Case Study: Why Under-fuelling Could Be Holding You Back From Your Ultra-Marathon Goals

Meet Sarah, a 38-year-old accountant, mother of two lively kids, and a determined recreational athlete.  She came to see me because she was feeling frustrated and exhausted.

Sarah had set herself the ambitious goal of running her first ultra-marathon.  She was a seasoned runner, and she wanted to challenge herself so she signed-up for a 90km race.  But despite training 6–7 days a week, logging 10–15km runs during the week and longer runs with interval training on weekends, her progress was stalling.

She complained of:

• Persistent fatigue.  She was tired during the day, and found herself hitting the snooze button in the morning, which was not typical for her.
• Muscle cramps during and after runs
• Restless legs at night, which was disturbing her sleep
• Hair fall.  She noticed clumps of hair in the shower after washing her hair, and her hair was visibly starting to thin.
• A recent flu that derailed her training for 3 weeks (and she was the type of person who never got sick)
• Recurring boils under her arms, which indicated a slump in her immune system
• Changes in her menstrual cycle (her periods had become lighter and less predictable)

Sound familiar? If you’re balancing intense training with a busy family and work life, it’s easy to fall into the same trap Sarah did: severely underestimating your body’s nutritional needs.

Sarah’s Typical Eating Pattern

Here’s what her day looked like:

☕ Morning: Cup of coffee + multivitamin
🥪 Lunch: Protein shake + tuna salad sandwich
🥜🍌 Afternoon snack (pre-run): Peanut butter & banana
🥤 During training: Sports/energy drink
🍗🥦🍚 Dinner: Chicken/fish/meat + rice or pasta + vegetables

At first glance, this doesn’t seem terrible.  But when we broke it down, Sarah’s diet was:

• Too low in total energy (calories): She wasn’t replacing the 700–1,000 kcal burned in her weekday runs, let alone her long weekend runs.
• Too low in protein: With ~50–60g of protein per day, she was nowhere near the 1.6–2.0g/kg recommended for endurance athletes.
• Over-reliance on sports drinks and supplements: Instead of real food that could better support recovery, immunity, and long-term health.
• Lacking key micronutrients: Especially iron, magnesium, and zinc — crucial for runners and for women.

What Was Happening to Sarah’s Body?

Training is a stressor.  Without enough fuel and nutrients:
⚡ Muscles can’t recover fully → fatigue & cramps
🩸 Iron and zinc depletion → hair thinning, restless legs
🛡️ Impaired immunity → frequent infections, prolonged recovery
🪫 Low energy availability → hormonal disruptions, poor sleep

This is sometimes called Relative Energy Deficiency in Sport (RED-S) – and it’s surprisingly common among recreational athletes.

How We Fixed It

Sarah acknowledged that her nutrition was a key issue holding her back from achieving her training goals.  And, she was happy to make some adjustments to her diet and eating schedule:

1️⃣ Increased Total Energy Intake

• Added a proper breakfast: Overnight oats or Chia seed pudding with Greek yogurt, nuts, seeds & berries (~400 kcal).
• Post-run snack:  Wholegrain toast or seed crackers with avocado and smoked salmon/ham and eggs, and 2-3 pieces of dark chocolate (~350 kcal).

2️⃣ Boosted Protein to 1.8g/kg (≈120g/day)

For anyone who is physically very active, protein is absolutely essential for repair of muscle and structural tissues.  For Sarah’s weight (67kg), she needed around 120g protein per day.  So, it was necessary to increase the VOLUME of protein-rich foods she was eating to achieve this, and to include protein with EVERY meal or snack.

• Added protein-rich foods at every meal/snack:
  • Eggs, cottage cheese, lentils, lean meats, fish
  • Post-run recovery snacks with 20–30g protein (boiled eggs, cheese, biltong, seed crackers, hummus)

3️⃣ Improved Carbohydrate Periodization

Sarah was not getting enough energy throughout the day.  She needed to replenish her energy stores more regularly, with healthy slow-release carbohydrates.

• Increased slow-burning / low-GI carbs before long runs (e.g., oats, bananas, toast)
• Post-run: To restore her energy in a gentle way without a rapid glucose spike, She agreed to have a low-GI carbohydrate with protein to replenish her glycogen stores and provide much-needed amino acids.

4️⃣ Corrected Micronutrient Deficiencies

Sarah was suffering with the consequences of malnutrition (fatigue, hair fall, muscle cramps, poor sleep, susceptibility to infections).  It was essential for her to increase the amounts of micro-nutrients she was getting from her food.  And, to supplement with specific micro-nutrients she needed.

• Added iron-rich foods (red meat, spinach, legumes) with vitamin C sources (peppers, citrus, carrots) for optimal absorption of iron and improved immune function
• Focused on magnesium and zinc from nuts, seeds, whole grains, and dark chocolate

5️⃣ Reduced Reliance on Supplements

Sarah was taking a multivitamin, but the amounts of micro-nutrients and bioavailability of those nutrients were not sufficient to meet the needs of her body.  It is far better to get your vitamins and minerals from food because they are packaged in their natural form, are most easily absorbed and come with additional co-factors that help them to work optimally.

• We swapped the daily protein shake for real food
• Sports drinks were reserved for runs >90 minutes.  Water + electrolyte tablets were better for shorter sessions
• Sarah’s blood work showed she was low in Vitamin D and Iron, so we supplemented with these micro-nutrients specifically

The Results

Within 6 weeks:

• Sarah’s energy levels improved – no more crashing at 3pm
• Her training felt stronger and she felt she recovered faster between sessions
• The restless legs resolved, and her sleep improved
• Her hair stopped shedding excessively
• She did not suffer any further infections – even her kids’ colds passed her by

📝 Key Takeaways for Recreational Endurance Athletes

✅ Training for a big event requires eating like an athlete – even if you don’t feel like one.
✅ Prioritize real food first, supplements second.
✅ Monitor signs of under-fueling:  Fatigue, poor recovery, hair loss, frequent illness.
✅ Aim for:

• 1.6–2.0g protein/kg body weight/day
• Adequate slow-burning carbs to match your training volume (At least 3-5g/kg per day for endurance athletes)
• Healthy fats (20–30% total energy)

💡 Your Nutrition Is Your Secret Weapon

Don’t let all your hard work on the road go to waste because your tank is empty.  The right nutrition plan can mean the difference between dragging through your training and crossing that finish line feeling strong.

If you’re unsure about your needs, talk to a professional – your body will thank you.