three main meals, two to three snacks. Stable energy beats heroic restriction.
If you're hungry, you need more food. Stop ignoring it.
Pre-bed snack is not failure. It's recovery.
5. Refuel within 30-60 minutes post-training
Carbs (oats, rice, banana, toast, cereal)
Protein (eggs, yoghurt, shake)
Electrolytes and hydration. Not just water.
6. Reduce stress. Improve sleep
Chronic stress and poor sleep spike cortisol. Cortisol worsens recovery and increases cravings. The food piece won't work in isolation.
Seven to nine hours of sleep is non-negotiable for athletes
Reduce caffeine after midday. Eat enough before bed. Wind down properly.
The Short Version
Low energy in female athletes is not normal. It's a fuelling problem until proven otherwise.
Five signs to look for: fatigue, underperforming, illness/injury, mood, cycle.
Missing two periods in a row is the moment to act. Not in three months.
The fix is carbs, protein, fats, regular meals, post-training refuelling, sleep.
You don't need to track forever. You need to eat enough to support your training.
Sound familiar?
You're training hard but performance isn't moving
You're tired all the time and you've been calling it "training fatigue"
Your cycle has gone irregular or stopped
You're suspicious you're under-eating but you're scared to eat more in case you "lose progress"
If you ticked two or more, this is exactly what my Hybrid and Nutrition coaching is built for. Female-specific. Built around your training and your cycle.
Apply to work with me → you're under-fuelling and want help fixing it without losing fitness, that's what I do.
Female-specific endurance coaching with integrated nutrition from a qualified Nutritionist and Fertility Nutrition Specialist. Built around your body, your training, and your cycle. Not generic meal plans.
The application form takes two minutes. read every one personally. I'll WhatsApp you within 24 hours on weekdays.
Frankie x
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