Case Study: The Hidden Risks of Under-fuelling in Young Athletes

When “Dehydration” Wasn’t the Whole Story

Meet Alex, a 16-year-old triathlete with huge potential.  He was training hard for the national championships – swimming, cycling, and running 6–7 days a week.  His coach described him as “talented and driven.”

But one day, during what should have been a routine training session, Alex felt his world spin.

He suddenly developed:
⚡ Faintness
🤲 Pins and needles in his arms and legs
💪 General weakness
😵 Shakiness and mild confusion that lasted for hours

He was rushed to the local emergency department and diagnosed with dehydration.

But his coach wasn’t convinced.  He asked me to take a closer look.

🕵️‍♀️ Digging Deeper: The Assessment

When I met Alex, he appeared thin and underweight for his age and height. His BMI was at the lower end of normal but considering his training volume, he had little margin for error.

🩺 On examination: No neurological or circulatory abnormalities.
🩸 Blood glucose: 7.8 mmol/L – unexpectedly high for a young, fit athlete.

His nutrition history offered more clues as to what was going on…

🍫 A Typical Day of Eating for Alex

🥤 Breakfast: Fruit juice + toast with butter and jam
🍫 Mid-morning snack: Energy bar + sports drink
🥪 Lunch: Sandwich with processed meat & cheese
🍬 Afternoon snacks: Packet of crisps and a small bag of jelly babies
🥤 Pre- and post-training shakes
🍗🥗 Dinner: Rice + chicken + salad
🍦 Evening snack: Ice cream

At first glance, Alex’s diet seemed “adequate” in terms of energy.  He was eating regularly and using sports supplements.  But the reality?

🚨 The Problem: Relative Energy Deficiency in Sport (RED-S)

Alex was consuming quick-energy, low-nutrient foods that couldn’t sustain his intense training schedule.  He was burning thousands of calories daily but not replenishing them adequately.

This led to low energy availability (LEA):
⚡ Calories in < Calories burned + basic bodily needs

In young athletes like Alex, getting too little energy and inadequate nutrition has serious consequences that go way beyond performance:

🔬 The Science of RED-S in Teens

RED-S is a condition that occurs when an athlete’s energy intake doesn’t meet the demands of training and basic physiological functions.  It’s an extension of the Female Athlete Triad (low energy availability, menstrual dysfunction, and low bone density) and affects both males and females.

In teenagers, the risks are even greater because their bodies are still growing and developing, so their baseline energy and nutrient requirement is higher than adults.

🏃‍♂️ What happens in the body?

1️⃣ Metabolic slowdown – The body prioritizes survival, downregulating “non-essential” processes like growth, reproduction, and immunity.

2️⃣ Hormonal disruption – In boys, low energy availability can suppress testosterone production. In girls, it can lead to irregular or absent periods.

3️⃣ Impaired recovery and immunity – Frequent infections, slow healing, and increased injury risk.

4️⃣ Bone health concerns – LEA during adolescence can compromise peak bone mass acquisition, increasing the risk of stress fractures and early osteoporosis.

5️⃣ Neurological symptoms – Like Alex’s shakiness, pins and needles, and disorientation… likely linked to transient hypoglycaemia during intense training.

All of these factors can significantly impact health and athletic performance.

📉 Red Flags for Coaches, Parents, and Athletes

• 🚩 Frequent fatigue or “hitting the wall” during training
• 🚩 Dizziness, fainting, or shakiness
• 🚩 Unintentional weight loss
• 🚩 Poor recovery from training
• 🚩 Mood changes (irritability, anxiety)
• 🚩 Recurrent injuries (especially stress fractures)
• 🚩 Irregular or absent menstrual cycles in girls

✅ How We Helped Alex

Alex’s nutrition plan needed a complete overhaul to match his energy demands.

1️⃣ Breakfast Reboot

Replaced fruit juice + toast with:
🥣 Overnight oats with milk, nuts, chia seeds and banana (~600 kcal)
🍳 Or wholegrain toast with eggs, avocado, and whole fruit

2️⃣ Smarter Snacks and Lunch

• Added trail mix, Greek yogurt, or nut butter sandwiches as snacks
• Upgraded lunch with lean protein (chicken, tuna, or legumes) + complex carbs (brown rice, wholegrain bread) + vegetables/salad

3️⃣ Pre- and Post-Workout Fuel

• Pre-training: Banana + peanut butter or home-made granola bar made from nut butter, dates, seeds and coconut
• Post-training: Fruit + wholegrain crackers with cheese or eggs (carbs + protein for glycogen replenishment and muscle repair)

4️⃣ Dinner and Evening Snacks

• Increased portion sizes at dinner, especially protein servings
• Added a bedtime snack: Greek yogurt with granola, or a few squares of dark chocolate to prevent overnight energy deficit

5️⃣ Micronutrient Focus

It was super-important to emphasize foods rich in vitamins and minerals.  It is always better to get micro-nutrients from whole, real foods rather than processed / factory-made supplements.  Alex needed more:

• Iron (red meat, leafy greens, lentils)
• Calcium and vitamin D (milk, yogurt, specific supplementation – Alex’s blood tests revealed that he was vitamin D deficient)
• Magnesium and zinc (nuts, seeds, whole grains)

The Results (Over 8 Weeks)

✅ Alex gained 2.5kg of lean mass
✅ No further dizzy spells or neurological symptoms
✅ Improved mood and energy levels
✅ Faster recovery and stronger training sessions
✅ His coach reported a “noticeable improvement” in endurance and focus

Key Takeaways for Young Athletes

✔️ You can’t out-train poor nutrition.
✔️ Under-fuelling may feel like “discipline,” but it sabotages your performance and health.
✔️ Teens need more energy, and more nutrition, to support growth, development, and training.

💡 Your Nutrition is Your Foundation

For young athletes chasing big goals, eating enough – and eating well – is your secret weapon.

If you’re unsure about your nutrition plan, seek professional guidance. It could mean the difference between burning out and achieving your potential.