Fasted training, it is one of the most debated topics in the endurance world. Some athletes swear by it, claiming it supercharges fat-burning and makes them more efficient runners or triathletes. Others argue it kills performance, increases fatigue, and sets you up for injury.
So, what’s the truth? Does training on an empty stomach make you a stronger endurance athlete, or is it just another overrated fad?
Let’s break it all down—the science, the myths, and whether fasted training has a place in your endurance routine!
What Is Fasted Training, and Why Do Athletes Do It?
Fasted training simply means training in a state where you haven’t eaten recently, typically after an overnight fast (8–12 hours). The theory is that by training with low glycogen levels, your body is forced to burn more fat for fuel instead of relying on carbohydrates.
Why Some Athletes Love It:
Athletes who promote fasted training claim benefits like:
✅ Increased Fat Adaptation – Training in a low-carb state teaches your body to burn fat more efficiently as a fuel source.
✅ Metabolic Flexibility – Helps the body become better at switching between carbs and fat during long races.
✅ Improved Insulin Sensitivity – Could help with blood sugar control over time.
✅ Lower GI Distress on Race Day – Since your body gets better at using fat, some athletes experience less stomach discomfort from gels and carbs during races.
Sounds great, right? But hold on… There’s more to the story.
The Science: Does Fasted Training Actually Work?
Yes, It Can Help You Burn More Fat… But Does That Matter?
A 2010 study in the Journal of Applied Physiology found that fasted training does increase fat oxidation (fat burning). However, burning more fat does not necessarily mean better performance.
💡 Your body still prefers the speed of carbohydrate metabolism for high-intensity exercise. During races, it needs quick energy—meaning glycogen (from carbs) will always be your #1 performance fuel.
👉 Takeaway: If your main goal is to optimize endurance performance, training in a carb-depleted state might not be the best approach.
The Downsides of Fasted Training for Endurance Athletes
Let’s be real—while fasted training can lead to benefits it isn’t magical, and for many endurance athletes, it does more harm than good.
Here’s why it can be a problem:
❌ Increased Fatigue – Training with low glycogen means lower energy levels, leading to slower workouts, higher perceived effort, and worse recovery.
❌ Reduced Training Intensity – High-intensity efforts require glycogen, and fasted training reduces your ability to push at race pace.
❌ Increased Muscle Breakdown – In a carb-depleted state, your body may break down muscle for energy, which isn’t ideal if you want to get stronger.
❌ Higher Cortisol Levels – Fasted training raises cortisol (stress hormone), which can lead to poor recovery, fatigue, and even immune suppression.
❌ Increased Injury Risk – Without proper fuel, your coordination, focus, and recovery suffer—which can lead to poor form and injuries.
The Bottom line: Training under-fueled too often will likely hurt more than it helps.
When (and How) to Use Fasted Training the Right Way
So, does this mean you should never train fasted? Not necessarily. It depends on how, when, and why you’re doing it.
When Fasted Training Might Be Useful:
✔️ For Low-Intensity, Easy Runs – Fasted training is best for slow aerobic sessions, not for intervals, tempo runs, or races.
✔️ To Improve Fat Adaptation – If your goal is to train your body to use fat efficiently, a few controlled fasted sessions (once or twice per week max) can help.
✔️ For Runners Who Struggle With Early-Morning Nutrition – Some athletes naturally prefer running before breakfast and feel fine doing so.
🚫 When to Avoid Fasted Training:
❌ Before Speed or Intense Workouts – If you’re doing intervals, hills, or tempo work, fasting will slow you down and make your training less effective.
❌ On Back-to-Back Hard Training Days – You need to recover properly—fasting after a hard session will delay glycogen replenishment.
❌ If You Struggle With Recovery – If you already feel fatigued, sore, or prone to injury, fasted training will only make things worse.
My Personal Take on Fasted Training
Here’s where I stand:
✅ Most endurance athletes don’t need fasted training. The benefits are minimal compared to the potential downsides.
✅ It’s not a magic bullet for fat loss or performance. Eating enough carbs and fueling smartly will always win.
✅ If you do fasted training, do it strategically. Use it only for short, easy sessions—not for long runs or high-intensity workouts.
✅ Performance should always come first if that is your main goal. If you feel sluggish or your workouts suffer, ditch the fasted training and focus on fueling better.
Final Thoughts: Should You Train Fasted?
If your goal is maximum endurance performance, proper fueling is always the better choice. Training in a well-fueled state means higher quality workouts, better recovery, and stronger race-day performance.
Fasted training might have a place in your routine—but only if used sparingly and intentionally.
My advice? Unless you have a specific reason for doing it, focus on fueling your workouts properly instead of depriving your body. You’ll recover faster, perform better, and enjoy your training more.
💬 What’s your take on fasted training? Have you tried it? Drop a comment or DM me—I’d love to hear about your experience!
Key Takeaways
✔️ Fasted training does increase fat burning, but that doesn’t mean it improves endurance performance.
✔️ Running low on glycogen can increase fatigue, lower training quality, and slow recovery.
✔️ If you try fasted training, keep it to short, low-intensity sessions only—never before hard workouts or races.
✔️ Fueling properly is always the best strategy for strong, high-quality training.
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