Blog Fitness Running On An Empty Stomach: Is It All It’s Cracked Up To Be?

Running On An Empty Stomach: Is It All It’s Cracked Up To Be?

If you’re an early riser who enjoys a morning run, the idea of eating that early in the day may be a struggle. It can be tempting to just hit the pavement on an empty stomach. Is running on an empty stomach really all it’s cracked up to be? There are a few things to consider before you lace up your sneakers and head out the door. First, it’s important to understand how running on an empty stomach can affect your body. Second, you’ll need to decide if the benefits outweigh the potential risks. So, what exactly happens when you run on an empty stomach, and should you be doing it? Let’s take a closer look.


What Is Fasted Cardio And How Does It Work?

Fasted cardio is any type of cardiovascular exercise that is performed in a fasted state. This means that you have not eaten anything for at least 6-7 hours before your workout.

For example, if you go for a run at 6 am and haven’t eaten since dinner the night before, you are running in a fasted state. The same would be true if you went on a run in the evening after skipping lunch or afternoon snacks.

When you exercise in a fasted state, your body must rely on stored energy sources for fuel. This can lead to some interesting changes in your body, both during and after your workout.

During exercise, your body will begin to break down stored glycogen for energy. Glycogen is a type of carbohydrate that is stored in your muscles and liver (5). Once your glycogen stores are depleted, your body will begin to burn fat for energy.

In theory, this sounds like a great way to lose weight. After all, who doesn’t want to burn more fat? However, the reality of fasted cardio is a bit more complicated than that.

To reach the fat-burning stage of the exercise, you must deplete your glycogen stores. This can take anywhere from 30 minutes to an hour or more, depending on how intense your workout is. Whether you can work out intensely minus breakfast or a snack is a whole other story.

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Read More: Smoking And Running: They Don’t Mix, Here’s Why

The Pros And Cons Of Fasted Cardio

Running in the morning on an empty stomach is touted as a great way to burn fat. And while it is true that fasted cardio can help you lose weight, it’s not necessarily the best way to do it.

Here are a few of the pros and cons of running on an empty stomach:

Pro: May Prevent Stomach Issues

If you have a sensitive stomach, running on an empty stomach may actually be better for you. When you eat before a run, blood flow to your stomach increases. This can cause indigestion, cramping, and other gastrointestinal issues (3). If you’re prone to these types of problems, running on an empty stomach may help prevent them.

Pro: May Improve Your Overall Performance

Mixing in some fasted cardio here and there while training may actually improve your athletic performance. When you deplete your glycogen stores, your body adapts by increasing its ability to burn fat for energy. This can lead to improved endurance and faster recovery times (4).

The findings of a small study published in the Journal of Science and Medicine in Sport seem to support this. In the study, eight female and six male untrained, healthy participants completed four weeks of fasted and fed cardio training.

After the four weeks were up, The fast group showed a significantly greater training-induced increase in VO2max and resting muscle glycogen concentration than the fed group (1).

VO2max is a measure of your body’s ability to use oxygen during exercise. It’s generally accepted that the higher your VO2max, the better your aerobic fitness and overall athletic performance will be. Resting muscle glycogen is a measure of the amount of carbohydrate stored in your muscles.

So, if you’re looking to improve your athletic performance, adding some fasted cardio to your training regime may help. Just keep in mind that more research is needed on this topic before any firm conclusions can be made.

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running on an empty stomach

Pro: Might Make You Eat Less Later

When your blood and muscle glycogen levels are depleted, your body turns into your liver glycogen stores. This activates the liver-brain neural network that regulates hunger. This may lead you to eat less later in the day, which can help you lose weight or maintain your current weight.

Interestingly, a few studies have found that exercise in the morning on an empty stomach might help reduce your overall food intake for the day. In a small 2019 study, for example, 12 men who ran on an empty stomach ate fewer calories over 24 hours (7).

More research is needed to confirm these findings as the stress of exercise may have different effects on hunger. 

Con: Makes It Harder To Work Out Intensely

If you’re hoping to do some high-intensity interval training (HIIT) or other strenuous exercise in a fasted state, you may be out of luck. When you haven’t eaten, your blood sugar levels tend to be lower than normal. This can make you feel fatigued, weak, and dizzy – not exactly ideal conditions for a killer workout.

Your risk of injury is also increased when you exercise on an empty stomach. This is because your blood sugar levels can drop too low, causing you to feel lightheaded and dizzy. When this happens, you’re more likely to lose your balance and fall or otherwise injure yourself.

Con: You’re More Likely To Overeat Later

Exercising on an empty stomach can make you more likely to overeat later in the day. After depleting your glycogen stores, your body will be searching for energy. This can lead to cravings and overeating later on. If you’re not careful, you could end up eating more calories than you burned during your workout. High cortisol levels may also increase your appetite (6).

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So, if you’re trying to lose weight or eat fewer calories, working out on an empty stomach is probably not the best idea.

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running on an empty stomach

Con: You Won’t Burn As Much Fat As You Think

Despite what you may have heard, fasted cardio isn’t necessarily the best way to burn fat. In fact, you may actually end up burning less fat in a fasted state than if you were to eat before working out.

This is because your body targets glycogen first, and fat second. You’ll need to work out at a high intensity for at least an hour to really start burning fat. And if you’re not eating before your workout, you probably won’t have the energy to sustain that level of intensity for very long.

Con: It May Lead To Muscle Loss

While you sleep, your body’s levels of insulin drop. Your liver glycogen stores are also depleted during this time. When you run on an empty stomach in the morning, your body’s only remaining source of glycogen is muscle glycogen. Once this is gone, your body will start to break down muscle protein for energy.

This can lead to muscle loss over time, which is the last thing you want if you’re trying to improve your athletic performance. Muscle loss can also lead to a decrease in your metabolism, making it harder to lose fat and keep it off in the long run.

Although the catabolic (muscle-wasting) effects of fasted cardio can be mitigated by consuming protein before or after your workout, it’s still something to keep in mind.

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What To Eat Before A Fasted Cardio Workout

If you decide to do fasted cardio, there are a few things you can eat or drink before your workout to help minimize the drawbacks.

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First, try drinking black coffee or green tea before your workout. Caffeine can help increase your metabolism and fat burning (8). It can also give you a much-needed energy boost. Hydrate with water or a low-calorie electrolyte drink to keep your energy levels up and minimize cramping.

Another option is to have a small protein shake before your workout. This will help preserve muscle mass and prevent cravings later on. Just be sure to keep it light – you don’t want to end up with an upset stomach during your workout.

Finally, consider taking branched-chain amino acids (BCAAs) before you exercise. BCAAs can help prevent muscle breakdown and preserve muscle glycogen stores. They may also help increase fat burning (2).

Other safety tips for a successful fasted cardio workout include:

  • Keep your run between 40 and 60 minutes long: Any longer and you risk running out of energy or experiencing cramping.
  • Start at a slow pace and keep your heart rate under 140 beats per minute: This will help you avoid feeling lightheaded or dizzy.
  • Wear loose, comfortable clothing and shoes:This will help you stay cool and avoid chafing.
  • Monitor your blood sugar levels: If you feel yourself getting lightheaded or dizzy, stop and have a snack.
  • Stay hydrated: Drink plenty of water before, during, and after your workout.

Read More: How To Increase Stamina For Running: 10 Expert-Approved Tips

Healthy Pre-Workout Snacks

If you’re looking for something more substantial to eat before your workout, try one of these healthy snacks:

  • A fruit and yogurt parfait: get some protein and carbs from the yogurt, and some natural sugar from the fruit.
  • A whole grain English muffin with peanut butter: this will give you sustained energy from the complex carbs in the muffin, and some protein and healthy fats from the peanut butter.
  • A banana with almond butter:this snack has simple carbs for quick energy, plus some protein and healthy fats from the almond butter.
  • A small bowl of oatmeal with berries:this is a great option if you’re working out first thing in the morning. The oatmeal will give you complex carbs for sustained energy, and the berries will provide natural sugar for a quick boost.
  • Rice cakes with avocado: the rice cakes will give you complex carbs for energy, while the avocado provides healthy fats.
  • A veggie wrap with hummus: this snack has complex carbs from the wrap, and protein and healthy fats from the hummus.
  • A small salad with chicken: this is a great option if you’re looking for something light but filling. The veggies will provide complex carbs and fiber, while the chicken will give you protein.
  • Greek yogurt with berries: this snack has protein and carbs from the yogurt, and natural sugar from the berries.
  • A hard-boiled egg with toast: this is a great option if you need something quick and easy. The egg will give you protein, while the toast provides complex carbs.
  • A fruit smoothie: this is a great option if you’re looking for something quick and easy. The fruit will provide natural sugar for energy, while the yogurt or milk will give you protein and carbs.
  • A trail mix: this snack has complex carbs from the nuts and dried fruit, and healthy fats from the nuts.
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running on an empty stomach

Final Thoughts

Working out on an empty stomach has some potential pros and cons. On the plus side, it might help improve your overall performance, make you eat less later in the day, and help you lose weight.

On the downside, it can make it harder to work out intensely, increase your risk of injury, and make you more likely to overeat later.If you decide to give it a try, be sure to listen to your body and stop if you feel faint or dizzy. And, as always, be sure to talk to your doctor before starting any new exercise regimen.



This article is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional advice or help and should not be relied on to make decisions of any kind. Any action you take upon the information presented in this article is strictly at your own risk and responsibility!


  1. Adaptations to skeletal muscle with endurance exercise training in the acutely fed versus overnight-fasted state (2010,
  2. Branched-chain Amino Acids: Catabolism in Skeletal Muscle and Implications for Muscle and Whole-body Metabolism (2021,
  3. Food-dependent, exercise-induced gastrointestinal distress (2011,
  4. Fundamentals of glycogen metabolism for coaches and athletes (2018,
  5. Glycogen metabolism in humans (2016,
  6. High/low cortisol reactivity and food intake in people with obesity and healthy weight (2020, nih,gov)
  7. Skipping Breakfast Before Exercise Creates a More Negative 24-hour Energy Balance: A Randomized Controlled Trial in Healthy Physically Active Young Men (2019,
  8. The effects of caffeine intake on weight loss: a systematic review and dos-response meta-analysis of randomized controlled trials (2019,
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