Fasted Running: Is Intermittent Fasting Good For Running?


Fasted running, a practice where athletes run on an empty stomach, typically after an overnight fast, is gaining traction in running circles for its claims to increase endurance and fat burning.

But the jury is still out on its effectiveness and practicality. After all, runners need fuel to provide energy to run, so how can fasting have practical benefits for most runners?

This article will explore the science behind fasted running, its benefits, and potential risks, Whether you’re a beginner or a marathon veteran, we’ll cover whether running on empty could be the missing piece in your training puzzle.

What Is Intermittent Fasting (IF)?

Intermittent fasting is a nutritional approach that involves alternating between fasting and eating. By “fasting,” we don’t mean simply “not eating”—we mean intentionally going without food and drinks like tea and coffee for certain periods of time, ranging from 8 to 20 hours.

Although it’s often considered a “diet,” intermittent fasting doesn’t restrict what you eat. Instead, it restricts the time when you eat, which can be effective in maintaining calorie restrictions as long as you eat healthy, nutritious food.

Is Intermittent Fasting Good for Runners?

Intermittent fasting can offer benefits for runners, but it’s not a one-size-fits-all solution. If you’re planning on losing fat, then intermittent fasting could be a way to help you reach those goals, along with your running.

But if you want to run faster or longer, then intermittent fasting might not be the right choice.

Energy Management

Running, especially for long distances, requires a substantial amount of energy. Intermittent fasting can affect how the body accesses and utilizes energy.

During fasting periods, your body may increase fat oxidation, which can be beneficial for long, slow runs where you are training your body to burn fat. However, this might not provide the immediate energy needed for high-intensity workouts.

Weight Management

Intermittent fasting can be an effective tool for weight management, which is crucial for many runners looking to achieve an optimal power-to-weight ratio. But it’s important to ensure that weight loss does not come at the expense of muscle mass or overall health.

Training Adaptation

Some research suggests that training in a fasted state can enhance metabolic adaptations, potentially improving endurance. However, the evidence is not conclusive, and responses can vary widely among individuals.

Recovery and Nutrition

Nutrition plays a key role in recovery. IF might complicate getting enough nutrients and calories, especially for runners who have higher energy needs. It’s crucial to plan eating windows to ensure adequate recovery and nutrient intake.

Benefits of Fasting for Runners

Intermittent fasting can benefit some runners interested in burning fat and better health. Let’s review some potential benefits.

Increase Your Body’s Ability to Burn Fat as Fuel

Fat loss is a great side effect of fasted training, as long as your diet is in check. When you train on an empty stomach, and there’s no glycogen left in your muscles, your body dips into fat stores for fuel, which is excellent for weight loss.

If you train fasted often enough, your body gets better and better at burning fat for fuel. This is a great bonus for those looking to lose weight, but it’s also a good thing for runners who want to perform better in general, as the body always has a back-up source of fuel that it can access more easily.

Reduced Inflammation

Research suggests that fasting can decrease inflammation throughout the body. Less inflammation means less chance of developing chronic diseases, better overall health, and even performance and recovery-related benefits, like less DOMS after workouts.

Improved Blood Sugar Regulation

Some studies show that intermittent fasting can improve insulin resistance, which may prove to be very beneficial for type 2 diabetic patients. Because it’s all about insulin, it might not be a good idea for those with low blood sugar because fasting for a long time can drop your blood sugar to dangerous levels.

Heart Health

Research indicates that intermittent fasting can be beneficial to your heart health. Scientists aren’t sure exactly how, but it may decrease bad cholesterol and reduce inflammation, both of which have a positive impact on heart health.

May Help to Boost the Immune System

Studies suggest intermittent fasting can boost the immune system by lowering inflammation, protecting the body from oxidative stress, and regulating circadian rhythm.

Mental Clarity and Focus

The reduced inflammation associated with fasting can have a positive effect on cognitive function, leading to improved alertness, mental clarity, and focus.

Types of Intermittent Fasting You Can Try

Want to give it a go? Here are some popular types of intermittent fasting you can try.

16/8 Method (Or the Leangains Protocol)

With this method, you’ll fast for 16 hours—no eating, just drinking water—and then eat your day’s worth of calories in the remaining 8 hours. You can structure this however you want.

The most common is to stop eating at 8 pm and resume eating at noon the next day, as you’ll lose a chunk of your fast to sleep, which makes it easier to handle. But you can structure it in a way that suits you and your schedule.


Rather than fasting every day, you’ll eat normally five days of the week but reduce your calories to 500 or 600 on two days of the week. This might be an easier way to begin for those who are new to intermittent fasting, and it can also be easier to structure your runs around.


This is a more extreme method that requires a 24-hour fast, once or twice a week. It might be difficult only to drink water for 24 hours, so this might be a little more advanced.

Alternate-Day Fasting

Similar to the 5:2 method, alternate-day fasting has you eating normally one day and restricting your calories or fasting completely the next day.

What Are the Potential Risks of Fasted Running?

Fasted running is not without its risks. It has a negative effect on performance because you’re running without an easy-access source of fuel, and it can also place strain on your immune system, making you more susceptible to getting sick, especially if you aren’t recovering properly.

There’s also a chance that runners who are less familiar with nutrition may unintentionally create dysfunctional eating habits. Intermittent fasting is meant to be used as a tool and not as a long-term dieting strategy.

When Should You Run Fasted?

Running fasted can be a good idea on certain runs and at specific times of day. Here’s when you should consider running fasted.

Low to Moderate Intensity

If you’re planning a low-intensity workout or a moderate-intensity run, then fasted training is a good idea. You won’t be overdoing it and depleting your body of energy.

Short to Moderate Duration

Fasted runs are better when they’re on the shorter side. The longer you run, the more your energy disappears. Stick to fasting for shorter runs. There’s no need to fast when you’re going for a long run—you’ll only set yourself up for failure.

Time of Day to Run Fasted

You can decide on whatever time you want to run. But it may be easier to do your run in the morning, because you’ll already be fasted for 7 to 8 hours.

However, you’ll need to work out the best time to run based on your schedule and your fasting schedule, so you can time your run to coincide with the end of your fasting period for your post-workout meal.

When Should You Not Run Fasted?

Fasted running isn’t for everyone, and it’s also not for every workout. Here’s when it might be best to fuel before your run instead of running on an empty stomach.

Intense or Long Workouts

When you’re fasted, your body dips into your fat stores for energy. This is what makes it such a great tool for weight loss, but it also means that if you push too hard, you’re going to be placing a lot of pressure on your body.

High-intensity runs like hill training and speedwork should be fueled. Your body needs all the help it can get to fuel itself through extra-intense exercise, and training fasted can lower your performance and exhaust you.

The same is true for long runs. The longer you run, the more energy your body draws to sustain your movement. Push yourself too far, and you’ll find it more tiring and harder to recover afterward.

Racing or Competition

When you’re competing, weight loss isn’t a factor. You need fuel to give you the edge, to give you energy, and to help you perform at your best. Even if you trained fasted, avoid running races fasted for this reason.

If You’re New to Running or Exercise

Training fasted when your body isn’t used to the feeling of exercise is a bad idea. Your body needs time to get used to the activity level you’re now giving it, so give it time to get used to that before you throw another spanner in the works.

Once your body has adapted to running, you can consider training fasted if weight loss is your goal. Start slow, though.

You Have a Medical Condition

If you have an underlying medical condition, get the go-ahead from your doctor before you start fasted training. Even if you’re an experienced runner, it’s a good idea to get a checkup and make sure you’re healthy enough to be able to fast without potentially negative side effects.

Fasted Running May Not Be Ideal for Recovery Runs

Although recovery runs are easygoing, they might be more effective for their purpose—recovery—if you’re fueled. Recovery runs in a fasted state might not kick the recovery process off very well, so you may be shooting yourself in the foot.

Can You Fast and Run Every Day?

Although you can fast and run every day, it’s not advised. Running in a fasted state puts extra stress on your body and needs extra time to recover. Running fasted every day is an easy way to overdo it.

While you can do intermittent fasting every day, we recommend only running in a fasted state on 2 or 3 days a week. Make sure you rest well on the days of and after your fasted runs, and if you exercise on the days in between, fuel yourself beforehand.

How Long Should You Fast Before Running?

This really depends on what kind of fasting you’re doing. If you’re doing 16:8, we recommend waiting until hour 15 to run so you can eat just after the 16th hour has passed.

On the other hand, if you’re doing something like the 5:2 method, it’s less cut-and-dry. Waiting 6 to 8 hours after your last meal will help you get the most benefit out of fasted running.

Tips On How to Run Fasted

Ready to try running fasted? Here’s our guide on how to do it safely to help you reach your goals.

Start Slowly

Take it easy when getting into intermittent fasting. Start with short, easy runs to get a good idea of how your body responds. As your body adapts and it gets easier and easier, you can increase the distance and the intensity of your runs.

Ensure You’re Well-Hydrated

Whether you’re feeling hungry or not, staying hydrated is essential when you’re fasted. It can take that edge off when you haven’t eaten for a while, but it’s also vital to keep your body hydrated because it’s already under stress from not eating.

Once you build up to longer runs in a fasted state, consider taking an electrolyte solution with you to replenish what you lose through sweat.

Adjust Intensity

Fasted runs should not be high-intensity. Stick to lower-intensity workouts on the days you’re fasted, because your body might struggle to up the intensity if you’re not fueled. Even if you do manage to work out, you’ll likely crash after the workout if you mix fasted training with increased intensity.

Plan Around Your Run

Try to run towards the end of your fasting window so you can refuel soon after your run and replenish your energy. Many runners find it easiest to run fasted in the morning, because you end up sleeping through most of your fast and can run and eat breakfast afterward.

However, you’ll need to work out a fast/run schedule that works for you. Not everyone will enjoy running fasted first thing in the morning, so experiment and see what works best.

Break Your Fast Properly

After your run, it’s time to break your fast, but do it right. Choose a healthy meal, high in good carbs, moderate protein, and low fats. Carbs will rapidly replenish your energy stores, and protein will kick-start muscle repair.

Maintain a Balanced Diet

Make sure you eat healthy throughout your “eating hours”. Don’t use fasting as an excuse to binge on junk food—your body still needs healthy nutrients to function properly!

Monitor Performance and Recovery

Pay attention to how you perform when running fasted. It’s normal for your performance to drop slightly, but if it drops significantly if you struggle to finish your runs due to low energy levels, and if you feel worse during the day, fasted training may not be for you.

Photo of author


Ben is an avid road and trail runner, and has completed multiple marathons and ultras. A former running store owner, he now shares his knowledge and experience writing these articles.