Fasted vs Fuelled Runs: Which Is Better for You?

If you’ve ever woken up for an early run and debated whether to eat first or just head out the door, you’re not alone. The question of running fasted versus fuelled divides runners more than almost any other training topic.

Some swear by training fasted, saying it helps the body burn fat more efficiently and teaches mental resilience. Others simply can’t imagine running without a pre-run snack or gel, arguing that it helps them perform better and recover faster.

So who’s right? And more importantly, should you run fasted at all? 

Let’s look at what actually happens in your body when you train without food, the potential benefits and risks, and when fuelling makes more sense.

But first, the obvious question for those who are new to this whole concept:

What Is Fasted Training?

Fasted training means exercising after a period without food, usually overnight. So if you wake up, skip breakfast, and head straight out for a run, you’re training in a fasted state.

Your body’s glycogen stores (its main source of quick energy) will be lower, which means it relies more on fat for fuel. That’s why fasted runs are often linked with improved fat metabolism.

But that doesn’t mean they’re always better. Whether fasted running helps or hinders you depends on the type of session, your fitness level, and your goals.

Benefits of Fasted Training

There are a few reasons runners often choose to train fasted, and some are backed by research while others come down to personal experience.

Here are the most common reasons:

1. Improved Fat Adaptation

When your glycogen stores are low, your body becomes more efficient at using fat for energy. Over time, this can train your body to tap into fat earlier during long runs. This is the primary reason that many long-distance runners include occasional fasted sessions in their training plan.

It doesn’t necessarily mean you’ll burn more fat overall, but it can improve metabolic flexibility, which is your body’s ability to switch between fuel sources. That can help during marathons or ultras when glycogen stores are inevitably going to run low. 

2. Mental Resilience

Running without fuel can be uncomfortable at first. Every step is likely to feel like it takes more effort, and your pace is likely to be slower. Despite this, some runners find this can help them to build mental strength. It teaches you how to manage low-energy patches and stay relaxed and moving when your body feels depleted.

That mental toughness can carry over to race day, especially if things don’t go to plan.

3. Convenience

If you’re heading out early, fasted training is sometimes just easier. There’s no waiting around to digest breakfast and no risk of stomach issues. You can roll out of bed, put your shoes on, and get going.

Risks of Fasted Training

While there are some perceived benefits, training fasted isn’t for everyone. There are a number of downsides worth knowing before you start experimenting.

1. Reduced Performance

When glycogen stores are low, your top-end energy output drops. That means your runs will start to get harder, you’ll feel more fatigued and you may end up hitting that dreaded wall. Before this happens, you’ll notice that you struggle to hit your target pace.

2. Muscle Breakdown

Running without energy available can increase muscle protein breakdown. Over time, that can affect recovery and strength, especially if you’re training regularly.

That’s one reason why runners should reach for some protein after a run like vegan protein shakes which provide high protein that’s quick and easy to consume. Vegan protein powder often settles on the stomach better than whey, and can be easily combined with a source of carbs (such as a banana) to help the body recover and rebuild muscle more efficiently.

3. Hormonal and Energy Issues

Some runners, particularly women, find that exercising in a fasted state can affect energy levels and hormones, especially if done too often. Feeling constantly drained, light-headed, or mentally exhausted are signs you may need more fuel.

Listening to your body is key, as is recovering effectively. If you finish a fasted run feeling wiped out for the rest of the day, it’s probably not helping you train better.

Benefits of Fuelled Running

Now let’s look at the other side: running after eating (otherwise known as taking on pre-run fuel). Whether that’s a banana, a small bowl of oats, or a natural energy gel, fuelling before a run has its own clear benefits.

1. Better Performance

Fuel means energy. With glycogen topped up, you can run faster, push harder, and sustain effort for longer.

For workouts, long runs, or races, that can make a huge difference. You’re not just getting through the session; you’re training your body to perform at a higher level.

2. Faster Recovery

Fuelling properly before, during and after a run helps your body recover more effectively. You’re giving your body, including your muscles, what they need to repair, adapt and recover.

3. Lower Injury and Illness Risk

Consistently under fuelling can lead to more than just tired legs. It can affect your immune system, hormone balance, and even bone health. In some cases this leads to RED-S (relative energy deficiency in sport) which is effectively your body breaking down through a lack of energy. This can have serious consequences and may require expert intervention. Fuelled running reduces these risks by keeping your body in a better energy balance.

Now that we’ve covered the key benefits and risks, to the key question:

Should You Run Fasted?

Some runners will swear by the use of fasted runs as part of their training, however there are more disadvantages than advantages, and this approach can be especially dangerous for women.

While fasted running is unlikely to cause big issues when the runs are short (under an hour) and just 2-3 times a week, a seasoned runner who trains daily should always look to fuel their training properly so they don’t end up in an energy deficit.

Common Myths About Fasted Running

Because fasted running gets a lot of attention online, a few myths have stuck around that are worth clearing up.

Myth 1: Fasted running burns more fat overall.
Not necessarily. You might burn a higher percentage of fat during the run, but total fat loss depends on your overall calorie balance and diet.

Myth 2: Running fasted is better for everyone.
It’s not. Some runners find it works for them, while others feel sluggish or nauseous. Women should also avoid fasted runs longer than an hour.

Myth 3: You’ll lose muscle from one fasted run.
Occasional fasted runs won’t eat away your muscles, but consistent under-fuelling over time will. That’s why recovery nutrition matters, especially after a fasted session.

A Runner’s Perspective

Some runners will enjoy fasted training, especially for early morning short runs, but it’s crucial to understand why you’re doing it and listen to your body. Fasted long runs are never wise and can actually damage your health, especially if your body is new to the whole concept of not fuelling. 

If you need a natural energy boost before and during your runs, Maple Ignite and Maple Coffee gels are both simple natural fuelling options that sit well even early in the morning.

To learn more about fuelling your runs, take a look at our guides to carb loading and what to eat before a long run.