What Happens When Female Athletes Don’t Fuel Enough? A Deep Dive into the Latest Research
For endurance athletes, fueling is training. Your body isn’t just burning calories—it’s adapting to stress, repairing muscle, and building resilience for future workouts. But what happens when energy intake doesn’t match training demands?
A new study, The Whole-Body and Skeletal Muscle Metabolic Response to 14 Days of Highly Controlled Low Energy Availability in Endurance-Trained Females (PMID: 39530548), sheds light on this exact question. The findings? Even short-term under-fueling can take a major toll on performance, with lingering effects even after refueling.
Let’s break down the research and explore why consistent energy intake is non-negotiable for endurance athletes.
🔍 Study Overview: Low Energy vs. Optimal Energy Availability
Who Participated?
The study followed 12 endurance-trained females (V̇O2max ~55.2 mL/kg/min), all maintaining an 8-hour/week training load.
Study Design
Researchers used a randomized, blinded, crossover design, comparing:
1️⃣ Optimal Energy Availability (OEA): 52 kcal/kg fat-free mass/day
2️⃣ Low Energy Availability (LEA): 22 kcal/kg fat-free mass/day
Each phase lasted 14 days, followed by a 3-day OEA refueling period to assess recovery.
Why This Matters
Many female endurance athletes unintentionally fall into LEA due to inadequate fueling, dieting pressures, or increased training loads. This study provides a controlled look at how this impacts performance, metabolism, and muscle recovery.
📊 Key Findings: The Cost of Under-Fueling
1️⃣ Performance Took a Hit—And Didn’t Fully Recover
Time trial performance dropped by 7.8% (Δ -16.8W).
Time to exhaustion fell by 18.9%—athletes fatigued much faster.
Even after 3 days of optimal refueling, performance remained impaired.
💡 What This Means for You:
Even if you correct your fueling later, the damage to endurance performance can linger. Under-fueling for just two weeks can lead to losses in power output, endurance capacity, and training quality that persist even after returning to adequate energy intake.
2️⃣ Metabolism Shifted—but Not in a Good Way
Resting fat oxidation increased by 28.2%.
Plasma free fatty acids spiked by 99.4% during LEA.
These changes reversed after refueling, meaning they don’t explain the sustained performance drop.
💡 What This Means for You:
Some athletes think "burning more fat" means better endurance performance, but this study shows that increased fat oxidation doesn’t compensate for poor fueling. Your body needs carbohydrates to sustain high-intensity efforts—without them, you’ll struggle to perform.
3️⃣ Muscle Health & Glucose Control Were Surprisingly Stable
Mitochondrial function, muscle glycogen, and insulin sensitivity remained unchanged.
This suggests other mechanisms—potentially hormonal, neuromuscular, or immune-related factors—are behind the performance decline.
💡 What This Means for You:
Even if basic metabolic markers don’t immediately shift, performance will suffer long before major changes show up in bloodwork or body composition. This highlights why listening to your body’s signals—fatigue, decreased endurance, or slower recovery—is just as important as lab data.
✨ Takeaways: What Every Female Endurance Athlete Needs to Know
This study confirms a crucial fact: under-fueling—even for a short time—can have lasting negative effects on endurance performance.
Key Lessons for Athletes
✔️ Performance Declines Quickly – A 7-8% loss in power and faster fatigue can mean the difference between hitting a PR or struggling through a race.
✔️ Fat Adaptation Isn’t the Answer – Increased fat oxidation doesn’t compensate for lost endurance capacity. Your body still needs carbohydrates to train and race well.
✔️ Recovery Takes Longer Than You Think – Even after 3 days of proper fueling, performance didn’t fully return to baseline. The longer you under-fuel, the longer it takes to bounce back.
✔️ Energy Deficiency May Not Show Up in Bloodwork Right Away – Metabolic markers like glycogen and insulin sensitivity remained stable, so performance decline happens before obvious clinical symptoms.
✔️ Consistent Fueling = Consistent Performance – Waiting until you feel exhausted or underperforming to adjust nutrition is too late. Prioritize energy availability daily to sustain long-term health and peak endurance.
🔑 How to Avoid Low Energy Availability (LEA)
If you’re an endurance athlete training multiple times per week, you need to ensure your fueling matches your output. Here’s how:
1️⃣ Prioritize Pre- and Post-Workout Nutrition
Aim for 1.2-1.5 g of carbs per kg of body weight before workouts.
Post-workout, pair protein (20-30g) with carbohydrates (1.0-1.2g/kg) to replenish glycogen and repair muscle.
2️⃣ Don’t Skip Meals or Underestimate Portions
Athletes often underestimate their needs, especially if appetite is suppressed post-exercise.
Include high-energy, nutrient-dense snacks (nuts, dried fruit, smoothies) if you struggle to eat enough at meals.
3️⃣ Listen to Your Body—Not Just the Scale or Data
If you notice fatigue, mood swings, disrupted sleep, or missed periods, it could indicate low energy availability.
Performance losses often show up before clinical markers, so take these signs seriously.
4️⃣ Work with a Sports Dietitian
Individual fueling needs vary based on training load, body composition, and goals.
A personalized fueling strategy ensures you’re meeting your energy needs while optimizing body composition and performance.
🚀 Ready to Optimize Your Fueling Strategy?
If you want to:
✅ Maximize endurance performance
✅ Improve recovery and reduce fatigue
✅ Prevent the long-term effects of under-fueling
I’m here to help! In my 1:1 Fueling & Strategy Session, we’ll create a customized plan so you can train stronger, recover faster, and race your best.
👉 Click HERE to book a discovery call!
Final Thoughts: Fuel Like You Mean It
Under-fueling might not seem like a big deal—until it drains your endurance, compromises recovery, and lingers longer than expected.
If you’re struggling with fatigue, underperformance, or slow recovery, low energy availability could be the cause. Don’t wait for it to affect your season—fuel smart from the start!