“Did I eat too much? Or maybe not enough?”
If you’ve been running for a while, this question has probably crossed your mind. Maybe once. Maybe every single time. Because—let’s be honest—the energy you start with isn’t just about how much you slept or the type of workout you’re doing: it also depends on what (and if) you ate beforehand. So, in a rare moment of clarity mixed with scientific spirit, I decided to become my own test subject: three runs, three different approaches. Fasted. After a full breakfast. And with an energy gel. Same distance, same route, same gear, same time of day (to be precise: 2 km warm-up + 8 km run, starting at 7:30 AM, 50% in zone 2 and 50% in zone 3, temperature around 14°C / 57°F, after roughly 7 hours of sleep).
Spoiler: none of the three was a disaster. But none was a walk in the park either.
1. Running on an empty stomach
If you’re into minimalism, this is as pure as it gets.
Wake up, shoes on, out the door. Not even a sip of coffee.
The feeling:
The first couple of kilometers felt light, almost euphoric. Then, around kilometer three, the engine started sputtering. My mind was sharp, but my legs were sending the bill. Breathing stayed under control, but the perceived effort spiked. It felt like I was trying to draw energy from a locked basement: it was there, but hard to reach.
The final time?
Average. But I came home with a strange feeling of emptiness (not just metaphorically) and hunted for food like a starving sloth.
What science says:
Running fasted (especially at an easy pace) increases fat usage as a fuel source. It can help train your metabolic efficiency, but it may hurt performance—especially on longer or more intense runs. It also increases the risk of muscle catabolism.
Pros:
- Good for light or slow runs
- Trains your body to burn fat
Cons:
- Risk of sudden energy drops
- Not ideal for long or intense sessions
- Effort feels higher
2. Running after a full breakfast
A classic breakfast: oats, banana, coffee, a handful of almonds. About 350 calories. Then I waited an hour.
The feeling:
Smooth start, legs felt solid, breathing full. From the third kilometer on, everything stayed steady. My focus was sharp, and it felt like I was running on “premium green fuel.” No hunger at the end, and I recovered quickly.
The time?
Slightly better than the other two runs. But the most interesting part was the consistent pace and lower perceived effort.
What science says:
A balanced breakfast boosts glycogen availability in your muscles and liver, reduces effort perception, and supports performance. Just be mindful of the timing: running too soon after eating can mess with digestion and lead to cramps or nausea.
Pros:
- Steady and long-lasting energy
- Best performance on medium or long runs
- Faster recovery
Cons:
- You need to wait 45–60 minutes
- Digestion varies person to person
- Not great if you’re on a tight schedule
3. Running after an energy gel
Fifteen minutes before heading out: a citrus-flavored gel with 25g of carbs. Nothing else.
The feeling:
Quick out of the gate, felt responsive. There was a good kick at the start, but it didn’t last. Once I hit zone 3, the “fuel light” started blinking. In the last two kilometers, I relied more on willpower than on any leftover energy.
The time?
Slightly better than the fasted run, but slower than the breakfast one. Recovery was a bit slower too, and I was seriously hungry afterward.
What science says:
Energy gels deliver fast-absorbing carbs and are ideal for a quick pre-race boost or during long runs. On their own, though, they’re not enough to support sustained efforts—especially if your stomach’s empty. They can also upset your gut if not taken with water.
Pros:
- Quick and easy to manage
- Immediate energy
- Perfect when you’re short on time
Cons:
- Short-lived effect
- Potential for sugar crashes
- Not very filling
So: what’s the best strategy?
Spoiler #2: there’s no single best strategy. But there is your best strategy.
It depends on what you’re aiming for: are you training your metabolism? Trying to feel light? Going full throttle? What time do you run? How much time do you have? Most importantly: how does your body respond?
This experiment isn’t meant to be universal, but it can give you a clearer idea:
- Fasted running works if you’re going slow and want to train efficiency.
- Full breakfast is your best bet for performance and stability.
- Energy gel is a middle ground—use it wisely.
In the end, running is also about this: listening. Figuring out what makes you feel good. And then maybe trying it again next time. Or the time after that.
Because it’s not just about going fast. It’s about knowing how you got there.