Fasted Running: Should You Do It and How?

Running on empty also has its place and time

Agnese Zimele
Runner's Life
4 min readFeb 26, 2023


Image by user14908974 on Freepik

I’ve never been a fan of early morning runs. Mainly because it usually meant skipping breakfast, my favorite meal of the day, and forcing my stiff body to do things it was not ready to handle.

There’ve been times, however, when I had no other option but to run in the morning on an empty stomach. And I realized that I felt much better going as I was than after I’d snacked on a banana.

It got me thinking that maybe running didn’t require as much fuel as I thought it did and I could easily use the energy accumulated from the previous day to get myself forward.

Yet, it didn’t seem to work when I had a hard time hitting all the intervals or tempo paces. So when can fasted running give you an edge and when should you avoid it?

Fasted running is a term used to describe a run or a jog that’s done without having eaten anything for more than 10 hours.

Usually, the only times when it’s practically possible are either in the morning or late in the evening (provided you’ve skipped lunch and the afternoon snack).

The idea of running with no extra carb-generated energy is nothing new. However, it probably became more visible and advocated with the rise of the intermittent fasting trend.

Given how much we’ve been told that it’s important to fuel ourselves properly before a run, it may be hard to believe that such a strategy could work in the long term.

But there are certain situations when it’s worth giving fasted running a try. And the benefits may considerably outweigh the perceived costs.

Fasting + running = more fuel

It may sound counterintuitive but the main benefit of going out for a run after several hours of zero food is increased energy production.

It’s not that your body would suddenly start generating energy out of nowhere. But without the traditional carb reserves (aka glycogen) readily available in your system, it has to look for new sources, like fat.

In other words, fasted running teaches your body to rely on existing supplies and convert them into usable fuel. That means kickstarting the fat-burning process and eventually giving access to the energy your muscles couldn’t use before.

This, however, doesn’t happen in an instant. Unlike carbs or better glucose, breaking down fat takes more time. That restricts you from getting the necessary energy right away and is the reason why you may feel sluggish and even slightly tired on your first fasted runs.

Photo by lucas Favre on Unsplash

Practice makes perfect, nonetheless, and as you opt for fasted running on a more regular basis, the fat conversion process will become more efficient. And what’s more — you’ll learn to save carbs for truly intense efforts.

Just don’t get carried away — sprints and long intervals still prefer sugar over fat. So if you want your first fasted running experience to work in your favor, easy runs will be your best bet.

Fasted running strategies

Some runners can’t imagine themselves saying “no” to a pre-workout meal. And then there are those for whom even a piece of chocolate half an hour before a run may feel too heavy.

Fasted running can be beneficial to both of these athletes. It all comes down to habits and bodily adaptations.

Running first thing in the morning is a huge strain on your system by itself. But opting for it on an empty stomach makes the stress hormones go even crazier.

The best thing to do if you’re new to fasted running and must do a workout at the end of your no-food period is to keep your runs relatively short (not more than 1,5h) and easy. Otherwise, you risk hitting the wall or even feeling dizzy.

Another aspect you shouldn’t forget is hydration and proper refueling. Drinking water and getting an adequate amount of carbs and protein soon after your workout is important particularly if you run after sleeping. That will boost muscle recovery and help replenish your glycogen reserves.

And finally, don’t suddenly introduce fasted running if you’re nearing a race and especially if you’re close to doing your first half or full marathon. Your energy demands will be far too high and your body may feel too weak to handle the training load.

So is fasted running for you? It certainly can be, but you’ll never know unless you try, and the off-season will be the best training period to test it out. Start with easy runs and work your way up if you feel like it.

Improved energy production, fat loss, greater aerobic endurance — there are several benefits associated with fasted running, and it’s no wonder that so many runners and coaches advocate it.

But it’s also not a one-size-fits-all kind of training method. You should mix it with your regular carb-powered workouts, especially in the beginning. And don’t forget that, as with everything in long-distance running, it will take time to see real results.

Get more training tips and running inspiration on my Instagram account and here on Medium.



Agnese Zimele
Runner's Life

Marketing specialist and running coach who's been passionate about writing since childhood.