Cardio • 19.04.2016 • Herwig Natmessnig

The 3 Biggest Myths About Running in the Morning on an Empty Stomach

Running on an empty stomach – yes or no? There are lots of different opinions on this topic. For some, it is a regular part of their training, while for others, working out on any empty stomach is out of the question. In today’s blog post, we are going to look at the three biggest myths and show you the truth behind them.

1. “Working out on an empty stomach leads to muscle loss”

The general opinion in the gym is that working out without breakfast leads to muscle loss. But don’t worry, your muscles won’t disappear right away. It is often wrongly assumed that without food intake, the body lacks the necessary carbohydrates and glucose (sugar) for a training session in the morning. According to this view, the body is forced to break down muscle protein to get the energy it requires. So in other words, the body loses muscle. But this is not exactly 100% accurate: The body stores glucose in the form of glycogen (stored form of sugar) in the liver and muscles. Over the course of the night, the body’s levels of insulin (which helps cells absorb sugar and inhibits fat loss) and liver glycogen decrease. But the body still has the muscle glycogen stores. So when you start your morning run, your body initially gets its energy from the glycogen stored in your muscles.

Thirsty African American athlete drinking water with wide open mouth.

But as your workout continues, the stores of glycogen – or simply, carbohydrates – in your muscles are virtually depleted. Therefore, your body is forced to find a different supply of energy and it increasingly resorts to free fatty acids for fuel. If you now crank up the intensity of your workout, your body, in order to make up for the lack of glycogen and the insufficient supply of energy from fats, will also obtain the energy it needs by breaking down proteins (i.e. amino acids). Only then do you run the risk of losing muscle. However, most runners will have already stopped their workout by this point. For a massive lack of glycogen is normally accompanied by symptoms such as dizziness, weakness and fatigue.

Group of friends running together.Feel better, look better! Get stylish workout gear!

2. “Working out on an empty stomach is the best method to lose weight”

Working out on an empty stomach is often touted as the best way to burn fat and lose weight. While it is true that running on an empty stomach, if done in the right way, can eventually force your body to increasingly obtain the energy it needs from free fatty acids, this is not the decisive factor in losing weight.
The percentage of energy produced by burning fat is quite high, but the total energy expenditure (TEE) and thus calorie consumption are relatively low due to the low training intensity. In the case of a high-intensity running session, like interval training, the percentage of energy produced by burning fat is significantly lower. However, the TEE and the calorie consumption are many times higher. At the end of the day, what matters most in weight loss is the energy balance: If you burn more calories than you consume, you lose weight. Therefore, high-intensity running sessions are preferable to running on an empty stomach when it comes to losing weight.

3. “Running on an empty stomach increases your endurance”

Workouts on an empty stomach are not a good idea for leisure athletes who want to improve their performance. Training duration and intensity are severely restricted by the lack of glycogen. Therefore, the intended training stimulus is rather low. A high-quality workout lasting longer and at a higher intensity is better for increasing your performance.
Scientific studies on professional athletes have shown that very positive effects can be achieved by specific workouts with previously emptied glycogen stores. This causes your body to optimize and economize its fat metabolism. The body learns to make do longer with the glycogen stored in the muscles. However, there is no substantial evidence showing that this leads to improved race performance. At the same time, it is important to note that regular training with previously emptied glycogen stores can adversely affect your health.

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Even if there are more effective methods of losing weight or improving endurance, running on an empty stomach can add some welcome variety to your training. This kind of training is particularly suited for morning people who want to get their workout in before breakfast.

So if you want to run on an empty stomach, here is what we recommend:

  • Depending on your fitness level, your run should last between 40 and 60 minutes. 
  • Choose a low intensity (at a recovery run or conversation pace). 
  • You should drink a glass of water before your run.

Our tip: For your breakfast afterwards, make sure to take advantage of the anabolic window (also known as the “open window”) in the first 30 minutes after your workout. During this time, your body can absorb nutrients faster than usual. This means that it can optimally replenish its empty stores.



Herwig Natmessnig

As a former professional athlete (white-water slalom), Herwig lives and breathes health and fitness. Whether in competition or just for fun, he can never turn down a physical challenge. And with his enthusiasm, the sports scientist feels right at home at Runtastic.

View all posts by Herwig Natmessnig »
  • Great advice and explanation. I do fasted cardio and love it. I never eat before a HIIT workout and depending on the length of my runs I always have a couple of gel packs to keep me fueled. Works for me, find what works for you!

  • Sam

    Thanks for this interesting article Herwig !

    • Runtastic Team

      We’re glad you like it, Sam!

      • Catalina

        hello, bottomline here is we should have light breakfast before running or brisk walking?

        • Runtastic Team

          Hi! It depends.. If you are running on low intensity (between 40-60 minutes) then it is perfectly fine to skip breakfast. If you are training longer or harder, we recommend eating a breakfast before.

          Your Runtastic Team

  • Brian Treacy

    What a great article, thanks for the information! I’ve been running for about ten years now in the morning, and never eat first. This wasn’t due to trying to lose weight, or any of the other points mentioned, simply, when I first started, I cramped. As I increased my distance, to five-six miles, friends encouraged me to eat something first. Again, i cramped, and therefore stopped eating first. Later increased to ten – 12 miles (I don’t usually do this in the morning before work, only when training for a half-marathon), and I still didn’t eat… but at the advice of others, took a light snack with me, usually in the form of home-made granola bar crammed full of chia seeds. On these longer runs, I usually don’t start eating my snack until around nine or ten miles, with no cramping. I always drink lots of water before my runs, and take plenty of water with me. Sometimes I’m pretty hungry after my runs, but have never experienced dizziness, weakness, or fatigue. Thanks again for the information!

    • Runtastic Team

      Hi Brian, thanks for your positive feedback. We’re happy that you like our content 😉

      Your Runtastic Team

  • Runtastic Team

    Hi Felippe! How about some oatmeal with fruits or an omelette with veggies and a piece of banana 😉 If you are working out after, please avoid fatty foods.

    Your Runtastic Team

  • Runtastic Team

    Hi Karleen, thanks for your positive feedback! We might have the perfect blog post for you:

    Your Runtastic Team

    • Karleen Phillips

      Perfect article for me , thank you so much 🙂

  • Emmanuel Kwabena Adu-Mensah

    This article is very educative.It has basically explained a lot of things that baffled my mind.Thank you .

  • Runtastic Team

    Good question – of course, you still have a training effect under 40 minutes, it’s just smaller!

    • Roy

      Thanks for the reply.

  • Anonymous Burger

    Would cycling for a longer time (around 40 minutes) have a same or better effect

    • Runtastic Team

      It’s also a good option 😉

  • Runtastic Team

    If you are feeling hungry before your workout, then these would be a good option!

  • Runtastic Team

    Hi Jules! If you are fine with waiting for a whole hour, it’s okay. Listen to your body 😉

  • Marcio

    I’m a morning runner, that most of time, training with empty stomach. I always wanted to know the benefits and risks of this pratice. This is the best article that I saw about this theme. Very good explanations. The tips about weakness and dizziness are very valuable. Thank you!

    • Runtastic Team

      Thanks so much for your positive feedback!

  • Runtastic Team

    Hey George! No, you’re not going to lose muscle. Just fuel up after your morning workout 😉

  • Runtastic Team

    Hi Paulo, no it’s not. As long as you feel good during your run and fuel up afterwards 😉 Stay active!

    Your Runtastic Team

  • Runtastic Team

    Hey Cathrin, congratulations on your new job 😉 Have you tried eating a little snack, for example a banana, before?

  • Adnan

    I did cardio on empty stomach for 2 years my diet was 100% on point afternoon i did weight traning as a fitness instructor i don t recomend it more than 4 weeks cuz in long periods u will loose muscle i did loose good amount of muscle i did it 12 weeks.But again if you lookin to be ripped fast i recomend it 4 weeks

  • Glen Correya

    Hello , I have a doubt that I always drink 2-3 glasses of water in the morning and I’m planning to start running this week onwards so is it ok for me to continue the same schedule even if I start running also?

    • Runtastic Team

      Hi Glen, thank you for your comment. Sure it is okay to drink a few glasses of water before running in the morning 😉

      Your Runtastic Team