Fasting & Running

What’s Included?

  • What is it?
  • Is it safe for runners?
  • Important things to consider with fasting

Whether you’re a morning runner who’s strapped for time or just looking to learn a little bit more about nutrition strategies – intermittent fasting is likely a term that you’ve heard. Fasting & other time-restricted fueling strategies are often controversial in nature, and that’s because each person is so different & has unique needs. It’s important to remember that when working on fuel and nutrition strategies, working 1:1 with a nutrition coach or dietitian will ensure you’re getting the best information and advice for your personal needs.

That being said, this article will dive into some of the basics: What is intermittent fasting? Is it safe for runners? And what are the key considerations when considering fasting as a nutrition strategy? So let’s get started!

What is it?

Intermittent fasting is a dieting strategy where calories are restricted for a given amount of time. There are several different ways to do intermittent fasting:

Alternate Day Fasting:

Just as the name implies, this strategy is done by eating a restricted intake one day followed by a normal intake the next day. Fasting days are typically done at 25% or less of normal daily calories while eating days are done based on eating by feel/eating at your normal amount.

5/2 Fasting:

This strategy is done by eating normal for 5 days of the week and fasting for two NON-consecutive days of the week (Example: fast on Monday, eat normal on Tuesday and Wednesday, fast on Thursday, eat normal Friday through Sunday). The fasting days should be cut to 25% or less of normal daily calories while the eating days are at your normal amount.

Time-restricted Feeding:

Time-restricted feeding: This strategy is done by restricting calories for a given amount of the 24-hour day. For example, fasting for 16 hours while sleeping/in the morning followed by an 8 hour window of eating. One might skip breakfast and then eat from 11 AM – 7 PM before fasting again.

Is it Safe for Runners?

The answer is like most things: it depends!

Intermittent fasting can come with some possible benefits when done correctly: increased fat-burning, increased metabolism efficiency, increased cellular repair, increased weight-loss, and even improved blood sugar control. However, when it comes to running – intermittent fasting can also come with a number of dangers: decreased performance, dizziness, fatigue, and even potential backfire when it comes to weight loss. Why is this?

Intermittent fasting can cause elevated levels of cortisol (stress hormone) in your body, which can hinder your progress in many ways – both within running and weight loss. Increased levels of cortisol can lead to increase fat storage, mood changes, acne, difficulty sleeping, and more. In addition, intermittent fasting requires your body to rely on fat as fuel during your runs instead of relying on carbohydrates – this can lead to increased weight loss but it can also lead to increased hunger and cravings, putting you at risk of binging later in the day.

While intermittent fasting can be a helpful strategy in itself for the general population, runners have to be way more cautious when considering whether this is a strategy that could work long-term for themselves. Working 1:1 with a dietitian can be a helpful way to determine whether this strategy is best for YOU personally & whether it will help you reach your personal desired goals.

Important Considerations

Keep it Short

If you’re experimenting with intermittent fasting + exercise, it’s important to keep things at your easy low-intensity zone (zones 1-2) when in a fasted state. Attempting to run at a harder effort or for a longer duration while fasted can lead to injury, exhaustion, and burnout.


After running in a fasted state, it’s incredibly important to prioritize fuel afterwards with both carbohydrates and protein.

Training & Fasting

It’s not recommended to use fasting when training for races, this is because we often need to perform at higher intensities or for longer durations during training cycles & proper fueling is key to performance. If you’re experimenting with fasted running, it’s best to do so during off-seasons or during seasons when your mileage and intensity is lower.

Is it Sustainable?

One extremely important considering is whether the strategy is sustainable for you & how long you want to use this strategy. Each person uses intermittent fasting for different goals, but for women it’s important to remember that there can be drawbacks and potential dangers to fasting – especially when it comes to your hormone health.

Listen to Your Body

Listening to your body is key when it comes to any nutrition strategies. Different people respond to different nutrition strategies in different ways – and it might take some time and experimenting to figure out what feels best for you & leads to positive results with your goals. Listen to your body to ensure that you’re feeling your best & making changes when necessary.

Are You Just Not a Morning Eater?

If you’re someone who just doesn’t have time to eat in the morning before your run or you don’t tolerate food well before your run, there are some other strategies you can use outside of intermittent fasting:

  • Start with very small amounts of food (1/4 banana or piece of toast, apple sauce pouch, etc)
  • Use a gel (or 1/2 if stomach is especially sensitive)
  • Have liquid calories (regular Gatorade, Powerade, juice, etc) before or during workout
  • Eat a bigger meal or carbohydrate heavy dinner the night before or a carb + protein snack before bed

If you’re looking to use intermittent fasting to accomplish specific goals (such as weight loss), working 1:1 with a dietitian would be the best way to ensure that you’re using strategies that will actually get you to those goals in a safe and sustainable way. If you’re in need of recommendations for dietitians, feel free to reach out to Amy at and I can offer some!

Amy Haas
Run with Aim, LLC
UESCA Certified Running Coach
NASM Certified Personal Trainer
NASM Certified Nutrition Coach